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IPS Working Group                                               B. Aboba
INTERNET-DRAFT                                                 Microsoft
Category: Standards Track                                   Joshua Tseng
<draft-ietf-ips-security-19.txt>                          Nishan Systems
14 January 2003                                             Jesse Walker
                                                                   Intel
                                                           Venkat Rangan
                                                  Rhapsody Networks Inc.
                                                       Franco Travostino
                                                         Nortel Networks

                Securing Block Storage Protocols over IP

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other groups
may also distribute working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time.  It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.

Copyright Notice

Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

This document discusses how to secure block storage and storage
discovery protocols running over IP using IPsec and IKE. Threat models
and security protocols are developed for iSCSI, iFCP and FCIP, as well
as the iSNS and SLPv2 discovery protocols.  Performance issues and
resource constraints are analyzed.





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Table of Contents

1.     Introduction ..........................................    4
   1.1       iSCSI overview ..................................    4
   1.2       iFCP overview ...................................    5
   1.3       FCIP overview ...................................    5
   1.4       IPsec overview ..................................    5
   1.5       Terminology .....................................    7
   1.6       Requirements language ...........................    8
2.     Block storage protocol security .......................    8
   2.1       Security requirements  ..........................    8
   2.2       Resource constraints ............................   11
   2.3       Security protocol ...............................   12
   2.4       iSCSI authentication ............................   16
   2.5       SLPv2 security ..................................   18
   2.6       iSNS security ....................................  25
3.     iSCSI security inter-operability guidelines ...........   29
   3.1       iSCSI security issues ...........................   29
   3.2       iSCSI and IPsec interaction .....................   29
   3.3       Initiating a new iSCSI session ..................   30
   3.4       Graceful iSCSI teardown .........................   31
   3.5       Non-graceful iSCSI teardown .....................   32
   3.6       Application layer CRC ...........................   32
4.     iFCP and FCIP security issues .........................   34
   4.1       iFCP and FCIP Authentication Requirements .......   34
   4.2       iFCP Interaction with IPsec and IKE .............   35
   4.3       FCIP Interaction with IPsec and IKE .............   36






















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5.     Security Considerations ...............................   37
   5.1       Transport mode versus tunnel mode ...............   37
   5.2       NAT traversal ...................................   39
   5.3       IKE issues ......................................   40
   5.4       Rekeying issues .................................   41
   5.5       Transform issues ................................   43
   5.6       Fragmentation issues ............................   45
   5.7       Security checks .................................   46
   5.8       Authentication issues ...........................   47
   5.9       Use of AES in counter mode ......................   51
6.     IANA Considerations ...................................   51
   6.1       Definition of terms .............................   52
   6.2       Recommended registration policies ...............   52
7.     Normative references ..................................   52
8.     Informative references ................................   55
Appendix A - Well Known Groups for Use with SRP  .............   59
Appendix B - Software Performance of IPsec Transforms  .......   61
   B.1       Authentication transforms .......................   61
   B.2       Encryption and Authentication transforms ........   65
Acknowledgments ..............................................   70
Authors' Addresses ...........................................   70
Intellectual Property Rights .................................   71
Full Copyright Statement .....................................   71


























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1.  Introduction

This specification discusses use of the IPsec protocol suite for
protecting block storage protocols over IP networks (including iSCSI,
iFCP and FCIP), as well as storage discovery protocols (iSNS and SLPv2).

1.1.  iSCSI overview

iSCSI, described in [iSCSI], is a connection-oriented command/response
protocol that runs over TCP, and is used to access disk, tape and other
devices.  iSCSI is a client-server protocol in which clients
(initiators) open connections to servers (targets) and perform an iSCSI
login.

This draft uses the SCSI terms initiator and target for clarity and to
avoid the common assumption that clients have considerably less
computational and memory resources than servers; the reverse is often
the case for SCSI, as targets are commonly dedicated devices of some
form.

The iSCSI protocol has a text based negotiation mechanism as part of its
initial (login) procedure.  The mechanism is extensible in what can be
negotiated (new text keys and values can be defined) and also in the
number of negotiation rounds (e.g., to accommodate functionality such as
challenge-response authentication).

After a successful login, the iSCSI initiator may issue SCSI commands
for execution by the iSCSI target, which returns a status response for
each command, over the same connection.  A single connection is used for
both command/status messages as well as transfer of data and/or optional
command parameters.  An iSCSI session may have multiple connections, but
a separate login is performed on each.  The iSCSI session terminates
when its last connection is closed.

iSCSI initiators and targets are application layer entities that are
independent of TCP ports and IP addresses.  initiators and targets have
names whose syntax is defined in [iSCSIName].  iSCSI sessions between a
given initiator and target are run over one or more TCP connections
between those entities.  That is, the login process establishes an
association between an iSCSI Session and the TCP connection(s) over
which iSCSI PDUs will be carried.

While the iSCSI login may include mutual authentication of the iSCSI
endpoints and negotiation of session parameters, iSCSI does not define
its own per-packet authentication, integrity, confidentiality or replay
protection mechanisms. Rather, it relies upon the IPsec protocol suite



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to provide per-packet data confidentiality and integrity and
authentication services, with IKE as the key management protocol. iSCSI
uses TCP to provide congestion control, error detection and error
recovery.

1.2.  iFCP overview

iFCP, defined in [iFCP], is a gateway-to-gateway protocol, which
provides transport services to Fibre Channel devices over a TCP/IP
network. iFCP allows interconnection and networking of existing Fibre
Channel devices at wire speeds over an IP network. iFCP implementations
emulate fabric services in order to improve fault tolerance and
scalability by fully leveraging IP technology. Each TCP connection is
used to support storage traffic between a unique pair of Fibre Channel
N_PORTs.

iFCP does not have a native, in-band security mechanism. Rather, it
relies upon the IPsec protocol suite to provide data confidentiality and
authentication services, and IKE as the key management protocol. iFCP
uses TCP to provide congestion control, error detection and error
recovery.

1.3.  FCIP overview

FCIP, defined in [FCIP], is a pure FC encapsulation protocol that
transports FC frames. Current specification work intends this for
interconnection of Fibre Channel switches over TCP/IP networks, but the
protocol is not inherently limited to connecting FC switches.  FCIP
differs from iFCP in that no interception or emulation of fabric
services is involved. One or more TCP connections are bound to an FCIP
Link, which is used to realize Inter-Switch Links (ISLs) between pairs
of Fibre Channel entities.

FCIP does not have a native, in-band security mechanism.  Rather, it
relies upon the IPsec protocol suite to provide data confidentiality and
authentication services, and IKE as the key management protocol.  FCIP
uses TCP to provide congestion control, error detection and error
recovery.

1.4.  IPsec overview

IPsec is a protocol suite which is used to secure communication at the
network layer between two peers.  The IPsec protocol suite is specified
within the IP Security Architecture [RFC2401], IKE [RFC2409], IPsec
Authentication Header (AH) [RFC2402] and IPsec Encapsulating Security
Payload (ESP) [RFC2406] documents.  IKE is the key management protocol



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while AH and ESP are used to protect IP traffic.

An IPsec SA is a one-way security association, uniquely identified by
the 3-tuple: Security Parameter Index (SPI), protocol (ESP) and
destination IP.  The parameters for an IPsec security association are
typically established by a key management protocol. These include the
encapsulation mode, encapsulation type, session keys and SPI values.

IKE is a two phase negotiation protocol based on the modular exchange of
messages defined by ISAKMP [RFC2408],and the IP Security Domain of
Interpretation (DOI) [RFC2407]. IKE has two phases, and accomplishes the
following functions:

[1]  Protected cipher suite and options negotiation - using keyed MACs
     and encryption and anti-replay mechanisms

[2]  Master key generation - such as via MODP Diffie-Hellman
     calculations

[3]  Authentication of end-points

[4]  IPsec SA management (selector negotiation, options negotiation,
     create, delete, and rekeying)

Items 1 through 3 are accomplished in IKE Phase 1, while item 4 is
handled in IKE Phase 2.

An IKE Phase 2 negotiation is performed to establish both an inbound and
an outbound IPsec SA.  The traffic to be protected by an IPsec SA is
determined by a selector which has been proposed by the IKE initiator
and accepted by the IKE Responder.  In IPsec transport mode, the IPsec
SA selector can be a "filter" or traffic classifier, defined as the
5-tuple: <Source IP address, Destination IP address, transport protocol
(UDP/SCTP/TCP), Source port, Destination port>.  The successful
establishment of a IKE Phase-2 SA results in the creation of two uni-
directional IPsec SAs fully qualified by the tuple <Protocol (ESP/AH),
destination address, SPI>.

The session keys for each IPsec SA are derived from a master key,
typically via a MODP Diffie-Hellman computation.  Rekeying of an
existing IPsec SA pair is accomplished by creating two new IPsec SAs,
making them active, and then optionally deleting the older IPsec SA
pair.  Typically the new outbound SA is used immediately, and the old
inbound SA is left active to receive packets for some locally defined
time, perhaps 30 seconds or 1 minute.




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1.5.  Terminology

Fibre Channel
          Fibre Channel (FC) is a gigabit speed networking technology
          primarily used to implement Storage Area Networks (SANs),
          although it also may be used to transport other frames types
          as well, including IP.  FC is standardized under American
          National Standard for Information Systems of the InterNational
          Committee for Informational Technology Standards (ANSI-INCITS)
          in its T11 technical committee.

FCIP      Fibre Channel over IP (FCIP) is a protocol for interconnecting
          Fibre Channel islands over IP Networks so as to form a unified
          SAN in a single Fibre Channel fabric. The principal FCIP
          interface point to the IP Network is the FCIP Entity. The FCIP
          Link represents one or more TCP connections that exist between
          a pair of FCIP Entities.

HBA       Host Bus Adapter (HBA) is a generic term for a SCSI interface
          to other device(s); it's roughly analogous to the term Network
          Interface Card (NIC) for a TCP/IP network interface, except
          that HBAs generally have on-board SCSI implementations,
          whereas most NICs do not implement TCP, UDP, or IP.

iFCP      iFCP is a gateway-to-gateway protocol, which provides Fibre
          Channel fabric services to Fibre Channel devices over a TCP/IP
          network.

IP block storage protocol
          Where used within this document, the term "IP block storage
          protocol" applies to all block storage protocols running over
          IP, including iSCSI, iFCP and FCIP.

iSCSI     iSCSI is a client-server protocol in which clients
          (initiators) open connections to servers (targets).

iSNS      The Internet Storage Name Server (iSNS) protocol provides for
          discovery and management of iSCSI and Fibre Channel (FCP)
          storage devices.  iSNS applications store iSCSI and FC device
          attributes and monitor their availability and reachability,
          providing a consolidated information repository for an
          integrated IP block storage network.  iFCP requires iSNS for
          discovery and management, while iSCSI may use iSNS for
          discovery, and FCIP does not use iSNS.





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initiator The iSCSI initiator connects to the target on well-known TCP
          port 3260. The iSCSI initiator then issues SCSI commands for
          execution by the iSCSI target.

target    The iSCSI target listens on a well-known TCP port for incoming
          connections, and  returns a status response for each command
          issued by the iSCSI initiator, over the same connection.

1.6.  Requirements language

In this document, the key words "MAY", "MUST,  "MUST  NOT",  "OPTIONAL",
"RECOMMENDED",  "SHALL", "SHALL NOT", "SHOULD",  and  "SHOULD  NOT", are
to be interpreted as described in [RFC2119].

Note that requirements specified in this document apply only to use of
IPsec and IKE with IP block storage protocols. Thus, these requirements
do not apply to IPsec implementations in general. Implementation
requirements language should therefore be assumed to relate to the
availability of features for use with IP block storage security only.

Although the security requirements in this document are already
incorporated into the iSCSI [iSCSI], iFCP [iFCP] and FCIP [FCIP]
standards track documents, they are reproduced here for convenience.  In
the event of a discrepancy, the individual protocol standards track
documents take precedence.

2.  Block storage protocol security

2.1.  Security requirements

IP Block storage protocols such as iSCSI, iFCP and FCIP are used to
transmit SCSI commands over IP networks.  Therefore, both the control
and data packets of these IP block storage protocols are vulnerable to
attack.  Examples of attacks include:

[1]  An adversary may attempt to acquire confidential data and
     identities by snooping data packets.

[2]  An adversary may attempt to modify packets containing data and
     control messages.

[3]  An adversary may attempt to inject packets into an IP block storage
     connection.

[4]  An adversary may attempt to hijack TCP connection(s) corresponding
     to an IP block storage session.



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[5]  An adversary may launch denial of service attacks against IP block
     storage devices such as by sending a TCP reset.

[6]  An adversary may attempt to disrupt security negotiation process,
     in order to weaken the authentication, or gain access to user
     passwords.  This includes disruption of application-layer
     authentication negotiations such as iSCSI Login.

[7]  An adversary may attempt to impersonate a legitimate IP block
     storage entity.

[8]  An adversary may launch a variety of attacks (packet modification
     or injection, denial of service) against the discovery (SLPv2
     [RFC2608]) or discovery and management (iSNS [iSNS]) process. iSCSI
     can use SLPv2 or iSNS. FCIP only uses SLPv2, and iFCP only uses
     iSNS.

Since iFCP and FCIP devices are the last line of defense for a whole
Fibre Channel island, the above attacks, if successful, could compromise
the security of all the Fibre Channel hosts behind the devices.

To address the above threats, IP block storage security protocols must
support confidentiality, data origin authentication, integrity, and
replay protection on a per-packet basis.  Confidentiality services are
important since IP block storage traffic may traverse insecure public
networks. The IP block storage security protocols must support perfect
forward secrecy in the rekeying process.

Bi-directional authentication of the communication endpoints MUST be
provided.  There is no requirement that the identities used in
authentication be kept confidential (e.g., from a passive eavesdropper).

For a security protocol to be useful, CPU overhead and hardware
availability must not preclude implementation at 1 Gbps today.
Implementation feasibility at 10 Gbps is highly desirable, but may not
be demonstrable at this time.  These performance levels apply to
aggregate throughput, and include all TCP connections used between IP
block storage endpoints.  IP block storage communications typically
involve multiple TCP connections.  Performance issues are discussed
further in Appendix B.

Enterprise data center networks are considered mission-critical
facilities that must be isolated and protected from possible security
threats.  Such networks are often protected by security gateways, which
at a minimum provide a shield against denial of service attacks.  The IP
block storage security architecture should be able to leverage the



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protective services of the existing security infrastructure, including
firewall protection, NAT and NAPT services, and VPN services available
on existing security gateways.

When iFCP or FCIP devices are deployed within enterprise networks, IP
addresses will be typically be statically assigned as is the case with
most routers and switches.  Consequently, support for dynamic IP
address assignment, as described in [DHCPIPsec], will typically not be
required, although it cannot be ruled out.  Such facilities will also be
relevant to iSCSI hosts whose addresses are dynamically assigned. As a
result, the IP block storage security protocols must not introduce
additional security vulnerabilities where dynamic address assignment is
supported.

While IP block storage security is mandatory to implement, it is not
mandatory to use.  The security services used depend on the
configuration and security policies put in place.  For example,
configuration will influence the authentication algorithm negotiated
within iSCSI Login, as well as the security services (confidentiality,
data origin authentication, integrity, replay protection) and transforms
negotiated when IPsec is used to protect IP block storage protocols such
as iSCSI, iFCP and FCIP.

FCIP implementations may allow enabling and disabling security
mechanisms at the granularity of an FCIP Link.  For iFCP, the
granularity corresponds to an iFCP Portal. For iSCSI, the granularity of
control is typically that of an iSCSI session, although it is possible
to exert control down to the granularity of the destination IP address
and TCP port.

Note that with IPsec, security services are negotiated at the
granularity of an IPsec SA, so that IP block storage connections
requiring a set of security services different from those negotiated
with existing IPsec SAs will need to negotiate a new IPsec SA. Separate
IPsec SAs are also advisable where quality of service considerations
dictate different handling of IP block storage connections. Attempting
to apply different quality of service to connections handled by the same
IPsec SA can result in reordering, and falling outside the replay
window. For a discussion of the issues, see [RFC2983].

IP block storage protocols can be expected to carry sensitive data and
provide access to systems and data that require protection against
security threats.  SCSI and Fibre Channel currently contain little in
the way of security mechanisms, and rely on physical security,
administrative security, and correct configuration of the communication
medium and systems/devices attached to it for their security properties.



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For most IP networks, it is inappropriate to assume physical security,
administrative security, and correct configuration of the network and
all attached nodes (a physically isolated network in a test lab may be
an exception).  Therefore, authentication SHOULD be used by IP block
storage protocols (e.g., iSCSI SHOULD use one of its in-band
authentication mechanisms or the authentication provided by IKE) in
order to provide a minimal assurance that connections have initially
been opened with the intended counterpart.

iSNS, described in [iSNS], is required in all iFCP deployments.  iSCSI
may use iSNS for discovery, and FCIP does not use iSNS.  iSNS
applications store iSCSI and FC device attributes and monitor their
availability and reachability, providing a consolidated information
repository for an integrated IP block storage network.  The iSNS
specification defines mechanisms to secure communication between an iSNS
server and its clients.

2.2.  Resource constraints

iFCP and FCIP devices will typically be embedded systems deployed on
racks in air-conditioned data center facilities.  Such embedded systems
may include hardware chipsets to provide data encryption,
authentication, and integrity processing.  Therefore, memory and CPU
resources are generally not a constraining factor.

iSCSI will be implemented on a variety of systems ranging from large
servers running general purpose operating systems to embedded host bus
adapters (HBAs). In general, a host bus adapter is the most constrained
iSCSI implementation environment, although an HBA may draw upon the
resources of the system to which it is attached in some cases (e.g.,
authentication computations required for connection setup).  More
resources should be available to iSCSI implementations for embedded and
general purpose operating systems.  The following guidelines indicate
the approximate level of resources that authentication, keying, and
rekeying functionality can reasonably expect to draw upon:

  - Low power processors with small word size are generally not used,
    as power is usually not a constraining factor, with the possible
    exception of HBAs, which can draw upon the computational resources
    of the system into which they are inserted.  Computational
    horsepower should be available to perform a reasonable amount of
    exponentiation as part of authentication and key derivation for
    connection setup.  The same is true of rekeying, although the
    ability to avoid exponentiation for rekeying may be desirable (but
    is not an absolute requirement).




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  - RAM and/or flash resources tend to be constrained in embedded
    implementations.  8-10 MB of code and data for authentication,
    keying, and rekeying is clearly excessive, 800-1000 KB is clearly
    larger than desirable, but tolerable if there is no other
    alternative and 80-100 KB should be acceptable.  These sizes are
    intended as rough order of magnitude guidance, and should not be
    taken as hard targets or limits (e.g., smaller code sizes are
    always better).  Software implementations for general purpose
    operating systems may have more leeway.

The primary resource concern for implementation of authentication and
keying mechanisms is code size, as iSCSI assumes that the computational
horsepower to do exponentiations will be available.

There is no dominant iSCSI usage scenario - the scenarios range from a
single connection constrained only by media bandwidth to hundreds of
initiator connections to a single target or communication endpoint.
SCSI sessions and hence the connections they use tend to be relatively
long lived; for disk storage, a host typically opens a SCSI connection
on boot and closes it on shutdown.  Tape session length tends to be
measured in hours or fractions thereof (i.e., rapid fire sharing of the
same tape device among different initiators is unusual), although tape
robot control sessions can be short when the robot is shared among tape
drives.  On the other hand, tape will not see a large number of
initiator connections to a single target or communication endpoint, as
each tape drive is dedicated to a single use at a single time, and a
dozen tape drives is a large tape device.

2.3.  Security protocol

2.3.1.  Transforms

All IP block storage security compliant implementations MUST support
IPsec ESP [RFC2406] to provide security for both control packets and
data packets, as well as the replay protection mechanisms of IPsec.
When ESP is utilized, per-packet data origin authentication, integrity
and replay protection MUST be used.

To provide confidentiality with ESP, ESP with 3DES in CBC mode [RFC2451]
MUST be supported, and AES in Counter mode, as described in [AESCTR],
SHOULD be supported.  To provide data origin authentication and
integrity with ESP, HMAC-SHA1 [RFC2404] MUST be supported, and AES in
CBC MAC mode with XCBC extensions [AESXCBC] SHOULD be supported. DES in
CBC mode SHOULD NOT be  used due to its inherent weakness.  ESP with
NULL encryption MUST be supported for authentication.




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2.3.2.  IPsec modes

Conformant IP block storage protocol implementations MUST support ESP
[RFC2406] in tunnel mode and MAY implement IPsec with ESP in transport
mode.

2.3.3.  IKE

Conformant IP block storage security implementations MUST support IKE
[RFC2409] for peer authentication, negotiation of security associations,
and key management, using the IPsec DOI [RFC2407].  Manual keying MUST
NOT be used since it does not provide the necessary rekeying support.
Conformant IP block storage security implementations MUST support peer
authentication using a pre-shared key, and MAY support certificate-based
peer authentication using digital signatures.  Peer authentication using
the public key encryption methods outlined in IKE's sections 5.2 and 5.3
[RFC2409] SHOULD NOT be used.

Conformant IP block storage security implementations MUST support IKE
Main Mode and SHOULD support Aggressive Mode.  IKE Main Mode with pre-
shared key authentication SHOULD NOT be used when either of the peers
use a dynamically assigned IP address. While Main Mode with pre-shared
key authentication offers good security in many cases, situations where
dynamically assigned addresses are used force use of a group pre-shared
key, which is vulnerable to man-in-the-middle attack.

When digital signatures are used for authentication, either IKE Main
Mode or IKE Aggressive Mode MAY be used.  In all cases, access to
locally stored secret information (pre-shared key,  or private  key for
digital signing) must be suitably restricted, since compromise of the
secret information nullifies the security properties of the IKE/IPsec
protocols.

When digital signatures are used to achieve authentication, an IKE
negotiator SHOULD use IKE Certificate Request Payload(s) to specify the
certificate authority (or authorities) that are trusted in accordance
with its local policy.  IKE negotiators SHOULD check the pertinent
Certificate Revocation List (CRL) before accepting a PKI certificate for
use in IKE's authentication procedures.

The IPsec DOI [RFC2407] provides for several types of identification
data. Within IKE Phase 1, for use within the IDii and IDir payloads,
conformant IP block storage security implementations MUST support the
ID_IPV4_ADDR, ID_IPV6_ADDR (if the protocol stack supports IPv6) and
ID_FQDN Identity Payloads. iSCSI security implementations SHOULD support
the ID_USER_FQDN Identity Payload; other IP block storage protocols



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(iFCP, FCIP) SHOULD NOT use the ID_USER_FQDN Identity Payload.
Identities other than ID_IPV4_ADDR and ID_IPV6_ADDR (such as ID_FQDN or
ID_USER_FQDN) SHOULD be employed in situations where Aggressive mode is
utilized along with pre-shared keys and IP addresses are dynamically
assigned.  The IP Subnet, IP Address Range, ID_DER_ASN1_DN,
ID_DER_ASN1_GN formats SHOULD NOT be used for IP block storage protocol
security; The ID_KEY_ID Identity Payload MUST NOT be used.  As described
in [RFC2407], within Phase 1 the ID port and protocol fields MUST be set
to zero or to UDP port 500. Also, as noted in [RFC2407]:

   When an IKE exchange is authenticated using certificates (of any
   format), any ID's used for input to local policy decisions SHOULD be
   contained in the certificate used in the authentication of the
   exchange.

The Phase 2 Quick Mode exchanges used by IP block storage protocol
implementations MUST explicitly carry the Identity Payload fields (IDci
and IDcr).  Each Phase 2 IDci and IDcr Payload SHOULD carry a single IP
address (ID_IPV4_ADDR, ID_IPV6_ADDR) and SHOULD NOT use the IP Subnet or
IP Address Range formats. Other ID payload formats MUST NOT be used.

Since IPsec acceleration hardware may only be able to handle a limited
number of active IKE Phase 2 SAs, Phase 2 delete messages may be sent
for idle SAs, as a means of keeping the number of active Phase 2 SAs to
a minimum. The receipt of an IKE Phase 2 delete message MUST NOT be
interpreted as a reason for tearing down an IP block storage connection.
Rather, it is preferable to leave the connection up, and if additional
traffic is sent on it, to bring up another IKE Phase 2 SA to protect it.
This avoids the potential for continually bringing connections up and
down.

2.3.4.  Security policy configuration

One of the goals of this specification is to enable a high level of
interoperability without requiring extensive configuration.  This
section provides guidelines on setting of IKE parameters so as to
enhance the probability of a successful negotiation. It also describes
how information on security policy configuration can be provided so as
to further enhance the chances of success.

To enhance the prospects for interoperability, some of the actions to
consider include:


[1]  Transform restriction. Since support for 3DES-CBC and HMAC-SHA1 is
     required of all implementations, offering these transforms enhances



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     the probability of a successful negotiation.  If AES-CTR [AESCTR]
     with XCBC-MAC [AESXCBC] is supported, this transform combination
     will typically be preferred, with 3DES-CBC/HMAC-SHA1 as a secondary
     offer.

[2]  Group Restriction. If 3DES-CBC/HMAC-SHA1 is offered, and DH groups
     are offered, then it is recommended that a DH group of at least
     1024 bits be offered along with it. If AES-CTR/XCBC-MAC is the
     preferred offer, and DH groups are offered, then it is recommended
     that a DH group of at least 2048 bits be offered along with it, as
     noted in [KeyLen]. If perfect forward secrecy is required in Quick
     Mode, then it is recommended that the QM PFS DH group be the same
     as the IKE Phase 1 DH group.  This reduces the total number of
     combinations, enhancing the chances for interoperability.

[3]  Key lifetimes. If a key lifetime is offered that is longer than
     desired, then rather than causing the IKE negotiation to fail, it
     is recommended that the Responder consider the offered lifetime as
     a maximum, and accept it. The key can then use a lesser value for
     the lifetime, and utilize a Lifetime Notify in order to inform the
     other peer of lifetime expiration.

Even when the above advice is taken, it still may be useful to be able
to provide additional configuration information in order to enhance the
chances of success, and it is useful to be able to manage security
configuration regardless of the scale of the deployment.

For example, it may be desirable to configure the security policy of an
IP block storage device. This can be done manually or automatically via
a security policy distribution mechanism. Alternatively, it can be
supplied via iSNS or SLPv2. If an IP block storage endpoint can obtain
the required security policy by other means (manually, or automatically
via a security policy distribution mechanism) then it need not request
this information via iSNS or SLPv2. However, if the required security
policy configuration is not available via other mechanisms, iSNS or
SLPv2 can be used to obtain it.

It may also be helpful to obtain information about the preferences of
the peer prior to initiating IKE.  While it is generally possible to
negotiate security parameters within IKE, there are situations in which
incompatible parameters can cause the IKE negotiation to fail.  The
following information can be provided via SLPv2 or iSNS:

[4]  IPsec or cleartext support. The minimum piece of peer configuration
     required is whether an IP block storage endpoint requires IPsec or
     cleartext. This cannot be determined from the IKE negotiation alone



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     without risking a long timeout, which is highly undesirable for a
     disk access protocol.

[5]  Perfect Forward Secrecy (PFS) support. It is helpful to know
     whether a peer allows PFS, since an IKE Phase 2 Quick Mode can fail
     if an initiator proposes PFS to a Responder that does not allow it.

[6]  Preference for tunnel mode. While it is legal to propose both
     transport and tunnel mode within the same offer, not all IKE
     implementations will support this. As a result, it is useful to
     know whether a peer prefers tunnel mode or transport mode, so that
     it is possible to negotiate the preferred mode on the first try.

[7]  Main Mode and Aggressive Mode support. Since the IKE negotiation
     can fail if a mode is proposed to a peer that doesn't allow it, it
     is helpful to know which modes a peer allows, so that an allowed
     mode can be negotiated on the first try.

Since iSNS or SLPv2 can be used to distribute IPsec security policy and
configuration information for use with IP block storage protocols, these
discovery protocols would constitute a 'weak link' were they not secured
at least as well as the protocols whose security they configure. Since
the major vulnerability is packet modification and replay, when iSNS or
SLPv2 are used to distribute security policy or configuration
information, at a minimum, per-packet data origin authentication,
integrity and replay protection MUST be used to protect the discovery
protocol.

2.4.  iSCSI authentication

2.4.1.  CHAP

Compliant iSCSI implementations MUST implement the CHAP authentication
method [RFC1994] (according to [iSCSI], section 11.1.4), which includes
support for bi-directional authentication, and the target authentication
option.

When CHAP is performed over non-encrypted channel, it is vulnerable to
an off-line dictionary attack. Implementations MUST support random CHAP
secrets of up to 128 bits, including the means to generate such secrets
and to accept them from an external generation source.  Implementations
MUST NOT provide secret generation (or expansion) means other than
random generation.

If CHAP is used with secret smaller than 96 bits, then IPsec encryption
(according to the implementation requirements in [iSCSI] section 8.3.2)



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MUST be used to protect the connection. Moreover, in this case IKE
authentication with group pre-shared keys SHOULD NOT be used. When CHAP
is used with a secret smaller then 96 bits, a compliant implementation
MUST NOT continue with the iSCSI login unless it can verify that IPsec
encryption is being used to protect the connection.

Originators MUST NOT reuse the CHAP challenge sent by the Responder for
the other direction of a bidirectional authentication.  Responders MUST
check for this condition and close the iSCSI TCP connection if it
occurs.

The same CHAP secret SHOULD NOT be configured for authentication of
multiple initiators or multiple targets, as this enables any of them to
impersonate any other one of them, and compromising one of them enables
the attacker to impersonate any of them. It is recommended that iSCSI
implementations check for use of identical CHAP secrets by different
peers when this check is feasible, and take appropriate measures to warn
users and/or administrators when this is detected.  A single CHAP secret
MAY be used for authentication of an individual initiator to multiple
targets. Likewise, a single CHAP secret MAY be used for authentication
of an individual target to multiple initiators.

A Responder MUST NOT send its CHAP response if the initiator has not
successfully authenticated.  For example, the following exchange:

       I->R     CHAP_A=<A1,A2,...>
       R->I     CHAP_A=<A1> CHAP_C=<C> CHAP_I=<I>
       I->R     CHAP_N=<N> CHAP_C=<C> CHAP_I=<I>

(Where N, (A1,A2), I, C, and R are correspondingly the Name,
Algorithms, Identifier, Challenge, and Response as defined in
[RFC1994])

MUST result in the Responder (target) closing the iSCSI TCP connection
because the initiator has failed to authenticate (there is no CHAP_R in
the third message).

Any CHAP secret used for initiator authentication MUST NOT be configured
for authentication of any target, and any CHAP secret used for target
authentication MUST NOT be configured for authentication of any
initiator. If the CHAP response received by one end of an iSCSI
connection is the same as the CHAP response that the receiving endpoint
would have generated for the same CHAP challenge, the response MUST be
treated as an authentication failure and cause the connection to close
(this ensures that the same CHAP secret is not used for authentication
in both directions). Also, if an iSCSI implementation can function as



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both initiator and target, different CHAP secrets and identities MUST be
configured for these two roles. The following is an example of the
attacks prevented by the above requirements:

   Rogue wants to impersonate Storage to Alice, and knows that a
      single secret is used for both directions of Storage-Alice
      authentication.

   Rogue convinces Alice to open two connections to Rogue, and
      Rogue identifies itself as Storage on both connections.

   Rogue issues a CHAP challenge on connection 1, waits for Alice
      to respond, and then reflects Alice's challenge as the initial
      challenge to Alice on connection 2.

   If Alice doesn't check for the reflection across connections,
   Alice's response on connection 2 enables Rogue to impersonate
   Storage on connection 1, even though Rogue does not know the
   Alice-Storage CHAP secret.

Note that RADIUS [RFC2865] does not support bi-directional CHAP
authentication.  Therefore, while a target acting as a RADIUS client
will be able to verify the initiator Response, it will not be able to
respond to an initiator challenge unless it has access to an appropriate
shared secret by some other means.

2.4.2.  SRP

iSCSI implementations MAY implement the SRP authentication method
[RFC2945] (see [iSCSI], Section 11.1.3).  The strength of SRP security
is dependent on the characteristics of the group being used (i.e., the
prime modulus N and generator g).  As described in [RFC2945], N is
required to be a Sophie-German prime (of the form N = 2q + 1, where q is
also prime) the generator g is a primitive root of GF(n) [SRPNDSS].

SRP well-known groups are included in Appendix A and additional groups
may be registered with IANA. iSCSI implementations MUST use one of these
well-known groups.  All the groups specified in Appendix A up to 1536
bits (i.e., SRP-768, SRP-1024, SRP-1280, SRP-1536) MUST be supported by
initiators and targets. To guarantee interoperability, targets MUST
always offer "SRP-1536" as one of the proposed groups.

2.5.  SLPv2 Security

Both iSCSI and FCIP protocols use SLPv2 as a way to discover peer
entities and management servers. SLPv2 may also be used to provide



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information on peer security configuration. When SLPv2 is deployed, the
SA advertisements as well as UA requests and/or responses are subject to
the following security threats:

[1]  An attacker could insert or alter SA advertisements or a response
     to a UA request in order to masquerade as the real peer or launch a
     denial of service attack.

[2]  An attacker could gain knowledge about an SA or a UA through
     snooping, and launch an attack against the peer. Given the
     potential value of iSCSI targets and FCIP entities, leaking of such
     information not only increases the possibility of an attack over
     the network; there is also the risk of physical theft.

[3]  An attacker could spoof a DAAdvert. This could cause UAs and SAs to
     use a rogue DAs.

To address these threats, the following capabilities are required:

[a]  Service information, as included in SrvRply, AttrRply, SrvReg and
     SrvDereg messages, needs to be kept confidential.

[b]  The UA has to be able to distinguish between legitimate and
     illegitimate service information from SrvRply and AttrRply
     messages.  In the SLPv2 security model SAs are trusted to sign
     data.

[c]  The DA has to be able to distinguish between legitimate and
     illegitimate SrvReg and SrvDereg messages.

[d]  The UA has to be able to distinguish between legitimate and
     illegitimate  DA Advertisements.  This allows the UA to avoid rogue
     DAs that will return incorrect data or no data at all.  In the
     SLPv2 security model, UAs trust DAs to store, answer queries on and
     forward data on services, but not necessarily to originate it.

[e]  SAs may have to trust DAs, especially if 'mesh-enhanced' SLPv2 is
     used.  In this case, SAs register with only one DA and trust that
     this DA will forward the registration to others.

By itself, SLPv2 security, defined in [RFC2608], does not satisfy these
security requirements.  SLPv2 only provides end-to-end authentication,
but does not support confidentiality. In SLPv2 authentication there is
no way to authenticate "zero result responses".  This enables an
attacker to mount a denial of service attack by sending UAs a "zero
results" SrvRply or AttrRply as if from a DA with whose source address



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corresponds to a legitimate DAAdvert.

In all cases, there is a potential for denial of service attack against
protocol service providers, but such an attack is possible even in the
absence of SLPv2 based discovery mechanisms.

2.5.1.  SLPv2 security protocol

SLPv2 message types include: SrvRqst, SrvRply, SrvReg, SrvDereg, SrvAck,
AttrRqst, AttrRply, DAAdvert, SrvTypeRqst, SrvTypeRply, SAAdvert.  SLPv2
requires that User Agents (UAs) and Service Agents (SAs) support
SrvRqst, SrvRply, and DAAdvert. SAs must additionally support SrvReg,
SrvAck, and SAAdvert.

Where no Directory Agent (DA) exists, the SrvRqst is multicast, but the
SrvRply is sent via unicast UDP. DAAdverts are also multicast. However,
all other SLPv2 messages are sent via UDP unicast.

In order to provide the required security functionality, iSCSI and FCIP
security implementations SHOULD protect SLPv2 messages sent via unicast
using IPsec ESP with a non-null transform. SLPv2 authentication blocks
(carrying digital signatures), described in [RFC2608] MAY also be used
to authenticate unicast and multicast messages.

The usage of SLPv2 by iSCSI is described in [iSCSISLP]. iSCSI initiators
and targets may enable IKE mechanisms to establish identity. In
addition, a subsequent user-level iSCSI session login can protect the
initiator-target nexus.  This will protect them from any compromise of
security in the SLPv2 discovery process.

The usage of SLPv2 by FCIP is described in [FCIPSLP]. FCIP Entities
assume that once the IKE identity of a peer is established, the FCIP
Entity Name carried in FCIP Short Frame is also implicitly accepted as
the authenticated peer.  Any such association between the IKE identity
and the FCIP Entity Name is administratively established.

For use in securing SLPv2, when digital signatures are used to achieve
authentication in IKE, an IKE negotiator SHOULD use IKE Certificate
Request Payload(s) to specify the certificate authority (or authorities)
that are trusted in accordance with its local policy.  IKE negotiators
SHOULD check the pertinent Certificate Revocation List (CRL) before
accepting a PKI certificate for use in IKE's authentication procedures.
If key management of SLPv2 DAs needs to be coordinated with the SAs and
the UAs as well as the protocol service implementations, one may use
certificate based key management, with a shared root Certificate
Authority (CA).



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One of the reasons for utilizing IPsec for SLPv2 security is that is
more likely that certificates will be deployed for IPsec than for SLPv2.
This both simplifies SLPv2 security and makes it more likely that it
will be implemented interoperably and more importantly, that it will be
used. As a result, it is desirable that little additional effort be
required to enable IPsec protection of SLPv2.

However, just because a certificate is trusted for use with IPsec does
not necessarily imply that the host is authorized to perform SLPv2
operations. When using IPsec to secure SLPv2, it may be desirable to
distinguish between certificates appropriate for use by UAs, SAs, and
DAs. For example, while a UA might be allowed to use any certificate
conforming to IKE certificate policy, the certificate used by an SA
might indicate that it is a legitimate source of service advertisements.
Similarly, a DA certificate might indicate that it is a valid DA. This
can be accomplished by using special CAs to issue certificates valid for
use by SAs and DAs; alternatively, SA and DA authorizations can be
employed.

Assume that the policy for issuing and distributing SLPv2 authorized
certificates to SAs and DAs limits them only to legitimate SAs and DAs.
In this case, IPsec is used to provide SLPv2 security as follows:

[a]  SLPv2 messages sent via unicast are IPsec protected, using ESP with
     a non-null transform.

[b]  SrvRply and AttrRply messages from either a DA or SA are unicast to
     UAs.  Assuming that the SA used a certificate authorized for SLPv2
     service advertisement in establishing the IKE Phase 1 SA, or that
     the DA used a certificate authorized for DA usage, the UA can
     accept the information sent, even if it has no SLPv2 authentication
     block.

     Note that where SrvRqst messages are multicast, they are not
     protected. An attacker may attempt to exploit this by spoofing a
     multicast SrvRqst from the UA, generating a SrvRply from an SA of
     the attacker's choosing.  Although the SrvRply is secured, it does
     not correspond to a legitimate SrvRqst sent by the UA. To avoid
     this attack, where SrvRqst messages are multicast, the UA MUST
     check that SrvRply messages represent a legitimate reply to the
     SrvRqst that was sent.

[c]  SrvReg and SrvDereg messages from a SA are unicast to DAs.
     Assuming that the SA used a certificate authorized for SLPv2
     service advertisement in establishing the IKE Phase 1 SA, the DA
     can accept the de/registration even if it has no SLPv2



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     authentication block. Typically, the SA will check the DA
     authorization prior to sending the service advertisement.

[d]  Multicast DAAdverts can be considered advisory.  The UA will
     attempt to contact DAs via unicast.  Assuming that the DA used a
     certificate authorized for SLPv2 DAAdverts in establishing the IKE
     Phase 1 SA, the UA can accept the DAAdvert even if it has no SLPv2
     authentication block.

[e]  SAs can accept DAAdverts as described in [d].

2.5.2.  Confidentiality of service information

Since SLPv2 messages can contain information that can potentially reveal
the vendor of the device or its other associated characteristics,
revealing service information constitutes a security risk. As an
example, the FCIP Entity Name may reveal a WWN from which an attacker
can learn potentially useful information about the Entity's
characteristics.

The SLPv2 security model assumes that service information is public, and
therefore does not provide for confidentiality. However, storage devices
represent mission critical infrastructure of substantial value, and so
iSCSI and FCIP security implementations MUST support confidentiality as
well as authentication of unicast SLPv2 messages.

Assuming that all unicast SLPv2 messages are protected by IPsec, and
that confidentiality is provided, then the risk of disclosure can be
limited to SLPv2 messages sent via multicast, namely the SrvRqst and
DAAdvert.

The information leaked in a multicast SrvRqst depends on the level of
detail in the query. If leakage is a concern, then a DA can be provided.
If this is not feasible, then a general query can be sent via multicast,
and then further detail can be obtained from the replying entities via
additional unicast queries, protected by IPsec.

Information leakage via a multicast DAAdvert is less of a concern than
the authenticity of the message, since knowing that a DA is present on
the network only enables an attacker to know that SLPv2 is in use, and
possibly that a directory service is also present. This information is
not considered very valuable.







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2.5.3.  SLPv2 security implications

Through the definition of security attributes, it is possible to use
SLPv2 to distribute information about security settings for IP block
storage entities.  SLPv2 distribution of security policy is not
necessary if the security settings can be determined by other means,
such as manual configuration or IPsec security policy distribution. If
an entity has already obtained its security configuration via other
mechanisms, then it MUST NOT request security policy via SLPv2.

Where SLPv2 is used to provide security policy information for use with
IP block storage protocols, SLPv2 MUST be protected by IPsec as
described in this document.  Where SLPv2 is not used to distribute
security policy information, implementations MAY implement SLPv2
security as described in this document.

Where SLPv2 is used, but security is not implemented, IP block storage
protocol implementations MUST support a negative cache for
authentication failures. This allows implementations to avoid
continually contacting discovered endpoints that fail authentication
within IPsec or at the application layer (in the case of iSCSI Login).
The negative cache need not be  maintained within the IPsec
implementation, but rather within the IP block storage protocol
implementation.

Since this document proposes that hop-by-hop security be used as the
primary mechanism to protect SLPv2, UAs have to trust DAs to accurately
relay data from SAs.  This is a change to the SLPv2 security model
described in [RFC2608].  However, SLPv2 authentication as defined in
[RFC2608] does not provide a way to authenticate "zero result
responses", leaving SLPv2 vulnerable to a denial of service attack.
Such an attack can be carried out on a UA by sending it a "zero results"
SrvRply or AttrRply, sent from a source address corresponding to a DA
issuing a legitimate DAAdvert.

In addition, SLPv2 security as defined in [RFC2608] does not support
confidentiality.  When IPsec with ESP and a non-null transform is used
to protect SLPv2, not only can unicast requests and replies be
authenticated, but confidentiality can also be provided. This includes
unicast requests to DAs and SAs as well as replies. It is also possible
to actively discover SAs using multicast SA discovery, and then to send
unicast requests to the discovered SAs.

As a result, for use with IP block storage protocols, it is believed
that use of IPsec for security is more appropriate than the SLPv2
security model defined in [RFC2608].



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Using IPsec to secure SLPv2 has performance implications.  Security
associations established between:

-    UAs and SAs may be reused (the client on the UA host will use the
     service on the SA host).

-    SAs and DAs may be reused (the SAs will reregister services)

-    UAs and DAs will probably not be reused (many idle security
     associations are likely to result, and build up on the DA).

When IPsec is used to protect SLPv2, it is not necessarily appropriate
for all hosts with whom an IPsec security association can be established
to be trusted to originate SLPv2 service advertisements. This is
particularly the case in environments where it is easy to obtain
certificates valid for use with IPsec (for example, where anyone with
access to the network can obtain a machine certificate valid for use
with IPsec).  If not all hosts are authorized to originate service
advertisements, then it is necessary to distinguish between authorized
and unauthorized hosts.

This can be accomplished by the following mechanisms:

[1]  Configuring SAs with the identities or certificate characteristics
     of valid DAs, and configuring DAs with the identities of SAs
     allowed to advertise IP block storage services. The DAs are then
     trusted to enforce policies on service registration. This approach
     involves manual configuration, but avoids certificate customization
     for SLPv2.

[2]  Restricting the issuance of certificates valid for use in SLPv2
     service advertisement. While all certificates allowed for use with
     IPsec will chain to a trusted root, certificates for hosts
     authorized to originate service advertisements could be signed by
     an SLPv2-authorized CA, or could contain explicit SLPv2
     authorizations within the certificate. After the IPsec security
     association is set up between the SLPv2 entities, the SLPv2
     implementations can then retrieve the certificates used in the
     negotiation in order to determine whether the entities are
     authorized for the operations that are being performed. This
     approach requires less configuration, but requires some certificate
     customization for use with SLPv2.







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2.6.  iSNS security

The iSCSI protocol may use iSNS for discovery and management services,
while the iFCP protocol is required to use iSNS for such services.  In
addition, iSNS can be used to store and distribute security policy and
authorization information to iSCSI and iFCP devices.  When the iSNS
protocol is deployed, the interaction between iSNS server and iSNS
clients are subject to the following additional security threats:

[1]  An attacker can alter iSNS protocol messages, directing iSCSI and
     iFCP devices to establish connections with rogue devices, or
     weakening IPsec protection for iSCSI or iFCP traffic.

[2]  An attacker can masquerade as the real iSNS server by sending false
     iSNS heartbeat messages.  This could deceive iSCSI and iFCP devices
     into using rogue iSNS servers.

[3]  An attacker can gain knowledge about iSCSI and iFCP devices by
     snooping iSNS protocol messages.  Such information could aid an
     attacker in mounting a direct attack on iSCSI and iFCP devices,
     such as a denial-of-service attack or outright physical theft.

To address these threats, the following capabilities are needed:

[a]  Unicast iSNS protocol messages may need to be authenticated.  In
     addition, to protect against threat [3] above, confidentiality
     support is desirable, and REQUIRED when certain functions of iSNS
     are used.

[b]  Multicast iSNS protocol messages such as the iSNS heartbeat message
     need to be authenticated. These messages need not be confidential
     since they do not leak critical information.

There is no requirement that the identities of iSNS entities be kept
confidential. Specifically, the identity and location of the iSNS server
need not be kept confidential.

In order to protect against an attacker masquerading as an iSNS server,
client devices MUST support authentication of broadcast or multicast
messages such as the iSNS heartbeat.  The iSNS authentication block
(which is identical in format to the SLP authentication block) MAY be
used for this purpose.  Note that the authentication block is used only
for iSNS broadcast or multicast messages, and SHOULD NOT be used in
unicast iSNS messages.





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Since iSNS is used to distribute authorizations determining which client
devices can communicate, IPsec authentication and data integrity MUST be
supported.  In addition, if iSNS is used to distribute security policy
for iFCP and iSCSI devices, then authentication, data integrity, and
confidentiality MUST be supported and used.

Where iSNS is used without security, IP block storage protocol
implementations MUST support a negative cache for authentication
failures. This allows implementations to avoid continually contacting
discovered endpoints that fail authentication within IPsec or at the
application layer (in the case of iSCSI Login).  The negative cache need
not be  maintained within the IPsec implementation, but rather within
the IP block storage protocol implementation.

2.6.1.  Use of iSNS to Discover Security Configuration of Peer Devices

In practice, within a single installation, iSCSI and/or iFCP devices may
have different security settings. For example, some devices may be
configured to initiate secure communication, while other devices may be
configured to respond to a request for secure communication, but not to
require security. Still other devices, while security capable, may
neither initiate nor respond securely.

In practice, these variations in configuration can result in devices
being unable to communicate with each other. For example, a device that
is configured to always initiate secure communication will experience
difficulties in communicating with a device that neither initiates nor
responds securely.

The iSNS protocol is used to transfer naming, discovery, and management
information between iSCSI devices, iFCP gateways, management stations,
and the iSNS server. This includes the ability to enable discovery of
security settings used for communication via the iSCSI and/or iFCP
protocols.

The iSNS server stores security settings for each iSCSI and iFCP device
interface.  These security settings, which can be retrieved by
authorized hosts, include use or non-use of IPsec, IKE, Main Mode,
Aggressive Mode, PFS, Pre-shared Key, and certificates.

For example, IKE may not be enabled for a particular device interface.
If a peer device can learn of this in advance by consulting the iSNS
server, it will not need to waste time and resources attempting to
initiate an IKE Phase 1 SA with that device interface.





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If iSNS is used to distribute security policy, then the minimum
information that should be learned from the iSNS server is the use or
non-use of IKE and IPsec by each iFCP or iSCSI peer device interface.
This information is encoded in the Security Bitmap field of each Portal
of the peer device, and is applicable on a per-interface basis for the
peer device.  iSNS queries to acquire security configuration data about
peer devices MUST be protected by IPsec/ESP authentication.

2.6.2.  Use of iSNS to Distribute iSCSI and iFCP Security Policies

Once communication between iSNS clients and the iSNS server are secured
through use of IPsec, iSNS clients have the capability to discover the
security settings required for communication via the iSCSI and/or iFCP
protocols.  Use of iSNS for distribution of security policies offers the
potential to reduce the burden of manual device configuration, and
decrease the probability of communications failures due to incompatible
security policies.  If iSNS is used to distribute security policies,
then IPsec authentication, data integrity, and confidentiality MUST be
used to protect all iSNS protocol messages.

The complete IKE/IPsec configuration of each iFCP and/or iSCSI device
can be stored in the iSNS server, including policies that are used for
IKE Phase 1 and Phase 2 negotiations between client devices.  The IKE
payload format includes a series of one or more proposals that the iSCSI
or iFCP device will use when negotiating the appropriate IPsec policy to
use to protect iSCSI or iFCP traffic.

Note that iSNS distribution of security policy is not necessary if the
security settings can be determined by other means, such as manual
configuration or IPsec security policy distribution. If an entity has
already obtained its security configuration via other mechanisms, then
it MUST NOT request security policy via iSNS.

For further details on how to store and retrieve IKE policy proposals in
the iSNS server, see [iSNS].

2.6.3.  iSNS Interaction with IKE and IPsec

When IPsec security is enabled, each iSNS client that is registered in
the iSNS database maintains at least one Phase 1 and one Phase 2
security association with the iSNS server.  All iSNS protocol messages
between iSNS clients and the iSNS server are to be protected by a phase-
2 security association.






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2.6.4.  iSNS Server Implementation Requirements

All iSNS implementations MUST support the replay protection mechanisms
of IPsec. ESP in tunnel mode MUST be implemented, and IPsec with ESP in
transport mode MAY be implemented.

To provide data origin authentication and integrity with ESP, HMAC-SHA1
MUST be supported, and AES in CBC MAC mode with XCBC extensions
[AESXCBC] SHOULD be supported.  When confidentiality is implemented,
3DES in CBC mode MUST be supported, and AES in Counter mode, as
described in [AESCTR], SHOULD be supported.  DES in CBC mode SHOULD NOT
be used due to its inherent weakness.  If confidentiality is not
required but data origin authentication and integrity is enabled, ESP
with NULL Encryption MUST be used.

Conformant iSNS implementations MUST support IKE for authentication,
negotiation of security associations, and key management, using the
IPsec DOI, described in [RFC2407]. IP block storage protocols can be
expected to send data in high volumes, thereby requiring rekey.  Since
manual keying does not provide rekeying support, its use is prohibited
with IP block storage protocols.  Although iSNS does not send a high
volume of data, and therefore rekey is not a major concern, manual
keying SHOULD NOT be used. This is for consistency, since dynamic keying
support is already required in IP storage security implementations.

Conformant iSNS security implementations MUST support authentication
using a pre- shared key, and MAY support certificate-based peer
authentication using digital signatures.  Peer authentication using the
public key encryption methods outlined in [RFC2409] sections 5.2 and 5.3
SHOULD NOT be used.

Conformant iSNS implementations MUST support IKE Main Mode and SHOULD
support Aggressive Mode. IKE Main Mode with pre-shared key
authentication SHOULD NOT be used when either of the peers use
dynamically assigned IP addresses. While Main Mode with pre-shared key
authentication offers good security in many cases, situations where
dynamically assigned addresses are used force use of a group pre-shared
key, which is vulnerable to man-in-the-middle attack.

When digital signatures are used for authentication, either IKE Main
Mode or IKE Aggressive Mode MAY be used.  In all cases, access to
locally stored secret information (pre-shared key or private key for
digital signing) MUST be suitably restricted, since compromise of the
secret information nullifies the security properties of the IKE/IPsec
protocols.




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When digital signatures are used to achieve authentication, an IKE
negotiator SHOULD use IKE Certificate Request Payload(s) to specify the
certificate authority (or authorities) that are trusted in accordance
with its local policy.  IKE negotiators SHOULD check the pertinent
Certificate Revocation List (CRL) before accepting a PKI certificate for
use in IKE's authentication procedures.

3.  iSCSI security interoperability guidelines

The following guidelines are established to meet iSCSI security
requirements using IPsec in practical situations.

3.1.  iSCSI security issues

iSCSI provides for iSCSI Login, outlined in [iSCSI], which includes
support for application-layer authentication.  This authentication is
logically between the iSCSI initiator and the iSCSI target (as opposed
to between the TCP/IP communication endpoints).  The intent of the iSCSI
design is that the initiator and target represent the systems (e.g.,
host and disk array or tape system) participating in the communication,
as opposed to network communication interfaces or endpoints.

The iSCSI protocol and iSCSI Login authentication do not meet the
security requirements for iSCSI. iSCSI Login authentication provides
mutual authentication between the iSCSI initiator and target at
connection origination, but does not protect control and data traffic on
a per packet basis, leaving the iSCSI connection vulnerable to attack.
iSCSI Login authentication can mutually authenticate the initiator to
the target, but does not by itself provide per-packet authentication,
integrity, confidentiality or replay protection. In addition, iSCSI
Login authentication does not provide for a protected ciphersuite
negotiation.  Therefore, iSCSI Login provides a weak security solution.

3.2.  iSCSI and IPsec interaction

An iSCSI session [iSCSI], comprised of one or more TCP connections, is
identified by the 2-tuple of the initiator-defined identifier and the
target-defined identifier, <ISID, TSIH>.  Each connection within a given
session is assigned a unique Connection Identification, CID. The TCP
connection is identified by the 5-tuple <Source IP address, Destination
IP address, Protocol (TCP), Source Port, Destination Port>.  An IPsec
Phase 2 SA is identified by the 3-tuple <Protocol (ESP),destination
address, SPI>.

The iSCSI session and connection information is carried within the iSCSI
Login Commands, transported over TCP.  Since an iSCSI initiator may have



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multiple interfaces, iSCSI connections within an iSCSI session may be
initiated from different IP addresses. Similarly, multiple iSCSI targets
may exist behind a single IP address, so that there may be multiple
iSCSI sessions between a given <source IP address, destination IP
address> pair.

When multiple iSCSI sessions are active between a given <initiator,
target> pair, the set of TCP connections used by a given iSCSI session
must be disjoint from those used by all other iSCSI sessions between the
same <initiator, target> pair. Therefore a TCP connection can be
associated with one and only one iSCSI session.

The relationship between iSCSI sessions, TCP connections and IKE Phase 1
and Phase 2 SAs is as follows:

[1]  An iSCSI initiator or target may have more than one interface, and
     therefore may have multiple IP addresses. Also, multiple iSCSI
     initiators and targets may exist behind a single IP address.  As a
     result, an iSCSI Session may correspond to multiple IKE Phase 1
     Security Associations, though typically a single IKE Phase 1
     security association will exist for an <initiator IP address,
     target IP address> tuple.

[2]  Each TCP connection within an iSCSI Session is protected by an IKE
     Phase 2 SA. The selectors may be specific to that TCP connection or
     may cover multiple connections. While each IKE Phase 2 SA may
     protect multiple TCP connections, each TCP connection is
     transported under only one IKE Phase 2 SA.

Given this, all the information needed for the iSCSI/IPsec binding is
contained within the iSCSI Login messages from the iSCSI initiator and
target. This includes the binding between an IKE Phase 1 SA and the
corresponding iSCSI sessions, as well as the binding between a TCP
connection, an IKE Phase 2 SA and the iSCSI connection ID.

3.3.  Initiating a New iSCSI Session

In order to create a new iSCSI Session, if an IKE Phase 1 SA does not
already exist, then it is established by an initiator implementing iSCSI
security.  Subsequent iSCSI connections established within the iSCSI
session will typically be protected by IKE Phase 2 SAs derived from that
IKE Phase 1 SA, although additional IKE Phase 1 SAs can also be brought
up.

The initiator and target implementations successfully complete the IKE
Phase 1 and Phase 2 negotiations before the iSCSI initiator contacts the



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target on well-known TCP port 3260, and sends the iSCSI Login command
over the TCP connection.  IPsec implementations configured with the
correct policies (e.g. use ESP with non-null transform for all traffic
destined for the iSCSI well-known TCP port 3260) will handle this
automatically.

The initiator fills in the ISID field, and leaves the TSIH field set to
zero, to indicate that it is the first message of a new session
establishment exchange.  The initiator also fills in a CID value, that
identifies the TCP connection over which the Login command is being
exchanged. When the iSCSI target replies with its Login Command, both
iSCSI devices will know the TSIH, and therefore the iSCSI session
identifier <ISID, TSIH>.

A single iSCSI session identifier may have multiple associated IKE Phase
1 SAs, and each IKE Phase 1 SA may correspond to multiple iSCSI session
identifiers. Each iSCSI connection (identified by the connection
identifier) corresponds to a single TCP connection (identified by the
5-tuple). Each IKE Phase 2 SA is identified by the <Protocol (ESP),
destination address, SPI> combination.  A Phase 2 SA may protect
multiple TCP connections, and corresponds to a single IKE Phase 1 SA.

Within IKE, each key refresh requires that a new security association be
established.  In practice there is a time interval during which an old,
about-to-expire SA and newly established SA will both be valid.  The
IPsec implementation will choose which security association to use based
on local policy, and iSCSI concerns play no role in this selection
process.

3.4.  Graceful iSCSI Teardown

Mechanisms within iSCSI provide for both graceful and non-graceful
teardown of iSCSI Sessions or individual TCP connections within a given
session.  The iSCSI Logout command is used to effect graceful teardown.
This command allows the iSCSI initiator to request that:

[a]  the session be closed

[b]  a specific connection within the session be closed

[c]  a specific connection be marked for recovery

When the iSCSI implementation wishes to close a session, it uses the
appropriate iSCSI commands to accomplish this.  After exchanging the
appropriate iSCSI control messages for session closure, the iSCSI
security implementation will typically initiate a half-close of each TCP



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connection within the iSCSI session.

When the iSCSI security implementation wishes to close an individual TCP
connection while leaving the parent iSCSI session active, it should
half-close the TCP connection. After the expiration of the TIME_WAIT
timeout, the TCP connection is closed.

3.5.  Non-graceful iSCSI Teardown

If a given TCP connection unexpectedly fails, the associated iSCSI
connection is torn down. There is no requirement that an IKE Phase 2
delete immediately follow iSCSI connection tear down or Phase 1
deletion.  Since an IKE Phase 2 SA may correspond to multiple TCP
connections, such a deletion might be inappropriate. Similarly, if the
IKE implementation receives a Phase 2 Delete message for a security
association corresponding to a TCP connection, this does not necessarily
imply that the TCP or iSCSI connection is to be torn down.

If a Logout Command/Logout Response sequence marks a connection for
removal from the iSCSI session, then after the iSCSI peer has executed
an iSCSI teardown process for the connection, the TCP connection will be
closed. The iSCSI connection state can then be safely removed.

Since an IKE Phase 2 SA may be used by multiple TCP connections, an
iSCSI implementation should not depend on receiving the IPsec Phase 2
delete as confirmation that the iSCSI peer has executed an iSCSI
teardown process for the connection.

Since IPsec acceleration hardware may only be able to handle a limited
number of active IKE Phase 2 SAs, Phase 2 delete messages may be sent
for idle SAs, as a means of keeping the number of active Phase 2 SAs to
a minimum. The receipt of an IKE Phase 2 delete message MUST NOT be
interpreted as a reason for tearing down the corresponding iSCSI
connection if no Logout Command/Logout Receive has been executed on the
connection.  Rather, it is preferable to leave the iSCSI connection up,
and if additional traffic is sent on it, to bring up another IKE Phase 2
SA to protect it. This avoids the potential for continually bringing
iSCSI connections up and down.

3.6.  Application-layer CRC

iSCSI's error detection and recovery assumes that the TCP and IP
checksums provide inadequate integrity protection for high speed
communications. As described in [CRCTCP], when operating at high speeds,
the 16-bit TCP checksum [RFC793] will not necessarily detect all errors,
resulting in possible data corruption.  iSCSI [iSCSI] therefore



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incorporates a 32-bit CRC to protect its headers and data.

When a CRC check fails (i.e.  CRC computed at receiver does not match
the received CRC), the iSCSI PDU covered by that CRC is discarded.
Since presumably the error was not detected by the TCP checksum, TCP
retransmission will not occur and thus cannot assist in recovering from
the error.  iSCSI contains both data and command retry mechanisms to
deal with the resulting situations, including SNACK, the ability to
reissue R2T commands, and the retry (X) bit for commands.

IPsec offers protection against an attacker attempting to modify packets
in transit, as well as unintentional packet modifications caused by
network malfunctions or other errors. In general, IPsec authentication
transforms afford stronger integrity protection than both the 16-bit TCP
checksum and the 32-bit application-layer CRC specified for use with
iSCSI. Since IPsec integrity protection occurs below TCP, if an error is
discovered, then the packet will be discarded and TCP retransmission
will occur, so that no recovery action need be taken at the iSCSI layer.

3.6.1.  Simplification of recovery logic

Where IPsec integrity protection is known to be in place end-to-end
between iSCSI endpoints (or the portion that requires additional
integrity protection), portions of iSCSI can be simplified. For example,
mechanisms to recover from CRC check failures are not necessary.

If the iSCSI CRC is negotiated, the recovery logic can be simplified to
regard any CRC check failure as fatal (e.g., generate a SCSI CHECK
CONDITION on data error, close the corresponding TCP connection on
header error) because it will be very rare for errors undetected by
IPsec integrity protection to be detected by the iSCSI CRC.

3.6.2.  Omission of iSCSI CRC

In some situations where IPsec is employed, the iSCSI CRC will not
provide additional protection and can be omitted.

For example, where IPsec processing as well as TCP checksum and iSCSI
CRC verification are offloaded within the NIC, each of these checks will
be verified prior to transferring data across the bus, so that
subsequent errors will not be detected by these mechanisms.  As a
result, where IPsec processing is offloaded to the NIC, the iSCSI CRC is
not necessary and the implementations may wish not to negotiate it.

However, in other circumstances, the TCP checksum and iSCSI CRC will
provide additional error coverage because they are computed and checked



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at a different point in the protocol stack or in devices different from
those that implement the IPsec integrity checks.  The resulting coverage
of additional possible errors may make it desirable to negotiate use of
the iSCSI CRC even when IPsec integrity protection is in use.  Examples
of these situations include where:

[1]  IPsec, TCP and iSCSI are implemented purely in software.  Here,
     additional failure modes may be detected by the TCP checksum and/or
     iSCSI CRC. For example, after the IPsec message integrity check is
     successfully verified, the segment is copied as part of TCP
     processing, and a memory error during this process might cause the
     TCP checksum or iSCSI CRC verification to fail.

[2]  The implementation is an iSCSI-iSCSI proxy or gateway. Here the
     iSCSI CRC can be propagated from one iSCSI connection to another.
     In this case, the iSCSI CRC is useful to protect iSCSI data against
     memory, bus, or software errors within the proxy or gateway, and
     requesting it is desirable.

[3]  IPsec is provided by a device external to the actual iSCSI device.
     Here the iSCSI header and data CRCs can be kept across the part of
     the connection that is not protected by IPsec. For instance, the
     iSCSI connection could traverse an extra bus, interface card,
     network, interface card, and bus between the iSCSI device and the
     device providing IPsec. In this case, the iSCSI CRC is desirable,
     and the iSCSI implementation behind the IPsec device may request
     it.

     Note that if both ends of the connection are on the same segment,
     then traffic will be effectively protected by the layer 2 CRC, so
     that negotiation of the iSCSI CRC is not necessary to protect
     against NIC and network errors, although it may be desirable for
     other reasons (e.g., [1] and [2] above).

4.  iFCP and FCIP security issues

4.1.  iFCP and FCIP Authentication Requirements

iFCP and FCIP are peer-to-peer protocols.  iFCP and FCIP sessions may be
initiated by either or both peer gateways. Consequently, bi-directional
authentication of peer gateways MUST be provided.

iFCP and FCIP are transport protocols that encapsulate SCSI and Fibre
Channel frames over IP. Therefore, Fibre Channel, operating system, and
user identities are transparent to the iFCP and FCIP protocols.




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iFCP gateways use Discovery Domain information obtained from the iSNS
server to determine whether the initiating Fibre Channel N_PORT should
be allowed access to the target N_PORT.  N_PORT identities used in the
Port Login (PLOGI) process will be considered authenticated provided
that they are received over a connection whose security complies with
the local security policy.

There is no requirement that the identities used in authentication be
kept confidential.

4.2.  iFCP Interaction with IPsec and IKE

A conformant iFCP Portal is capable of establishing one or more IKE
Phase-1 Security Associations (SAs) to a peer iFCP Portal. A Phase-1 SA
may be established when an iFCP Portal is initialized, or may be
deferred until the first TCP connection with security requirements is
established.

An IKE Phase-2 SA protects one or more TCP connections within the same
iFCP Portal. More specifically, the successful establishment of an IKE
Phase-2 SA results in the creation of two uni-directional IPsec SAs
fully qualified by the tuple <SPI, destination IP address, ESP>. These
SAs protect the setup process of the underlying TCP connections and all
their subsequent TCP traffic. Each of the TCP connections protected by
an SA is either in the unbound state, or is bound to a specific iFCP
session.

In summary, at any point in time:

[1] There exist 0..M IKE Phase-1 SAs between peer iFCP portals
[2] Each IKE Phase-1 SAs has 0..N IKE Phase-2 SAs
[3] Each IKE Phase-2 SA protects 0..Z TCP connections

The creation of an IKE Phase-2 SA may be triggered by security policy
rules retrieved from an iSNS server.  Alternately, the creation of an SA
may be triggered by policy rules configured through a management
interface, reflecting iSNS-resident policy rules.  Likewise, the use of
a Key Exchange payload in Quick Mode for perfect forward secrecy may be
driven by security policy rules retrieved from the iSNS server, or set
through a management interface.

If an iFCP implementation makes use of unbound TCP connections, and such
connections belong to an iFCP Portal with security requirements, then
the unbound connections MUST be protected by an SA at all times just
like bound connections.




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Upon receiving an IKE Phase-2 delete message, there is no requirement to
terminate the protected TCP connections or delete the associated IKE
Phase-1 SA. Since an IKE Phase-2 SA may be associated with multiple TCP
connections, terminating such connections might in fact be inappropriate
and untimely.

To minimize the number of active Phase-2 SAs, IKE Phase-2 delete
messages may be sent for Phase-2 SAs whose TCP connections have not
handled data traffic for a while. To minimize the use of SA resources
while the associated TCP connections are idle, creation of a new SA
should be deferred until new data are to be sent over the connections.

4.3.  FCIP Interaction with IPsec and IKE

FCIP Entities establish tunnels with other FCIP Entities in order to
transfer IP encapsulated FC frames. Each tunnel is a separate FCIP Link,
and can encapsulate multiple TCP connections.  The binding of TCP
connections to an FCIP Link is performed using the Fibre Channel World
Wide Names (WWNs) of the two FCIP Entities.

FCIP Entities may have more than one interface and IP address, and it is
possible for an FCIP Link to contain multiple TCP connections whose FCIP
endpoint IP Addresses are different. In this case, an IKE Phase 1 SA is
typically established for each FCIP endpoint IP Address pair. For the
purposes of establishing an IKE Phase 1 SA, static IP addresses are
typically used for identification.

Each TCP connection within an FCIP Link corresponds to an IKE Phase 2
(Quick Mode) SA. This is established prior to sending the initial TCP
SYN packet and applies to the life of the connection. Phase 2
negotiation is also required for rekeying, in order to protect against
replay attacks.

FCIP implementations MAY provide administrative management of
Confidentiality usage. These management interfaces SHOULD be provided in
a secure manner, so as to prevent an attacker from subverting the
security process by attacking the management interface.

FCIP Entities do not require any user-level authentication, since all
FCIP Entities participate in a machine-level tunnel function.  FCIP uses
SLP for discovery, but not to distribute security policies.








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5.  Security Considerations

5.1.  Transport mode versus tunnel mode

With respect to block storage protocols, the major differences between
the IPsec tunnel mode and transport mode are as follows:

[1]  MTU considerations. Tunnel mode introduces an additional IP header
     into the datagram that reflects itself in a corresponding decrease
     in the path MTU seen by packets traversing the tunnel. This may
     result in a decrease in the maximum segment size of TCP connections
     running over the tunnel.

[2]  Address assignment and configuration.  Within IPsec tunnel mode, it
     is necessary for inner and outer source addresses to be configured,
     and for inner and outer destination addresses to be discovered.
     Within transport mode it is only necessary to discover a single
     destination address and configure a single source address.  IPsec
     tunnel mode address usage considerations are discussed in more
     detail below.

[3]  NAT traversal. As noted in [IPsecNATReq], IPsec tunnel mode ESP can
     traverse NAT in limited circumstances, whereas transport mode ESP
     cannot traverse NAT.  To enable NAT traversal in the general case,
     the IPsec NAT traversal functionality described in [IPsecNATReq],
     [UDPIPsec] and [NATIKE] can be implemented.  More details are
     provided in the next section.

[4]  Firewall traversal. Where a block storage protocol is to traverse
     administrative domains, the firewall administrator may desire to
     verify the integrity and authenticity of each transiting packet,
     rather than opening a hole in the firewall for the block storage
     protocol. IPsec tunnel mode lends itself to such verification,
     since the firewall can terminate the tunnel mode connection while
     still allowing the endpoints to communicate end-to-end. If desired,
     the endpoints can in addition utilize IPsec transport mode for end-
     to-end security, so that they can also verify authenticity and
     integrity of each packet for themselves.

     In contrast, carrying out this verification with IPsec transport
     mode is more complex, since the firewall will need to terminate the
     IPsec transport mode connection and will need to act as an iSCSI,
     iFCP or FCIP gateway or TCP proxy, originating a new IPsec
     transport mode connection from the firewall to the internal
     endpoint. Such an implementation cannot provide end-to-end
     authenticity or integrity protection, and an application-layer CRC



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     (iSCSI) or forwarding of the Fibre Channel frame CRC (iFCP and
     FCIP) is necessary to protect against errors introduced by the
     firewall.

[5]  IPsec-application integration. Where IPsec and the application
     layer protocol are implemented on the same device or host, it is
     possible to enable tight integration between them. For example, the
     application layer can request and verify that connections are
     protected by IPsec, and can obtain attributes of the IPsec security
     association. While in transport mode implementations the IPsec and
     application protocol implementations typically reside on the same
     host, with IPsec tunnel mode they may reside on different hosts.
     Where IPsec is implemented on an external gateway, integration
     between the application and IPsec is typically not possible. This
     limits the ability of the application to control and verify IPsec
     behavior.

5.1.1.  IPsec tunnel mode addressing considerations

IPsec tunnels include both inner and outer source as well as destination
addresses.

When used with IP block storage protocols, the inner destination address
represents the address of the IP block storage protocol peer (e.g. the
ultimate destination for the packet). The inner destination address can
be discovered using SLPv2 or iSNS, or can be resolved from an FQDN via
DNS, so that obtaining this address is typically not an issue.

The outer destination address represents the address of the IPsec
security gateway used to reach the peer. Several mechanisms have been
proposed for discovering the IPsec security gateway used to reach a
particular peer.  [RFC2230] discusses the use of KX Resource Records
(RRs) for IPsec gateway discovery. However, while KX RRs are supported
by many DNS server implementations, they have not yet been widely
deployed. Alternatively, DNS SRV [RFC2782] can be used for this purpose.
Where DNS is used for gateway location, DNS security mechanisms such as
DNSSEC ([RFC2535], [RFC2931]), TSIG [RFC2845], and Simple Secure Dynamic
Update [RFC3007] are advisable.

When used with IP block storage protocols, the outer source address is
configured either statically or dynamically, using mechanisms such as
DHCPv4 [RFC2131], DHCPV6 [DHCPv6], or stateless address
autoconfiguration [RFC2373].

The inner source address SHOULD be included in the Quick Mode ID payload
when the peer establishes a tunnel mode SA with the IPsec security



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gateway. This enables the IPsec security gateway to properly route
packets back to the remote peer. The inner source address can be
configured via a variety of mechanisms, depending on the scenario. Where
the IP block storage peers are located within the same administrative
domain, it is typically possible for the inner and outer source
addresses to be the same. This will work because the outer source
address is presumably assigned from within a prefix assigned to the
administrative domain, and is therefore routable within the domain.
Assuming that the IPsec security gateway is aware of the inner source
address used by the connecting peer and plumbs a host route for it, then
packets arriving at the IPsec security gateway destined for the address
can be correctly encapsulated and sent down the correct tunnel.

Where IP block storage peers are located within different administrative
domains, it may be necessary for the inner source address to be assigned
by the IPsec security gateway, effectively "joining" the remote host to
the LAN attached to the IPsec security gateway. For example, if the
remote peer were to use its assigned (outer) source address as the inner
source address, then a number of problems might result:

[1]  Intrusion detection systems sniffing the LAN behind the IPsec
     security gateway would notice source addresses originating outside
     the administrative domain.

[2]  Reply packets might not reach their destination, since the IPsec
     security gateway typically does not advertise the default route,
     but rather only the prefix that it allocates addresses from. Since
     the remote peer's address does not originate from with a prefix
     native to the administrative domain, it is likely that routers
     within the domain would not have a route for it, and would send the
     packet off to the router advertising the default route (perhaps a
     border router) instead of to the IPsec security gateway.

For these reasons, for inter-domain use, assignment of inner source
addresses may be needed. At present this is not a very common scenario;
however, if address assignment is provided, then DHCP-based address
assignment within IPsec tunnel mode [DHCPIPsec] MUST be supported.  Note
that this mechanism is not yet widely deployed within IPsec security
gateways; existing IPsec tunnel mode servers typically implement this
functionality via proprietary extensions to IKE.

5.2.  NAT traversal

As noted in [IPsecNATJust], tunnel mode ESP can traverse NAT in a
limited set of circumstances. For example, if there is only one protocol
endpoint behind a NAT, "ANY to ANY" selectors are negotiated, and the



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receiver does not perform source address validation, then tunnel mode
ESP may successfully traverse NATs.  Since ignoring source address
validation introduces new security vulnerabilities, and negotiation of
specific selectors is desirable so as to limit the traffic that can be
sent down the tunnel, these conditions may not necessarily apply, and
tunnel mode NAT traversal will not always be possible.

TCP carried within Transport mode ESP cannot traverse NAT, even though
ESP itself does not include IP header fields within its message
integrity check. This is because the 16-bit TCP checksum is calculated
based on a "pseudo-header" that includes IP header fields, and the
checksum is protected by the IPsec ESP message integrity check. As a
result, the TCP checksum will be invalidated by a NAT located between
the two endpoints.

Since TCP checksum calculation and verification is mandatory in both
IPv4 and IPv6, it is not possible to omit checksum verification while
remaining standards compliant.  In order to enable traversal of NATs
existing while remaining in compliance, iSCSI, iFCP or FCIP security
implementations can implement IPsec/IKE NAT traversal, as described in
[IPsecNATReq], [UDPIPsec], and [NATIKE].

The IKE [NATIKE] and IPsec [UDPIPsec] NAT traversal specifications
enable UDP encapsulation of IPsec to be negotiated if a NAT is detected
in the path. By determining the IP address of the NAT, the TCP checksum
can be calculated based on a pseudo-header including the NAT-adjusted
address and ports. If this is done prior to calculating the IPsec
message integrity check, TCP checksum verification will not fail.

5.3.  IKE issues

There are situations where it is necessary for IKE to be implemented in
firmware.  In such situations, it is important to keep the size of the
IKE implementation within strict limits.  An upper bound on the size of
an IKE implementation might be considered to be 800 KB, with 80 KB
enabling implementation in a wide range of situations.

As noted in Table 5.3-1 on the next page, IKE implementations currently
exist which meet the requirements. Therefore, while removal of seldom
used IKE functionality (such as the nonce authentication methods) would
reduce complexity, implementations typically will not require this in
order to fit within the code size budget.







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5.4.  Rekeying issues

It is expected that IP block storage implementations will need to
operate at high speed. For example, implementations operating at 1 Gbps
are currently in design, with 10 Gbps implementations to follow shortly
thereafter. At these speeds, a single IPsec SA could rapidly cycle
through the 32-bit IPsec sequence number space.

For example, a single SA operating at 1 Gbps line rate and sending 64
octet packets would exhaust the 32-bit sequence number space in 2200
seconds, or 37 minutes. With 1518 octet packets, exhaustion would occur
in 14.5 hours.  At 10 Gbps, exhaustion would occur in 220 seconds or
3.67 minutes. With 1518 octet packets, this would occur within 1.45
hours.

In the future, it may be desirable for implementations operating at
speeds of 1 Gbps or greater to implement IPsec sequence number
extension, described in [Seq].  Note that depending on the transform in
use, it is possible that rekeying will be required prior to exhaustion
of the sequence number space.

In CBC-mode ciphers the ciphertext of one block depends on the plaintext
of that block as well as the ciphertext of the previous block. This
implies that if the ciphertext of two blocks are identical, and the
plaintext of the next block is also identical, then the ciphertext of
the next block will be identical. Thus, if identical ciphertext blocks
can be found with matching subsequent blocks, an attacker can determine
the existence of matching plaintext.

Such "Birthday attacks" were examined by Bellare et. al. in [DESANALY].
On average, a ciphertext block of size n bits will be expected to repeat
every 2^[n/2] blocks. Although a single "birthday attack" does not
provide much information to an attacker, multiple such attacks might
provide useful information.  To  make this unlikely, it is recommended
that a rekey occur before 2^[n/2] blocks have been sent on a given SA.
Bellare et. al. have formalized this in [DESANALY], showing that the
insecurity of CBC mode increases as O(s^2/2^n), where n is the block
size in bits, and s is the total number of blocks encrypted.  These
conclusions do not apply to counter mode.










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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               | Code size   |             |
|Implementation |  (octets)   | Release     |
|               |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |             | Linux       |
| Pluto         |  258KB      | FreeSWAN    |
|(FreeSWAN)     |             | x86         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |             |             |
| Racoon        |  400KB      | NetBSD 1.5  |
| (KAME)        |             | x86         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |             |             |
| Isakmpd       |  283KB      | NetBSD 1.5  |
| (Erickson)    |             | x86         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |             |             |
| WindRiver     |  142KB      | PowerPC     |
|               |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |             |             |
| Cisco         |  222KB      | PowerPC     |
| VPN1700       |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |             |             |
| Cisco         |  350K       | PowerPC     |
| VPN3000       |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |             |             |
| Cisco         |  228KB      | MIPS        |
| VPN7200       |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


Table 5.3-1 - Code Size for IKE implementations

The formula below sets a limit on the bytes that can be sent on a CBC SA
before a rekey is required:

            B = (n/8) * 2^[n/2]
Where:
            B = maximum bytes sent on the SA
            n = block size in bits





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This means that cipher block size as well as key length needs to be
considered in the rekey decision. 3DES uses a block size n = 64 bits
(2^3 bytes); this implies that the SA must be rekeyed before B = (64/8)
* (2^32) = 2^35 bytes are sent. At 1 Gbps, this implies that a rekey
will be required every 274.9 seconds (4.6 minutes); at 10 Gbps, a rekey
is required every 27.5 seconds.

In terms of the sequence number space, for a 3DES encrypted message of
512 = 2^9 bytes (2^6 blocks) this implies that the key has become
insecure after about 2^26 messages.

5.5.  Transform issues

Since IP block storage implementations may operate at speeds of 1 Gbps
or greater, the ability to offer IPsec security services at high speeds
is of intense concern. Since support for multiple algorithms multiplies
the complexity and expense of hardware design, one of the goals of the
transform selection effort is to find a minimal set of confidentiality
and authentication algorithms implementable in hardware at speeds of up
to 10 Gbps, as well as being efficient for implementation in software at
speeds of 100 Mbps or slower.

In this specification, we primarily concern ourselves with IPsec
transforms that have already been specified, and for which parts are
available that can run at 1 Gbps line rate. Where existing algorithms do
not gracefully scale to 10 Gbps, we further consider algorithms for
which transform specifications are not yet complete, but for which parts
are expected to be available for inclusion in products shipping within
the next 12 months. As the state of the art advances, the range of
feasible algorithms will broaden and additional mandatory-to-implement
algorithms may be considered.

Section 5 of [RFC2406] states:

   "A compliant ESP implementation MUST support the following
   mandatory-to-implement algorithms:

         - DES in CBC mode
         - HMAC with MD5
         - HMAC with SHA-1
         - NULL Authentication algorithm
         - NULL Encryption algorithm
   "

The DES algorithm is specified in [FIPS46-3]; implementation guidelines
are found in [FIPS74], and security issues are discussed in



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[DESDIFF],[DESINT], [DESCRACK]. The DES IPsec transform is defined in
[RFC2405] and the 3DES in CBC mode IPsec transform is specified in
[RFC2451].

The MD5 algorithm is specified in [MD5]; HMAC is defined in [RFC2104]
and security issues with MD5 are discussed in [MD5Attack]. The HMAC-MD5
IPsec transform is specified in [HMACMD5IPsec].  The HMAC-SHA1 IPsec
transform is specified in [RFC2404].

In addition to these existing algorithms, NIST is currently evaluating
the following modes [NSPUE2] of AES, defined in [FIPS197]:

     AES in Electronic Codebook (ECB) confidentiality mode
     AES in Cipher Block Chaining (CBC) confidentiality mode
     AES in Cipher Feedback (CFB) confidentiality mode
     AES in Output Feedback (OFB) confidentiality mode
     AES in Counter (CTR) confidentiality mode
     AES CBC-MAC authentication mode

When utilizing AES modes, it may be necessary to use larger public keys;
the tradeoffs are described in [KeyLen]. Additional MODP Diffie-Hellman
groups for use with IKE are described in [MODP].

The Modes [NSPUE2] effort is also considering a number of additional
algorithms, including the following:

     PMAC

To provide authentication, integrity and replay protection, IP block
storage security implementations MUST support HMAC-SHA1 [RFC2404] for
authentication, and AES in CBC MAC mode with XCBC extensions SHOULD be
supported [AESXCBC].

HMAC-SHA1 [RFC2404] is to be preferred to HMAC-MD5, due to concerns that
have been raised about the security of MD5 [MD5Attack].  HMAC-SHA1 parts
are currently available that run at 1 Gbps, the algorithm is
implementable in hardware at speeds up to 10 Gbps, and an IPsec
transform specification [RFC2404] exists. As a result, it is most
practical to utilize HMAC-SHA1 as the authentication algorithm for
products shipping in the near future.  AES in CBC-MAC authentication
mode with XCBC extensions was selected since it avoids adding
substantial additional code if AES is already being implemented for
encryption; an IPsec transform document is available [AESCBC].

Authentication transforms also exist that are considerably more
efficient to implement than HMAC-SHA1, or AES in CBC-MAC authentication



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mode.  UMAC [UMAC],[UMACKR] is more efficient to implement in software
and PMAC [PMAC] is more efficient to implement in hardware.  PMAC is
currently being evaluated as part of the NIST modes effort [NSPUE2] but
an IPsec transform does not yet exist; neither does a UMAC transform.

For confidentiality, the ESP mandatory-to-implement algorithm (DES) is
unacceptable.  As noted in [DESCRACK], DES is crackable with modest
computation resources, and so is inappropriate for use in situations
requiring high levels of security.

To provide confidentiality for iSCSI, iFCP, and FCIP, 3DES in CBC mode
[RFC2451] MUST be supported and AES in Counter Mode [AESCTR] SHOULD be
supported. For use in high speed implementations, 3DES has significant
disadvantages. However, a 3DES IPsec transform has been specified and
parts are available that can run at 1 Gbps, so implementing 3DES in
products is practical for the short term.

As described in Appendix B, 3DES software implementations make excessive
computational demands at speeds of 100 Mbps or greater, effectively
ruling out software-only implementations.  In addition, 3DES
implementations  require rekeying prior to exhaustion of the current
32-bit IPsec sequence number space, and thus would not be able to make
use of sequence space extensions if they were available. This means that
3DES will require very frequent rekeying at speeds of 10 Gbps or faster.
Thus, 3DES is inconvenient for use at very high speeds, as well as being
impractical for implementation in software at slower speeds (100+ Mbps).

5.6.  Fragmentation Issues

When certificate authentication is used, IKE fragmentation can be
encountered. This can occur when certificate chains are used, or even
when exchanging a single certificate if the key size or size of other
certificate fields (such as the distinguished name and other OIDs) is
large enough. Many Network Address Translators (NATs) and firewalls do
not handle fragments properly, dropping them on inbound and/or outbound.

Routers in the path will also frequently discard fragments after the
initial one, since they typically will not contain full IP headers that
can be compared against an Access List.

As a result, where IKE fragmentation occurs, the endpoints will often be
unable to establish an IPsec security association.  The solution to this
problem is to install NAT, firewall or router code load that can
properly support fragments. If this cannot be done, then the following
alternatives can be considered:




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[1]  Obtaining certificates by other means.

[2]  Reducing the size of the certificate chain.

[3]  Reducing  the size of fields within the certificates. This includes
     reduction in the key size, the distinguished name or other fields.
     This should be considered only as a last resort.

Fragmentation can become a concern when prepending IPsec headers to a
frame. One mechanism that can be used to reduce this problem is to
utilize path MTU discovery.  For example, when TCP is used as the
transport for iSCSI, iFCP or FCIP then path MTU discovery, described in
[RFC1191], [RFC1435], [RFC1981], can be used to enable the TCP endpoints
to discover the correct MTU, including effects due to IPsec
encapsulation.

However, Path MTU discovery fails when appropriate ICMP messages are not
received by the host. This occurs in IPsec implementations that drop
unauthenticated ICMP packets.  This can result in blackholing in naive
TCP implementations, as described in [RFC2923].  Appropriate TCP
behavior is described in section 2.1 of [RFC2923]:

   "TCP should notice that the connection is timing out. After several
   timeouts, TCP should attempt to send smaller packets, perhaps turning
   off the DF flag for each packet. If this succeeds, it should continue
   to turn off PMTUD for the connection for some reasonable period of
   time, after which it should probe again to try to determine if the
   path has changed."

If an ICMP PMTU is received by an IPsec implementation that processes
unauthenticated ICMP packets, this value should be stored in the SA as
proposed in [RFC2401], and IPsec should also provide notification of
this event to TCP so that the new MTU value can be correctly reflected.

5.7.  Security Checks

When a connection is opened which requires security, IP block storage
security implementations may wish to check that the connection is
protected by IPsec. If security is desired and IPsec protection is
removed on a connection, it is reinstated before non-protected IP block
storage packets are sent.  Since IPsec verifies that each packet arrives
on the correct SA, as long as it can be ensured that IPsec protection is
in place, then IP block storage implementations can be assured that each
received packet was sent by a trusted peer.





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When used with IP block storage protocols, each TCP connection MUST be
protected by an IKE Phase 2 SA. Traffic from one or more than one TCP
connection may flow within each IPsec Phase 2 SA. IP block storage
security implementations need not verify that the IP addresses and TCP
port values in the packet match the socket information that was used to
setup the connection. This check will be performed by IPsec, preventing
malicious peers from sending commands on inappropriate Quick Mode SAs.

5.8.  Authentication issues

5.8.1.  Machine versus user certificates

The certificate credentials provided by the iSCSI initiator during the
IKE negotiation may be those of the machine or of the iSCSI entity. When
machine authentication is used, the machine certificate is typically
stored on the iSCSI initiator and target during an enrollment process.
When user certificates are used, the user certificate can be stored
either on the machine or on a smartcard. For iFCP and FCIP, the
certificate credentials provided will almost always be those of the
device and will be stored on the device.

Since the value of a machine certificate is inversely proportional to
the ease with which an attacker can obtain one under false pretenses, it
is advisable that the machine certificate enrollment process be strictly
controlled. For example, only administrators may have the ability to
enroll a machine with a machine certificate.

While smartcard certificate storage lessens the probability of
compromise of the private key, smartcards are not necessarily desirable
in all situations. For example, some organizations deploying machine
certificates use them so as to restrict use of non-approved hardware.
Since user authentication can be provided within iSCSI login (keeping in
mind the weaknesses described earlier), support for machine
authentication in IPsec makes it is possible to authenticate both the
machine as well as the user. Since iFCP and FCIP have no equivalent of
iSCSI Login, for these protocols only the machine is authenticated.

In circumstances in which this dual assurance is considered valuable,
enabling movement of the machine certificate from one machine to
another, as would be possible if the machine certificate were stored on
a smart card, may be undesirable.

Similarly, when user certificate are deployed, it is advisable for the
user enrollment process to be strictly controlled. If for example, a
user password can be readily used to obtain a certificate (either a
temporary or a longer term one), then that certificate has no more



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security value than the password. To limit the ability of an attacker to
obtain a user certificate from a stolen password, the enrollment period
can be limited, after which password access will be turned off.  Such a
policy will prevent an attacker obtaining the password of an unused
account from obtaining a user certificate once the enrollment period has
expired.

5.8.2.  Pre-shared keys

Use of pre-shared keys in IKE Main Mode is vulnerable to man-in-the-
middle attacks when used with dynamically addressed hosts (such as with
iSCSI initiators). In Main Mode it is necessary for SKEYID_e to be used
prior to the receipt of the identification payload. Therefore the
selection of the pre-shared key may only be based on information
contained in the IP header. However, where dynamic IP address assignment
is typical, it is often not possible to identify the required pre-shared
key based on the IP address.

Thus when pre-shared key authentication is used in Main Mode  along with
entities whose address is dynamically assigned, the same pre-shared key
is shared by a group and is no longer able to function as an effective
shared secret.  In this situation, neither the initiator nor Responder
identifies itself during IKE Phase 1; it is only known that both parties
are a member of the group with knowledge of the pre-shared key. This
permits anyone with access to the group pre-shared key to act as a man-
in-the-middle.  This vulnerability is typically not of concern where IP
addresses are typically statically assigned (such as with iFCP and
FCIP), since in this situation individual pre-shared keys are possible
within IKE Main Mode.

However, where IP addresses are dynamically assigned and Main Mode is
used along with pre-shared keys, the Responder is not authenticated
unless application-layer mutual authentication is performed (e.g. iSCSI
login authentication). This enables an attacker in possession of the
group pre-shared key to masquerade as the Responder. In addition to
enabling the attacker to present false data, the attacker would also be
able to mount a dictionary attack on legacy authentication methods such
as CHAP [RFC1994], potentially compromising many passwords at a time.
This vulnerability is widely present in existing IPsec implementations.

Group pre-shared keys are not required in Aggressive Mode since the
identity payload is sent earlier in the exchange, and therefore the pre-
shared key can be selected based on the identity.  However, when
Aggressive Mode is used the user identity is exposed and this is often
considered undesirable.




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Note that care needs to be taken with IKE Phase 1 Identity Payload
selection in order to enable mapping of identities to pre-shared keys
even with Aggressive Mode. Where the ID_IPV4_ADDR or ID_IPV6_ADDR
Identity Payloads are used and addresses are dynamically assigned,
mapping of identities to keys is not possible, so that group pre-shared
keys are still a practical necessity. As a result, identities other than
ID_IPV4_ADDR and ID_IPV6_ADDR (such as ID_FQDN or ID_USER_FQDN) SHOULD
be employed in situations where Aggressive mode is utilized along with
pre-shared keys and IP addresses are dynamically assigned.

5.8.3.  IKE and application-layer authentication

In addition to IKE authentication, iSCSI implementations utilize their
own authentication methods.  Currently, work is underway on Fibre
Channel security, so that a similar authentication process may
eventually also apply to iFCP and FCIP as well.

While iSCSI provides initial authentication, it does not provide per-
packet authentication, integrity or replay protection. This implies that
the identity verified in the iSCSI Login is not subsequently verified on
reception of each packet.

With IPsec, when the identity asserted in IKE is authenticated, the
resulting derived keys are used to provide per-packet authentication,
integrity and replay protection. As a result, the identity verified in
the IKE conversation is subsequently verified on reception of each
packet.

Let us assume that the identity claimed in iSCSI Login is a user
identity, while the identity claimed within IKE is a machine identity.
Since only the machine identity is verified on a per-packet basis, there
is no way for the recipient to verify that only the user authenticated
via iSCSI Login is using the IPsec SA.

In fact, IPsec implementations that only support machine authentication
typically have no way to distinguish between user traffic within the
kernel. As a result, where machine authentication is used, once an IPsec
SA is opened, another user on a multi-user machine may be able to send
traffic down the IPsec SA. This is true for both transport mode and
tunnel mode SAs.

To limit the potential vulnerability, IP block storage implementations
MUST do the following:

[1]  Ensure that socket access is appropriately controlled.  On a multi-
     user operating system, this implies that sockets opened for use by



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     IP block storage protocols MUST be exclusive.

[2]  In the case of iSCSI, implementations MUST also ensure that
     application layer login credentials (such as iSCSI login
     credentials) are protected from unauthorized access.

If these directives are followed, then a rogue process will not be able
to access an IP block storage volume.

While the identity asserted within IKE is verified on a per-packet
basis, to avoid interference between users on a given machine, operating
system support is required. In order to segregate traffic between users
when user authentication is supported, the IPsec endpoints must ensure
that only traffic from that particular user is sent or received within
the IPsec SA.  Enforcement of this restriction is the responsibility of
the operating system.

In kernel mode iSCSI drivers there typically is no user context to
perform user authentication. In this case the authentication is closer
to machine authentication. In most operating systems device permissions
would control the ability to read/write to the device prior to mounting.
Once the device is mounted, ACLs set by the filesystem control access to
the device. An administrator can access the blocks on the device
directly (for instance, by sending pass through requests to the port
driver directly such as in Windows NT). In the same way, an
administrator can open a raw socket and send IPsec protected packets to
an iSCSI target. The situation is analogous, and in this respect no new
vulnerability is created that didn't previously exist. The Operating
system's ACLs need to be effective to protect a device (whether it is a
SCSI device or an iSCSI device).

5.8.4.  IP block storage authorization

IP block storage protocols can use a variety of mechanisms for
authorization. Where ID_FQDN is used as the Identity Payload, IP block
storage endpoints can be configured with a list of authorized FQDNs. The
configuration can occur manually, or automatically via iSNS or the iSCSI
MIB, defined in [AuthMIB].

Assuming that IPsec authentication is successful, this list of FQDNs can
be examined to determine authorization levels.  Where certificate
authentication is used, it is possible to configure IP block storage
protocol endpoints with trusted roots. The trusted roots used with IP
block storage protocols might be different from the trusted roots used
for other purposes. If this is the case, then the burden of negotiating
use of the proper certificates lies with the IPsec initiator.



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Note that because IKE does not deal well with certificate chains, and is
typically configured with a limited set of trusted roots, it is most
appropriate for intra-domain usage.

Since iSCSI supports Login authentication, it is also possible to use
the identities presented within the iSCSI Login for authorization
purposes.

In iFCP, basic access control properties stem from the requirement that
two communicating iFCP gateways be known to one or more iSNS servers
before they can engage in iFCP exchanges. The optional use of discovery
domains in iSNS yields access control schemas of greater complexity.

5.9.  Use of AES in counter mode

When utilizing AES modes, it may be necessary to use larger public keys;
the tradeoffs are described in [KeyLen]. Additional MODP Diffie-Hellman
groups for use with IKE are described in [MODP].

When AES in counter mode is used, it is important to avoid reuse of the
counter with the same key, even across all time. Counter mode creates
ciphertext by XORing generated key stream with plaintext. It is fairly
easy to recover the plaintext from two messages counter mode encrypted
under the same counter value, simply by XORing together the two packets.
The implication of this is that it is an error to use IPsec manual
keying with counter mode, except when the implementation takes heroic
measures to maintain state across sessions.  In any case, manual keying
MUST NOT be used since it does not provide the necessary rekeying
support.

Another counter mode issue is it makes forgery of correct packets
trivial. Counter mode should therefore never be used without also using
data authentication.

6.  IANA Considerations

IANA considerations for the iSCSI protocol are described in [iSCSI],
Section 13; for the iFCP protocol in [iFCP], Section 12; and for the
FCIP protocol in [FCIP], Appendix B.

This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values of the SRP_GROUP key
parameter within iSCSI, in accordance with BCP 26, [RFC2434].






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6.1.  Definition of Terms

The following terms are used here with the meanings defined in BCP 26:
"name space", "assigned value", "registration".

The following policies are used here with the meanings defined in BCP
26: "Private Use", "First Come First Served", "Expert Review",
"Specification Required", "IETF Consensus", "Standards Action".

6.2.  Recommended Registration Policies

For registration requests where a Designated Expert should be consulted,
the responsible IESG Area Director should appoint the Designated Expert.

For registration requests requiring Expert Review, the IPS mailing list
should be consulted, or if the IPS WG is disbanded, to a mailing list
designated by the IESG Area Director.

This document defines the following SRP_GROUP keys:

   SRP-768, SRP-1024, SRP-1280, SRP-1536, SRP-2048, MODP-3072,
   MODP-4096, MODP-6144, MODP-8192

New SRP_GROUP keys MUST conform to the iSCSI extension item-label format
described in [iSCSI] Section 13.5.4.

Registration of new SRP_GROUP keys is by Designated Expert with
Specification Required. The request is posted to the IPS WG mailing list
or its successor for comment and security review, and MUST include a
non-probabalistic proof of primality for the proposed SRP group.  After
a period of one month as passed, the Designated Expert will either
approve or deny the registration request.

7.  Normative references

[RFC793]    Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
            September 1981

[RFC1191]   Mogul, J., and S. Deering, "Path MTU Discovery", RFC 1191,
            November 1990

[RFC1435]   Knowles, S., "IESG Advice from Experience with Path MTU
            Discovery", RFC 1435, March 1993

[RFC1981]   McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery
            for IP version 6", RFC 1981, August 1996



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[RFC2104]   Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-
            Hashing for Message Authentication", RFC 2104, February 1997

[RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997

[RFC2401]   Atkinson, R. and Kent, S., "Security Architecture for the
            Internet Protocol", RFC 2401, November 1998

[RFC2404]   Madson, C., Glenn, R., "The Use of HMAC-SHA-1-96 within ESP
            and AH", RFC 2404, November 1998

[RFC2406]   Kent, S., Atkinson, R., "IP Encapsulating Security Payload
            (ESP)", RFC 2406, November 1998

[RFC2407]   Piper, D., "The Internet IP Security Domain of
            Interpretation of ISAKMP", RFC 2407, November 1998

[RFC2408]   Maughan, D., Schertler, M., Schneider, M., Turner, J.,
            "Internet Security Association and Key Management Protocol
            (ISAKMP), RFC 2408, November 1998

[RFC2409]   Harkins, D., Carrel, D., "The Internet Key Exchange (IKE)",
            RFC 2409, November 1998

[RFC2412]   Orman, H., "The OAKLEY Key Determination Protocol", RFC
            2412, November 1998

[RFC2434]   Narten, T., Alvestrand, H., "Guidelines for Writing an IANA
            Considerations Section in RFCs", RFC 2434, October 1998

[RFC2451]   Pereira, R., Adams, R., "The ESP CBC-Mode Cipher
            Algorithms", RFC 2451, November 1998

[RFC2608]   Guttman, E., Perkins, C., Veizades, J., Day, M, "Service
            Location Protocol, Version 2", RFC 2608, June 1999

[RFC2923]   Lahey, K., TCP Problems with Path MTU Discovery", RFC 2923,
            September 2000

[RFC2945]   Wu, T., "The SRP Authentication and Key Exchange System,"
            RFC 2945, September 2000

[3DESANSI]  American National Standard for Financial Services
            X9.52-1998, "Triple Data Encryption Algorithm Modes of
            Operation", American Bankers Association, Washington, D.C.,



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            July 29, 1998

[AESXCBC]   Frankel, S., Herbert, H., "The AES-XCBC-MAC-96 Algorithm and
            Its Use with IPsec", Internet draft (work in progress),
            draft-ietf-ipsec-ciph-aes-xcbc-mac-02.txt, June 2002

[AESCTR]    Housley, R., "Using AES Counter Mode With IPsec ESP",
            Internet draft (work in progress), draft-ietf-ipsec-ciph-
            aes-ctr-01.txt, September 2002

[DHCPIPsec] Patel, B., Aboba, B., Kelly, S., Gupta, V., "DHCPv4
            Configuration of IPsec Tunnel Mode", Internet draft (work in
            progress), draft-ietf-ipsec-dhcp-13.txt, June 2001

[iSCSI]     Satran, J., et al., "iSCSI", Internet draft (work in
            progress), draft-ietf-ips-iSCSI-19.txt, November 2002

[iFCP]      Monia, C., et al., "iFCP - A Protocol for Internet Fibre
            Channel Storage Networking", Internet drafts (work in
            progress), draft-ietf-ips-ifcp-13.txt, August 2002

[FCIP]      Rajagopal, M., et al., "Fibre Channel over TCP/IP (FCIP)",
            Internet draft (work in progress), draft-ietf-ips-
            fcovertcpip-12.txt, August 2002

[iSCSIName] Bakke, M., et al., "iSCSI Naming and Discovery", draft-ietf-
            ips-iscsi-name-disc-08.txt, Work in Progress, October 2002

[FCIPSLP]   Petersen, D., "Finding FCIP Entities Using SLPv2", Internet
            draft (work in progress), draft-ietf-ips-fcip-slp-04.txt,
            September 2002

[iSCSISLP]  Bakke, M., "Finding iSCSI targets and Name Servers Using
            SLP", Internet draft (work in progress), draft-ietf-ips-
            iscsi-slp-03.txt, March 2002

[iSNS]      Gibbons, K., et al., "iSNS Internet Storage Name Service",
            Internet draft (work in progress), draft-ietf-ips-
            isns-12.txt, August 2002

[SRPNDSS]   Wu, T., "The Secure Remote Password Protocol", in
            Proceedings of the 1998 Internet Society Symposium on
            Network and Distributed Systems Security, San Diego, CA, pp.
            97-111





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[MODP]      Kivinen, T., Kojo, M., "More MODP Diffie-Hellman groups for
            IKE", Internet draft (work in progress), draft-ietf-ipsec-
            ike-modp-groups-04.txt, December 2001

8.  Informative references

[RFC2230]   Atkinson, R., "Key Exchange Delegation Record for the DNS",
            RFC 2230, November 1997.

[RFC2373]   Hinden, R. and S. Deering, "IP Version 6 Addressing
            Architecture", RFC 2373, July 1998

[RFC2402]   Kent, S., Atkinson, R., "IP Authentication Header", RFC
            2402, November 1998

[RFC2535]   Eastlake, D., "Domain Name System Security Extensions", RFC
            2535, March 1999

[RFC2782]   Gulbrandsen, A., Vixie, P., Esibov, L. "A DNS RR for
            specifying the location of services (DNS SRV)", RFC 2782,
            February 2000

[RFC2845]   Vixie, P., Gudmundsson, O., Eastlake, D., Wellington, B.,
            "Secret Key Transaction Authentication for DNS (TSIG)", RFC
            2845, May 2000

[RFC2865]   Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote
            Authentication Dial In User Service (RADIUS)", RFC 2865,
            June 2000

[RFC2931]   Eastlake, D., "DNS Request and Transaction Signatures
            (SIG(0)s )", RFC 2931, September 2000

[RFC2983]   Black, D. "Differentiated Services and Tunnels", RFC 2983,
            October 2000.

[RFC3007]   Wellington, B., "Simple Secure Domain Name System (DNS)
            Dynamic Update", RFC 3007, November 2000

[AuthMIB]   Bakke, M., et al., "Definitions of Managed Objects for
            iSCSI", Internet draft (work in progress), draft-ietf-ips-
            iscsi-mib-06.txt, September 2002

[MD5]       Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
            April 1992




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[MD5Attack] Dobbertin, H., "The Status of MD5 After a Recent Attack",
            CryptoBytes Vol.2 No.2, Summer 1996

[CRCTCP]    Stone J., Partridge, C., "When the CRC and TCP checksum
            disagree", ACM Sigcomm, Sept. 2000

[DESCRACK]  Cracking DES, O'Reilly & Associates, Sebastapol, CA 2000

[KeyLen]    Orman, H., Hoffman, P., "Determining Strengths For Public
            Keys Used For Exchanging Symmetric Keys", Internet draft
            (work in progress), draft-orman-public-key-lengths-05.txt,
            December 2001

[iSCSIREQ]  Krueger, M., et al., "SCSI over the Internet (isCSI)
            Requirements and Design Considerations", RFC 3347, July 2002

[IPsecNatReq]
            Aboba, B., "IPsec-NAT Compatibility Requirements", draft-
            ietf-ipsec-nat-reqts-02.txt, Work in Progress, August 2002

[UDPIPsec]  Huttunen, A. et. al., "UDP Encapsulation of IPsec Packets",
            draft-ietf-ipsec-udp-encaps-03.txt, June 2002

[Seq]       Kent, S., "IP Encapsulating Security Payload (ESP)",
            Internet draft (work in progress), draft-ietf-ipsec-esp-
            v3-03.txt, July 2002

[NATIKE]    Kivinen, T., et al., "Negotiation of NAT-Traversal in the
            IKE", Internet draft (work in progress), draft-ietf-ipsec-
            nat-t-ike-03.txt, June 2002

[HMACMD5IPsec]
            Madson, C., Glenn, R., "The Use of HMAC-MD5-96 within ESP
            and AH", RFC 2403, November 1998

[PMAC]      Rogaway, P., Black, J., "PMAC: Proposal to NIST for a
            parallelizable message authentication code",
            http://csrc.nist.gov/encryption/modes/proposedmodes/
            pmac/pmac-spec.pdf

[UMAC]      Black, J., Halevi, S., Krawczyk, H., Krovetz, T., Rogaway,
            P., "UMAC: Fast and provably secure message authentication",
            Advances in Cryptology - CRYPTO '99, LNCS vol. 1666, pp.
            216-233.  Full version available from
            http://www.cs.ucdavis.edu/~rogaway/umac




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[FIPS46-3]  U.S. DoC/NIST, "Data encryption standard (DES)", FIPS 46-3,
            October 25, 1999

[FIPS74]    U.S. DoC/NIST, "Guidelines for implementing and using the
            nbs data encryption standard", FIPS 74, Apr 1981

[FIPS197]   U.S. DoC/NIST, "Advanced Encryption Standard (AES)", FIPS
            197, November 2001, http://csrc.nist.gov/publications/

[DESDIFF]   Biham, E., Shamir, A., "Differential Cryptanalysis of DES-
            like cryptosystems", Journal of Cryptology Vol 4, Jan 1991

[RFC2405]   Madson, C., Doraswamy, N., "The ESP DES-CBC Cipher Algorithm
            With Explicit IV", RFC 2405, November 1998

[NSPUE2]    "Recommendation for Block Cipher Modes of Operation",
            National Institute of Standards and Technology (NIST)
            Special Publication 800-38A, CODEN: NSPUE2, U.S. Government
            Printing Office, Washington, DC, July 2001

[CTR-MODE]  Lipmaa, H., Rogaway, P., Wagner, D., "CTR-MODE encryption",
            Comment on mode of operations NIST, Jan 2001

[AESPERF]   Schneier, B., J. Kelsey, D. Whiting, D. Wagner, C.  Hall,
            and N. Ferguson, "Performance Comparison of the AES
            Submissions", http://www.counterpane.com/AES-
            performance.html

[PENTPERF]  A. Bosselaers, "Performance of Pentium implementations",
            http://www.esat.kuleuven.ac.be/~bosselae/

[UMACPERF]  Rogaway, P., "UMAC Performance",
            http://www.cs.ucdavis.edu/~rogaway/umac/perf00.html

[DESINT]    Bellovin, S., "An Issue With DES-CBC When Used Without
            Strong Integrity", Proceedings of the 32nd IETF, Danvers,
            MA, April 1995

[UMACKR]    Krovetz, T., Black, J., Halevi, S., Hevia, A., Krawczyk, H.,
            Rogaway, P., "UMAC: Message Authentication Code using
            Universal Hashing", Internet draft (work in progress),
            draft-krovetz-umac-01.txt, October 2000. Also available at:
            http://www.cs.ucdavis.edu/~rogaway/umac/draft-krovetz-
            umac-01.txt





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[RFC1994]   Simpson, W.,"PPP Challenge Handshake Authentication Protocol
            (CHAP)," RFC 1994, August 1996.

[DESANALY]  Bellare, Desai, Jokippi, Rogaway, "A Concrete Treatment of
            Symmetric Encryption: Analysis of the DES Modes of
            Operation", 1997, http://www-cse.ucsd.edu/users/mihir/

[SRPDIST]   Wu, T., "SRP Distribution", http://www-cs-
            students.stanford.edu/~tjw/srp/download.html








































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Appendix A - Well Known Groups for Use with SRP

Modulus (N) and generator (g) values for various modulus lengths are
given below.  The values below are taken from software developed by Tom
Wu and Eugene Jhong for the Stanford SRP distribution [SRPDIST], and
subsequently rigorously verified to be prime. Implementations supporting
SRP authentication MUST support groups up to 1536 bits, with 1536 bits
being the default.

iSCSI Key="SRP-768" [768 bits]
Modulus (base 16) =
B344C7C4F8C495031BB4E04FF8F84EE95008163940B9558276744D91F7CC9F40
2653BE7147F00F576B93754BCDDF71B636F2099E6FFF90E79575F3D0DE694AFF
737D9BE9713CEF8D837ADA6380B1093E94B6A529A8C6C2BE33E0867C60C3262B
Generator = 2

iSCSI Key="SRP-1024" [1024 bits]
Modulus (base 16) =
EEAF0AB9ADB38DD69C33F80AFA8FC5E86072618775FF3C0B9EA2314C9C256576
D674DF7496EA81D3383B4813D692C6E0E0D5D8E250B98BE48E495C1D6089DAD1
5DC7D7B46154D6B6CE8EF4AD69B15D4982559B297BCF1885C529F566660E57EC
68EDBC3C05726CC02FD4CBF4976EAA9AFD5138FE8376435B9FC61D2FC0EB06E3
Generator = 2

iSCSI Key="SRP-1280" [1280 bits]
Modulus (base 16) =
D77946826E811914B39401D56A0A7843A8E7575D738C672A090AB1187D690DC4
3872FC06A7B6A43F3B95BEAEC7DF04B9D242EBDC481111283216CE816E004B78
6C5FCE856780D41837D95AD787A50BBE90BD3A9C98AC0F5FC0DE744B1CDE1891
690894BC1F65E00DE15B4B2AA6D87100C9ECC2527E45EB849DEB14BB2049B163
EA04187FD27C1BD9C7958CD40CE7067A9C024F9B7C5A0B4F5003686161F0605B
Generator = 2

iSCSI Key="SRP-1536" [1536 bits]
Modulus (base 16) =
9DEF3CAFB939277AB1F12A8617A47BBBDBA51DF499AC4C80BEEEA9614B19CC4D
5F4F5F556E27CBDE51C6A94BE4607A291558903BA0D0F84380B655BB9A22E8DC
DF028A7CEC67F0D08134B1C8B97989149B609E0BE3BAB63D47548381DBC5B1FC
764E3F4B53DD9DA1158BFD3E2B9C8CF56EDF019539349627DB2FD53D24B7C486
65772E437D6C7F8CE442734AF7CCB7AE837C264AE3A9BEB87F8A2FE9B8B5292E
5A021FFF5E91479E8CE7A28C2442C6F315180F93499A234DCF76E3FED135F9BB
Generator = 2







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iSCSI Key="SRP-2048" [2048 bits]
Modulus (base 16) =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 = 2

In addition to these groups, the following groups MAY be supported, each
of which has also been rigorously proven to be prime:

[1]  iSCSI Key="MODP-3072": the 3072-bit [MODP] group, generator: 5

[2]  iSCSI Key="MODP-4096": the 4096-bit [MODP] group, generator: 5

[3]  iSCSI Key="MODP-6144": the 6144-bit [MODP] group, generator: 5

[4]  iSCSI Key="MODP-8192": the 8192-bit [MODP] group, generator: 19



























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Appendix B - Software Performance of IPsec Transforms

This Appendix provides data on the performance of IPsec encryption and
authentication transforms in software. Since the performance of IPsec
transforms is heavily implementation dependent, the data presented here
may not be representative of performance in a given situation, and are
presented solely for purposes of comparison. Other performance data is
available in [AESPERF],[PENTPERF] and [UMACPERF].

B.1 Authentication transforms

Table B-1 presents the cycles/byte required by the AES-PMAC, AES-CBC-
MAC, AES-UMAC, HMAC-MD5, and HMAC-SHA1 algorithms at various packet
sizes, implemented in software.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         |         |           |         |         |         |
|  Data   |  AES-   | AES-CBC-  |  AES-   |  HMAC-  |  HMAC-  |
|  Size   |  PMAC   | MAC       |  UMAC   |  MD5    |  SHA1   |
|         |         |           |         |         |         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   64    |  31.22  |   26.02   |  19.51  |  93.66  | 109.27  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  128    |  33.82  |   28.62   |  11.06  |  57.43  |  65.04  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  192    |  34.69  |   26.02   |   8.67  |  45.09  |  48.56  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  256    |  33.82  |   27.32   |   7.15  |  41.63  |  41.63  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  320    |  33.3   |   27.06   |   6.24  |  36.42  |  37.46  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  384    |  33.82  |   26.88   |   5.42  |  34.69  |  34.69  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  448    |  33.45  |   26.76   |   5.39  |  32.71  |  31.96  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  512    |  33.82  |   26.67   |   4.88  |  31.22  |  30.57  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  576    |  33.53  |   26.59   |   4.77  |  30.64  |  29.48  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  640    |  33.3   |   26.54   |   4.42  |  29.66  |  28.62  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+








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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         |         |           |         |         |         |
|  Data   |  AES-   | AES-CBC-  |  AES-   |  HMAC-  |  HMAC-  |
|  Size   |  PMAC   | MAC       |  UMAC   |  MD5    |  SHA1   |
|         |         |           |         |         |         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  768    |  33.82  |   26.88   |   4.23  |  28.18  |  27.32  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  896    |  33.45  |   27.13   |   3.9   |  27.5   |  25.64  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1024    |  33.5   |   26.67   |   3.82  |  26.99  |  24.71  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1152    |  33.53  |   27.17   |   3.69  |  26.3   |  23.99  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1280    |  33.56  |   26.8    |   3.58  |  26.28  |  23.67  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1408    |  33.58  |   26.96   |   3.55  |  25.54  |  23.41  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1500    |  33.52  |   26.86   |   3.5   |  25.09  |  22.87  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Table B-1: Cycles/byte consumed by the AES-PMAC, AES-CBC-MAC,
AES-UMAC, HMAC-MD5, and HMAC-SHA1 authentication algorithms at
various packet sizes.

Source: Jesse Walker, Intel























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Table B-2 presents the cycles/second required by the AES-PMAC, AES-CBC-
MAC, AES-UMAC, HMAC-MD5, and HMAC-SHA1 algorithms, implemented in
software, assuming a 1500 byte packet.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             | Cycles/     |  Cycles/sec | Cycles/sec  |  Cycles/sec |
|  Transform  |  octet      |     @       |    @        |     @       |
|             | (software)  |  100 Mbps   |   1 Gbps    |   10 Gbps   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
| AES-UMAC    |     3.5     |  43,750,000 | 437,500,000 |  4.375  B   |
| (8 octets)  |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
| HMAC-SHA1   |    22.87    | 285,875,000 |   2.8588 B  |  28.588 B   |
| (20 octets) |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
| HMAC-MD5    |    25.09    | 313,625,000 |   3.1363 B  |  31.363 B   |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
| AES-CBC-MAC |    26.86    | 335,750,000 |   3.358 B   |  33.575 B   |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
| AES-PMAC    |    33.52    | 419,000,000 |   4.19  B   |  41.900 B   |
| (8 octets)  |             |             |             |             |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Table B-2: Software performance of the HMAC-SHA1, HMAC-MD5,
AES-CBC-MAC and AES-PMAC authentication algorithms at 100 Mbps,
1 Gbps, and 10 Gbps line rates (1500 byte packet).

Source: Jesse Walker, Intel

At speeds of 100 Mbps, AES-UMAC is implementable with only a modest
processor, and the other algorithms are implementable, assuming that a
single high-speed processor can be dedicated to the task. At 1 Gbps,
only AES-UMAC is implementable on a single high-speed processor;
multiple high speed processors (1+ Ghz) will be required for the other
algorithms.  At 10 Gbps, only AES-UMAC is implementable even with
multiple high speed processors; the other algorithms will require a
prodigious number of cycles/second. Thus at 10 Gbps, hardware
acceleration will be required for all algorithms with the possible



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exception of AES-UMAC.

B.2 Encryption and Authentication transforms

Table B-3 presents the cycles/byte required by the AES-CBC, AES-CTR and
3DES-CBC encryption algorithms (no MAC), implemented in software, for
various packet sizes.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |             |             |             |
|  Data size    |   AES-CBC   |   AES-CTR   |  3DES-CBC   |
|               |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      64       |   31.22     |    26.02    |  156.09     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     128       |   31.22     |    28.62    |  150.89     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     192       |   31.22     |    27.75    |  150.89     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     256       |   28.62     |    27.32    |  150.89     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     320       |   29.14     |    28.1     |  150.89     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     384       |   28.62     |    27.75    |  148.29     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     448       |   28.99     |    27.5     |  149.4      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     512       |   28.62     |    27.32    |  148.29     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     576       |   28.33     |    27.75    |  147.72     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     640       |   28.62     |    27.06    |  147.77     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
















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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |             |             |             |
|  Data size    |   AES-CBC   |   AES-CTR   |  3DES-CBC   |
|               |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     768       |   28.18     |    27.32    |  147.42     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     896       |   28.25     |    27.5     |  147.55     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1024       |   27.97     |    27.32    |  148.29     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1152       |   28.33     |    27.46    |  147.13     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1280       |   28.1      |    27.58    |  146.99     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1408       |   27.91     |    27.43    |  147.34     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1500       |   27.97     |    27.53    |  147.85     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Table B-3: Cycles/byte consumed by the AES-CBC, AES-CTR and
3DES-CBC encryption algorithms at various packet sizes,
implemented in software.

Source: Jesse Walker, Intel
























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Table B-4 presents the cycles/second required by the AES-CBC, AES-CTR
and 3DES-CBC encryption algorithms (no MAC), implemented in software, at
100 Mbps, 1 Gbps, and 10 Gbps line rates (assuming a 1500 byte packet).

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             | Cycles/     |  Cycles/sec | Cycles/sec  |  Cycles/sec |
|   Transform |  octet      |     @       |    @        |     @       |
|             | (software)  |  100 Mbps   |   1 Gbps    |   10 Gbps   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
| AES-CBC     |   27.97     | 349,625,000 |   3.4963 B  |  34.963 B   |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
| AES-CTR     |   27.53     | 344,125,000 |   3.4413 B  |  34.413 B   |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
| 3DES -CBC   |  147.85     | 1.84813 B   |  18.4813 B  | 184.813 B   |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Table B-4: Software performance of the AES-CBC, AES-CTR, and 3DES
encryption algorithms at 100 Mbps, 1 Gbps, and 10 Gbps line rates
(1500 byte packet).

Source: Jesse Walker, Intel

At speeds of 100 Mbps, AES-CBC and AES-CTR mode are implementable with a
high-speed processor, while 3DES would require multiple high speed
processors. At speeds of 1 Gbps, multiple high speed processors are
required for AES-CBC and AES-CTR mode. At speeds of 1+ Gbps for 3DES,
and 10 Gbps for all algorithms, implementation in software is
infeasible, and hardware acceleration is required.















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Table B-5 presents the cycles/byte required for combined
encryption/authentication algorithms: AES CBC + CBCMAC, AES CTR +
CBCMAC, AES CTR + UMAC, and AES-OCB at various packet sizes, implemented
in software.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |  AES      | AES     |  AES    |         |
|  Data size    |  CBC +    | CTR +   |  CTR +  |  AES-   |
|               |  CBCMAC   | CBCMAC  |  UMAC   |  OCB    |
|               |           |         |         |         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      64       |  119.67   |  52.03  |  52.03  |  57.23  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     128       |   70.24   |  57.23  |  39.02  |  44.23  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     192       |   58.97   |  55.5   |  36.42  |  41.63  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     256       |   57.23   |  55.93  |  35.12  |  40.32  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     320       |   57.23   |  55.15  |  33.3   |  38.5   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     384       |   57.23   |  55.5   |  32.95  |  37.29  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     448       |   58.72   |    55   |  32.71  |  37.17  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     512       |   58.54   |  55.28  |  32.52  |  36.42  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+






















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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               |  AES      | AES     |  AES    |         |
|  Data size    |  CBC +    | CTR +   |  CTR +  |  AES-   |
|               |  CBCMAC   | CBCMAC  |  UMAC   |  OCB    |
|               |           |         |         |         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     576       |   57.81   |  55.5   |  31.8   |  37     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     640       |   57.75   |  55.15  |  31.74  |  36.42  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     768       |   57.67   |  55.5   |  31.65  |  35.99  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     896       |   57.61   |  55.75  |  31.22  |  35.68  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1024       |   57.56   |  55.61  |  31.22  |  35.45  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1152       |   57.52   |  55.21  |  31.22  |  35.55  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1280       |   57.75   |  55.15  |  31.22  |  36.16  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1408       |   57.47   |  55.34  |  30.75  |  35.24  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    1500       |   57.72   |  55.5   |  30.86  |  35.3   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Table B-5: Cycles/byte of combined encryption/authentication
algorithms:  AES CBC + CBCMAC, AES CTR + CBCMAC, AES CTR + UMAC,
and AES-OCB at various packet sizes, implemented in software.





















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Table B-6 presents the cycles/second required for the AES CBC + CBCMAC,
AES CTR + CBCMAC, AES CTR + UMAC, and AES-OCB encryption and
authentication algorithms operating at line rates of 100 Mbps, 1 Gbps
and 10 Gbps, assuming 1500 byte packets.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             | Cycles/     |  Cycles/sec | Cycles/sec  |  Cycles/sec |
|  Transform  |  octet      |      @      |    @        |     @       |
|             | (software)  |  100 Mbps   |   1 Gbps    |   10 Gbps   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
|     AES     |             |             |             |             |
|CBC + CBCMAC |   57.72     | 721,500,000 |  7.215 B    |  72.15 B    |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
|     AES     |             |             |             |             |
|CTR + CBCMAC |   55.5      | 693,750,000 |  6.938 B    |  69.38 B    |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
|     AES     |             |             |             |             |
| CTR + UMAC  |   30.86     | 385,750,000 |  3.858 B    |  38.58 B    |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             |             |             |             |             |
|             |             |             |             |             |
|   AES-OCB   |   35.3      | 441,250,000 |   4.413 B   |  44.13 B    |
|             |             |             |             |             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Table B-6: Cycles/second required for the AES CBC + CBCMAC,
AES CTR + CBCMAC, AES CTR + UMAC, and AES-OCB encryption and
authentication algorithms, operating at line rates of 100 Mbps,
1 Gbps and 10 Gbps, assuming 1500 octet packets.

Source: Jesse Walker, Intel

At speeds of 100 Mbps, the algorithms are implementable on a high speed
processor. At speeds of 1 Gbps, multiple high speed processors are
required, and none of the algorithms are implementable in software at 10
Gbps line rate.







Aboba, et al.                Standards Track                   [Page 69]

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Acknowledgments

Thanks to Steve Bellovin of AT&T Research, William Dixon of Microsoft,
David Black of EMC, Joseph Tardo and Uri Elzur of Broadcom, Julo Satran,
Ted Ts'o, Ofer Biran, and Charles Kunzinger of IBM, Allison Mankin of
ISI, Mark Bakke and Steve Senum of Cisco, Erik Guttman of Sun
Microsystems and Howard Herbert of Intel for useful discussions of this
problem space.

Authors' Addresses

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

Phone: +1 425 706 6605
Fax:   +1 425 936 7329
EMail: bernarda@microsoft.com

Joshua Tseng
Nishan Systems
3850 North First Street
San Jose, CA 95134-1702

Phone: +1 408 519 3749
EMail: jtseng@nishansystems.com

Jesse Walker
Intel Corporation
2211 NE 25th Avenue
Hillboro, OR 97124

Phone: +1 503 712 1849
Fax:   +1 503 264 4843
Email: jesse.walker@intel.com

Venkat Rangan
Rhapsody Networks Inc.
3450 W. Warren Ave.
Fremont, CA 94538

Phone: +1 510 743 3018
Fax: +1 510 687 0136
EMail: venkat@rhapsodynetworks.com




Aboba, et al.                Standards Track                   [Page 70]

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Franco Travostino
Director, Content Internetworking Lab
Nortel Networks
3 Federal Street
Billerica, MA  01821

Phone: +1 978 288 7708
EMail: travos@nortelnetworks.com

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Aboba, et al.                Standards Track                   [Page 71]

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Aboba, et al.                Standards Track                   [Page 72]


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