draft-ietf-tcpinc-tcpcrypt-07.txt   draft-ietf-tcpinc-tcpcrypt-08.txt 
Network Working Group A. Bittau Network Working Group A. Bittau
Internet-Draft Google Internet-Draft Google
Intended status: Experimental D. Giffin Intended status: Experimental D. Giffin
Expires: April 7, 2018 Stanford University Expires: April 24, 2018 Stanford University
M. Handley M. Handley
University College London University College London
D. Mazieres D. Mazieres
Stanford University Stanford University
Q. Slack Q. Slack
Sourcegraph Sourcegraph
E. Smith E. Smith
Kestrel Institute Kestrel Institute
October 4, 2017 October 21, 2017
Cryptographic protection of TCP Streams (tcpcrypt) Cryptographic protection of TCP Streams (tcpcrypt)
draft-ietf-tcpinc-tcpcrypt-07 draft-ietf-tcpinc-tcpcrypt-08
Abstract Abstract
This document specifies tcpcrypt, a TCP encryption protocol designed This document specifies tcpcrypt, a TCP encryption protocol designed
for use in conjunction with the TCP Encryption Negotiation Option for use in conjunction with the TCP Encryption Negotiation Option
(TCP-ENO). Tcpcrypt coexists with middleboxes by tolerating (TCP-ENO). Tcpcrypt coexists with middleboxes by tolerating
resegmentation, NATs, and other manipulations of the TCP header. The resegmentation, NATs, and other manipulations of the TCP header. The
protocol is self-contained and specifically tailored to TCP protocol is self-contained and specifically tailored to TCP
implementations, which often reside in kernels or other environments implementations, which often reside in kernels or other environments
in which large external software dependencies can be undesirable. in which large external software dependencies can be undesirable.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 7, 2018. This Internet-Draft will expire on April 24, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Requirements language . . . . . . . . . . . . . . . . . . . . 3 1. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Encryption protocol . . . . . . . . . . . . . . . . . . . . . 3 3. Encryption Protocol . . . . . . . . . . . . . . . . . . . . . 3
3.1. Cryptographic algorithms . . . . . . . . . . . . . . . . 3 3.1. Cryptographic Algorithms . . . . . . . . . . . . . . . . 3
3.2. Protocol negotiation . . . . . . . . . . . . . . . . . . 4 3.2. Protocol Negotiation . . . . . . . . . . . . . . . . . . 5
3.3. Key exchange . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Key Exchange . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Session ID . . . . . . . . . . . . . . . . . . . . . . . 8 3.4. Session ID . . . . . . . . . . . . . . . . . . . . . . . 8
3.5. Session resumption . . . . . . . . . . . . . . . . . . . 8 3.5. Session Resumption . . . . . . . . . . . . . . . . . . . 9
3.6. Data encryption and authentication . . . . . . . . . . . 11 3.6. Data Encryption and Authentication . . . . . . . . . . . 12
3.7. TCP header protection . . . . . . . . . . . . . . . . . . 12 3.7. TCP Header Protection . . . . . . . . . . . . . . . . . . 13
3.8. Re-keying . . . . . . . . . . . . . . . . . . . . . . . . 13 3.8. Re-Keying . . . . . . . . . . . . . . . . . . . . . . . . 13
3.9. Keep-alive . . . . . . . . . . . . . . . . . . . . . . . 14 3.9. Keep-Alive . . . . . . . . . . . . . . . . . . . . . . . 14
4. Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4. Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1. Key exchange messages . . . . . . . . . . . . . . . . . . 14 4.1. Key-Exchange Messages . . . . . . . . . . . . . . . . . . 15
4.2. Encryption frames . . . . . . . . . . . . . . . . . . . . 16 4.2. Encryption Frames . . . . . . . . . . . . . . . . . . . . 17
4.2.1. Plaintext . . . . . . . . . . . . . . . . . . . . . . 17 4.2.1. Plaintext . . . . . . . . . . . . . . . . . . . . . . 17
4.2.2. Associated data . . . . . . . . . . . . . . . . . . . 18 4.2.2. Associated Data . . . . . . . . . . . . . . . . . . . 18
4.2.3. Frame nonce . . . . . . . . . . . . . . . . . . . . . 18 4.2.3. Frame Nonce . . . . . . . . . . . . . . . . . . . . . 19
4.3. Constant values . . . . . . . . . . . . . . . . . . . . . 18 4.3. Constant Values . . . . . . . . . . . . . . . . . . . . . 19
5. Key agreement schemes . . . . . . . . . . . . . . . . . . . . 19 5. Key-Agreement Schemes . . . . . . . . . . . . . . . . . . . . 19
6. AEAD algorithms . . . . . . . . . . . . . . . . . . . . . . . 20 6. AEAD Algorithms . . . . . . . . . . . . . . . . . . . . . . . 20
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 20 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8. Security considerations . . . . . . . . . . . . . . . . . . . 21 8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
8.1. Asymmetric roles . . . . . . . . . . . . . . . . . . . . 22 8.1. Asymmetric Roles . . . . . . . . . . . . . . . . . . . . 23
8.2. Verified liveness . . . . . . . . . . . . . . . . . . . . 23 8.2. Verified Liveness . . . . . . . . . . . . . . . . . . . . 23
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23 8.3. Mandatory Key-Agreement Schemes . . . . . . . . . . . . . 24
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 23 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
11.1. Normative References . . . . . . . . . . . . . . . . . . 24 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
11.2. Informative References . . . . . . . . . . . . . . . . . 25 11.1. Normative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 11.2. Informative References . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Requirements language 1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in [RFC2119]. "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Introduction 2. Introduction
This document describes tcpcrypt, an extension to TCP for This document describes tcpcrypt, an extension to TCP for
cryptographic protection of session data. Tcpcrypt was designed to cryptographic protection of session data. Tcpcrypt was designed to
meet the following goals: meet the following goals:
o Meet the requirements of the TCP Encryption Negotiation Option o Meet the requirements of the TCP Encryption Negotiation Option
(TCP-ENO) [I-D.ietf-tcpinc-tcpeno] for protecting connection data. (TCP-ENO) [I-D.ietf-tcpinc-tcpeno] for protecting connection data.
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o Minimize additional latency at connection startup. o Minimize additional latency at connection startup.
o As much as possible, prevent connection failure in the presence of o As much as possible, prevent connection failure in the presence of
NATs and other middleboxes that might normalize traffic or NATs and other middleboxes that might normalize traffic or
otherwise manipulate TCP segments. otherwise manipulate TCP segments.
o Operate independently of IP addresses, making it possible to o Operate independently of IP addresses, making it possible to
authenticate resumed sessions efficiently even when either end authenticate resumed sessions efficiently even when either end
changes IP address. changes IP address.
3. Encryption protocol A companion document [I-D.ietf-tcpinc-api] describes recommended
interfaces for configuring certain parameters of this protocol.
3. Encryption Protocol
This section describes the tcpcrypt protocol at an abstract level. This section describes the tcpcrypt protocol at an abstract level.
The concrete format of all messages is specified in Section 4. The concrete format of all messages is specified in Section 4.
3.1. Cryptographic algorithms 3.1. Cryptographic Algorithms
Setting up a tcpcrypt connection employs three types of cryptographic Setting up a tcpcrypt connection employs three types of cryptographic
algorithms: algorithms:
o A _key agreement scheme_ is used with a short-lived public key to o A _key agreement scheme_ is used with a short-lived public key to
agree upon a shared secret. agree upon a shared secret.
o An _extract function_ is used to generate a pseudo-random key o An _extract function_ is used to generate a pseudo-random key
(PRK) from some initial keying material, typically the output of (PRK) from some initial keying material, typically the output of
the key agreement scheme. The notation Extract(S, IKM) denotes the key agreement scheme. The notation Extract(S, IKM) denotes
the output of the extract function with salt S and initial keying the output of the extract function with salt S and initial keying
material IKM. material IKM.
o A _collision-resistant pseudo-random function (CPRF)_ is used to o A _collision-resistant pseudo-random function (CPRF)_ is used to
generate multiple cryptographic keys from a pseudo-random key, generate multiple cryptographic keys from a pseudo-random key,
typically the output of the extract function. The CPRF is defined typically the output of the extract function. The CPRF produces
to produce an arbitrary amount of Output Keying Material (OKM), an arbitrary amount of Output Keying Material (OKM), and we use
and we use the notation CPRF(K, CONST, L) to designate the first L the notation CPRF(K, CONST, L) to designate the first L bytes of
bytes of the OKM produced by the pseudo-random function identified the OKM produced by the CPRF when parameterized by key K and the
by key K on CONST. constant CONST.
The Extract and CPRF functions used by default are the Extract and The Extract and CPRF functions used by the tcpcrypt variants defined
Expand functions of HKDF [RFC5869]. These are defined as follows in in this document are the Extract and Expand functions of HKDF
terms of the function "HMAC-Hash(key, value)" for a negotiated "Hash" [RFC5869], which is built on HMAC [RFC2104]. These are defined as
function; the symbol | denotes concatenation, and the counter follows in terms of the function "HMAC-Hash(key, value)" for a
concatenated to the right of CONST occupies a single octet. negotiated "Hash" function such as SHA-256; the symbol | denotes
concatenation, and the counter concatenated to the right of CONST
occupies a single octet.
HKDF-Extract(salt, IKM) -> PRK HKDF-Extract(salt, IKM) -> PRK
PRK = HMAC-Hash(salt, IKM) PRK = HMAC-Hash(salt, IKM)
HKDF-Expand(PRK, CONST, L) -> OKM HKDF-Expand(PRK, CONST, L) -> OKM
T(0) = empty string (zero length) T(0) = empty string (zero length)
T(1) = HMAC-Hash(PRK, T(0) | CONST | 0x01) T(1) = HMAC-Hash(PRK, T(0) | CONST | 0x01)
T(2) = HMAC-Hash(PRK, T(1) | CONST | 0x02) T(2) = HMAC-Hash(PRK, T(1) | CONST | 0x02)
T(3) = HMAC-Hash(PRK, T(2) | CONST | 0x03) T(3) = HMAC-Hash(PRK, T(2) | CONST | 0x03)
... ...
OKM = first L octets of T(1) | T(2) | T(3) | ... OKM = first L octets of T(1) | T(2) | T(3) | ...
where L < 255*OutputLength(Hash)
Figure 1: HKDF functions used for key derivation Figure 1: HKDF functions used for key derivation
Lastly, once tcpcrypt has been successfully set up and encryption Lastly, once tcpcrypt has been successfully set up and encryption
keys have been derived, an algorithm for Authenticated Encryption keys have been derived, an algorithm for Authenticated Encryption
with Associated Data (AEAD) is used to protect the confidentiality with Associated Data (AEAD) is used to protect the confidentiality
and integrity of all transmitted application data. AEAD algorithms and integrity of all transmitted application data. AEAD algorithms
use a single key to encrypt their input data and also to generate a use a single key to encrypt their input data and also to generate a
cryptographic tag to accompany the resulting ciphertext; when cryptographic tag to accompany the resulting ciphertext; when
decryption is performed, the tag allows authentication of the decryption is performed, the tag allows authentication of the
encrypted data and of optional, associated plaintext data. encrypted data and of optional, associated plaintext data.
3.2. Protocol negotiation 3.2. Protocol Negotiation
Tcpcrypt depends on TCP-ENO [I-D.ietf-tcpinc-tcpeno] to negotiate Tcpcrypt depends on TCP-ENO [I-D.ietf-tcpinc-tcpeno] to negotiate
whether encryption will be enabled for a connection, and also which whether encryption will be enabled for a connection, and also which
key agreement scheme to use. TCP-ENO negotiates the use of a key-agreement scheme to use. TCP-ENO negotiates the use of a
particular TCP encryption protocol or _TEP_ by including protocol particular TCP encryption protocol or _TEP_ by including protocol
identifiers in ENO suboptions. This document associates four TEP identifiers in ENO suboptions. This document associates four TEP
identifiers with the tcpcrypt protocol, as listed in Table 2. Each identifiers with the tcpcrypt protocol, as listed in Table 2. Each
identifier indicates the use of a particular key-agreement scheme. identifier indicates the use of a particular key-agreement scheme,
Future standards may associate additional identifiers with tcpcrypt. with an associated CPRF and length parameters. Future standards may
associate additional TEP identifiers with tcpcrypt, following the
assignment policy specified by TCP-ENO.
An active opener that wishes to negotiate the use of tcpcrypt An active opener that wishes to negotiate the use of tcpcrypt
includes an ENO option in its SYN segment. That option includes includes an ENO option in its SYN segment. That option includes
suboptions with tcpcrypt TEP identifiers indicating the key-agreement suboptions with tcpcrypt TEP identifiers indicating the key-agreement
schemes it is willing to enable. The active opener MAY additionally schemes it is willing to enable. The active opener MAY additionally
include suboptions indicating support for encryption protocols other include suboptions indicating support for encryption protocols other
than tcpcrypt, as well as global suboptions as specified by TCP-ENO. than tcpcrypt, as well as global suboptions as specified by TCP-ENO.
If a passive opener receives an ENO option including tcpcrypt TEPs it If a passive opener receives an ENO option including tcpcrypt TEPs it
supports, it MAY then attach an ENO option to its SYN-ACK segment, supports, it MAY then attach an ENO option to its SYN-ACK segment,
including _solely_ the TEP it wishes to enable. including _solely_ the TEP it wishes to enable.
To establish distinct roles for the two hosts in each connection, To establish distinct roles for the two hosts in each connection,
tcpcrypt depends on the role-negotiation mechanism of TCP-ENO. As tcpcrypt depends on the role-negotiation mechanism of TCP-ENO. As
one result of the negotiation process, TCP-ENO assigns hosts unique one result of the negotiation process, TCP-ENO assigns hosts unique
roles abstractly called "A" at one end of the connection and "B" at roles abstractly called "A" at one end of the connection and "B" at
the other. Generally, an active opener plays the "A" role and a the other. Generally, an active opener plays the "A" role and a
passive opener plays the "B" role; but in the case of simultaneous passive opener plays the "B" role; but in the case of simultaneous
open, an additional mechanism breaks the symmetry and assigns open, an additional mechanism breaks the symmetry and assigns a
different roles to the two hosts. This document adopts the terms distinct role to each host. TCP-ENO uses the terms "host A" and
"host A" and "host B" to identify each end of a connection uniquely, "host B" to identify each end of a connection uniquely, and this
following TCP-ENO's designation. document employs those terms in the same way.
ENO suboptions include a flag "v" which indicates the presence of An ENO suboption includes a flag "v" which indicates the presence of
associated, variable-length data. In order to propose fresh key associated, variable-length data. In order to propose fresh key
agreement with a particular tcpcrypt TEP, a host sends a one-byte agreement with a particular tcpcrypt TEP, a host sends a one-byte
suboption containing the TEP identifier and "v = 0". In order to suboption containing the TEP identifier and "v = 0". In order to
propose session resumption (described further below) with a propose session resumption (described further below) with a
particular TEP, a host sends a variable-length suboption containing particular TEP, a host sends a variable-length suboption containing
the TEP identifier, the flag "v = 1", and an identifier for a session the TEP identifier, the flag "v = 1", and an identifier derived from
previously negotiated with the same host and the same TEP. a session secret previously negotiated with the same host and the
same TEP.
Once two hosts have exchanged SYN segments, TCP-ENO defines the Once two hosts have exchanged SYN segments, TCP-ENO defines the
_negotiated TEP_ to be the last valid TEP identifier in the SYN _negotiated TEP_ to be the last valid TEP identifier in the SYN
segment of host B (that is, the passive opener in the absence of segment of host B (that is, the passive opener in the absence of
simultaneous open) that also occurs in that of host A. If there is simultaneous open) that also occurs in that of host A. If there is
no such TEP, hosts MUST disable TCP-ENO and tcpcrypt. no such TEP, hosts MUST disable TCP-ENO and tcpcrypt.
If the negotiated TEP was sent by host B with "v = 0", it means that If the negotiated TEP was sent by host B with "v = 0", it means that
fresh key agreement will be performed as described below in fresh key agreement will be performed as described below in
Section 3.3. If it had "v = 1", the key-exchange messages will be Section 3.3. If it had "v = 1", the key-exchange messages will be
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agreement will be performed. That is, sending a resumption suboption agreement will be performed. That is, sending a resumption suboption
also implies willingness to perform fresh key agreement with the also implies willingness to perform fresh key agreement with the
indicated TEP. indicated TEP.
As required by TCP-ENO, once a host has both sent and received an ACK As required by TCP-ENO, once a host has both sent and received an ACK
segment containing a valid ENO option, encryption MUST be enabled and segment containing a valid ENO option, encryption MUST be enabled and
plaintext application data MUST NOT ever be exchanged on the plaintext application data MUST NOT ever be exchanged on the
connection. If the negotiated TEP is among those listed in Table 2, connection. If the negotiated TEP is among those listed in Table 2,
a host MUST follow the protocol described in this document. a host MUST follow the protocol described in this document.
3.3. Key exchange 3.3. Key Exchange
Following successful negotiation of a tcpcrypt TEP, all further Following successful negotiation of a tcpcrypt TEP, all further
signaling is performed in the Data portion of TCP segments. Except signaling is performed in the Data portion of TCP segments. Except
when resumption was negotiated (described below in Section 3.5), the when resumption was negotiated (described below in Section 3.5), the
two hosts perform key exchange through two messages, "Init1" and two hosts perform key exchange through two messages, "Init1" and
"Init2", at the start of the data streams of host A and host B, "Init2", at the start of the data streams of host A and host B,
respectively. These messages may span multiple TCP segments and need respectively. These messages may span multiple TCP segments and need
not end at a segment boundary. However, the segment containing the not end at a segment boundary. However, the segment containing the
last byte of an "Init1" or "Init2" message MUST have TCP's push flag last byte of an "Init1" or "Init2" message MUST have TCP's push flag
(PSH) set. (PSH) set.
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ss[i] = CPRF(ss[i-1], CONST_NEXTK, K_LEN) ss[i] = CPRF(ss[i-1], CONST_NEXTK, K_LEN)
The value "ss[0]" is used to generate all key material for the The value "ss[0]" is used to generate all key material for the
current connection. The values "ss[i]" for "i > 0" can be used to current connection. The values "ss[i]" for "i > 0" can be used to
avoid public key cryptography when establishing subsequent avoid public key cryptography when establishing subsequent
connections between the same two hosts, as described in Section 3.5. connections between the same two hosts, as described in Section 3.5.
The "CONST_*" values are constants defined in Table 1. The length The "CONST_*" values are constants defined in Table 1. The length
"K_LEN" depends on the tcpcrypt TEP in use, and is specified in "K_LEN" depends on the tcpcrypt TEP in use, and is specified in
Section 5. Section 5.
Given a session secret "ss", the two sides compute a series of master Given a session secret "ss[i]", the two sides compute a series of
keys as follows: master keys as follows:
mk[0] = CPRF(ss, CONST_REKEY, K_LEN) mk[0] = CPRF(ss[i], CONST_REKEY, K_LEN)
mk[i] = CPRF(mk[i-1], CONST_REKEY, K_LEN) mk[j] = CPRF(mk[j-1], CONST_REKEY, K_LEN)
The particular master key in use is advanced as described in The process of advancing through the series of master keys is
Section 3.8. described in Section 3.8.
Finally, each master key "mk" is used to generate keys for Finally, each master key "mk[j]" is used to generate keys for
authenticated encryption for the "A" and "B" roles. Key "k_ab" is authenticated encryption:
used by host A to encrypt and host B to decrypt, while "k_ba" is used
by host B to encrypt and host A to decrypt.
k_ab = CPRF(mk, CONST_KEY_A, ae_keylen) k_ab[j] = CPRF(mk[j], CONST_KEY_A, ae_keylen)
k_ba = CPRF(mk, CONST_KEY_B, ae_keylen) k_ba[j] = CPRF(mk[j], CONST_KEY_B, ae_keylen)
In the first session derived from fresh key-agreement, keys "k_ab[j]"
are used by host A to encrypt and host B to decrypt, while keys
"k_ba[j]" are used by host B to encrypt and host A to decrypt. In a
resumed session, as described more thoroughly below in Section 3.5,
each host uses the keys in the same way as it did in the original
session, regardless of its role in the current session: for example,
if a host played role "A" in the first session, it will use keys
"k_ab[j]" to encrypt in each derived session.
The value "ae_keylen" depends on the authenticated-encryption The value "ae_keylen" depends on the authenticated-encryption
algorithm selected, and is given under "Key Length" in Table 3. algorithm selected, and is given under "Key Length" in Table 3.
After host B sends "Init2" or host A receives it, that host may After host B sends "Init2" or host A receives it, that host may
immediately begin transmitting protected application data as immediately begin transmitting protected application data as
described in Section 3.6. described in Section 3.6.
If host A receives "Init2" with a "sym-cipher" value that was not If host A receives "Init2" with a "sym-cipher" value that was not
present in the "sym-cipher-list" it previously transmitted in present in the "sym-cipher-list" it previously transmitted in
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Throughout this document, to "abort the connection" means to issue Throughout this document, to "abort the connection" means to issue
the "Abort" command as described in [RFC0793], Section 3.8. That is, the "Abort" command as described in [RFC0793], Section 3.8. That is,
the TCP connection is destroyed, RESET is transmitted, and the local the TCP connection is destroyed, RESET is transmitted, and the local
user is alerted to the abort event. user is alerted to the abort event.
3.4. Session ID 3.4. Session ID
TCP-ENO requires each TEP to define a _session ID_ value that TCP-ENO requires each TEP to define a _session ID_ value that
uniquely identifies each encrypted connection. uniquely identifies each encrypted connection.
As required, a tcpcrypt session ID begins with the negotiated TEP As required, a tcpcrypt session ID begins with the byte transmitted
identifier along with the "v" bit as transmitted by host B. The by host B that contains the negotiated TEP identifier along with the
remainder of the ID is derived from the session secret, as follows: "v" bit. The remainder of the ID is derived from the session secret,
as follows:
session_id[i] = TEP-byte | CPRF(ss[i], CONST_SESSID, K_LEN) session_id[i] = TEP-byte | CPRF(ss[i], CONST_SESSID, K_LEN)
Again, the length "K_LEN" depends on the TEP, and is specified in Again, the length "K_LEN" depends on the TEP, and is specified in
Section 5. Section 5.
3.5. Session resumption 3.5. Session Resumption
When two hosts have already negotiated session secret "ss[i-1]", they If two hosts have previously negotiated a session with a particular
can establish a new connection without public-key operations using session secret, they can establish a new connection without public-
"ss[i]". A host signals willingness to resume with a particular key operations using the next session secret in the sequence derived
session secret by sending a SYN segment with a resumption suboption: from the original PRK.
that is, an ENO suboption containing the negotiated TEP identifier
from the original session and part of an identifier for the session. A host signals willingness to resume with a particular session secret
by sending a SYN segment with a resumption suboption: that is, an ENO
suboption whose value is the negotiated TEP identifier of the session
concatenated with half of the "resumption identifier" for the
session.
The resumption identifier is calculated from a session secret "ss[i]" The resumption identifier is calculated from a session secret "ss[i]"
as follows: as follows:
resume[i] = CPRF(ss[i], CONST_RESUME, 18) resume[i] = CPRF(ss[i], CONST_RESUME, 18)
To name a session for resumption, a host sends either the first or To name a session for resumption, a host sends either the first or
second half of the resumption identifier, according to the role it second half of the resumption identifier, according to the role it
played in the original session with secret "ss[0]". played in the original session with secret "ss[0]".
skipping to change at page 9, line 34 skipping to change at page 10, line 14
byte 0 1 9 (10 bytes total) byte 0 1 9 (10 bytes total)
+--------+--------+---...---+--------+ +--------+--------+---...---+--------+
| TEP- | resume[i]{9..17} | | TEP- | resume[i]{9..17} |
| byte | | | byte | |
+--------+--------+---...---+--------+ +--------+--------+---...---+--------+
Figure 3: Resumption suboption sent when original role was B. The Figure 3: Resumption suboption sent when original role was B. The
TEP-byte contains a tcpcrypt TEP identifier and v = 1. TEP-byte contains a tcpcrypt TEP identifier and v = 1.
If a passive opener recognizes the identifier-half in a resumption If a passive opener receives a resumption suboption containing an
suboption it has received and knows "ss[i]", it SHOULD (with identifier-half it recognizes as being derived from a session secret
exceptions specified below) agree to resume from the cached session that it has cached, it SHOULD (with exceptions specified below) agree
by sending its own resumption suboption, which will contain the other to resume from the cached session by sending its own resumption
half of the identifier. suboption, which will contain the other half of the identifier.
If it does not agree to resumption with a particular TEP, the passive If the passive opener does not agree to resumption with a particular
opener may either request fresh key exchange by responding with a TEP, it may either request fresh key exchange by responding with a
non-resumption suboption using the same TEP, or else respond to any non-resumption suboption using the same TEP, or else respond to any
other received suboption. other received suboption.
If an active opener receives a resumption suboption for a particular If an active opener receives a resumption suboption for a particular
TEP and the received identifier-half does not match the "resume[i]" TEP and the received identifier-half does not match the "resume[i]"
value whose other half it previously sent in a resumption suboption value whose other half it previously sent in a resumption suboption
for the same TEP, it MUST ignore that suboption. In the typical case for the same TEP, it MUST ignore that suboption. In the typical case
that this was the only ENO suboption received, this means the host that this was the only ENO suboption received, this means the host
MUST disable TCP-ENO and tcpcrypt: that is, it MUST NOT send any more MUST disable TCP-ENO and tcpcrypt: that is, it MUST NOT send any more
ENO options and MUST NOT encrypt the connection. ENO options and MUST NOT encrypt the connection.
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In the case of simultaneous open where TCP-ENO is able to establish In the case of simultaneous open where TCP-ENO is able to establish
asymmetric roles, two hosts that simultaneously send SYN segments asymmetric roles, two hosts that simultaneously send SYN segments
with compatible resumption suboptions may resume the associated with compatible resumption suboptions may resume the associated
session. session.
In a particular SYN segment, a host SHOULD NOT send more than one In a particular SYN segment, a host SHOULD NOT send more than one
resumption suboption, and MUST NOT send more than one resumption resumption suboption, and MUST NOT send more than one resumption
suboption with the same TEP identifier. But in addition to any suboption with the same TEP identifier. But in addition to any
resumption suboptions, an active opener MAY include non-resumption resumption suboptions, an active opener MAY include non-resumption
suboptions describing other key-agreement schemes it supports (in suboptions describing other TEPs it supports (in addition to the TEP
addition to that indicated by the TEP in the resumption suboption). in the resumption suboption).
After using "ss[i]" to compute "mk[0]", implementations SHOULD After using "ss[i]" to compute "mk[0]", implementations SHOULD
compute and cache "ss[i+1]" for possible use by a later session, then compute and cache "ss[i+1]" for possible use by a later session, then
erase "ss[i]" from memory. Hosts SHOULD retain "ss[i+1]" until it is erase "ss[i]" from memory. Hosts SHOULD retain "ss[i+1]" until it is
used or the memory needs to be reclaimed. Hosts SHOULD NOT write a used or the memory needs to be reclaimed. Hosts SHOULD NOT write a
cached "ss[i+1]" value to non-volatile storage. cached "ss[i+1]" value to non-volatile storage.
When proposing resumption, the active opener MUST use the lowest When proposing resumption, the active opener MUST use the lowest
value of "i" that has not already been used (successfully or not) to value of "i" that has not already been used (successfully or not) to
negotiate resumption with the same host and for the same pre-session negotiate resumption with the same host and for the same pre-session
skipping to change at page 10, line 49 skipping to change at page 11, line 29
connection. To prevent this, a host MUST NOT resume with a session connection. To prevent this, a host MUST NOT resume with a session
secret if it has ever enabled encryption in the past with the same secret if it has ever enabled encryption in the past with the same
secret, in either role. In the event that two hosts simultaneously secret, in either role. In the event that two hosts simultaneously
send SYN segments to each other that propose resumption with the same send SYN segments to each other that propose resumption with the same
session secret but the two segments are not part of a simultaneous session secret but the two segments are not part of a simultaneous
open, both connections will have to revert to fresh key-exchange. To open, both connections will have to revert to fresh key-exchange. To
avoid this limitation, implementations MAY choose to implement avoid this limitation, implementations MAY choose to implement
session resumption such that a given pre-session key "ss[0]" is only session resumption such that a given pre-session key "ss[0]" is only
used for either passive or active opens at the same host, not both. used for either passive or active opens at the same host, not both.
When two hosts have previously negotiated a tcpcrypt session, either If two hosts have previously negotiated a tcpcrypt session, either
host may initiate session resumption regardless of which host was the host may later initiate session resumption regardless of which host
active opener or played the "A" role in the previous session. was the active opener or played the "A" role in the previous session.
However, a given host must either encrypt with "k_ab" for all However, a given host must either encrypt with keys "k_ab[j]" for all
sessions derived from the same pre-session key "ss[0]", or with sessions derived from the same pre-session key "ss[0]", or with keys
"k_ba". Thus, which keys a host uses to send segments is not "k_ba[j]". Thus, which keys a host uses to send segments is not
affected by the role it plays in the current connection: it depends affected by the role it plays in the current connection: it depends
only on whether the host played the "A" or "B" role in the initial only on whether the host played the "A" or "B" role in the initial
session. session.
Implementations that perform session caching MUST provide a means for Implementations that cache session secrets MUST provide a means for
applications to control session caching, including flushing cached applications to control that caching. In particular, when an
session secrets associated with an ESTABLISHED connection or application requests a new TCP connection, it must be able to specify
disabling the use of caching for a particular connection. that during the connection no session secrets will be cached and all
resumption requests will be ignored in favor of fresh key exchange.
And for an established connection, an application must be able to
cause any cache state that was used in or resulted from establishing
the connection to be flushed. A companion document
[I-D.ietf-tcpinc-api] describes recommended interfaces for this
purpose.
3.6. Data encryption and authentication 3.6. Data Encryption and Authentication
Following key exchange (or its omission via session resumption), all Following key exchange (or its omission via session resumption), all
further communication in a tcpcrypt-enabled connection is carried out further communication in a tcpcrypt-enabled connection is carried out
within delimited _encryption frames_ that are encrypted and within delimited _encryption frames_ that are encrypted and
authenticated using the agreed keys. authenticated using the agreed keys.
This protection is provided via algorithms for Authenticated This protection is provided via algorithms for Authenticated
Encryption with Associated Data (AEAD). The particular algorithms Encryption with Associated Data (AEAD). The particular algorithms
that may be used are listed in Table 3. One algorithm is selected that may be used are listed in Table 3, and additional algorithms may
during the negotiation described in Section 3.3. be specified according to the policy in Section 7. One algorithm is
selected during the negotiation described in Section 3.3.
The format of an encryption frame is specified in Section 4.2. A The format of an encryption frame is specified in Section 4.2. A
sending host breaks its stream of application data into a series of sending host breaks its stream of application data into a series of
chunks. Each chunk is placed in the "data" portion of a "plaintext" chunks. Each chunk is placed in the "data" portion of a "plaintext"
value, which is then encrypted to yield a frame's "ciphertext" field. value, which is then encrypted to yield a frame's "ciphertext" field.
Chunks must be small enough that the ciphertext (whose length depends Chunks must be small enough that the ciphertext (whose length depends
on the AEAD cipher used, and is generally slightly longer than the on the AEAD cipher used, and is generally slightly longer than the
plaintext) has length less than 2^16 bytes. plaintext) has length less than 2^16 bytes.
An "associated data" value (see Section 4.2.2) is constructed for the An "associated data" value (see Section 4.2.2) is constructed for the
frame. It contains the frame's "control" field and the length of the frame. It contains the frame's "control" field and the length of the
ciphertext. ciphertext.
A "frame nonce" value (see Section 4.2.3) is also constructed for the A "frame nonce" value (see Section 4.2.3) is also constructed for the
frame but not explicitly transmitted. It contains an "offset" field frame but not explicitly transmitted. It contains an "offset" field
whose integer value is the zero-indexed byte offset of the beginning whose integer value is the zero-indexed byte offset of the beginning
of the current encryption frame in the underlying TCP datastream. of the current encryption frame in the underlying TCP datastream.
(That is, the offset in the framing stream, not the plaintext (That is, the offset in the framing stream, not the plaintext
application stream.) Because it is strictly necessary for the application stream.) Because it is strictly necessary for the
security of the AEAD algorithm, an implementation MUST NOT ever security of the AEAD algorithms specified in this document, an
transmit distinct frames with the same nonce value under the same implementation MUST NOT ever transmit distinct frames with the same
encryption key. In particular, a retransmitted TCP segment MUST nonce value under the same encryption key. In particular, a
contain the same payload bytes for the same TCP sequence numbers, and retransmitted TCP segment MUST contain the same payload bytes for the
a host MUST NOT transmit more than 2^64 bytes in the underlying TCP same TCP sequence numbers, and a host MUST NOT transmit more than
datastream (which would cause the "offset" field to wrap) before re- 2^64 bytes in the underlying TCP datastream (which would cause the
keying. "offset" field to wrap) before re-keying.
With reference to the "AEAD Interface" described in Section 2 of With reference to the "AEAD Interface" described in Section 2 of
[RFC5116], tcpcrypt invokes the AEAD algorithm with the secret key [RFC5116], tcpcrypt invokes the AEAD algorithm with the secret key
"K" set to k_ab or k_ba, according to the host's role as described in "K" set to "k_ab[j]" or "k_ba[j]" for some "j", according to the
Section 3.3. The plaintext value serves as "P", the associated data host's role as described in Section 3.3. The plaintext value serves
as "A", and the frame nonce as "N". The output of the encryption as "P", the associated data as "A", and the frame nonce as "N". The
operation, "C", is transmitted in the frame's "ciphertext" field. output of the encryption operation, "C", is transmitted in the
frame's "ciphertext" field.
When a frame is received, tcpcrypt reconstructs the associated data When a frame is received, tcpcrypt reconstructs the associated data
and frame nonce values (the former contains only data sent in the and frame nonce values (the former contains only data sent in the
clear, and the latter is implicit in the TCP stream), and provides clear, and the latter is implicit in the TCP stream), and provides
these and the ciphertext value to the the AEAD decryption operation. these and the ciphertext value to the the AEAD decryption operation.
The output of this operation is either a plaintext value "P" or the The output of this operation is either a plaintext value "P" or the
special symbol FAIL. In the latter case, the implementation MUST special symbol FAIL. In the latter case, the implementation MUST
either drop the TCP segment(s) containing the frame or abort the either drop the TCP segment(s) containing the frame or abort the
connection; but if it aborts, the implementation MUST raise an error connection; but if it aborts, the implementation MUST raise an error
condition distinct from the end-of-file condition. condition distinct from the end-of-file condition.
3.7. TCP header protection 3.7. TCP Header Protection
The "ciphertext" field of the encryption frame contains protected The "ciphertext" field of the encryption frame contains protected
versions of certain TCP header values. versions of certain TCP header values.
When the "URGp" bit is set, the "urgent" value indicates an offset When the "URGp" bit is set, the "urgent" value indicates an offset
from the current frame's beginning offset; the sum of these offsets from the current frame's beginning offset; the sum of these offsets
gives the index of the last byte of urgent data in the application gives the index of the last byte of urgent data in the application
datastream. datastream.
A sender MUST set the "FINp" bit on the last frame it sends in the A sender MUST set the "FINp" bit on the last frame it sends in the
skipping to change at page 12, line 46 skipping to change at page 13, line 37
on any other frame. on any other frame.
TCP sets the FIN flag when a sender has no more data, which with TCP sets the FIN flag when a sender has no more data, which with
tcpcrypt means setting FIN on the segment containing the last byte of tcpcrypt means setting FIN on the segment containing the last byte of
the last frame. However, a receiver MUST report the end-of-file the last frame. However, a receiver MUST report the end-of-file
condition to the connection's local user when and only when it condition to the connection's local user when and only when it
receives a frame with the "FINp" bit set. If a host receives a receives a frame with the "FINp" bit set. If a host receives a
segment with the TCP FIN flag set but the received datastream segment with the TCP FIN flag set but the received datastream
including this segment does not contain a frame with "FINp" set, the including this segment does not contain a frame with "FINp" set, the
host SHOULD abort the connection and raise an error condition host SHOULD abort the connection and raise an error condition
distinct from the end-of-file condition; but if there are distinct from the end-of-file condition. But if there are
unacknowledged segments whose retransmission could potentially result unacknowledged segments whose retransmission could potentially result
in a valid frame, the host MAY instead drop the segment with the TCP in a valid frame, the host MAY instead drop the segment with the TCP
FIN flag set. FIN flag set.
3.8. Re-keying 3.8. Re-Keying
Re-keying allows hosts to wipe from memory keys that could decrypt Re-keying allows hosts to wipe from memory keys that could decrypt
previously transmitted segments. It also allows the use of AEAD previously transmitted segments. It also allows the use of AEAD
ciphers that can securely encrypt only a bounded number of messages ciphers that can securely encrypt only a bounded number of messages
under a given key. under a given key.
We refer to the two encryption keys (k_ab, k_ba) as a _key-set_. We As described above in Section 3.3, a master key "mk[j]" is used to
refer to the key-set generated by mk[i] as the key-set with generate two encryption keys "k_ab[j]" and "k_ba[j]". We refer to
_generation number_ "i" within a session. Each host maintains a these as a _key-set_ with _generation number_ "j". Each host
_local generation number_ that determines which key-set it uses to maintains a _local generation number_ that determines which key-set
encrypt outgoing frames, and a _remote generation number_ equal to it uses to encrypt outgoing frames, and a _remote generation number_
the highest generation used in frames received from its peer. equal to the highest generation used in frames received from its
Initially, these two values are set to zero. peer. Initially, these two generation numbers are set to zero.
A host MAY increment its local generation number beyond the remote A host MAY increment its local generation number beyond the remote
generation number it has recorded. We call this action _initiating generation number it has recorded. We call this action _initiating
re-keying_. re-keying_.
When a host has incremented its local generation number and uses the When a host has incremented its local generation number and uses the
new key-set for the first time to encrypt an outgoing frame, it MUST new key-set for the first time to encrypt an outgoing frame, it MUST
set "rekey = 1" for that frame. It MUST set this field to zero in set "rekey = 1" for that frame. It MUST set this field to zero in
all other cases. all other cases.
skipping to change at page 13, line 42 skipping to change at page 14, line 30
MUST immediately increment its local generation number to match. MUST immediately increment its local generation number to match.
Moreover, if the receiver has not yet transmitted a segment with the Moreover, if the receiver has not yet transmitted a segment with the
FIN flag set, it MUST immediately send a frame (with empty FIN flag set, it MUST immediately send a frame (with empty
application data if necessary) with "rekey = 1". application data if necessary) with "rekey = 1".
A host SHOULD NOT initiate more than one concurrent re-key operation A host SHOULD NOT initiate more than one concurrent re-key operation
if it has no data to send; that is, it should not initiate re-keying if it has no data to send; that is, it should not initiate re-keying
with an empty encryption frame more than once while its record of the with an empty encryption frame more than once while its record of the
remote generation number is less than its own. remote generation number is less than its own.
When retransmitting, implementations must always transmit the same Note that when parts of the datastream are retransmitted, TCP
bytes for the same TCP sequence numbers. Thus, a frame in a requires that implementations always send the same data bytes for the
retransmitted segment MUST always be encrypted with the same key as same TCP sequence numbers. Thus, frame data in retransmitted
when it was originally transmitted. segments must be encrypted with the same key as when it was first
transmitted, regardless of the current local generation number.
Implementations SHOULD delete older-generation keys from memory once Implementations SHOULD delete older-generation keys from memory once
they have received all frames they will need to decrypt with the old they have received all frames they will need to decrypt with the old
keys and have encrypted all outgoing frames under the old keys. keys and have encrypted all outgoing frames under the old keys.
3.9. Keep-alive 3.9. Keep-Alive
Instead of using TCP Keep-Alives to verify that the remote endpoint Instead of using TCP Keep-Alives to verify that the remote endpoint
is still responsive, tcpcrypt implementations SHOULD employ the re- is still responsive, tcpcrypt implementations SHOULD employ the re-
keying mechanism for this purpose, as follows. When necessary, a keying mechanism for this purpose, as follows. When necessary, a
host SHOULD probe the liveness of its peer by initiating re-keying host SHOULD probe the liveness of its peer by initiating re-keying
and transmitting a new frame immediately (with empty application data and transmitting a new frame immediately (with empty application data
if necessary). if necessary).
As described in Section 3.8, a host receiving a frame encrypted under As described in Section 3.8, a host receiving a frame encrypted under
a generation number greater than its own MUST increment its own a generation number greater than its own MUST increment its own
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application data if necessary). application data if necessary).
Implementations MAY use TCP Keep-Alives for purposes that do not Implementations MAY use TCP Keep-Alives for purposes that do not
require endpoint authentication, as discussed in Section 8.2. require endpoint authentication, as discussed in Section 8.2.
4. Encodings 4. Encodings
This section provides byte-level encodings for values transmitted or This section provides byte-level encodings for values transmitted or
computed by the protocol. computed by the protocol.
4.1. Key exchange messages 4.1. Key-Exchange Messages
The "Init1" message has the following encoding: The "Init1" message has the following encoding:
byte 0 1 2 3 byte 0 1 2 3
+-------+-------+-------+-------+ +-------+-------+-------+-------+
| INIT1_MAGIC | | INIT1_MAGIC |
| | | |
+-------+-------+-------+-------+ +-------+-------+-------+-------+
4 5 6 7 4 5 6 7
+-------+-------+-------+-------+ +-------+-------+-------+-------+
| message_len | | message_len |
| = M | | = M |
+-------+-------+-------+-------+ +-------+-------+-------+-------+
8 8 K + 8
+--------+-------+-------+---...---+-------+ +--------+---------+---------+---...---+-----------+
|nciphers|sym- |sym- | |sym- | |nciphers|sym- |sym- | |sym- |
| =K+1 |cipher0|cipher1| |cipherK| | = K |cipher[0]|cipher[1]| |cipher[K-1]|
+--------+-------+-------+---...---+-------+ +--------+---------+---------+---...---+-----------+
K + 10 K + 10 + N_A_LEN K + 9 K + 9 + N_A_LEN
| | | |
v v v v
+-------+---...---+-------+-------+---...---+-------+ +-------+---...---+-------+-------+---...---+-------+
| N_A | PK_A | | N_A | PK_A |
| | | | | |
+-------+---...---+-------+-------+---...---+-------+ +-------+---...---+-------+-------+---...---+-------+
M - 1 M - 1
+-------+---...---+-------+ +-------+---...---+-------+
| ignored | | ignored |
| | | |
+-------+---...---+-------+ +-------+---...---+-------+
The constant "INIT1_MAGIC" is defined in Table 1. The four-byte The constant "INIT1_MAGIC" is defined in Table 1. The four-byte
field "message_len" gives the length of the entire "Init1" message, field "message_len" gives the length of the entire "Init1" message,
encoded as a big-endian integer. The "nciphers" field contains an encoded as a big-endian integer. The "nciphers" field contains an
integer value that specifies the number of one-byte symmetric-cipher integer value that specifies the number of one-byte symmetric-cipher
identifiers that follow. The "sym-cipher" bytes identify identifiers that follow. The "sym-cipher" bytes identify
cryptographic algorithms in Table 3. The length "N_A_LEN" and the cryptographic algorithms in Table 3. The length "N_A_LEN" and the
length of "PK_A" are both determined by the negotiated key-agreement length of "PK_A" are both determined by the negotiated TEP, as
scheme, as described in Section 5. described in Section 5.
When sending "Init1", implementations of this protocol MUST omit the Implementations of this protocol MUST construct "Init1" such that the
field "ignored"; that is, they must construct the message such that field "ignored" has zero length; that is, they must construct the
its end, as determined by "message_len", coincides with the end of message such that its end, as determined by "message_len", coincides
the field "PK_A". When receiving "Init1", however, implementations with the end of the field "PK_A". When receiving "Init1", however,
MUST permit and ignore any bytes following "PK_A". implementations MUST permit and ignore any bytes following "PK_A".
The "Init2" message has the following encoding: The "Init2" message has the following encoding:
byte 0 1 2 3 byte 0 1 2 3
+-------+-------+-------+-------+ +-------+-------+-------+-------+
| INIT2_MAGIC | | INIT2_MAGIC |
| | | |
+-------+-------+-------+-------+ +-------+-------+-------+-------+
4 5 6 7 8 4 5 6 7 8
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+-------+---...---+-------+ +-------+---...---+-------+
| ignored | | ignored |
| | | |
+-------+---...---+-------+ +-------+---...---+-------+
The constant "INIT2_MAGIC" is defined in Table 1. The four-byte The constant "INIT2_MAGIC" is defined in Table 1. The four-byte
field "message_len" gives the length of the entire "Init2" message, field "message_len" gives the length of the entire "Init2" message,
encoded as a big-endian integer. The "sym-cipher" value is a encoded as a big-endian integer. The "sym-cipher" value is a
selection from the symmetric-cipher identifiers in the previously- selection from the symmetric-cipher identifiers in the previously-
received "Init1" message. The length "N_B_LEN" and the length of received "Init1" message. The length "N_B_LEN" and the length of
"PK_B" are both determined by the negotiated key-agreement scheme, as "PK_B" are both determined by the negotiated TEP, as described in
described in Section 5. Section 5.
When sending "Init2", implementations of this protocol MUST omit the Implementations of this protocol MUST construct "Init2" such that the
field "ignored"; that is, they must construct the message such that field "ignored" has zero length; that is, they must construct the
its end, as determined by "message_len", coincides with the end of message such that its end, as determined by "message_len", coincides
the "PK_B" field. When receiving "Init2", however, implementations with the end of the "PK_B" field. When receiving "Init2", however,
MUST permit and ignore any bytes following "PK_B". implementations MUST permit and ignore any bytes following "PK_B".
4.2. Encryption frames 4.2. Encryption Frames
An _encryption frame_ comprises a control byte and a length-prefixed An _encryption frame_ comprises a control byte and a length-prefixed
ciphertext value: ciphertext value:
byte 0 1 2 3 clen+2 byte 0 1 2 3 clen+2
+-------+-------+-------+-------+---...---+-------+ +-------+-------+-------+-------+---...---+-------+
|control| clen | ciphertext | |control| clen | ciphertext |
+-------+-------+-------+-------+---...---+-------+ +-------+-------+-------+-------+---...---+-------+
The field "clen" is an integer in big-endian format and gives the The field "clen" is an integer in big-endian format and gives the
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The six-bit value "fres" is reserved; implementations MUST set these The six-bit value "fres" is reserved; implementations MUST set these
six bits to zero when sending, and MUST ignore them when receiving. six bits to zero when sending, and MUST ignore them when receiving.
When the "URGp" bit is set, it indicates that the "urgent" field is When the "URGp" bit is set, it indicates that the "urgent" field is
present, and thus that the plaintext value has the second structure present, and thus that the plaintext value has the second structure
variant above; otherwise the first variant is used. variant above; otherwise the first variant is used.
The meaning of "urgent" and of the flag bits is described in The meaning of "urgent" and of the flag bits is described in
Section 3.7. Section 3.7.
4.2.2. Associated data 4.2.2. Associated Data
An encryption frame's "associated data" (which is supplied to the An encryption frame's "associated data" (which is supplied to the
AEAD algorithm when decrypting the ciphertext and verifying the AEAD algorithm when decrypting the ciphertext and verifying the
frame's integrity) has this format: frame's integrity) has this format:
byte 0 1 2 byte 0 1 2
+-------+-------+-------+ +-------+-------+-------+
|control| clen | |control| clen |
+-------+-------+-------+ +-------+-------+-------+
It contains the same values as the frame's "control" and "clen" It contains the same values as the frame's "control" and "clen"
fields. fields.
4.2.3. Frame nonce 4.2.3. Frame Nonce
Lastly, a "frame nonce" (provided as input to the AEAD algorithm) has Lastly, a "frame nonce" (provided as input to the AEAD algorithm) has
this format: this format:
byte byte
+------+------+------+------+ +------+------+------+------+
0 | FRAME_NONCE_MAGIC | 0 | FRAME_NONCE_MAGIC |
+------+------+------+------+ +------+------+------+------+
4 | | 4 | |
+ offset + + offset +
8 | | 8 | |
+------+------+------+------+ +------+------+------+------+
The 4-byte magic constant is defined in Table 1. The 8-byte "offset" The 4-byte magic constant is defined in Table 1. The 8-byte "offset"
field contains an integer in big-endian format. Its value is field contains an integer in big-endian format. Its value is
specified in Section 3.6. specified in Section 3.6.
4.3. Constant values 4.3. Constant Values
The table below defines values for the constants used in the The table below defines values for the constants used in the
protocol. protocol.
+------------+-------------------+ +------------+-------------------+
| Value | Name | | Value | Name |
+------------+-------------------+ +------------+-------------------+
| 0x01 | CONST_NEXTK | | 0x01 | CONST_NEXTK |
| 0x02 | CONST_SESSID | | 0x02 | CONST_SESSID |
| 0x03 | CONST_REKEY | | 0x03 | CONST_REKEY |
| 0x04 | CONST_KEY_A | | 0x04 | CONST_KEY_A |
| 0x05 | CONST_KEY_B | | 0x05 | CONST_KEY_B |
| 0x06 | CONST_RESUME | | 0x06 | CONST_RESUME |
| 0x15101a0e | INIT1_MAGIC | | 0x15101a0e | INIT1_MAGIC |
| 0x097105e0 | INIT2_MAGIC | | 0x097105e0 | INIT2_MAGIC |
| 0x44415441 | FRAME_NONCE_MAGIC | | 0x44415441 | FRAME_NONCE_MAGIC |
+------------+-------------------+ +------------+-------------------+
Table 1: Constant values used in the protocol Table 1: Constant values used in the protocol
5. Key agreement schemes 5. Key-Agreement Schemes
The TEP negotiated via TCP-ENO may indicate the use of one of the The TEP negotiated via TCP-ENO indicates the use of one of the key-
key-agreement schemes named in Table 2. For example, agreement schemes named in Table 2. For example,
"TCPCRYPT_ECDHE_P256" names the tcpcrypt protocol with key-agreement "TCPCRYPT_ECDHE_P256" names the tcpcrypt protocol using ECDHE-P256
scheme ECDHE-P256. together with the CPRF and length parameters specified below.
All schemes listed there use HKDF-Expand-SHA256 as the CPRF, and All the TEPs specified in this document require the use of HKDF-
these lengths for nonces and session keys: Expand-SHA256 as the CPRF, and these lengths for nonces and session
keys:
N_A_LEN: 32 bytes N_A_LEN: 32 bytes
N_B_LEN: 32 bytes N_B_LEN: 32 bytes
K_LEN: 32 bytes K_LEN: 32 bytes
If future documents assign additional TEPs for use with tcpcrypt,
they may specify different values for the lengths above. Note that
the minimum session ID length required by TCP-ENO, together with the
way tcpcrypt constructs session IDs, implies that "K_LEN" must have
length at least 32 bytes.
Key-agreement schemes ECDHE-P256 and ECDHE-P521 employ the ECSVDP-DH Key-agreement schemes ECDHE-P256 and ECDHE-P521 employ the ECSVDP-DH
secret value derivation primitive defined in [ieee1363]. The named secret value derivation primitive defined in [ieee1363]. The named
curves are defined in [nist-dss]. When the public-key values "PK_A" curves are defined in [nist-dss]. When the public-key values "PK_A"
and "PK_B" are transmitted as described in Section 4.1, they are and "PK_B" are transmitted as described in Section 4.1, they are
encoded with the "Elliptic Curve Point to Octet String Conversion encoded with the "Elliptic Curve Point to Octet String Conversion
Primitive" described in Section E.2.3 of [ieee1363], and are prefixed Primitive" described in Section E.2.3 of [ieee1363], and are prefixed
by a two-byte length in big-endian format: by a two-byte length in big-endian format:
byte 0 1 2 L - 1 byte 0 1 2 L - 1
+-------+-------+-------+---...---+-------+ +-------+-------+-------+---...---+-------+
skipping to change at page 20, line 11 skipping to change at page 20, line 43
Implementations SHOULD encode these "pubkey" values in "compressed Implementations SHOULD encode these "pubkey" values in "compressed
format", and MUST accept values encoded in "compressed", format", and MUST accept values encoded in "compressed",
"uncompressed" or "hybrid" formats. "uncompressed" or "hybrid" formats.
Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 use the Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 use the
functions X25519 and X448, respectively, to perform the Diffie-Helman functions X25519 and X448, respectively, to perform the Diffie-Helman
protocol as described in [RFC7748]. When using these ciphers, protocol as described in [RFC7748]. When using these ciphers,
public-key values "PK_A" and "PK_B" are transmitted directly with no public-key values "PK_A" and "PK_B" are transmitted directly with no
length prefix: 32 bytes for Curve25519, and 56 bytes for Curve448. length prefix: 32 bytes for Curve25519, and 56 bytes for Curve448.
A tcpcrypt implementation MUST support at least the schemes The TEP "TCPCRYPT_ECDHE_Curve25519" is mandatory to implement. This
ECDHE-P256 and ECDHE-P521, although system administrators need not means a tcpcrypt implementation MUST support at least this TEP,
enable them. although system administrators need not enable it.
6. AEAD algorithms 6. AEAD Algorithms
Specifiers and key-lengths for AEAD algorithms are given in Table 3. Specifiers and key-lengths for AEAD algorithms are given in Table 3.
The algorithms "AEAD_AES_128_GCM" and "AEAD_AES_256_GCM" are The algorithms "AEAD_AES_128_GCM" and "AEAD_AES_256_GCM" are
specified in [RFC5116]. The algorithm "AEAD_CHACHA20_POLY1305" is specified in [RFC5116]. The algorithm "AEAD_CHACHA20_POLY1305" is
specified in [RFC7539]. specified in [RFC7539].
7. IANA considerations 7. IANA Considerations
Tcpcrypt's TEP identifiers will need to be incorporated in IANA's Tcpcrypt's TEP identifiers will need to be incorporated in IANA's
"TCP encryption protocol identifiers" registry under the "TCP encryption protocol identifiers" registry under the
"Transmission Control Protocol (TCP) Parameters" registry, as in the "Transmission Control Protocol (TCP) Parameters" registry, as in the
following table. The various key-agreement schemes used by these following table. The various key-agreement schemes used by these
tcpcrypt variants are defined in Section 5. tcpcrypt variants are defined in Section 5.
+-------+---------------------------+-----------+ +-------+---------------------------+-----------+
| Value | Meaning | Reference | | Value | Meaning | Reference |
+-------+---------------------------+-----------+ +-------+---------------------------+-----------+
skipping to change at page 21, line 16 skipping to change at page 21, line 44
| Value | AEAD Algorithm | Key Length | Reference | | Value | AEAD Algorithm | Key Length | Reference |
+-------+------------------------+------------+-----------+ +-------+------------------------+------------+-----------+
| 0x01 | AEAD_AES_128_GCM | 16 bytes | [RFC-TBD] | | 0x01 | AEAD_AES_128_GCM | 16 bytes | [RFC-TBD] |
| 0x02 | AEAD_AES_256_GCM | 32 bytes | [RFC-TBD] | | 0x02 | AEAD_AES_256_GCM | 32 bytes | [RFC-TBD] |
| 0x10 | AEAD_CHACHA20_POLY1305 | 32 bytes | [RFC-TBD] | | 0x10 | AEAD_CHACHA20_POLY1305 | 32 bytes | [RFC-TBD] |
+-------+------------------------+------------+-----------+ +-------+------------------------+------------+-----------+
Table 3: Authenticated-encryption algorithms corresponding to sym- Table 3: Authenticated-encryption algorithms corresponding to sym-
cipher specifiers in Init1 and Init2 messages. cipher specifiers in Init1 and Init2 messages.
8. Security considerations 8. Security Considerations
Public-key generation, public-key encryption, and shared-secret Public-key generation, public-key encryption, and shared-secret
generation all require randomness. Other tcpcrypt functions may also generation all require randomness. Other tcpcrypt functions may also
require randomness, depending on the algorithms and modes of require randomness, depending on the algorithms and modes of
operation selected. A weak pseudo-random generator at either host operation selected. A weak pseudo-random generator at either host
will compromise tcpcrypt's security. Many of tcpcrypt's will compromise tcpcrypt's security. Many of tcpcrypt's
cryptographic functions require random input, and thus any host cryptographic functions require random input, and thus any host
implementing tcpcrypt MUST have access to a cryptographically-secure implementing tcpcrypt MUST have access to a cryptographically-secure
source of randomness or pseudo-randomness. source of randomness or pseudo-randomness.
Most implementations will rely on system-wide pseudo-random Most implementations will rely on a device's pseudo-random generator,
generators seeded from hardware events and a seed carried over from seeded from hardware events and a seed carried over from the previous
the previous boot. Once a pseudo-random generator has been properly boot. Once a pseudo-random generator has been properly seeded, it
seeded, it can generate effectively arbitrary amounts of pseudo- can generate effectively arbitrary amounts of pseudo-random data.
random data. However, until a pseudo-random generator has been However, until a pseudo-random generator has been seeded with
seeded with sufficient entropy, not only will tcpcrypt be insecure, sufficient entropy, not only will tcpcrypt be insecure, it will
it will reveal information that further weakens the security of the reveal information that further weakens the security of the pseudo-
pseudo-random generator, potentially harming other applications. As random generator, potentially harming other applications. As
required by TCP-ENO, implementations MUST NOT send ENO options unless required by TCP-ENO, implementations MUST NOT send ENO options unless
they have access to an adequate source of randomness. they have access to an adequate source of randomness.
The cipher-suites specified in this document all use HMAC-SHA256 to The cipher-suites specified in this document all use HMAC-SHA256 to
implement the collision-resistant pseudo-random function denoted by implement the collision-resistant pseudo-random function denoted by
"CPRF". A collision-resistant function is one on which, for "CPRF". A collision-resistant function is one for which, for
sufficiently large L, an attacker cannot find two distinct inputs sufficiently large L, an attacker cannot find two distinct inputs
"K_1", "CONST_1" and "K_2", "CONST_2" such that "CPRF(K_1, CONST_1, "K_1", "CONST_1" and "K_2", "CONST_2" such that "CPRF(K_1, CONST_1,
L) = CPRF(K_2, CONST_2, L)". Collision resistance is important to L) = CPRF(K_2, CONST_2, L)". Collision resistance is important to
assure the uniqueness of session IDs, which are generated using the assure the uniqueness of session IDs, which are generated using the
CPRF. CPRF.
All of the security considerations of TCP-ENO apply to tcpcrypt. In All of the security considerations of TCP-ENO apply to tcpcrypt. In
particular, tcpcrypt does not protect against active eavesdroppers particular, tcpcrypt does not protect against active eavesdroppers
unless applications authenticate the session ID. If it can be unless applications authenticate the session ID. If it can be
established that the session IDs computed at each end of the established that the session IDs computed at each end of the
skipping to change at page 22, line 29 skipping to change at page 23, line 10
There is no "key confirmation" step in tcpcrypt. This is not There is no "key confirmation" step in tcpcrypt. This is not
required because tcpcrypt's threat model includes the possibility of required because tcpcrypt's threat model includes the possibility of
a connection to an adversary. If key negotiation is compromised and a connection to an adversary. If key negotiation is compromised and
yields two different keys, all subsequent frames will be ignored due yields two different keys, all subsequent frames will be ignored due
to failed integrity checks, causing the application's connection to to failed integrity checks, causing the application's connection to
hang. This is not a new threat because in plain TCP, an active hang. This is not a new threat because in plain TCP, an active
attacker could have modified sequence and acknowledgement numbers to attacker could have modified sequence and acknowledgement numbers to
hang the connection anyway. hang the connection anyway.
Tcpcrypt uses short-lived public keys to provide forward secrecy. Tcpcrypt uses short-lived public keys to provide forward secrecy.
All currently specified key agreement schemes involve ECDHE-based key That is, once an implementation removes these keys from memory, a
agreement, meaning a new key can be efficiently computed for each compromise of the system will not provide any means to derive the
connection. If implementations reuse these parameters, they SHOULD session keys for past connections. All currently-specified key
limit the lifetime of the private parameters, ideally to no more than agreement schemes involve ECDHE-based key agreement, meaning a new
two minutes. keypair can be efficiently computed for each connection. If
implementations reuse these parameters, they SHOULD limit the
lifetime of the private parameters as far as practical in order to
minimize the number of past connections that are vulnerable.
Attackers cannot force passive openers to move forward in their Attackers cannot force passive openers to move forward in their
session resumption chain without guessing the content of the session resumption chain without guessing the content of the
resumption identifier, which will be difficult without key knowledge. resumption identifier, which will be difficult without key knowledge.
8.1. Asymmetric roles 8.1. Asymmetric Roles
Tcpcrypt transforms a shared pseudo-random key (PRK) into Tcpcrypt transforms a shared pseudo-random key (PRK) into
cryptographic session keys for each direction. Doing so requires an cryptographic session keys for each direction. Doing so requires an
asymmetry in the protocol, as the key derivation function must be asymmetry in the protocol, as the key derivation function must be
perturbed differently to generate different keys in each direction. perturbed differently to generate different keys in each direction.
Tcpcrypt includes other asymmetries in the roles of the two hosts, Tcpcrypt includes other asymmetries in the roles of the two hosts,
such as the process of negotiating algorithms (e.g., proposing vs. such as the process of negotiating algorithms (e.g., proposing vs.
selecting cipher suites). selecting cipher suites).
8.2. Verified liveness 8.2. Verified Liveness
Many hosts implement TCP Keep-Alives [RFC1122] as an option for Many hosts implement TCP Keep-Alives [RFC1122] as an option for
applications to ensure that the other end of a TCP connection still applications to ensure that the other end of a TCP connection still
exists even when there is no data to be sent. A TCP Keep-Alive exists even when there is no data to be sent. A TCP Keep-Alive
segment carries a sequence number one prior to the beginning of the segment carries a sequence number one prior to the beginning of the
send window, and may carry one byte of "garbage" data. Such a send window, and may carry one byte of "garbage" data. Such a
segment causes the remote side to send an acknowledgment. segment causes the remote side to send an acknowledgment.
Unfortunately, tcpcrypt cannot cryptographically verify Keep-Alive Unfortunately, tcpcrypt cannot cryptographically verify Keep-Alive
acknowledgments. Hence, an attacker could prolong the existence of a acknowledgments. Hence, an attacker could prolong the existence of a
session at one host after the other end of the connection no longer session at one host after the other end of the connection no longer
exists. (Such an attack might prevent a process with sensitive data exists. (Such an attack might prevent a process with sensitive data
from exiting, giving an attacker more time to compromise a host and from exiting, giving an attacker more time to compromise a host and
extract the sensitive data.) extract the sensitive data.)
Thus, tcpcrypt specifies a way to stimulate the remote host to send To counter this threat, tcpcrypt specifies a way to stimulate the
verifiably fresh and authentic data, described in Section 3.9. remote host to send verifiably fresh and authentic data, described in
Section 3.9.
The TCP keep-alive mechanism has also been used for its effects on The TCP keep-alive mechanism has also been used for its effects on
intermediate nodes in the network, such as preventing flow state from intermediate nodes in the network, such as preventing flow state from
expiring at NAT boxes or firewalls. As these purposes do not require expiring at NAT boxes or firewalls. As these purposes do not require
the authentication of endpoints, implementations may safely the authentication of endpoints, implementations may safely
accomplish them using either the existing TCP keep-alive mechanism or accomplish them using either the existing TCP keep-alive mechanism or
tcpcrypt's verified keep-alive mechanism. tcpcrypt's verified keep-alive mechanism.
8.3. Mandatory Key-Agreement Schemes
This document mandates that tcpcrypt implementations provide support
for at least one key-agreement scheme: ECDHE using Curve25519. This
choice of a single mandatory algorithm is the result of a difficult
tradeoff between cryptographic diversity and the ease and security of
actual deployment.
The IETF's appraisal of best current practice on this matter
[RFC7696] says, "Ideally, two independent sets of mandatory-to-
implement algorithms will be specified, allowing for a primary suite
and a secondary suite. This approach ensures that the secondary
suite is widely deployed if a flaw is found in the primary one."
To meet that ideal, it might appear natural to also mandate ECDHE
using P-256, as this scheme is well-studied, widely implemented, and
sufficiently different from the Curve25519-based scheme that it is
unlikely they will both suffer from a single cryptoanalytic advance.
However, implementing the Diffie-Hellman function using NIST elliptic
curves (including those specified for use with tcpcrypt, P-256 and
P-521) appears to be very difficult to achieve without introducing
vulnerability to side-channel attacks [nist-ecc]. Although well-
trusted implementations are available as part of large cryptographic
libraries, these may be difficult to extract for use in operating-
system kernels where tcpcrypt is usually best implemented. In
contrast, the characteristics of Curve25519 together with its recent
popularity has led to many safe and efficient implementations,
including some that fit naturally into the kernel environment.
[RFC7696] insists that, "The selected algorithms need to be resistant
to side-channel attacks and also meet the performance, power, and
code size requirements on a wide variety of platforms." On this
principle, tcpcrypt excludes the NIST curves from the set of
mandatory-to-implement key-agreement algorithms.
9. Acknowledgments 9. Acknowledgments
We are grateful for contributions, help, discussions, and feedback We are grateful for contributions, help, discussions, and feedback
from the TCPINC working group, including Marcelo Bagnulo, David from the TCPINC working group, including Marcelo Bagnulo, David
Black, Bob Briscoe, Jana Iyengar, Tero Kivinen, Mirja Kuhlewind, Yoav Black, Bob Briscoe, Jana Iyengar, Tero Kivinen, Mirja Kuhlewind, Yoav
Nir, Christoph Paasch, Eric Rescorla, and Kyle Rose. Nir, Christoph Paasch, Eric Rescorla, and Kyle Rose.
This work was funded by gifts from Intel (to Brad Karp) and from This work was funded by gifts from Intel (to Brad Karp) and from
Google; by NSF award CNS-0716806 (A Clean-Slate Infrastructure for Google; by NSF award CNS-0716806 (A Clean-Slate Infrastructure for
Information Flow Control); by DARPA CRASH under contract Information Flow Control); by DARPA CRASH under contract
skipping to change at page 24, line 12 skipping to change at page 25, line 25
Dan Boneh and Michael Hamburg were co-authors of the draft that Dan Boneh and Michael Hamburg were co-authors of the draft that
became this document. became this document.
11. References 11. References
11.1. Normative References 11.1. Normative References
[I-D.ietf-tcpinc-tcpeno] [I-D.ietf-tcpinc-tcpeno]
Bittau, A., Giffin, D., Handley, M., Mazieres, D., and E. Bittau, A., Giffin, D., Handley, M., Mazieres, D., and E.
Smith, "TCP-ENO: Encryption Negotiation Option", draft- Smith, "TCP-ENO: Encryption Negotiation Option", draft-
ietf-tcpinc-tcpeno-10 (work in progress), October 2017. ietf-tcpinc-tcpeno-11 (work in progress), October 2017.
[ieee1363] [ieee1363]
"IEEE Standard Specifications for Public-Key Cryptography IEEE, "IEEE Standard Specifications for Public-Key
(IEEE Std 1363-2000)", 2000. Cryptography (IEEE Std 1363-2000)", 2000.
[nist-dss] [nist-dss]
"Digital Signature Standard, FIPS 186-2", 2000. NIST, "FIPS PUB 186-4: Digital Signature Standard (DSS)",
2013.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981, RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>. <https://www.rfc-editor.org/info/rfc793>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997, <https://www.rfc-
editor.org/info/rfc2104>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>. editor.org/info/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>. <https://www.rfc-editor.org/info/rfc5116>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
skipping to change at page 25, line 10 skipping to change at page 26, line 27
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves [RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>. 2016, <https://www.rfc-editor.org/info/rfc7748>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
11.2. Informative References 11.2. Informative References
[I-D.ietf-tcpinc-api]
Bittau, A., Boneh, D., Giffin, D., Handley, M., Mazieres,
D., and E. Smith, "Interface Extensions for TCP-ENO and
tcpcrypt", draft-ietf-tcpinc-api-05 (work in progress),
September 2017.
[nist-ecc]
Bernstein, D. and T. Lange, "Failures in NIST's ECC
standards", 2016, <https://cr.yp.to/newelliptic/nistecc-
20160106.pdf>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989, <https://www.rfc- DOI 10.17487/RFC1122, October 1989, <https://www.rfc-
editor.org/info/rfc1122>. editor.org/info/rfc1122>.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<https://www.rfc-editor.org/info/rfc7696>.
[tcpcrypt] [tcpcrypt]
Bittau, A., Hamburg, M., Handley, M., Mazieres, D., and D. Bittau, A., Hamburg, M., Handley, M., Mazieres, D., and D.
Boneh, "The case for ubiquitous transport-level Boneh, "The case for ubiquitous transport-level
encryption", USENIX Security , 2010. encryption", USENIX Security , 2010.
Authors' Addresses Authors' Addresses
Andrea Bittau Andrea Bittau
Google Google
345 Spear Street 345 Spear Street
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