draft-ietf-tcpinc-tcpcrypt-15.txt   rfc8548.txt 
Network Working Group A. Bittau Internet Engineering Task Force (IETF) A. Bittau
Internet-Draft Google Request for Comments: 8548 Google
Intended status: Experimental D. Giffin Category: Experimental D. Giffin
Expires: June 14, 2019 Stanford University ISSN: 2070-1721 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
December 11, 2018 May 2019
Cryptographic protection of TCP Streams (tcpcrypt) Cryptographic Protection of TCP Streams (tcpcrypt)
draft-ietf-tcpinc-tcpcrypt-15
Abstract Abstract
This document specifies tcpcrypt, a TCP encryption protocol designed This document specifies "tcpcrypt", a TCP encryption protocol
for use in conjunction with the TCP Encryption Negotiation Option designed for use in conjunction with the TCP Encryption Negotiation
(TCP-ENO). Tcpcrypt coexists with middleboxes by tolerating Option (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.
Because the size of TCP options is limited, the protocol requires one Because the size of TCP options is limited, the protocol requires one
additional one-way message latency to perform key exchange before additional one-way message latency to perform key exchange before
application data can be transmitted. However, the extra latency can application data can be transmitted. However, the extra latency can
be avoided between two hosts that have recently established a be avoided between two hosts that have recently established a
previous tcpcrypt connection. previous tcpcrypt connection.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This document is not an Internet Standards Track specification; it is
provisions of BCP 78 and BCP 79. published for examination, experimental implementation, and
evaluation.
Internet-Drafts are working documents of the Internet Engineering This document defines an Experimental Protocol for the Internet
Task Force (IETF). Note that other groups may also distribute community. This document is a product of the Internet Engineering
working documents as Internet-Drafts. The list of current Internet- Task Force (IETF). It represents the consensus of the IETF
Drafts is at https://datatracker.ietf.org/drafts/current/. community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are candidates for any level of
Internet Standard; see Section 2 of RFC 7841.
Internet-Drafts are draft documents valid for a maximum of six months Information about the current status of this document, any errata,
and may be updated, replaced, or obsoleted by other documents at any and how to provide feedback on it may be obtained at
time. It is inappropriate to use Internet-Drafts as reference https://www.rfc-editor.org/info/rfc8548.
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 14, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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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. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4
3. Encryption Protocol . . . . . . . . . . . . . . . . . . . . . 3 3. Encryption Protocol . . . . . . . . . . . . . . . . . . . . . 4
3.1. Cryptographic Algorithms . . . . . . . . . . . . . . . . 3 3.1. Cryptographic Algorithms . . . . . . . . . . . . . . . . 4
3.2. Protocol Negotiation . . . . . . . . . . . . . . . . . . 5 3.2. Protocol Negotiation . . . . . . . . . . . . . . . . . . 6
3.3. Key Exchange . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Key Exchange . . . . . . . . . . . . . . . . . . . . . . 7
3.4. Session ID . . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Session ID . . . . . . . . . . . . . . . . . . . . . . . 10
3.5. Session Resumption . . . . . . . . . . . . . . . . . . . 9 3.5. Session Resumption . . . . . . . . . . . . . . . . . . . 10
3.6. Data Encryption and Authentication . . . . . . . . . . . 13 3.6. Data Encryption and Authentication . . . . . . . . . . . 14
3.7. TCP Header Protection . . . . . . . . . . . . . . . . . . 14 3.7. TCP Header Protection . . . . . . . . . . . . . . . . . . 16
3.8. Re-Keying . . . . . . . . . . . . . . . . . . . . . . . . 15 3.8. Rekeying . . . . . . . . . . . . . . . . . . . . . . . . 16
3.9. Keep-Alive . . . . . . . . . . . . . . . . . . . . . . . 16 3.9. Keep-Alive . . . . . . . . . . . . . . . . . . . . . . . 17
4. Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4. Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1. Key-Exchange Messages . . . . . . . . . . . . . . . . . . 16 4.1. Key-Exchange Messages . . . . . . . . . . . . . . . . . . 18
4.2. Encryption Frames . . . . . . . . . . . . . . . . . . . . 18 4.2. Encryption Frames . . . . . . . . . . . . . . . . . . . . 20
4.2.1. Plaintext . . . . . . . . . . . . . . . . . . . . . . 19 4.2.1. Plaintext . . . . . . . . . . . . . . . . . . . . . . 20
4.2.2. Associated Data . . . . . . . . . . . . . . . . . . . 20 4.2.2. Associated Data . . . . . . . . . . . . . . . . . . . 21
4.2.3. Frame ID . . . . . . . . . . . . . . . . . . . . . . 20 4.2.3. Frame ID . . . . . . . . . . . . . . . . . . . . . . 21
4.3. Constant Values . . . . . . . . . . . . . . . . . . . . . 20 4.3. Constant Values . . . . . . . . . . . . . . . . . . . . . 22
5. Key-Agreement Schemes . . . . . . . . . . . . . . . . . . . . 21 5. Key-Agreement Schemes . . . . . . . . . . . . . . . . . . . . 22
6. AEAD Algorithms . . . . . . . . . . . . . . . . . . . . . . . 22 6. AEAD Algorithms . . . . . . . . . . . . . . . . . . . . . . . 24
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
8. Security Considerations . . . . . . . . . . . . . . . . . . . 24 8. Security Considerations . . . . . . . . . . . . . . . . . . . 25
8.1. Asymmetric Roles . . . . . . . . . . . . . . . . . . . . 25 8.1. Asymmetric Roles . . . . . . . . . . . . . . . . . . . . 27
8.2. Verified Liveness . . . . . . . . . . . . . . . . . . . . 26 8.2. Verified Liveness . . . . . . . . . . . . . . . . . . . . 27
8.3. Mandatory Key-Agreement Schemes . . . . . . . . . . . . . 26 8.3. Mandatory Key-Agreement Schemes . . . . . . . . . . . . . 27
9. Experiments . . . . . . . . . . . . . . . . . . . . . . . . . 27 9. Experiments . . . . . . . . . . . . . . . . . . . . . . . . . 28
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28 10.1. Normative References . . . . . . . . . . . . . . . . . . 29
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 10.2. Informative References . . . . . . . . . . . . . . . . . 30
12.1. Normative References . . . . . . . . . . . . . . . . . . 28 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 31
12.2. Informative References . . . . . . . . . . . . . . . . . 29 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31
1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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 1. 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) [RFC8547] for protecting connection data.
o Be amenable to small, self-contained implementations inside TCP o Be amenable to small, self-contained implementations inside TCP
stacks. stacks.
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.
A companion document [I-D.ietf-tcpinc-api] describes recommended A companion document [TCPINC-API] describes recommended interfaces
interfaces for configuring certain parameters of this protocol. for configuring certain parameters of this protocol.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"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.
3. Encryption Protocol 3. Encryption Protocol
This section describes the operation of the tcpcrypt protocol. The This section describes the operation of the tcpcrypt protocol. The
wire format of all messages is specified in Section 4. wire 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)
(PRK) from some initial keying material produced by the key from some initial keying material produced by the key agreement
agreement scheme. The notation Extract(S, IKM) denotes the output scheme. The notation Extract(S, IKM) denotes the output of the
of the extract function with salt S and initial keying material extract function with salt S and initial keying material IKM.
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 produces typically the output of the extract function. The CPRF produces
an arbitrary amount of Output Keying Material (OKM), and we use an arbitrary amount of Output Keying Material (OKM), and we use
the notation CPRF(K, CONST, L) to designate the first L bytes of the notation CPRF(K, CONST, L) to designate the first L bytes of
the OKM produced by the CPRF when parameterized by key K and the the OKM produced by the CPRF when parameterized by key K and the
constant CONST. constant CONST.
The Extract and CPRF functions used by the tcpcrypt variants defined The Extract and CPRF functions used by the tcpcrypt variants defined
in this document are the Extract and Expand functions of HKDF in this document are the Extract and Expand functions of the HMAC-
[RFC5869], which is built on HMAC [RFC2104]. These are defined as based Key Derivation Function (HKDF) [RFC5869], which is built on
follows in terms of the function "HMAC-Hash(key, value)" for a Keyed-Hashing for Message Authentication (HMAC) [RFC2104]. These are
negotiated "Hash" function such as SHA-256; the symbol "|" denotes defined as follows in terms of the function HMAC-Hash(key, value) for
a negotiated Hash function such as SHA-256; the symbol "|" denotes
concatenation, and the counter concatenated to the right of CONST concatenation, and the counter concatenated to the right of CONST
occupies a single octet. 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) 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 [RFC8547] to negotiate whether encryption
whether encryption will be enabled for a connection, and also which will be enabled for a connection as well as which key-agreement
key-agreement scheme to use. TCP-ENO negotiates the use of a scheme to use. TCP-ENO negotiates the use of a particular TCP
particular TCP encryption protocol or _TEP_ by including protocol encryption protocol (TEP) by including protocol identifiers in ENO
identifiers in ENO suboptions. This document associates four TEP suboptions. This document associates four TEP identifiers with the
identifiers with the tcpcrypt protocol, as listed in Table 4 in tcpcrypt protocol as listed in Table 4 of Section 7. Each identifier
Section 7. Each identifier indicates the use of a particular key- indicates the use of a particular key-agreement scheme, with an
agreement scheme, with an associated CPRF and length parameter. associated CPRF and length parameter. Future standards can associate
Future standards can associate additional TEP identifiers with additional TEP identifiers with tcpcrypt following the assignment
tcpcrypt, following the assignment policy specified by TCP-ENO. 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
supports, it MAY then attach an ENO option to its SYN-ACK segment, that it supports, it MAY then attach an ENO option to its SYN-ACK
including solely the TEP it wishes to enable. segment, 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 a open, an additional mechanism breaks the symmetry and assigns a
distinct role to each host. TCP-ENO uses the terms "host A" and distinct role to each host. TCP-ENO uses the terms "host A" and
"host B" to identify each end of a connection uniquely, and this "host B" to identify each end of a connection uniquely; this document
document employs those terms in the same way. employs those terms in the same way.
An ENO suboption includes 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", an identifier derived from a the TEP identifier, the flag v = 1, an identifier derived from a
session secret previously negotiated with the same host and the same session secret previously negotiated with the same host and the same
TEP, and a nonce. TEP, and a nonce.
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
segment of host B (that is, the passive opener in the absence of of host B (that is, the passive opener in the absence of simultaneous
simultaneous open) that also occurs in that of host A. If there is open) that also occurs in that of host A. If there is no such TEP,
no such TEP, hosts MUST disable TCP-ENO and tcpcrypt. 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 in Section 3.3.
Section 3.3. If, on the other hand, host B sent the TEP with "v = 1" If, on the other hand, host B sent the TEP with v = 1 and both hosts
and both hosts sent appropriate resumption identifiers in their sent appropriate resumption identifiers in their suboption data, then
suboption data, then the key-exchange messages will be omitted in the key-exchange messages will be omitted in favor of determining
favor of determining keys via session resumption as described in keys via session resumption as described in Section 3.5. With
Section 3.5. With session resumption, protected application data MAY session resumption, protected application data MAY be sent
be sent immediately as detailed in Section 3.6. immediately as detailed in Section 3.6.
Note that the negotiated TEP is determined without reference to the Note that the negotiated TEP is determined without reference to the
"v" bits in ENO suboptions, so if host A offers resumption with a "v" bits in ENO suboptions, so if host A offers resumption with a
particular TEP and host B replies with a non-resumption suboption particular TEP and host B replies with a non-resumption suboption
with the same TEP, that could become the negotiated TEP and fresh key with the same TEP, that could become the negotiated TEP, in which
agreement will be performed. That is, sending a resumption suboption case fresh key agreement will be performed. That is, sending a
also implies willingness to perform fresh key agreement with the resumption suboption also implies willingness to perform fresh key
indicated TEP. agreement with the 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 4, connection. If the negotiated TEP is among those listed in Table 4,
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 in Section 3.5), the two
two hosts perform key exchange through two messages, "Init1" and hosts perform key exchange through two messages, Init1 and Init2, at
"Init2", at the start of the data streams of host A and host B, the start of the data streams of host A and host B, respectively.
respectively. These messages MAY span multiple TCP segments and need These messages MAY span multiple TCP segments and need not end at a
not end at a segment boundary. However, the segment containing the segment boundary. However, the segment containing the last byte of
last byte of an "Init1" or "Init2" message MUST have TCP's push flag an Init1 or Init2 message MUST have TCP's push flag (PSH) set.
(PSH) set.
The key exchange protocol, in abstract, proceeds as follows: The key exchange protocol, in abstract, proceeds as follows:
A -> B: Init1 = { INIT1_MAGIC, sym_cipher_list, N_A, Pub_A } A -> B: Init1 = { INIT1_MAGIC, sym_cipher_list, N_A, Pub_A }
B -> A: Init2 = { INIT2_MAGIC, sym_cipher, N_B, Pub_B } B -> A: Init2 = { INIT2_MAGIC, sym_cipher, N_B, Pub_B }
The concrete format of these messages is specified in Section 4.1. The concrete format of these messages is specified in Section 4.1.
The parameters are defined as follows: The parameters are defined as follows:
o "INIT1_MAGIC", "INIT2_MAGIC": constants defined in Section 4.3. o INIT1_MAGIC, INIT2_MAGIC: Constants defined in Section 4.3.
o "sym_cipher_list": a list of identifiers of symmetric ciphers o sym_cipher_list: A list of identifiers of symmetric ciphers (AEAD
(AEAD algorithms) acceptable to host A. These are specified in algorithms) acceptable to host A. These are specified in Table 5
Table 5 in Section 7. of Section 7.
o "sym_cipher": the symmetric cipher selected by host B from the o sym_cipher: The symmetric cipher selected by host B from the
"sym_cipher_list" sent by host A. sym_cipher_list sent by host A.
o "N_A", "N_B": nonces chosen at random by hosts A and B, o N_A, N_B: Nonces chosen at random by hosts A and B, respectively.
respectively.
o "Pub_A", "Pub_B": ephemeral public keys for hosts A and B, o Pub_A, Pub_B: Ephemeral public keys for hosts A and B,
respectively. These, as well as their corresponding private keys, respectively. These, as well as their corresponding private keys,
are short-lived values that MUST be refreshed frequently. The are short-lived values that MUST be refreshed frequently. The
private keys SHOULD NOT ever be written to persistent storage. private keys SHOULD NOT ever be written to persistent storage.
The security risks associated with the storage of these keys are The security risks associated with the storage of these keys are
discussed in Section 8. discussed in Section 8.
If a host receives an ephemeral public key from its peer and a key- If a host receives an ephemeral public key from its peer and a key-
validation step fails (see Section 5), it MUST abort the connection validation step fails (see Section 5), it MUST abort the connection
and raise an error condition distinct from the end-of-file condition. and raise an error condition distinct from the end-of-file condition.
The ephemeral secret "ES" is the result of the key-agreement The ephemeral secret ES is the result of the key-agreement algorithm
algorithm (see Section 5) indicated by the negotiated TEP. The (see Section 5) indicated by the negotiated TEP. The inputs to the
inputs to the algorithm are the local host's ephemeral private key algorithm are the local host's ephemeral private key and the remote
and the remote host's ephemeral public key. For example, host A host's ephemeral public key. For example, host A would compute ES
would compute "ES" using its own private key (not transmitted) and using its own private key (not transmitted) and host B's public key,
host B's public key, "Pub_B". Pub_B.
The two sides then compute a pseudo-random key "PRK", from which all The two sides then compute a pseudo-random key, PRK, from which all
session secrets are derived, as follows: session secrets are derived, as follows:
PRK = Extract(N_A, eno-transcript | Init1 | Init2 | ES) PRK = Extract(N_A, eno_transcript | Init1 | Init2 | ES)
Above, "|" denotes concatenation; "eno-transcript" is the protocol- Above, "|" denotes concatenation, eno_transcript is the protocol-
negotiation transcript defined in Section 4.8 of negotiation transcript defined in Section 4.8 of [RFC8547], and Init1
[I-D.ietf-tcpinc-tcpeno]; and "Init1" and "Init2" are the transmitted and Init2 are the transmitted encodings of the messages described in
encodings of the messages described in Section 4.1. Section 4.1.
A series of "session secrets" are computed from "PRK" as follows: A series of session secrets are computed from PRK as follows:
ss[0] = PRK ss[0] = PRK
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
current connection. The values "ss[i]" for "i > 0" are used by connection. The values ss[i] for i > 0 are used by session
session resumption to avoid public key cryptography when establishing resumption to avoid public key cryptography when establishing
subsequent connections between the same two hosts, as described later subsequent connections between the same two hosts as described in
in Section 3.5. The "CONST_*" values are constants defined in Section 3.5. The CONST_* values are constants defined in
Section 4.3. The length "K_LEN" depends on the tcpcrypt TEP in use, Section 4.3. The length K_LEN depends on the tcpcrypt TEP in use,
and is specified in Section 5. and is specified in Section 5.
Given a session secret "ss[i]", the two sides compute a series of Given a session secret ss[i], the two sides compute a series of
master keys as follows: master keys as follows:
mk[0] = CPRF(ss[i], CONST_REKEY | sn[i], K_LEN) mk[0] = CPRF(ss[i], CONST_REKEY | sn[i], K_LEN)
mk[j] = CPRF(mk[j-1], CONST_REKEY, K_LEN) mk[j] = CPRF(mk[j-1], CONST_REKEY, K_LEN)
The process of advancing through the series of master keys is The process of advancing through the series of master keys is
described in Section 3.8. The values "sn[i]" are "session nonces." described in Section 3.8. The values represented by sn[i] are
For the initial session with "i = 0", the session nonce is zero bytes session nonces. For the initial session with i = 0, the session
long. The values for subsequent sessions are derived from fresh nonce is zero bytes long. The values for subsequent sessions are
connection data as described in Section 3.5. derived from fresh connection data as described in Section 3.5.
Finally, each master key "mk[j]" is used to generate traffic keys for Finally, each master key mk[j] is used to generate traffic keys for
protecting application data using authenticated encryption: protecting application data using authenticated encryption:
k_ab[j] = CPRF(mk[j], CONST_KEY_A, ae_key_len + ae_nonce_len) k_ab[j] = CPRF(mk[j], CONST_KEY_A, ae_key_len + ae_nonce_len)
k_ba[j] = CPRF(mk[j], CONST_KEY_B, ae_key_len + ae_nonce_len) k_ba[j] = CPRF(mk[j], CONST_KEY_B, ae_key_len + ae_nonce_len)
In the first session derived from fresh key-agreement, traffic keys In the first session derived from fresh key agreement, traffic keys
"k_ab[j]" are used by host A to encrypt and host B to decrypt, while 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. keys k_ba[j] are used by host B to encrypt and host A to decrypt. In
In a resumed session, as described more thoroughly below in a resumed session, as described more thoroughly in Section 3.5, each
Section 3.5, each host uses the keys in the same way as it did in the host uses the keys in the same way as it did in the original session,
original session, regardless of its role in the current session: for regardless of its role in the current session; for example, if a host
example, if a host played role "A" in the first session, it will use played role "A" in the first session, it will use keys k_ab[j] to
keys "k_ab[j]" to encrypt in each derived session. encrypt in each derived session.
The values "ae_key_len" and "ae_nonce_len" depend on the The values ae_key_len and ae_nonce_len depend on the authenticated-
authenticated-encryption algorithm selected, and are given in Table 3 encryption algorithm selected and are given in Table 3 of Section 6.
in Section 6. The algorithm uses the first "ae_key_len" bytes of The algorithm uses the first ae_key_len bytes of each traffic key as
each traffic key as an authenticated-encryption key, and the an authenticated-encryption key, and it uses the following
following "ae_nonce_len" bytes as a "nonce randomizer". ae_nonce_len bytes as a nonce randomizer.
Implementations SHOULD provide an interface allowing the user to Implementations SHOULD provide an interface allowing the user to
specify, for a particular connection, the set of AEAD algorithms to specify, for a particular connection, the set of AEAD algorithms to
advertize in "sym_cipher_list" (when playing role "A") and also the advertise in sym_cipher_list (when playing role "A") and also the
order of preference to use when selecting an algorithm from those order of preference to use when selecting an algorithm from those
offered (when playing role "B"). A companion document offered (when playing role "B"). A companion document [TCPINC-API]
[I-D.ietf-tcpinc-api] describes recommended interfaces for this describes recommended interfaces for this purpose.
purpose.
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
present in the "sym_cipher_list" it previously transmitted in in the sym_cipher_list it previously transmitted in Init1, it MUST
"Init1", it MUST abort the connection and raise an error condition abort the connection and raise an error condition distinct from the
distinct from the end-of-file condition. end-of-file condition.
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 Section 3.8 of [RFC793]. That
the TCP connection is destroyed, RESET is transmitted, and the local is, the TCP connection is destroyed, RESET is transmitted, and the
user is alerted to the abort event. local 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
uniquely identifies each encrypted connection. identifies each encrypted connection.
A tcpcrypt session ID begins with the byte transmitted by host B that A tcpcrypt session ID begins with the byte transmitted by host B that
contains the negotiated TEP identifier along with the "v" bit. The contains the negotiated TEP identifier along with the "v" bit. The
remainder of the ID is derived from the session secret and session remainder of the ID is derived from the session secret and session
nonce, as follows: nonce, as follows:
session_id[i] = TEP-byte | CPRF(ss[i], CONST_SESSID | sn[i], K_LEN) session_id[i] = TEP-byte | CPRF(ss[i], CONST_SESSID | sn[i], 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
If two hosts have previously negotiated a session with secret If two hosts have previously negotiated a session with secret
"ss[i-1]", they can establish a new connection without public-key ss[i-1], they can establish a new connection without public-key
operations using "ss[i]", the next session secret in the sequence operations using ss[i], the next session secret in the sequence
derived from the original PRK. derived from the original PRK.
A host signals willingness to resume with a particular session secret A host signals its willingness to resume with a particular session
by sending a SYN segment with a resumption suboption: that is, an ENO secret by sending a SYN segment with a resumption suboption, i.e., an
suboption containing the negotiated TEP identifier of the previous ENO suboption containing the negotiated TEP identifier of the
session, half of the "resumption identifier" for the new session, and previous session, half of the resumption identifier for the new
a "resumption nonce". session, and a resumption nonce.
The resumption nonce MUST have a minimum length of zero bytes and The resumption nonce MUST have a minimum length of zero bytes and
maximum length of eight bytes. The value MUST be chosen randomly or maximum length of eight bytes. The value MUST be chosen randomly or
using a mechanism that guarantees uniqueness even in the face of using a mechanism that guarantees uniqueness even in the face of
virtual machine cloning or other re-execution of the same session. virtual-machine cloning or other re-execution of the same session.
An attacker who can force either side of a connection to reuse a An attacker who can force either side of a connection to reuse a
session secret with the same nonce will completely break the security session secret with the same nonce will completely break the security
of tcpcrypt. Reuse of session secrets is possible in the event of of tcpcrypt. Reuse of session secrets is possible in the event of
virtual machine cloning or reuse of system-level hibernation state. virtual-machine cloning or reuse of system-level hibernation state.
Implementations SHOULD provide an API through which to set the Implementations SHOULD provide an API through which to set the
resumption nonce length, and MUST default to eight bytes if they resumption nonce length and MUST default to eight bytes if they
cannot prohibit the reuse of session secrets. cannot prohibit the reuse of session secrets.
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].
A host that originally played role "A" and wishes to resume from a A host that originally played role "A" and wishes to resume from a
cached session sends a suboption with the first half of the cached session sends a suboption with the first half of the
resumption identifier: resumption identifier:
byte 0 1 9 10 byte 0 1 9 10
+------+------+--...--+------+------+--...--+------+ +------+------+--...--+------+------+--...--+------+
| TEP- | resume[i]{0..8} | nonce_a | | TEP- | resume[i]{0..8} | nonce_a |
| byte | | | | byte | | |
+------+------+--...--+------+------+--...--+------+ +------+------+--...--+------+------+--...--+------+
Figure 2: Resumption suboption sent when original role was "A". The Figure 2: Resumption suboption sent when original role was "A".
TEP-byte contains a tcpcrypt TEP identifier and v = 1. The nonce
value MUST have length between 0 and 8 bytes. The TEP-byte contains a tcpcrypt TEP identifier and v = 1. The nonce
value MUST have length between 0 and 8 bytes.
Similarly, a host that originally played role "B" sends a suboption Similarly, a host that originally played role "B" sends a suboption
with the second half of the resumption identifier: with the second half of the resumption identifier:
byte 0 1 9 10 byte 0 1 9 10
+------+------+--...--+------+------+--...--+------+ +------+------+--...--+------+------+--...--+------+
| TEP- | resume[i]{9..17} | nonce_b | | TEP- | resume[i]{9..17} | nonce_b |
| byte | | | | byte | | |
+------+------+--...--+------+------+--...--+------+ +------+------+--...--+------+------+--...--+------+
Figure 3: Resumption suboption sent when original role was "B". The Figure 3: Resumption suboption sent when original role was "B".
TEP-byte contains a tcpcrypt TEP identifier and v = 1. The nonce
value MUST have length between 0 and 8 bytes. The TEP-byte contains a tcpcrypt TEP identifier and v = 1. The nonce
value MUST have length between 0 and 8 bytes.
If a passive opener receives a resumption suboption containing an If a passive opener receives a resumption suboption containing an
identifier-half that names a session secret that it has cached and identifier-half that names a session secret that it has cached, and
the subobtion's TEP matches the TEP used in the previous session, it the subobtion's TEP matches the TEP used in the previous session, it
SHOULD (with exceptions specified below) agree to resume from the SHOULD (with exceptions specified below) agree to resume from the
cached session by sending its own resumption suboption, which will cached session by sending its own resumption suboption, which will
contain the other half of the identifier. Otherwise, it MUST NOT contain the other half of the identifier. Otherwise, it MUST NOT
agree to resumption. agree to resumption.
If a passive opener does not agree to resumption with a particular If a passive opener does not agree to resumption with a particular
TEP, it 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 TEP suboption. other received TEP suboption.
If a passive opener receives an ENO suboption with a TEP identifier If a passive opener receives an ENO suboption with a TEP identifier
and "v = 1", but the suboption data is less than 9 bytes in length, and v = 1, but the suboption data is less than 9 bytes in length, it
it MUST behave as if the same TEP had been sent with "v = 0". That MUST behave as if the same TEP had been sent with v = 0. That is,
is, the suboption MUST be interpreted as an offer to negotiate fresh the suboption MUST be interpreted as an offer to negotiate fresh key
key exchange with that TEP. exchange with that TEP.
If an active opener sends a resumption suboption with a particular If an active opener sends a resumption suboption with a particular
TEP and the appropriate half of a resumption identifier and then, in TEP and the appropriate half of a resumption identifier, and then, in
the same TCP handshake, receives a resumption suboption with the same the same TCP handshake, it receives a resumption suboption with the
TEP and an identifier-half that does not match that resumption same TEP and an identifier-half that does not match that resumption
identifier, it MUST ignore that suboption. In the typical case that identifier, it MUST ignore that suboption. In the typical case that
this was the only ENO suboption received, this means the host MUST 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 ENO disable TCP-ENO and tcpcrypt; it MUST NOT send any more ENO options
options and MUST NOT encrypt the connection. and MUST NOT encrypt the connection.
When a host concludes that TCP-ENO negotiation has succeeded for some When a host concludes that TCP-ENO negotiation has succeeded for some
TEP that was received in a resumption suboption, it MUST then enable TEP that was received in a resumption suboption, it MUST then enable
encryption with that TEP using the cached session secret. To do encryption with that TEP using the cached session secret. To do
this, it first constructs "sn[i]" as follows: this, it first constructs sn[i] as follows:
sn[i] = nonce_a | nonce_b sn[i] = nonce_a | nonce_b
Master keys are then computed from "s[i]" and "sn[i]" as described in Master keys are then computed from s[i] and sn[i] as described in
Section 3.3, and application data encrypted as described in Section 3.3 as well as from application data encrypted as described
Section 3.6. in Section 3.6.
The session ID (Section 3.4) is constructed in the same way for The session ID (Section 3.4) is constructed in the same way for
resumed sessions as it is for fresh ones. In this case the first resumed sessions as it is for fresh ones. In this case, the first
byte will always have "v = 1". The remainder of the ID is derived byte will always have v = 1. The remainder of the ID is derived from
from the cached session secret and the session nonce that was the cached session secret and the session nonce that was generated
generated during resumption. during resumption.
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 (because this consumes TCP option space and is resumption suboption (because this consumes TCP option space and is
unlikely to be a useful practice), and MUST NOT send more than one unlikely to be a useful practice), and it MUST NOT send more than one
resumption suboption with the same TEP identifier. But in addition resumption suboption with the same TEP identifier. But in addition
to any resumption suboptions, an active opener MAY include non- to any resumption suboptions, an active opener MAY include
resumption suboptions describing other TEPs it supports (in addition non-resumption suboptions describing other TEPs it supports (in
to the TEP in the resumption suboption). addition to the TEP in the resumption suboption).
After using the session secret "ss[i]" to compute "mk[0]", After using the session secret ss[i] to compute mk[0],
implementations SHOULD compute and cache "ss[i+1]" for possible use implementations SHOULD compute and cache ss[i+1] for possible use by
by a later session, then erase "ss[i]" from memory. Hosts MAY retain a later session and then erase ss[i] from memory. Hosts MAY retain
"ss[i+1]" until it is used or the memory needs to be reclaimed. ss[i+1] until it is used or the memory needs to be reclaimed. Hosts
Hosts SHOULD NOT write any session secrets to non-volatile storage. SHOULD NOT write any session secrets 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 original negotiate resumption with the same host and for the same original
session secret "ss[0]". session secret ss[0].
A given session secret "ss[i]" MUST NOT be used to secure more than A given session secret ss[i] MUST NOT be used to secure more than one
one TCP connection. To prevent this, a host MUST NOT resume with a TCP connection. To prevent this, a host MUST NOT resume with a
session secret if it has ever enabled encryption in the past with the session secret if it has ever enabled encryption in the past with the
same secret, in either role. In the event that two hosts same secret, in either role. In the event that two hosts
simultaneously send SYN segments to each other that propose simultaneously send SYN segments to each other that propose
resumption with the same session secret but the two segments are not resumption with the same session secret but with both segments not
part of a simultaneous open, both connections would need to revert to part of a simultaneous open, both connections would need to revert to
fresh key-exchange. To avoid this limitation, implementations MAY fresh key exchange. To avoid this limitation, implementations MAY
choose to implement session resumption such that all session secrets choose to implement session resumption such that all session secrets
derived from a given "ss[0]" are used for either passive or active derived from a given ss[0] are used for either passive or active
opens at the same host, not both. opens at the same host, not both.
If two hosts have previously negotiated a tcpcrypt session, either If two hosts have previously negotiated a tcpcrypt session, either
host MAY later initiate session resumption regardless of which host host MAY later initiate session resumption regardless of which host
was the 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 keys "k_ab[j]" for all However, a given host MUST either encrypt with keys k_ab[j] for all
sessions derived from the same original session secret "ss[0]", or sessions derived from the same original session secret ss[0], or with
with keys "k_ba[j]". Thus, which keys a host uses to send segments keys k_ba[j]. Thus, which keys a host uses to send segments is not
is not affected by the role it plays in the current connection: it affected by the role it plays in the current connection: it depends
depends only on whether the host played the "A" or "B" role in the only on whether the host played the "A" or "B" role in the initial
initial session. session.
Implementations that cache session secrets MUST provide a means for Implementations that cache session secrets MUST provide a means for
applications to control that caching. In particular, when an applications to control that caching. In particular, when an
application requests a new TCP connection, it MUST have a way to application requests a new TCP connection, it MUST have a way to
specify two policies for the duration of the connection: 1) that specify two policies for the duration of the connection: 1) that
resumption requests will be ignored, and thus fresh key exchange will resumption requests will be ignored, and thus fresh key exchange will
be necessary; and 2) that no session secrets will be cached. (These be necessary; and 2) that no session secrets will be cached. (These
policies can be specified independently or as a unit.) And for an policies can be specified independently or as a unit.) And for an
established connection, an application MUST have a means to cause any established connection, an application MUST have a means to cause any
cache state that was used in or resulted from establishing the cache state that was used in or resulted from establishing the
connection to be flushed. A companion document [I-D.ietf-tcpinc-api] connection to be flushed. A companion document [TCPINC-API]
describes recommended interfaces for this purpose. 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 upon keys. authenticated using the agreed-upon keys.
This protection is provided via algorithms for Authenticated This protection is provided via algorithms for Authenticated
Encryption with Associated Data (AEAD). The permitted algorithms are Encryption with Associated Data (AEAD). The permitted algorithms are
listed in Table 5 in Section 7. Additional algorithms can be listed in Table 5 of Section 7. Additional algorithms can be
specified in the future according to the policy in that section. One specified in the future according to the policy in that section. One
algorithm is selected during the negotiation described in algorithm is selected during the negotiation described in
Section 3.3. The lengths "ae_key_len" and "ae_nonce_len" associated Section 3.3. The lengths ae_key_len and ae_nonce_len associated with
with each algorithm are found in Table 3 in Section 6, together with each algorithm are found in Table 3 of Section 6 along with
requirements for which algorithms MUST be implemented. requirements for which algorithms MUST be implemented.
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 field of a plaintext value,
value, which is then encrypted to yield a frame's "ciphertext" field. which is then encrypted to yield a frame's ciphertext field. Chunks
Chunks MUST be small enough that the ciphertext (whose length depends MUST be small enough that the ciphertext (whose length depends on the
on the AEAD cipher used, and is generally slightly longer than 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 ID" value (see Section 4.2.3) is also constructed for the A "frame ID" value (see Section 4.2.3) is also constructed for the
frame, but not explicitly transmitted. It contains a 64-bit "offset" frame, but not explicitly transmitted. It contains a 64-bit offset
field whose integer value is the zero-indexed byte offset of the field whose integer value is the zero-indexed byte offset of the
beginning of the current encryption frame in the underlying TCP beginning of the current encryption frame in the underlying TCP
datastream. (That is, the offset in the framing stream, not the datastream. (That is, the offset in the framing stream, not the
plaintext application stream.) The offset is then left-padded with plaintext application stream.) The offset is then left-padded with
zero-valued bytes to form a value of length "ae_nonce_len". Because zero-valued bytes to form a value of length ae_nonce_len. Because it
it is strictly necessary for the security of the AEAD algorithms is strictly necessary for the security of the AEAD algorithms
specified in this document, an implementation MUST NOT ever transmit specified in this document, an implementation MUST NOT ever transmit
distinct frames with the same frame ID value under the same distinct frames with the same frame ID value under the same
encryption key. In particular, a retransmitted TCP segment MUST encryption key. In particular, a retransmitted TCP segment MUST
contain the same payload bytes for the same TCP sequence numbers, and contain the same payload bytes for the same TCP sequence numbers, and
a host MUST NOT transmit more than 2^64 bytes in the underlying TCP a host MUST NOT transmit more than 2^64 bytes in the underlying TCP
datastream (which would cause the "offset" field to wrap) before re- datastream (which would cause the offset field to wrap) before
keying as decribed in Section 3.8. rekeying as described in Section 3.8.
With reference to the "AEAD Interface" described in Section 2 of
[RFC5116], tcpcrypt invokes the AEAD algorithm with values taken from
the traffic key "k_ab[j]" or "k_ba[j]" for some "j", according to the
host's role as described in Section 3.3.
First, the traffic key is divided into two parts: Keys for AEAD encryption are taken from the traffic key k_ab[j] or
k_ba[j] for some "j", according to the host's role as described in
Section 3.3. First, the appropriate traffic key is divided into two
parts:
ae_key_len + ae_nonce_len - 1 ae_key_len + ae_nonce_len - 1
| |
byte 0 ae_key_len | byte 0 ae_key_len |
| | | | | |
v v v v v v
+----+----+--...--+----+----+----+--...--+----+ +----+----+--...--+----+----+----+--...--+----+
| K | NR | | K | NR |
+----+----+--...--+----+----+----+--...--+----+ +----+----+--...--+----+----+----+--...--+----+
\_____________________________________________/ Figure 4: Format of Traffic Key
traffic key
The first "ae_key_len" bytes of the traffic key provide the AEAD key With reference to the "AEAD Interface" described in Section 2 of
"K", while the remaining "ae_nonce_len" bytes provide a "nonce [RFC5116], the first ae_key_len bytes of the traffic key provide the
randomizer" value "NR". The frame ID is then combined via bitwise AEAD key K. The remaining ae_nonce_len bytes provide a nonce
exclusive-or with the nonce randomizer to yield "N", the AEAD nonce randomizer value NR, which is combined via bitwise exclusive-or with
for the frame: the frame ID to yield N, the AEAD nonce for the frame:
N = frame_ID XOR NR N = frame_ID XOR NR
The plaintext value serves as "P", and the associated data as "A". The remaining AEAD inputs, P and A, are provided by the frame's
The output of the encryption operation, "C", is transmitted in the plaintext value and associated data, respectively. The output of the
frame's "ciphertext" field. AEAD 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 ID values (the former contains only data sent in the clear, and frame ID values (the former contains only data sent in the clear,
and the latter is implicit in the TCP stream), computes the nonce "N" and the latter is implicit in the TCP stream), computes the nonce N
as above, and provides these and the ciphertext value to the AEAD as above, and provides these and the ciphertext value to the AEAD
decryption operation. The output of this operation is either a decryption operation. The output of this operation is either a
plaintext value "P" or the special symbol FAIL. In the latter case, plaintext value P or the special symbol FAIL. In the latter case,
the implementation SHOULD abort the connection and raise an error the implementation SHOULD abort the connection and raise an error
condition distinct from the end-of-file condition. But if none of condition distinct from the end-of-file condition. But if none of
the TCP segment(s) containing the frame have been acknowledged and the TCP segment(s) containing the frame have been acknowledged and
retransmission could potentially result in a valid frame, an retransmission could potentially result in a valid frame, an
implementation MAY instead drop these segments (and "renege" if they implementation MAY instead drop these segments (and renege if they
have been SACKed, according to [RFC2018] Section 8). have been selectively acknowledged (SACKed), according to Section 8
of [RFC2018]).
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 field indicates an offset from
from the current frame's beginning offset; the sum of these offsets the current frame's beginning offset; the sum of these offsets gives
gives the index of the last byte of urgent data in the application 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
connection (unless it aborts the connection), and MUST NOT set "FINp" connection (unless it aborts the connection) and MUST NOT set FINp on
on any other frame. 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
segment with the TCP FIN flag set but the received datastream with the TCP FIN flag set but the received datastream including this
including this segment does not contain a frame with "FINp" set, the segment does not contain a frame with FINp set, the host SHOULD abort
host SHOULD abort the connection and raise an error condition the connection and raise an error condition distinct from the end-of-
distinct from the end-of-file condition. But if there are file condition. But if there are unacknowledged segments whose
unacknowledged segments whose retransmission could potentially result retransmission could potentially result in a valid frame, the host
in a valid frame, the host MAY instead drop the segment with the TCP MAY instead drop the segment with the TCP FIN flag set (and renege if
FIN flag set (and "renege" if it has been SACKed, according to it has been SACKed, according to Section 8 of [RFC2018]).
[RFC2018] Section 8).
3.8. Re-Keying 3.8. Rekeying
Re-keying allows hosts to wipe from memory keys that could decrypt Rekeying 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.
As described above in Section 3.3, a master key "mk[j]" is used to As described in Section 3.3, a master key mk[j] is used to generate
generate two encryption keys "k_ab[j]" and "k_ba[j]". We refer to two encryption keys k_ab[j] and k_ba[j]. We refer to these as a key
these as a _key-set_ with _generation number_ "j". Each host set with generation number "j". Each host maintains both a local
maintains a _local generation number_ that determines which key-set generation number that determines which key set it uses to encrypt
it uses to encrypt outgoing frames, and a _remote generation number_ outgoing frames and a remote generation number equal to the highest
equal to the highest generation used in frames received from its generation used in frames received from its peer. Initially, these
peer. Initially, these two generation numbers are set to zero. 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_. rekeying".
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 "rekey = 0" in all other set rekey = 1 for that frame. It MUST set rekey = 0 in all other
cases. cases.
When a host receives a frame with "rekey = 1", it increments its When a host receives a frame with rekey = 1, it increments its record
record of the remote generation number. If the remote generation of the remote generation number. If the remote generation number is
number is now greater than the local generation number, the receiver now greater than the local generation number, the receiver MUST
MUST immediately increment its local generation number to match. 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 MUST NOT initiate more than one concurrent re-key operation if A host MUST NOT initiate more than one concurrent rekey operation if
it has no data to send; that is, it MUST NOT initiate re-keying with it has no data to send; that is, it MUST NOT initiate rekeying with
an empty encryption frame more than once while its record of the 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.
Note that when parts of the datastream are retransmitted, TCP Note that when parts of the datastream are retransmitted, TCP
requires that implementations always send the same data bytes for the requires that implementations always send the same data bytes for the
same TCP sequence numbers. Thus, frame data in retransmitted same TCP sequence numbers. Thus, frame data in retransmitted
segments MUST be encrypted with the same key as when it was first segments MUST be encrypted with the same key as when it was first
transmitted, regardless of the current local generation number. 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
keying mechanism for this purpose, as follows. When necessary, a rekeying 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 rekeying and
and transmitting a new frame immediately (with empty application data transmitting a new frame immediately (with empty application data if
if necessary). 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
generation number and (if it has not already transmitted a segment generation number and (if it has not already transmitted a segment
with FIN set) immediately transmit a new frame (with zero-length with FIN set) immediately transmit a new frame (with zero-length
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 |
skipping to change at page 17, line 37 skipping to change at page 18, line 46
| N_A | Pub_A | | N_A | Pub_A |
| | | | | |
+-------+---...---+-------+-------+---...---+-------+ +-------+---...---+-------+-------+---...---+-------+
M - 1 M - 1
+-------+---...---+-------+ +-------+---...---+-------+
| ignored | | ignored |
| | | |
+-------+---...---+-------+ +-------+---...---+-------+
The constant "INIT1_MAGIC" is defined in Section 4.3. The four-byte The constant INIT1_MAGIC is defined in Section 4.3. 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 two-byte symmetric-cipher integer value that specifies the number of two-byte symmetric-cipher
identifiers that follow. The "sym_cipher[i]" identifiers indicate identifiers that follow. The sym_cipher[i] identifiers indicate
cryptographic algorithms in Table 5 in Section 7. The length cryptographic algorithms in Table 5 in Section 7. The length N_A_LEN
"N_A_LEN" and the length of "Pub_A" are both determined by the and the length of Pub_A are both determined by the negotiated TEP as
negotiated TEP, as described in Section 5. described in Section 5.
Implementations of this protocol MUST construct "Init1" such that the Implementations of this protocol MUST construct Init1 such that the
field "ignored" has zero length; that is, they MUST construct the ignored field has zero length; that is, they MUST construct the
message such that its end, as determined by "message_len", coincides message such that its end, as determined by message_len, coincides
with the end of the field "Pub_A". When receiving "Init1", however, with the end of the field Pub_A. When receiving Init1, however,
implementations MUST permit and ignore any bytes following "Pub_A". implementations MUST permit and ignore any bytes following Pub_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 9 4 5 6 7 8 9
+-------+-------+-------+-------+-------+-------+ +-------+-------+-------+-------+-------+-------+
| message_len | sym_cipher | | message_len | sym_cipher |
skipping to change at page 18, line 31 skipping to change at page 19, line 42
| N_B | Pub_B | | N_B | Pub_B |
| | | | | |
+-------+---...---+-------+-------+---...---+-------+ +-------+---...---+-------+-------+---...---+-------+
M - 1 M - 1
+-------+---...---+-------+ +-------+---...---+-------+
| ignored | | ignored |
| | | |
+-------+---...---+-------+ +-------+---...---+-------+
The constant "INIT2_MAGIC" is defined in Section 4.3. The four-byte The constant INIT2_MAGIC is defined in Section 4.3. 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
selection from the symmetric-cipher identifiers in the previously- from the symmetric-cipher identifiers in the previously-received
received "Init1" message. The length "N_B_LEN" and the length of Init1 message. The length N_B_LEN and the length of Pub_B are both
"Pub_B" are both determined by the negotiated TEP, as described in determined by the negotiated TEP as described in Section 5.
Section 5.
Implementations of this protocol MUST construct "Init2" such that the Implementations of this protocol MUST construct Init2 such that the
field "ignored" has zero length; that is, they MUST construct the field "ignored" has zero length; that is, they MUST construct the
message such that its end, as determined by "message_len", coincides message such that its end, as determined by message_len, coincides
with the end of the "Pub_B" field. When receiving "Init2", however, with the end of the Pub_B field. When receiving Init2, however,
implementations MUST permit and ignore any bytes following "Pub_B". implementations MUST permit and ignore any bytes following Pub_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
length of the "ciphertext" field. length of the ciphertext field.
The byte "control" has this structure: The control field has this structure:
bit 7 1 0 bit 7 1 0
+-------+---...---+-------+-------+ +-------+---...---+-------+-------+
| cres | rekey | | cres | rekey |
+-------+---...---+-------+-------+ +-------+---...---+-------+-------+
The seven-bit field "cres" is reserved; implementations MUST set The seven-bit field cres is reserved; implementations MUST set these
these bits to zero when sending, and MUST ignore them when receiving. bits to zero when sending and MUST ignore them when receiving.
The use of the "rekey" field is described in Section 3.8. The use of the rekey field is described in Section 3.8.
4.2.1. Plaintext 4.2.1. Plaintext
The "ciphertext" field is the result of applying the negotiated The ciphertext field is the result of applying the negotiated
authenticated-encryption algorithm to a "plaintext" value, which has authenticated-encryption algorithm to a plaintext value, which has
one of these two formats: one of these two formats:
byte 0 1 plen-1 byte 0 1 plen-1
+-------+-------+---...---+-------+ +-------+-------+---...---+-------+
| flags | data | | flags | data |
+-------+-------+---...---+-------+ +-------+-------+---...---+-------+
byte 0 1 2 3 plen-1 byte 0 1 2 3 plen-1
+-------+-------+-------+-------+---...---+-------+ +-------+-------+-------+-------+---...---+-------+
| flags | urgent | data | | flags | urgent | data |
+-------+-------+-------+-------+---...---+-------+ +-------+-------+-------+-------+---...---+-------+
(Note that "clen" in the previous section will generally be greater (Note that clen in the previous section will generally be greater
than "plen", as the ciphertext produced by the authenticated- than plen, as the ciphertext produced by the authenticated-encryption
encryption scheme both encrypts the application data and provides scheme both encrypts the application data and provides redundancy
redundancy with which to verify its integrity.) with which to verify its integrity.)
The "flags" byte has this structure: The flags field has this structure:
bit 7 6 5 4 3 2 1 0 bit 7 6 5 4 3 2 1 0
+----+----+----+----+----+----+----+----+ +----+----+----+----+----+----+----+----+
| fres |URGp|FINp| | fres |URGp|FINp|
+----+----+----+----+----+----+----+----+ +----+----+----+----+----+----+----+----+
The six-bit value "fres" is reserved; implementations MUST set these The six-bit field 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 the urgent field 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
AEAD algorithm when decrypting the ciphertext and verifying the algorithm when decrypting the ciphertext and verifying the frame's
frame's integrity) has this format: 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 ID 4.2.3. Frame ID
Lastly, a "frame ID" (used to construct the nonce for the AEAD Lastly, a frame ID (used to construct the nonce for the AEAD
algorithm) has this format: algorithm) has this format:
byte 0 ae_nonce_len - 8 ae_nonce_len - 1 byte 0 ae_nonce_len - 8 ae_nonce_len - 1
| | | | | |
v v v v v v
+-----+--...--+-----+-----+--...--+-----+ +-----+--...--+-----+-----+--...--+-----+
| 0 | | 0 | offset | | 0 | | 0 | offset |
+-----+--...--+-----+-----+--...--+-----+ +-----+--...--+-----+-----+--...--+-----+
The 8-byte "offset" field contains an integer in big-endian format. The 8-byte offset field contains an integer in big-endian format.
Its value is specified in Section 3.6. Zero-valued bytes are Its value is specified in Section 3.6. Zero-valued bytes are
prepended to the "offset" field to form a structure of length prepended to the offset field to form a structure of length
"ae_nonce_len". ae_nonce_len.
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 |
+------------+--------------+ +------------+--------------+
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 indicates the use of one of the key- The TEP negotiated via TCP-ENO indicates the use of one of the key-
agreement schemes named in Table 4 in Section 7. For example, agreement schemes named in Table 4 in Section 7. For example,
"TCPCRYPT_ECDHE_P256" names the tcpcrypt protocol using ECDHE-P256 TCPCRYPT_ECDHE_P256 names the tcpcrypt protocol using ECDHE-P256
together with the CPRF and length parameters specified below. together with the CPRF and length parameters specified below.
All the TEPs specified in this document require the use of HKDF- All the TEPs specified in this document require the use of HKDF-
Expand-SHA256 as the CPRF, and these lengths for nonces and session Expand-SHA256 as the CPRF, and these lengths for nonces and session
secrets: secrets:
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
Future documents assigning additional TEPs for use with tcpcrypt Future documents assigning additional TEPs for use with tcpcrypt
mmight specify different values for the lengths above. Note that the might specify different values for the lengths above. Note that the
minimum session ID length specified by TCP-ENO, together with the way minimum session ID length specified by TCP-ENO, together with the way
tcpcrypt constructs session IDs, implies that "K_LEN" MUST have tcpcrypt constructs session IDs, implies that K_LEN MUST have length
length at least 32 bytes. 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 Elliptic
secret value derivation primitive defined in [IEEE-1363]. The named Curve Secret Value Derivation Primitive, Diffie-Hellman version
curves are defined in [NIST-DSS]. When the public-key values "Pub_A" (ECSVDP-DH) defined in [IEEE-1363]. The named curves are defined in
and "Pub_B" are transmitted as described in Section 4.1, they are [NIST-DSS]. When the public-key values Pub_A and Pub_B are
encoded with the "Elliptic Curve Point to Octet String Conversion transmitted as described in Section 4.1, they are encoded with the
Primitive" described in Section E.2.3 of [IEEE-1363], and are "Elliptic Curve Point to Octet String Conversion Primitive" described
prefixed by a two-byte length in big-endian format: in Section E.2.3 of [IEEE-1363] and are prefixed by a two-byte length
in big-endian format:
byte 0 1 2 L - 1 byte 0 1 2 L - 1
+-------+-------+-------+---...---+-------+ +-------+-------+-------+---...---+-------+
| pubkey_len | pubkey | | pubkey_len | pubkey |
| = L | | | = L | |
+-------+-------+-------+---...---+-------+ +-------+-------+-------+---...---+-------+
Implementations MUST encode these "pubkey" values in "compressed Implementations MUST encode these pubkey values in "compressed
format". Implementations MUST validate these "pubkey" values format". Implementations MUST validate these pubkey values according
according to the algorithm in [IEEE-1363] Section A.16.10. to the algorithm in Section A.16.10 of [IEEE-1363].
Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 perform the Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 perform the
Diffie-Helman protocol using the functions X25519 and X448, Diffie-Hellman protocol using the functions X25519 and X448,
respectively. Implementations SHOULD compute these functions using respectively. Implementations SHOULD compute these functions using
the algorithms described in [RFC7748]. When they do so, the algorithms described in [RFC7748]. When they do so,
implementations MUST check whether the computed Diffie-Hellman shared implementations MUST check whether the computed Diffie-Hellman shared
secret is the all-zero value and abort if so, as described in secret is the all-zero value and abort if so, as described in
Section 6 of [RFC7748]. Alternative implementations of these Section 6 of [RFC7748]. Alternative implementations of these
functions SHOULD abort when either input forces the shared secret to functions SHOULD abort when either input forces the shared secret to
one of a small set of values, as discussed in Section 7 of [RFC7748]. one of a small set of values as discussed in Section 7 of [RFC7748].
For these schemes, public-key values "Pub_A" and "Pub_B" are For these schemes, public-key values Pub_A and Pub_B are transmitted
transmitted directly with no length prefix: 32 bytes for ECDHE- directly with no length prefix: 32 bytes for ECDHE-Curve25519 and 56
Curve25519, and 56 bytes for ECDHE-Curve448. bytes for ECDHE-Curve448.
Table 2 below specifies the requirement levels of the four TEPs Table 2 below specifies the requirement levels of the four TEPs
specified in this document. In particular, all implementations of specified in this document. In particular, all implementations of
tcpcrypt MUST support TCPCRYPT_ECDHE_Curve25519. However, system tcpcrypt MUST support TCPCRYPT_ECDHE_Curve25519. However, system
administrators MAY configure which TEPs a host will negotiate administrators MAY configure which TEPs a host will negotiate
independent of these implementation requirements. independent of these implementation requirements.
+-------------+---------------------------+ +-------------+---------------------------+
| Requirement | TEP | | Requirement | TEP |
+-------------+---------------------------+ +-------------+---------------------------+
| REQUIRED | TCPCRYPT_ECDHE_Curve25519 | | REQUIRED | TCPCRYPT_ECDHE_Curve25519 |
| RECOMMENDED | TCPCRYPT_ECDHE_Curve448 | | RECOMMENDED | TCPCRYPT_ECDHE_Curve448 |
| OPTIONAL | TCPCRYPT_ECDHE_P256 | | OPTIONAL | TCPCRYPT_ECDHE_P256 |
| OPTIONAL | TCPCRYPT_ECDHE_P521 | | OPTIONAL | TCPCRYPT_ECDHE_P521 |
+-------------+---------------------------+ +-------------+---------------------------+
Table 2: Requirements for implementation of TEPs Table 2: Requirements for Implementation of TEPs
6. AEAD Algorithms 6. AEAD Algorithms
This document uses "sym-cipher" identifiers in the messages "Init1" This document uses sym_cipher identifiers in the messages Init1 and
and "Init2" (see Section 3.3) to negotiate the use of AEAD Init2 (see Section 3.3) to negotiate the use of AEAD algorithms; the
algorithms; the values of these identifiers are given in Table 5 in values of these identifiers are given in Table 5 in Section 7. The
Section 7. The algorithms "AEAD_AES_128_GCM" and "AEAD_AES_256_GCM" algorithms AEAD_AES_128_GCM and AEAD_AES_256_GCM are specified in
are specified in [RFC5116]. The algorithm "AEAD_CHACHA20_POLY1305" [RFC5116]. The algorithm AEAD_CHACHA20_POLY1305 is specified in
is specified in [RFC7539]. [RFC8439].
Implementations MUST support certain AEAD algorithms according to Implementations MUST support certain AEAD algorithms according to
Table 3 below. Note that system administrators MAY configure which Table 3. Note that system administrators MAY configure which
algorithms a host will negotiate independent of these requirements. algorithms a host will negotiate independently of these requirements.
Lastly, this document uses the lengths "ae_key_len" and Lastly, this document uses the lengths ae_key_len and ae_nonce_len to
"ae_nonce_len" to specify aspects of encryption and data formats. specify aspects of encryption and data formats. These values depend
These values depend on the negotiated AEAD algorithm, also according on the negotiated AEAD algorithm, also according to the table below.
to the table below.
+------------------------+-------------+------------+--------------+ +------------------------+-------------+------------+--------------+
| AEAD Algorithm | Requirement | ae_key_len | ae_nonce_len | | AEAD Algorithm | Requirement | ae_key_len | ae_nonce_len |
+------------------------+-------------+------------+--------------+ +------------------------+-------------+------------+--------------+
| AEAD_AES_128_GCM | REQUIRED | 16 bytes | 12 bytes | | AEAD_AES_128_GCM | REQUIRED | 16 bytes | 12 bytes |
| AEAD_AES_256_GCM | RECOMMENDED | 32 bytes | 12 bytes | | AEAD_AES_256_GCM | RECOMMENDED | 32 bytes | 12 bytes |
| AEAD_CHACHA20_POLY1305 | RECOMMENDED | 32 bytes | 12 bytes | | AEAD_CHACHA20_POLY1305 | RECOMMENDED | 32 bytes | 12 bytes |
+------------------------+-------------+------------+--------------+ +------------------------+-------------+------------+--------------+
Table 3: Requirement and lengths for each AEAD algorithm Table 3: Requirement and Lengths for Each AEAD Algorithm
7. IANA Considerations 7. IANA Considerations
For use with TCP-ENO's negotiation mechanism, tcpcrypt's TEP For use with TCP-ENO's negotiation mechanism, tcpcrypt's TEP
identifiers will need to be incorporated in IANA's "TCP encryption identifiers have been incorporated in IANA's "TCP Encryption Protocol
protocol identifiers" registry under the "Transmission Control Identifiers" registry under the "Transmission Control Protocol (TCP)
Protocol (TCP) Parameters" registry, as in Table 4 below. The Parameters" registry, as in Table 4. The various key-agreement
various key-agreement schemes used by these tcpcrypt variants are schemes used by these tcpcrypt variants are defined in Section 5.
defined in Section 5.
+-------+---------------------------+-----------+ +-------+---------------------------+-----------+
| Value | Meaning | Reference | | Value | Meaning | Reference |
+-------+---------------------------+-----------+ +-------+---------------------------+-----------+
| 0x21 | TCPCRYPT_ECDHE_P256 | [RFC-TBD] | | 0x21 | TCPCRYPT_ECDHE_P256 | [RFC8548] |
| 0x22 | TCPCRYPT_ECDHE_P521 | [RFC-TBD] | | 0x22 | TCPCRYPT_ECDHE_P521 | [RFC8548] |
| 0x23 | TCPCRYPT_ECDHE_Curve25519 | [RFC-TBD] | | 0x23 | TCPCRYPT_ECDHE_Curve25519 | [RFC8548] |
| 0x24 | TCPCRYPT_ECDHE_Curve448 | [RFC-TBD] | | 0x24 | TCPCRYPT_ECDHE_Curve448 | [RFC8548] |
+-------+---------------------------+-----------+ +-------+---------------------------+-----------+
Table 4: TEP identifiers for use with tcpcrypt Table 4: TEP Identifiers for Use with tcpcrypt
In Section 6, this document defines the use of several AEAD In Section 6, this document defines the use of several AEAD
algorithms for encrypting application data. To name these algorithms for encrypting application data. To name these
algorithms, the tcpcrypt protocol uses two-byte identifiers in the algorithms, the tcpcrypt protocol uses two-byte identifiers in the
range 0x0001 to 0xFFFF inclusive, for which IANA is to maintain a new range 0x0001 to 0xFFFF, inclusively, for which IANA maintains a new
"tcpcrypt AEAD Algorithm" registry under the "Transmission Control "tcpcrypt AEAD Algorithms" registry under the "Transmission Control
Protocol (TCP) Parameters" registry. The initial values for this Protocol (TCP) Parameters" registry. The initial values for this
registry are given in Table 5 below. Future assignments are to be registry are given in Table 5. Future assignments are to be made
made upon satisfying either of two policies defined in [RFC8126]: upon satisfying either of two policies defined in [RFC8126]: "IETF
"IETF Review" or (for non-IETF stream specifications) "Expert Review Review" or (for non-IETF stream specifications) "Expert Review with
with RFC Required." IANA will furthermore provide early allocation RFC Required." IANA will furthermore provide early allocation
[RFC7120] to facilitate testing before RFCs are finalized. [RFC7120] to facilitate testing before RFCs are finalized.
+--------+------------------------+---------------------+ +--------+------------------------+----------------------+
| Value | AEAD Algorithm | Reference | | Value | AEAD Algorithm | Reference |
+--------+------------------------+---------------------+ +--------+------------------------+----------------------+
| 0x0001 | AEAD_AES_128_GCM | [RFC-TBD] Section 6 | | 0x0001 | AEAD_AES_128_GCM | [RFC8548], Section 6 |
| 0x0002 | AEAD_AES_256_GCM | [RFC-TBD] Section 6 | | 0x0002 | AEAD_AES_256_GCM | [RFC8548], Section 6 |
| 0x0010 | AEAD_CHACHA20_POLY1305 | [RFC-TBD] Section 6 | | 0x0010 | AEAD_CHACHA20_POLY1305 | [RFC8548], Section 6 |
+--------+------------------------+---------------------+ +--------+------------------------+----------------------+
Table 5: Authenticated-encryption algorithms for use with tcpcrypt Table 5: Authenticated-Encryption Algorithms for Use with tcpcrypt
8. Security Considerations 8. Security Considerations
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 network particular, tcpcrypt does not protect against active network
attackers unless applications authenticate the session ID. If it can attackers unless applications authenticate the session ID. If it can
be established that the session IDs computed at each end of the be established that the session IDs computed at each end of the
connection match, then tcpcrypt guarantees that no man-in-the-middle connection match, then tcpcrypt guarantees that no man-in-the-middle
attacks occurred unless the attacker has broken the underlying attacks occurred unless the attacker has broken the underlying
cryptographic primitives (e.g., ECDH). A proof of this property for cryptographic primitives, e.g., Elliptic Curve Diffie-Hellman (ECDH).
an earlier version of the protocol has been published [tcpcrypt]. A proof of this property for an earlier version of the protocol has
been published [tcpcrypt].
To ensure middlebox compatibility, tcpcrypt does not protect TCP To ensure middlebox compatibility, tcpcrypt does not protect TCP
headers. Hence, the protocol is vulnerable to denial-of-service from headers. Therefore, the protocol is vulnerable to denial-of-service
off-path attackers just as plain TCP is. Possible attacks include from off-path attackers just as plain TCP is. Possible attacks
desynchronizing the underlying TCP stream, injecting RST or FIN include desynchronizing the underlying TCP stream, injecting RST or
segments, and forging re-key bits. These attacks will cause a FIN segments, and forging rekey bits. These attacks will cause a
tcpcrypt connection to hang or fail with an error, but not in any tcpcrypt connection to hang or fail with an error, but not in any
circumstance where plain TCP could continue uncorrupted. circumstance where plain TCP could continue uncorrupted.
Implementations MUST give higher-level software a way to distinguish Implementations MUST give higher-level software a way to distinguish
such errors from a clean end-of-stream (indicated by an authenticated such errors from a clean end-of-stream (indicated by an authenticated
"FINp" bit) so that applications can avoid semantic truncation FINp bit) so that applications can avoid semantic truncation attacks.
attacks.
There is no "key confirmation" step in tcpcrypt. This is not needed There is no "key confirmation" step in tcpcrypt. This is not needed
because tcpcrypt's threat model includes the possibility of a because tcpcrypt's threat model includes the possibility of a
connection to an adversary. If key negotiation is compromised and connection to an adversary. If key negotiation is compromised and
yields two different keys, failed integrity checks on every yields two different keys, failed integrity checks on every
subsequent frame will cause the connection either to hang or to subsequent frame will cause the connection either to hang or to
abort. This is not a new threat as an active attacker can achieve abort. This is not a new threat as an active attacker can achieve
the same results against a plain TCP connection by injecting RST the same results against a plain TCP connection by injecting RST
segments or modifying sequence and acknowledgement numbers. segments or modifying sequence and acknowledgement numbers.
Tcpcrypt uses short-lived public keys to provide forward secrecy. Tcpcrypt uses short-lived public keys to provide forward secrecy;
That is, once an implementation removes these keys from memory, a once an implementation removes these keys from memory, a compromise
compromise of the system will not provide any means to derive the of the system will not provide any means to derive the session
session secrets for past connections. All currently-specified key secrets for past connections. All currently-specified key agreement
agreement schemes involve ECDHE-based key agreement, meaning a new schemes involve key agreement based on Ephemeral Elliptic Curve
key-pair can be efficiently computed for each connection. If Diffie-Hellman (ECDHE), meaning a new key pair can be efficiently
implementations reuse these parameters, they MUST limit the lifetime computed for each connection. If implementations reuse these
of the private parameters as far as practical in order to minimize parameters, they MUST limit the lifetime of the private parameters as
the number of past connections that are vulnerable. Of course, far as is practical in order to minimize the number of past
placing private keys in persistent storage introduces severe risks connections that are vulnerable. Of course, placing private keys in
that they will not be destroyed reliably and in a timely fashion, and persistent storage introduces severe risks that they will not be
SHOULD be avoided whenever possible. destroyed reliably and in a timely fashion, and it SHOULD be avoided
whenever possible.
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.
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 for 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, L) = (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 assure CPRF(K_2, CONST_2, L). Collision resistance is important to assure
the uniqueness of session IDs, which are generated using the CPRF. the uniqueness of session IDs, which are generated using the CPRF.
Lastly, many of tcpcrypt's cryptographic functions require random Lastly, many of tcpcrypt's cryptographic functions require random
input, and thus any host implementing tcpcrypt MUST have access to a input, and thus any host implementing tcpcrypt MUST have access to a
cryptographically-secure source of randomness or pseudo-randomness. cryptographically-secure source of randomness or pseudo-randomness.
[RFC4086] provides recommendations on how to achieve this. [RFC4086] provides recommendations on how to achieve this.
skipping to change at page 26, line 9 skipping to change at page 27, line 17
Tcpcrypt transforms a shared pseudo-random key (PRK) into Tcpcrypt transforms a shared pseudo-random key (PRK) into
cryptographic traffic keys for each direction. Doing so requires an cryptographic traffic 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
segment causes the remote side to send an acknowledgment. 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. Therefore, an attacker could prolong the existence
session at one host after the other end of the connection no longer of a session at one host after the other end of the connection no
exists. (Such an attack might prevent a process with sensitive data longer exists. (Such an attack might prevent a process with
from exiting, giving an attacker more time to compromise a host and sensitive data from exiting, giving an attacker more time to
extract the sensitive data.) compromise a host and extract the sensitive data.)
To counter this threat, tcpcrypt specifies a way to stimulate the To counter this threat, tcpcrypt specifies a way to stimulate the
remote host to send verifiably fresh and authentic data, described in remote host to send verifiably fresh and authentic data, described in
Section 3.9. 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
skipping to change at page 27, line 19 skipping to change at page 28, line 26
together with its recent popularity has led to many safe and together with its recent popularity has led to many safe and
efficient implementations, including some that fit naturally into the efficient implementations, including some that fit naturally into the
kernel environment. kernel environment.
[RFC7696] insists that, "The selected algorithms need to be resistant [RFC7696] insists that, "The selected algorithms need to be resistant
to side-channel attacks and also meet the performance, power, and to side-channel attacks and also meet the performance, power, and
code size requirements on a wide variety of platforms." On this code size requirements on a wide variety of platforms." On this
principle, tcpcrypt excludes the NIST curves from the set of principle, tcpcrypt excludes the NIST curves from the set of
mandatory-to-implement key-agreement algorithms. mandatory-to-implement key-agreement algorithms.
Lastly, this document encourages support for key-agreement with Lastly, this document encourages support for key agreement with
Curve448, categorizing it as RECOMMENDED. Curve448 appears likely to Curve448, categorizing it as RECOMMENDED. Curve448 appears likely to
admit safe and efficient implementations. However, support is not admit safe and efficient implementations. However, support is not
REQUIRED because existing implementations might not yet be REQUIRED because existing implementations might not yet be
sufficiently well-proven. sufficiently well proven.
9. Experiments 9. Experiments
Some experience will be required to determine whether the tcpcrypt Some experience will be required to determine whether the tcpcrypt
protocol can be deployed safely and successfully across the diverse protocol can be deployed safely and successfully across the diverse
environments of the global internet. environments of the global internet.
Safety means that TCP implementations that support tcpcrypt are able Safety means that TCP implementations that support tcpcrypt are able
to communicate reliably in all the same settings as they would to communicate reliably in all the same settings as they would
without tcpcrypt. As described in [I-D.ietf-tcpinc-tcpeno] without tcpcrypt. As described in Section 9 of [RFC8547], this
Section 9, this property can be subverted if middleboxes strip ENO property can be subverted if middleboxes strip ENO options from
options from non-SYN segments after allowing them in SYN segments; or non-SYN segments after allowing them in SYN segments, or if the
if the particular communication patterns of tcpcrypt offend the particular communication patterns of tcpcrypt offend the policies of
policies of middleboxes doing deep-packet inspection. middleboxes doing deep-packet inspection.
Success, in addition to safety, means hosts that implement tcpcrypt Success, in addition to safety, means hosts that implement tcpcrypt
actually enable encryption when connecting to one another. This actually enable encryption when connecting to one another. This
property depends on the network's treatment of the TCP-ENO handshake, property depends on the network's treatment of the TCP-ENO handshake
and can be subverted if middleboxes merely strip unknown TCP options and can be subverted if middleboxes merely strip unknown TCP options
or if they terminate TCP connections and relay data back and forth or terminate TCP connections and relay data back and forth
unencrypted. unencrypted.
Ease of implementation will be a further challenge to deployment. Ease of implementation will be a further challenge to deployment.
Because tcpcrypt requires encryption operations on frames that may Because tcpcrypt requires encryption operations on frames that may
span TCP segments, kernel implementations are forced to buffer span TCP segments, kernel implementations are forced to buffer
segments in different ways than are necessary for plain TCP. More segments in different ways than are necessary for plain TCP. More
implementation experience will show how much additional code implementation experience will show how much additional code
complexity is required in various operating systems, and what kind of complexity is required in various operating systems and what kind of
performance effects can be expected. performance effects can be expected.
10. Acknowledgments 10. References
We are grateful for contributions, help, discussions, and feedback
from the TCPINC working group and from other IETF reviewers,
including Marcelo Bagnulo, David Black, Bob Briscoe, Jana Iyengar,
Stephen Kent, Tero Kivinen, Mirja Kuhlewind, Yoav Nir, Christoph
Paasch, Eric Rescorla, Kyle Rose, and Dale Worley.
This work was funded by gifts from Intel (to Brad Karp) and from
Google; by NSF award CNS-0716806 (A Clean-Slate Infrastructure for
Information Flow Control); by DARPA CRASH under contract
#N66001-10-2-4088; and by the Stanford Secure Internet of Things
Project.
11. Contributors
Dan Boneh and Michael Hamburg were co-authors of the draft that
became this document.
12. References
12.1. Normative References
[I-D.ietf-tcpinc-tcpeno] 10.1. Normative References
Bittau, A., Giffin, D., Handley, M., Mazieres, D., and E.
Smith, "TCP-ENO: Encryption Negotiation Option", draft-
ietf-tcpinc-tcpeno-19 (work in progress), June 2018.
[IEEE-1363] [IEEE-1363]
IEEE, "IEEE Standard Specifications for Public-Key IEEE, "IEEE Standard Specifications for Public-Key
Cryptography (IEEE Std 1363-2000)", 2000. Cryptography", IEEE Standard 1363-2000,
DOI 10.1109/IEEESTD.2000.92292.
[NIST-DSS] [NIST-DSS] National Institute of Standards and Technology (NIST),
NIST, "FIPS PUB 186-4: Digital Signature Standard (DSS)", "Digital Signature Standard (DSS)", FIPS PUB 186-4,
2013. DOI 10.6028/NIST.FIPS.186-4, July 2013.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC793] 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>.
[RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP [RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
Selective Acknowledgment Options", RFC 2018, Selective Acknowledgment Options", RFC 2018,
DOI 10.17487/RFC2018, October 1996, DOI 10.17487/RFC2018, October 1996,
<https://www.rfc-editor.org/info/rfc2018>. <https://www.rfc-editor.org/info/rfc2018>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, Hashing for Message Authentication", RFC 2104,
skipping to change at page 29, line 28 skipping to change at page 30, line 9
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869, Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010, DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>. <https://www.rfc-editor.org/info/rfc5869>.
[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code [RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
2014, <https://www.rfc-editor.org/info/rfc7120>. 2014, <https://www.rfc-editor.org/info/rfc7120>.
[RFC7539] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
<https://www.rfc-editor.org/info/rfc7539>.
[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 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References [RFC8439] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 8439, DOI 10.17487/RFC8439, June 2018,
<https://www.rfc-editor.org/info/rfc8439>.
[I-D.ietf-tcpinc-api] [RFC8547] Bittau, A., Giffin, D., Handley, M., Mazieres, D., and
Bittau, A., Boneh, D., Giffin, D., Handley, M., Mazieres, E. Smith, "TCP-ENO: Encryption Negotiation Option",
D., and E. Smith, "Interface Extensions for TCP-ENO and RFC 8547, DOI 10.17487/RFC8547, May 2019,
tcpcrypt", draft-ietf-tcpinc-api-06 (work in progress), <https://www.rfc-editor.org/info/rfc8547>.
June 2018.
10.2. Informative References
[NIST-fail] [NIST-fail]
Bernstein, D. and T. Lange, "Failures in NIST's ECC Bernstein, D. and T. Lange, "Failures in NIST's ECC
standards", 2016, Standards", January 2016,
<https://cr.yp.to/newelliptic/nistecc-20160106.pdf>. <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, DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>. <https://www.rfc-editor.org/info/rfc1122>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086, "Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005, DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/info/rfc4086>. <https://www.rfc-editor.org/info/rfc4086>.
[RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm [RFC7696] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms", Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015, BCP 201, RFC 7696, DOI 10.17487/RFC7696, November 2015,
<https://www.rfc-editor.org/info/rfc7696>. <https://www.rfc-editor.org/info/rfc7696>.
[tcpcrypt] [tcpcrypt] Bittau, A., Hamburg, M., Handley, M., Mazieres, D., and
Bittau, A., Hamburg, M., Handley, M., Mazieres, D., and D. D. Boneh, "The case for ubiquitous transport-level
Boneh, "The case for ubiquitous transport-level encryption", USENIX Security Symposium, August 2010.
encryption", USENIX Security , 2010.
[TCPINC-API]
Bittau, A., Boneh, D., Giffin, D., Handley, M., Mazieres,
D., and E. Smith, "Interface Extensions for TCP-ENO and
tcpcrypt", Work in Progress, draft-ietf-tcpinc-api-06,
June 2018.
Acknowledgments
We are grateful for contributions, help, discussions, and feedback
from the TCPINC Working Group and from other IETF reviewers,
including Marcelo Bagnulo, David Black, Bob Briscoe, Jana Iyengar,
Stephen Kent, Tero Kivinen, Mirja Kuhlewind, Yoav Nir, Christoph
Paasch, Eric Rescorla, Kyle Rose, and Dale Worley.
This work was funded by gifts from Intel (to Brad Karp) and from
Google; by NSF award CNS-0716806 (A Clean-Slate Infrastructure for
Information Flow Control); by DARPA CRASH under contract
#N66001-10-2-4088; and by the Stanford Secure Internet of Things
Project.
Contributors
Dan Boneh and Michael Hamburg were coauthors of the draft that became
this document.
Authors' Addresses Authors' Addresses
Andrea Bittau Andrea Bittau
Google Google
345 Spear Street 345 Spear Street
San Francisco, CA 94105 San Francisco, CA 94105
US United States of America
Email: bittau@google.com Email: bittau@google.com
Daniel B. Giffin Daniel B. Giffin
Stanford University Stanford University
353 Serra Mall, Room 288 353 Serra Mall, Room 288
Stanford, CA 94305 Stanford, CA 94305
US United States of America
Email: daniel@beech-grove.net
Email: dbg@scs.stanford.edu
Mark Handley Mark Handley
University College London University College London
Gower St. Gower St.
London WC1E 6BT London WC1E 6BT
UK United Kingdom
Email: M.Handley@cs.ucl.ac.uk Email: M.Handley@cs.ucl.ac.uk
David Mazieres David Mazieres
Stanford University Stanford University
353 Serra Mall, Room 290 353 Serra Mall, Room 290
Stanford, CA 94305 Stanford, CA 94305
US United States of America
Email: dm@uun.org Email: dm@uun.org
Quinn Slack Quinn Slack
Sourcegraph Sourcegraph
121 2nd St Ste 200 121 2nd St Ste 200
San Francisco, CA 94105 San Francisco, CA 94105
US United States of America
Email: sqs@sourcegraph.com Email: sqs@sourcegraph.com
Eric W. Smith Eric W. Smith
Kestrel Institute Kestrel Institute
3260 Hillview Avenue 3260 Hillview Avenue
Palo Alto, CA 94304 Palo Alto, CA 94304
US United States of America
Email: eric.smith@kestrel.edu Email: eric.smith@kestrel.edu
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