draft-ietf-tcpinc-tcpcrypt-11.txt   draft-ietf-tcpinc-tcpcrypt-12.txt 
Network Working Group A. Bittau Network Working Group A. Bittau
Internet-Draft Google Internet-Draft Google
Intended status: Experimental D. Giffin Intended status: Experimental D. Giffin
Expires: June 3, 2018 Stanford University Expires: December 31, 2018 Stanford University
M. Handley M. Handley
University College London University College London
D. Mazieres D. Mazieres
Stanford University Stanford University
Q. Slack Q. Slack
Sourcegraph Sourcegraph
E. Smith E. Smith
Kestrel Institute Kestrel Institute
November 30, 2017 June 29, 2018
Cryptographic protection of TCP Streams (tcpcrypt) Cryptographic protection of TCP Streams (tcpcrypt)
draft-ietf-tcpinc-tcpcrypt-11 draft-ietf-tcpinc-tcpcrypt-12
Abstract Abstract
This document specifies tcpcrypt, a TCP encryption protocol designed This document specifies tcpcrypt, a TCP encryption protocol designed
for use in conjunction with the TCP Encryption Negotiation Option for use in conjunction with the TCP Encryption Negotiation Option
(TCP-ENO). Tcpcrypt coexists with middleboxes by tolerating (TCP-ENO). Tcpcrypt coexists with middleboxes by tolerating
resegmentation, NATs, and other manipulations of the TCP header. The resegmentation, NATs, and other manipulations of the TCP header. The
protocol is self-contained and specifically tailored to TCP protocol is self-contained and specifically tailored to TCP
implementations, which often reside in kernels or other environments implementations, which often reside in kernels or other environments
in which large external software dependencies can be undesirable. in which large external software dependencies can be undesirable.
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 may be transmitted. However, this cost can be application data can be transmitted. However, the extra latency can
avoided between two hosts that have recently established a previous be avoided between two hosts that have recently established a
tcpcrypt connection. previous tcpcrypt connection.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 3, 2018. This Internet-Draft will expire on December 31, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 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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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 1. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Encryption Protocol . . . . . . . . . . . . . . . . . . . . . 3 3. Encryption Protocol . . . . . . . . . . . . . . . . . . . . . 3
3.1. Cryptographic Algorithms . . . . . . . . . . . . . . . . 3 3.1. Cryptographic Algorithms . . . . . . . . . . . . . . . . 3
3.2. Protocol Negotiation . . . . . . . . . . . . . . . . . . 5 3.2. Protocol Negotiation . . . . . . . . . . . . . . . . . . 5
3.3. Key Exchange . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Key Exchange . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Session ID . . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Session ID . . . . . . . . . . . . . . . . . . . . . . . 9
3.5. Session Resumption . . . . . . . . . . . . . . . . . . . 9 3.5. Session Resumption . . . . . . . . . . . . . . . . . . . 9
3.6. Data Encryption and Authentication . . . . . . . . . . . 12 3.6. Data Encryption and Authentication . . . . . . . . . . . 13
3.7. TCP Header Protection . . . . . . . . . . . . . . . . . . 14 3.7. TCP Header Protection . . . . . . . . . . . . . . . . . . 14
3.8. Re-Keying . . . . . . . . . . . . . . . . . . . . . . . . 15 3.8. Re-Keying . . . . . . . . . . . . . . . . . . . . . . . . 15
3.9. Keep-Alive . . . . . . . . . . . . . . . . . . . . . . . 16 3.9. Keep-Alive . . . . . . . . . . . . . . . . . . . . . . . 16
4. Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . 16 4. Encodings . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1. Key-Exchange Messages . . . . . . . . . . . . . . . . . . 16 4.1. Key-Exchange Messages . . . . . . . . . . . . . . . . . . 16
4.2. Encryption Frames . . . . . . . . . . . . . . . . . . . . 18 4.2. Encryption Frames . . . . . . . . . . . . . . . . . . . . 18
4.2.1. Plaintext . . . . . . . . . . . . . . . . . . . . . . 19 4.2.1. Plaintext . . . . . . . . . . . . . . . . . . . . . . 19
4.2.2. Associated Data . . . . . . . . . . . . . . . . . . . 20 4.2.2. Associated Data . . . . . . . . . . . . . . . . . . . 20
4.2.3. Frame ID . . . . . . . . . . . . . . . . . . . . . . 20 4.2.3. Frame ID . . . . . . . . . . . . . . . . . . . . . . 20
4.3. Constant Values . . . . . . . . . . . . . . . . . . . . . 20 4.3. Constant Values . . . . . . . . . . . . . . . . . . . . . 20
skipping to change at page 4, line 9 skipping to change at page 4, line 9
3.1. Cryptographic Algorithms 3.1. Cryptographic Algorithms
Setting up a tcpcrypt connection employs three types of cryptographic Setting up a tcpcrypt connection employs three types of cryptographic
algorithms: algorithms:
o A _key agreement scheme_ is used with a short-lived public key to o A _key agreement scheme_ is used with a short-lived public key to
agree upon a shared secret. agree upon a shared secret.
o An _extract function_ is used to generate a pseudo-random key o An _extract function_ is used to generate a pseudo-random key
(PRK) from some initial keying material, typically the output of (PRK) from some initial keying material produced by the key
the key agreement scheme. The notation Extract(S, IKM) denotes agreement scheme. The notation Extract(S, IKM) denotes the output
the output of the extract function with salt S and initial keying of the extract function with salt S and initial keying material
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
skipping to change at page 4, line 41 skipping to change at page 4, line 41
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
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3.2. Protocol Negotiation 3.2. Protocol Negotiation
Tcpcrypt depends on TCP-ENO [I-D.ietf-tcpinc-tcpeno] to negotiate Tcpcrypt depends on TCP-ENO [I-D.ietf-tcpinc-tcpeno] to negotiate
whether encryption will be enabled for a connection, and also which whether encryption will be enabled for a connection, and also which
key-agreement scheme to use. TCP-ENO negotiates the use of a key-agreement scheme to use. TCP-ENO negotiates the use of a
particular TCP encryption protocol or _TEP_ by including protocol particular TCP encryption protocol or _TEP_ by including protocol
identifiers in ENO suboptions. This document associates four TEP identifiers in ENO suboptions. This document associates four TEP
identifiers with the tcpcrypt protocol, as listed in Table 4 in identifiers with the tcpcrypt protocol, as listed in Table 4 in
Section 7. Each identifier indicates the use of a particular key- Section 7. Each identifier indicates the use of a particular key-
agreement scheme, with an associated CPRF and length parameters. agreement scheme, with an associated CPRF and length parameter.
Future standards may associate additional TEP identifiers with Future standards can associate additional TEP identifiers with
tcpcrypt, following the assignment policy specified by TCP-ENO. tcpcrypt, following the assignment policy specified by TCP-ENO.
An active opener that wishes to negotiate the use of tcpcrypt An active opener that wishes to negotiate the use of tcpcrypt
includes an ENO option in its SYN segment. That option includes includes an ENO option in its SYN segment. That option includes
suboptions with tcpcrypt TEP identifiers indicating the key-agreement suboptions with tcpcrypt TEP identifiers indicating the key-agreement
schemes it is willing to enable. The active opener MAY additionally schemes it is willing to enable. The active opener MAY additionally
include suboptions indicating support for encryption protocols other include suboptions indicating support for encryption protocols other
than tcpcrypt, as well as global suboptions as specified by TCP-ENO. than tcpcrypt, as well as global suboptions as specified by TCP-ENO.
If a passive opener receives an ENO option including tcpcrypt TEPs it If a passive opener receives an ENO option including tcpcrypt TEPs it
supports, it MAY then attach an ENO option to its SYN-ACK segment, supports, it MAY then attach an ENO option to its SYN-ACK segment,
including solely the TEP it wishes to enable. including solely the TEP it wishes to enable.
To establish distinct roles for the two hosts in each connection, To establish distinct roles for the two hosts in each connection,
tcpcrypt depends on the role-negotiation mechanism of TCP-ENO. As tcpcrypt depends on the role-negotiation mechanism of TCP-ENO. As
one result of the negotiation process, TCP-ENO assigns hosts unique one result of the negotiation process, TCP-ENO assigns hosts unique
roles abstractly called "A" at one end of the connection and "B" at roles abstractly called "A" at one end of the connection and "B" at
the other. Generally, an active opener plays the "A" role and a the other. Generally, an active opener plays the "A" role and a
passive opener plays the "B" role; but in the case of simultaneous passive opener plays the "B" role, but in the case of simultaneous
open, an additional mechanism breaks the symmetry and assigns 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, and this
document employs those terms in the same way. document 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", and an identifier derived from the TEP identifier, the flag "v = 1", an identifier derived from a
a session secret previously negotiated with the same host and the session secret previously negotiated with the same host and the same
same TEP. 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 of host B (that is, the passive opener in the absence of segment of host B (that is, the passive opener in the absence of
simultaneous open) that also occurs in that of host A. If there is simultaneous open) that also occurs in that of host A. If there is
no such TEP, hosts MUST disable TCP-ENO and tcpcrypt. no such TEP, hosts MUST disable TCP-ENO and tcpcrypt.
If the negotiated TEP was sent by host B with "v = 0", it means that If the negotiated TEP was sent by host B with "v = 0", it means that
fresh key agreement will be performed as described below in fresh key agreement will be performed as described below in
Section 3.3. If it had "v = 1", the key-exchange messages will be Section 3.3. If, on the other hand, host B sent the TEP with "v = 1"
omitted in favor of determining keys via session-resumption as and both hosts sent appropriate resumption identifiers in their
described in Section 3.5, and protected application data may suboption data, then the key-exchange messages will be omitted in
immediately be sent as detailed in Section 3.6. favor of determining keys via session resumption as described in
Section 3.5. With session resumption, protected application data MAY
be sent 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 may become the negotiated TEP and fresh key with the same TEP, that could become the negotiated TEP and fresh key
agreement will be performed. That is, sending a resumption suboption agreement will be performed. That is, sending a resumption suboption
also implies willingness to perform fresh key agreement with the also implies willingness to perform fresh key agreement with the
indicated TEP. indicated TEP.
As required by TCP-ENO, once a host has both sent and received an ACK As REQUIRED by TCP-ENO, once a host has both sent and received an ACK
segment containing a valid ENO option, encryption MUST be enabled and segment containing a valid ENO option, encryption MUST be enabled and
plaintext application data MUST NOT ever be exchanged on the plaintext application data MUST NOT ever be exchanged on the
connection. If the negotiated TEP is among those listed in Table 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 below in Section 3.5), the
two hosts perform key exchange through two messages, "Init1" and two hosts perform key exchange through two messages, "Init1" and
"Init2", at the start of the data streams of host A and host B, "Init2", at the start of the data streams of host A and host B,
respectively. These messages may span multiple TCP segments and need respectively. These messages MAY span multiple TCP segments and need
not end at a segment boundary. However, the segment containing the not end at a segment boundary. However, the segment containing the
last byte of an "Init1" or "Init2" message MUST have TCP's push flag last byte of an "Init1" or "Init2" message MUST have TCP's push flag
(PSH) set. (PSH) set.
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.
skipping to change at page 7, line 17 skipping to change at page 7, line 17
Table 5 in Section 7. Table 5 in 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 as frequently as are short-lived values that MUST be refreshed frequently. The
practically possible. The private keys SHOULD NOT ever be written private keys SHOULD NOT ever be written to persistent storage.
to persistent storage. The security risks associated with the The security risks associated with the storage of these keys are
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 If a host receives an ephemeral public key from its peer and a key-
required key-validation step fails (see Section 5), it MUST abort the validation step fails (see Section 5), it MUST abort the connection
connection and raise an error condition distinct from the end-of-file and raise an error condition distinct from the end-of-file condition.
condition.
The ephemeral secret "ES" is the result of the key-agreement The ephemeral secret "ES" is the result of the key-agreement
algorithm (see Section 5) indicated by the negotiated TEP. The algorithm (see Section 5) indicated by the negotiated TEP. The
inputs to the algorithm are the local host's ephemeral private key inputs to the algorithm are the local host's ephemeral private key
and the remote host's ephemeral public key. For example, host A and the remote host's ephemeral public key. For example, host A
would compute "ES" using its own private key (not transmitted) and would compute "ES" using its own private key (not transmitted) and
host B's public key, "Pub_B". host B's public key, "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
[I-D.ietf-tcpinc-tcpeno]; and "Init1" and "Init2" are the transmitted [I-D.ietf-tcpinc-tcpeno]; and "Init1" and "Init2" are the transmitted
encodings of the messages described in Section 4.1. encodings of the messages described in Section 4.1.
A series of "session secrets" are then computed from "PRK" as A series of "session secrets" are computed from "PRK" as follows:
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 connection. The values "ss[i]" for "i > 0" can be used to current connection. The values "ss[i]" for "i > 0" are used by
avoid public key cryptography when establishing subsequent session resumption to avoid public key cryptography when establishing
connections between the same two hosts, as described in Section 3.5. subsequent connections between the same two hosts, as described later
The "CONST_*" values are constants defined in Section 4.3. The in Section 3.5. The "CONST_*" values are constants defined in
length "K_LEN" depends on the tcpcrypt TEP in use, and is specified Section 4.3. The length "K_LEN" depends on the tcpcrypt TEP in use,
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, 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. described in Section 3.8. The values "sn[i]" are "session nonces."
For the initial session with "i = 0", the session nonce is zero bytes
long. The values for subsequent sessions are 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.
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following "ae_nonce_len" bytes as a "nonce randomizer". following "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 advertize 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
[I-D.ietf-tcpinc-api] describes recommended interfaces for this [I-D.ietf-tcpinc-api] 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 in the "sym_cipher_list" it previously transmitted in present in the "sym_cipher_list" it previously transmitted in
"Init1", it MUST abort the connection and raise an error condition "Init1", it MUST abort the connection and raise an error condition
distinct from the end-of-file condition. distinct from the 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 [RFC0793], Section 3.8. That is,
the TCP connection is destroyed, RESET is transmitted, and the local the TCP connection is destroyed, RESET is transmitted, and the local
user is alerted to the abort event. user is alerted to the abort event.
3.4. Session ID 3.4. Session ID
TCP-ENO requires each TEP to define a _session ID_ value that TCP-ENO requires each TEP to define a _session ID_ value that
uniquely identifies each encrypted connection. uniquely identifies each encrypted connection.
As required, a tcpcrypt session ID begins with the byte transmitted A tcpcrypt session ID begins with the byte transmitted by host B that
by host B that contains the negotiated TEP identifier along with the contains the negotiated TEP identifier along with the "v" bit. The
"v" bit. The remainder of the ID is derived from the session secret, remainder of the ID is derived from the session secret and session
as follows: nonce, as follows:
session_id[i] = TEP-byte | CPRF(ss[i], CONST_SESSID, 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 willingness to resume with a particular session secret
by sending a SYN segment with a resumption suboption: that is, an ENO by sending a SYN segment with a resumption suboption: that is, an ENO
suboption whose value is the negotiated TEP identifier of the suboption containing the negotiated TEP identifier of the previous
previous session concatenated with half of the "resumption session, half of the "resumption identifier" for the new session, and
identifier" for the new session. a "resumption nonce".
The resumption nonce MUST have a minimum length of zero bytes and
maximum length of eight bytes. An implementation MUST either send
four or more bytes of nonce for all resumption attempts, or else
default to a minimum of four bytes and provide an interface for
system administrators to configure other minimum lengths. In the
latter case, documentation accompanying the configuration interface
MUST explain that using nonce values shorter than four bytes is only
safe if there is no risk of the system participating in multiple
resumptions from the same session secret, as could happen with live
virtual-machine cloning. The resumption nonce MUST be chosen
randomly or using a mechanism that guarantees uniqueness even in the
face of virtual machine cloning or other re-execution of the same
session.
The resumption identifier is calculated from a session secret "ss[i]" The resumption identifier is calculated from a session secret "ss[i]"
as follows: as follows:
resume[i] = CPRF(ss[i], CONST_RESUME, 18) resume[i] = CPRF(ss[i], CONST_RESUME, 18)
To name a session for resumption, a host sends either the first or To name a session for resumption, a host sends either the first or
second half of the resumption identifier, according to the role it second half of the resumption identifier, according to the role it
played in the original session with secret "ss[0]". played in the original session with secret "ss[0]".
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 bytes total) byte 0 1 9 10
+--------+--------+---...---+--------+ +------+------+--...--+------+------+--...--+------+
| TEP- | resume[i]{0..8} | | 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". The
TEP-byte contains a tcpcrypt TEP identifier and v = 1. 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 bytes total) byte 0 1 9 10
+--------+--------+---...---+--------+ +------+------+--...--+------+------+--...--+------+
| TEP- | resume[i]{9..17} | | 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". The
TEP-byte contains a tcpcrypt TEP identifier and v = 1. 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 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 does not have length 9 bytes, it and "v = 1", but the suboption data is less than 9 bytes in length,
MUST behave as if the same TEP had been sent with "v = 0". That is, it MUST behave as if the same TEP had been sent with "v = 0". That
the suboption MUST be interpreted as an offer to negotiate fresh key is, the suboption MUST be interpreted as an offer to negotiate fresh
exchange with that TEP. key 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, receives a resumption suboption with the same
TEP and an identifier-half that does not match that resumption 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: that is, it MUST NOT send any more ENO
options and MUST NOT encrypt the connection. options 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, as encryption with that TEP using the cached session secret. To do
described in Section 3.6. this, it first constructs "sn[i]" as follows:
sn[i] = nonce_a | nonce_b
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 3.6.
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 the cached session secret. from the cached session secret and the session nonce that was
generated 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 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 non-
resumption suboptions describing other TEPs it supports (in addition resumption suboptions describing other TEPs it supports (in addition
to the TEP in the resumption suboption). 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 a later session, then erase "ss[i]" from memory. Hosts SHOULD by a later session, then erase "ss[i]" from memory. Hosts MAY retain
retain "ss[i+1]" until it is used or the memory needs to be "ss[i+1]" until it is used or the memory needs to be reclaimed.
reclaimed. Hosts SHOULD NOT write any session secrets to non- Hosts SHOULD NOT write any session secrets to non-volatile storage.
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 session secret may not be used to secure more than one TCP A given session secret "ss[i]" MUST NOT be used to secure more than
connection. To prevent this, a host MUST NOT resume with a session one TCP connection. To prevent this, a host MUST NOT resume with a
secret if it has ever enabled encryption in the past with the same session secret if it has ever enabled encryption in the past with the
secret, in either role. In the event that two hosts simultaneously same secret, in either role. In the event that two hosts
send SYN segments to each other that propose resumption with the same simultaneously send SYN segments to each other that propose
session secret but the two segments are not part of a simultaneous resumption with the same session secret but the two segments are not
open, both connections will have to revert to fresh key-exchange. To part of a simultaneous open, both connections would need to revert to
avoid this limitation, implementations MAY choose to implement fresh key-exchange. To avoid this limitation, implementations MAY
session resumption such that all session secrets derived from a given choose to implement session resumption such that all session secrets
"ss[0]" are used for either passive or active opens at the same host, derived from a given "ss[0]" are used for either passive or active
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 keys "k_ba[j]". Thus, which keys a host uses to send segments with keys "k_ba[j]". Thus, which keys a host uses to send segments
is not affected by the role it plays in the current connection: it is not affected by the role it plays in the current connection: it
depends only on whether the host played the "A" or "B" role in the depends only on whether the host played the "A" or "B" role in the
initial session. initial 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 be able to specify application requests a new TCP connection, it MUST have a way to
two policies for the duration of the connection: 1) that resumption specify two policies for the duration of the connection: 1) that
requests will be ignored, and thus fresh key exchange will be resumption requests will be ignored, and thus fresh key exchange will
required; and 2) that no session secrets will be cached. (These be necessary; and 2) that no session secrets will be cached. (These
policies may 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 be able 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 [I-D.ietf-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 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 particular algorithms Encryption with Associated Data (AEAD). The permitted algorithms are
that may be used are listed in Table 5 in Section 7. Additional listed in Table 5 in Section 7. Additional algorithms can be
algorithms may be specified according to the policy in that section. specified in the future according to the policy in that section. One
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 each algorithm are found in Table 3 in Section 6, together with with each algorithm are found in Table 3 in Section 6, together 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" portion of a "plaintext"
value, which is then encrypted to yield a frame's "ciphertext" field. value, which is then encrypted to yield a frame's "ciphertext" field.
Chunks must be small enough that the ciphertext (whose length depends Chunks MUST be small enough that the ciphertext (whose length depends
on the AEAD cipher used, and is generally slightly longer than the on the AEAD cipher used, and is generally slightly longer than the
plaintext) has length less than 2^16 bytes. plaintext) has length less than 2^16 bytes.
An "associated data" value (see Section 4.2.2) is constructed for the An "associated data" value (see Section 4.2.2) is constructed for the
frame. It contains the frame's "control" field and the length of the frame. It contains the frame's "control" field and the length of the
ciphertext. ciphertext.
A "frame 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
skipping to change at page 14, line 5 skipping to change at page 14, line 25
\_____________________________________________/ \_____________________________________________/
traffic key traffic key
The first "ae_key_len" bytes of the traffic key provide the AEAD key The first "ae_key_len" bytes of the traffic key provide the AEAD key
"K", while the remaining "ae_nonce_len" bytes provide a "nonce "K", while the remaining "ae_nonce_len" bytes provide a "nonce
randomizer" value "NR". The frame ID is then combined via bitwise randomizer" value "NR". The frame ID is then combined via bitwise
exclusive-or with the nonce randomizer to yield "N", the AEAD nonce exclusive-or with the nonce randomizer to yield "N", the AEAD nonce
for the frame: 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 plaintext value serves as "P", and the associated data as "A".
The output of the encryption operation, "C", is transmitted in the The output of the encryption operation, "C", is transmitted in the
frame's "ciphertext" field. 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
skipping to change at page 15, line 26 skipping to change at page 15, line 44
it uses to encrypt outgoing frames, and a _remote generation number_ it uses to encrypt outgoing frames, and a _remote generation number_
equal to the highest generation used in frames received from its equal to the highest generation used in frames received from its
peer. Initially, these two generation numbers are set to zero. peer. Initially, these two generation numbers are set to zero.
A host MAY increment its local generation number beyond the remote A host MAY increment its local generation number beyond the remote
generation number it has recorded. We call this action _initiating generation number it has recorded. We call this action _initiating
re-keying_. re-keying_.
When a host has incremented its local generation number and uses the When a host has incremented its local generation number and uses the
new key-set for the first time to encrypt an outgoing frame, it MUST new key-set for the first time to encrypt an outgoing frame, it MUST
set "rekey = 1" for that frame. It MUST set this field to zero in set "rekey = 1" for that frame. It MUST set "rekey = 0" in all other
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 of the remote generation number. If the remote generation record of the remote generation number. If the remote generation
number is now greater than the local generation number, the receiver number is now greater than the local generation number, the receiver
MUST immediately increment its local generation number to match. MUST immediately increment its local generation number to match.
Moreover, if the receiver has not yet transmitted a segment with the Moreover, if the receiver has not yet transmitted a segment with the
FIN flag set, it MUST immediately send a frame (with empty FIN flag set, it MUST immediately send a frame (with empty
application data if necessary) with "rekey = 1". application data if necessary) with "rekey = 1".
A host MUST NOT initiate more than one concurrent re-key operation if A host MUST NOT initiate more than one concurrent re-key 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 re-keying 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 re-
skipping to change at page 17, line 47 skipping to change at page 17, line 47
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" and the length of "Pub_A" are both determined by the "N_A_LEN" and the length of "Pub_A" are both determined by the
negotiated TEP, as described in Section 5. negotiated TEP, as 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 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 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 |
| | | |
skipping to change at page 18, line 40 skipping to change at page 18, line 40
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 from the symmetric-cipher identifiers in the previously- selection from the symmetric-cipher identifiers in the previously-
received "Init1" message. The length "N_B_LEN" and the length of received "Init1" message. The length "N_B_LEN" and the length of
"Pub_B" are both determined by the negotiated TEP, as described in "Pub_B" are both 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
skipping to change at page 19, line 43 skipping to change at page 19, line 43
| 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 scheme must both encrypt the application data and provide encryption scheme both encrypts the application data and provides
a way to verify its integrity.) redundancy with which to verify its integrity.)
The "flags" byte has this structure: The "flags" byte 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 value "fres" is reserved; implementations MUST set these
six bits to zero when sending, and MUST ignore them when receiving. six bits to zero when sending, and MUST ignore them when receiving.
skipping to change at page 21, line 35 skipping to change at page 21, line 35
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
If future documents assign additional TEPs for use with tcpcrypt, Future documents assigning additional TEPs for use with tcpcrypt
they may specify different values for the lengths above. Note that mmight specify different values for the lengths above. Note that the
the minimum session ID length required by TCP-ENO, together with the minimum session ID length specified by TCP-ENO, together with the way
way tcpcrypt constructs session IDs, implies that "K_LEN" must have tcpcrypt constructs session IDs, implies that "K_LEN" MUST have
length at least 32 bytes. length at least 32 bytes.
Key-agreement schemes ECDHE-P256 and ECDHE-P521 employ the ECSVDP-DH Key-agreement schemes ECDHE-P256 and ECDHE-P521 employ the ECSVDP-DH
secret value derivation primitive defined in [IEEE-1363]. The named secret value derivation primitive defined in [IEEE-1363]. The named
curves are defined in [NIST-DSS]. When the public-key values "Pub_A" curves are defined in [NIST-DSS]. When the public-key values "Pub_A"
and "Pub_B" are transmitted as described in Section 4.1, they are and "Pub_B" are transmitted as described in Section 4.1, they are
encoded with the "Elliptic Curve Point to Octet String Conversion encoded with the "Elliptic Curve Point to Octet String Conversion
Primitive" described in Section E.2.3 of [IEEE-1363], and are Primitive" described in Section E.2.3 of [IEEE-1363], and are
prefixed by a two-byte length in big-endian format: prefixed by a two-byte length in big-endian format:
skipping to change at page 22, line 21 skipping to change at page 22, line 21
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 to the algorithm in [IEEE-1363] Section A.16.10. according to the algorithm in [IEEE-1363] Section A.16.10.
Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 use the Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 use the
functions X25519 and X448, respectively, to perform the Diffie-Helman functions X25519 and X448, respectively, to perform the Diffie-Helman
protocol as described in [RFC7748]. When using these ciphers, protocol as described in [RFC7748]. When using these ciphers,
public-key values "Pub_A" and "Pub_B" are transmitted directly with public-key values "Pub_A" and "Pub_B" are transmitted directly with
no length prefix: 32 bytes for Curve25519, and 56 bytes for Curve448. no length prefix: 32 bytes for Curve25519, and 56 bytes for Curve448.
Implementations are required to implement certain TEPs, according to Table 2 below specifies the requirement levels of the four TEPs
Table 2 below. Note that system administrators may configure which specified in this document. In particular, all implementations of
TEPs a host will negotiate, independent of these requirements. tcpcrypt MUST support TCPCRYPT_ECDHE_Curve25519. However, system
administrators MAY configure which TEPs a host will negotiate
independent of these implementation requirements.
+-------------+---------------------------+ +-------------+---------------------------+
| Requirement | TEP | | Requirement | TEP |
+-------------+---------------------------+ +-------------+---------------------------+
| MUST | TCPCRYPT_ECDHE_Curve25519 | | REQUIRED | TCPCRYPT_ECDHE_Curve25519 |
| SHOULD | TCPCRYPT_ECDHE_Curve448 | | RECOMMENDED | TCPCRYPT_ECDHE_Curve448 |
| MAY | TCPCRYPT_ECDHE_P256 | | OPTIONAL | TCPCRYPT_ECDHE_P256 |
| MAY | 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 "Init2" (see Section 3.3) to negotiate the use of AEAD and "Init2" (see Section 3.3) to negotiate the use of AEAD
algorithms; the values of these identifiers are given in Table 5 in algorithms; the values of these identifiers are given in Table 5 in
Section 7. The algorithms "AEAD_AES_128_GCM" and "AEAD_AES_256_GCM" Section 7. The algorithms "AEAD_AES_128_GCM" and "AEAD_AES_256_GCM"
are specified in [RFC5116]. The algorithm "AEAD_CHACHA20_POLY1305" are specified in [RFC5116]. The algorithm "AEAD_CHACHA20_POLY1305"
is specified in [RFC7539]. is specified in [RFC7539].
Implementations are required to support certain AEAD algorithms Implementations MUST support certain AEAD algorithms according to
according to Table 3 below. Note that system administrators may Table 3 below. Note that system administrators MAY configure which
configure which algorithms a host will negotiate, independent of algorithms a host will negotiate independent of these requirements.
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 specify aspects of encryption and data formats. "ae_nonce_len" to specify aspects of encryption and data formats.
These values depend on the negotiated AEAD algorithm, also according These values depend 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 | MUST | 16 bytes | 12 bytes | | AEAD_AES_128_GCM | REQUIRED | 16 bytes | 12 bytes |
| AEAD_AES_256_GCM | SHOULD | 32 bytes | 12 bytes | | AEAD_AES_256_GCM | RECOMMENDED | 32 bytes | 12 bytes |
| AEAD_CHACHA20_POLY1305 | SHOULD | 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 will need to be incorporated in IANA's "TCP encryption
protocol identifiers" registry under the "Transmission Control protocol identifiers" registry under the "Transmission Control
Protocol (TCP) Parameters" registry, as in Table 4 below. The Protocol (TCP) Parameters" registry, as in Table 4 below. The
skipping to change at page 24, line 18 skipping to change at page 24, line 18
| 0x0001 | AEAD_AES_128_GCM | [RFC-TBD] Section 6 | | 0x0001 | AEAD_AES_128_GCM | [RFC-TBD] Section 6 |
| 0x0002 | AEAD_AES_256_GCM | [RFC-TBD] Section 6 | | 0x0002 | AEAD_AES_256_GCM | [RFC-TBD] Section 6 |
| 0x0010 | AEAD_CHACHA20_POLY1305 | [RFC-TBD] Section 6 | | 0x0010 | AEAD_CHACHA20_POLY1305 | [RFC-TBD] 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 eavesdroppers particular, tcpcrypt does not protect against active network
unless applications authenticate the session ID. If it can be attackers unless applications authenticate the session ID. If it can
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., ECDH). A proof of this property for
an earlier version of the protocol has been published [tcpcrypt]. 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. Hence, the protocol is vulnerable to denial-of-service from
off-path attackers just as plain TCP is. Possible attacks include off-path attackers just as plain TCP is. Possible attacks include
desynchronizing the underlying TCP stream, injecting RST or FIN desynchronizing the underlying TCP stream, injecting RST or FIN
segments, and forging re-key bits. These attacks will cause a segments, and forging re-key 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 There is no "key confirmation" step in tcpcrypt. This is not needed
required because tcpcrypt's threat model includes the possibility of because tcpcrypt's threat model includes the possibility of a
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, all subsequent frames will be ignored due yields two different keys, failed integrity checks on every
to failed integrity checks, causing the application's connection to subsequent frame will cause the connection either to hang or to
hang. This is not a new threat because in plain TCP, an active abort. This is not a new threat as an active attacker can achieve
attacker could have modified sequence and acknowledgement numbers to the same results against a plain TCP connection by injecting RST
hang the connection anyway. 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 That is, once an implementation removes these keys from memory, a
compromise of the system will not provide any means to derive the compromise of the system will not provide any means to derive the
session secrets for past connections. All currently-specified key session secrets for past connections. All currently-specified key
agreement schemes involve ECDHE-based key agreement, meaning a new agreement schemes involve ECDHE-based key agreement, meaning a new
key-pair can be efficiently computed for each connection. If key-pair can be efficiently computed for each connection. If
implementations reuse these parameters, they MUST limit the lifetime implementations reuse these parameters, they MUST limit the lifetime
of the private parameters as far as practical in order to minimize of the private parameters as far as practical in order to minimize
the number of past connections that are vulnerable. Of course, the number of past connections that are vulnerable. Of course,
placing private keys in persistent storage introduces severe risks placing private keys in persistent storage introduces severe risks
that they may not be destroyed reliably and in a timely fashion, and that they will not be destroyed reliably and in a timely fashion, and
SHOULD be avoided at all costs. SHOULD be avoided at all costs.
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.
Recommendations on how to achieve this may be found in [RFC4086]. [RFC4086] provides recommendations on how to achieve this.
Most implementations will rely on a device's pseudo-random generator, Most implementations will rely on a device's pseudo-random generator,
seeded from hardware events and a seed carried over from the previous seeded from hardware events and a seed carried over from the previous
boot. Once a pseudo-random generator has been properly seeded, it boot. Once a pseudo-random generator has been properly seeded, it
can generate effectively arbitrary amounts of pseudo-random data. can generate effectively arbitrary amounts of pseudo-random data.
However, until a pseudo-random generator has been seeded with However, until a pseudo-random generator has been seeded with
sufficient entropy, not only will tcpcrypt be insecure, it will sufficient entropy, not only will tcpcrypt be insecure, it will
reveal information that further weakens the security of the pseudo- reveal information that further weakens the security of the pseudo-
random generator, potentially harming other applications. As random generator, potentially harming other applications. As
required by TCP-ENO, implementations MUST NOT send ENO options unless REQUIRED by TCP-ENO, implementations MUST NOT send ENO options unless
they have access to an adequate source of randomness. they have access to an adequate source of randomness.
8.1. Asymmetric Roles 8.1. Asymmetric Roles
Tcpcrypt transforms a shared pseudo-random key (PRK) into Tcpcrypt transforms a shared pseudo-random key (PRK) into
cryptographic 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.
skipping to change at page 26, line 28 skipping to change at page 26, line 28
from exiting, giving an attacker more time to compromise a host and from exiting, giving an attacker more time to compromise a host and
extract the sensitive data.) extract the sensitive data.)
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
tcpcrypt's verified keep-alive mechanism. tcpcrypt's verified keep-alive mechanism.
8.3. Mandatory Key-Agreement Schemes 8.3. Mandatory Key-Agreement Schemes
This document mandates that tcpcrypt implementations provide support This document mandates that tcpcrypt implementations provide support
for at least one key-agreement scheme: ECDHE using Curve25519. This for at least one key-agreement scheme: ECDHE using Curve25519. This
choice of a single mandatory algorithm is the result of a difficult choice of a single mandatory algorithm is the result of a difficult
tradeoff between cryptographic diversity and the ease and security of tradeoff between cryptographic diversity and the ease and security of
actual deployment. actual deployment.
skipping to change at page 27, line 10 skipping to change at page 27, line 10
using P-256, as this scheme is well-studied, widely implemented, and using P-256, as this scheme is well-studied, widely implemented, and
sufficiently different from the Curve25519-based scheme that it is sufficiently different from the Curve25519-based scheme that it is
unlikely they will both suffer from a single (non-quantum) unlikely they will both suffer from a single (non-quantum)
cryptanalytic advance. cryptanalytic advance.
However, implementing the Diffie-Hellman function using NIST elliptic However, implementing the Diffie-Hellman function using NIST elliptic
curves (including those specified for use with tcpcrypt, P-256 and curves (including those specified for use with tcpcrypt, P-256 and
P-521) appears to be very difficult to achieve without introducing P-521) appears to be very difficult to achieve without introducing
vulnerability to side-channel attacks [NIST-fail]. Although well- vulnerability to side-channel attacks [NIST-fail]. Although well-
trusted implementations are available as part of large cryptographic trusted implementations are available as part of large cryptographic
libraries, these may be difficult to extract for use in operating- libraries, these can be difficult to extract for use in operating-
system kernels where tcpcrypt is usually best implemented. In system kernels where tcpcrypt is usually best implemented. In
contrast, the characteristics of Curve25519 together with its recent contrast, the characteristics of Curve25519 together with its recent
popularity has led to many safe and efficient implementations, popularity has led to many safe and efficient implementations,
including some that fit naturally into the kernel environment. including some that fit naturally into the 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 (via SHOULD) support for key- Lastly, this document encourages support for key-agreement with
agreement with Curve448 as this scheme appears likely to admit safe Curve448, categorizing it as RECOMMENDED. Curve448 appears likely to
and efficient implementations; but it does not absolutely require admit safe and efficient implementations. However, support is not
such support, as well-proven implementations may not yet be REQUIRED because existing implementations might not yet be
available. 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 [I-D.ietf-tcpinc-tcpeno]
Section 9, this property can be subverted if middleboxes strip ENO Section 9, this property can be subverted if middleboxes strip ENO
options from non-SYN segments after allowing them in SYN segments; or options from non-SYN segments after allowing them in SYN segments; or
if the particular communication patterns of tcpcrypt offend the if the particular communication patterns of tcpcrypt offend the
policies of middleboxes doing deep-packet-inspection. policies of middleboxes doing deep-packet inspection.
Success, in addition to safety, means that hosts which implement Success, in addition to safety, means hosts that implement tcpcrypt
tcpcrypt actually enable encryption when they connect to each other. actually enable encryption when connecting to one another. This
This property depends on the network's treatment of the TCP-ENO property depends on the network's treatment of the TCP-ENO handshake,
handshake, and can be subverted if middleboxes merely strip unknown and can be subverted if middleboxes merely strip unknown TCP options
TCP options or if they terminate TCP connections and relay data back or if they terminate TCP connections and relay data back and forth
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. Acknowledgments
skipping to change at page 28, line 34 skipping to change at page 28, line 34
Dan Boneh and Michael Hamburg were co-authors of the draft that Dan Boneh and Michael Hamburg were co-authors of the draft that
became this document. became this document.
12. References 12. References
12.1. Normative References 12.1. Normative References
[I-D.ietf-tcpinc-tcpeno] [I-D.ietf-tcpinc-tcpeno]
Bittau, A., Giffin, D., Handley, M., Mazieres, D., and E. Bittau, A., Giffin, D., Handley, M., Mazieres, D., and E.
Smith, "TCP-ENO: Encryption Negotiation Option", draft- Smith, "TCP-ENO: Encryption Negotiation Option", draft-
ietf-tcpinc-tcpeno-13 (work in progress), November 2017. ietf-tcpinc-tcpeno-18 (work in progress), November 2017.
[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 Std 1363-2000)", 2000.
[NIST-DSS] [NIST-DSS]
NIST, "FIPS PUB 186-4: Digital Signature Standard (DSS)", NIST, "FIPS PUB 186-4: Digital Signature Standard (DSS)",
2013. 2013.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981, RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>. <https://www.rfc-editor.org/info/rfc793>.
[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, <https://www.rfc- DOI 10.17487/RFC2018, October 1996,
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,
DOI 10.17487/RFC2104, February 1997, <https://www.rfc- DOI 10.17487/RFC2104, February 1997,
editor.org/info/rfc2104>. <https://www.rfc-editor.org/info/rfc2104>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008, Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>. <https://www.rfc-editor.org/info/rfc5116>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand [RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869, Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010, <https://www.rfc- DOI 10.17487/RFC5869, May 2010,
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 [RFC7539] Nir, Y. and A. Langley, "ChaCha20 and Poly1305 for IETF
Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015, Protocols", RFC 7539, DOI 10.17487/RFC7539, May 2015,
<https://www.rfc-editor.org/info/rfc7539>. <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
skipping to change at page 30, line 7 skipping to change at page 30, line 7
12.2. Informative References 12.2. Informative References
[I-D.ietf-tcpinc-api] [I-D.ietf-tcpinc-api]
Bittau, A., Boneh, D., Giffin, D., Handley, M., Mazieres, Bittau, A., Boneh, D., Giffin, D., Handley, M., Mazieres,
D., and E. Smith, "Interface Extensions for TCP-ENO and D., and E. Smith, "Interface Extensions for TCP-ENO and
tcpcrypt", draft-ietf-tcpinc-api-05 (work in progress), tcpcrypt", draft-ietf-tcpinc-api-05 (work in progress),
September 2017. September 2017.
[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, <https://cr.yp.to/newelliptic/nistecc- standards", 2016,
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, <https://www.rfc- DOI 10.17487/RFC1122, October 1989,
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, <https://www.rfc- DOI 10.17487/RFC4086, June 2005,
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 D. Bittau, A., Hamburg, M., Handley, M., Mazieres, D., and D.
Boneh, "The case for ubiquitous transport-level Boneh, "The case for ubiquitous transport-level
encryption", USENIX Security , 2010. encryption", USENIX Security , 2010.
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