< draft-ietf-tcpinc-tcpcrypt-10.txt		draft-ietf-tcpinc-tcpcrypt-15.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: May 21, 2018 Stanford University		Expires: June 14, 2019 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 17, 2017		December 11, 2018
	Cryptographic protection of TCP Streams (tcpcrypt)		Cryptographic protection of TCP Streams (tcpcrypt)
	draft-ietf-tcpinc-tcpcrypt-10		draft-ietf-tcpinc-tcpcrypt-15
	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 May 21, 2018.		This Internet-Draft will expire on June 14, 2019.
	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.
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	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
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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 . . . . . . . . . . . . . . . . . . . . . . . . 14		3.8. Re-Keying . . . . . . . . . . . . . . . . . . . . . . . . 15
	3.9. Keep-Alive . . . . . . . . . . . . . . . . . . . . . . . 15		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 . . . . . . . . . . . . . . . . . . . . . . 18		4.2.1. Plaintext . . . . . . . . . . . . . . . . . . . . . . 19
	4.2.2. Associated Data . . . . . . . . . . . . . . . . . . . 19		4.2.2. Associated Data . . . . . . . . . . . . . . . . . . . 20
	4.2.3. Frame ID . . . . . . . . . . . . . . . . . . . . . . 19		4.2.3. Frame ID . . . . . . . . . . . . . . . . . . . . . . 20
	4.3. Constant Values . . . . . . . . . . . . . . . . . . . . . 20		4.3. Constant Values . . . . . . . . . . . . . . . . . . . . . 20
	5. Key-Agreement Schemes . . . . . . . . . . . . . . . . . . . . 20		5. Key-Agreement Schemes . . . . . . . . . . . . . . . . . . . . 21
	6. AEAD Algorithms . . . . . . . . . . . . . . . . . . . . . . . 21		6. AEAD Algorithms . . . . . . . . . . . . . . . . . . . . . . . 22
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 23		8. Security Considerations . . . . . . . . . . . . . . . . . . . 24
	8.1. Asymmetric Roles . . . . . . . . . . . . . . . . . . . . 24		8.1. Asymmetric Roles . . . . . . . . . . . . . . . . . . . . 25
	8.2. Verified Liveness . . . . . . . . . . . . . . . . . . . . 25		8.2. Verified Liveness . . . . . . . . . . . . . . . . . . . . 26
	8.3. Mandatory Key-Agreement Schemes . . . . . . . . . . . . . 25		8.3. Mandatory Key-Agreement Schemes . . . . . . . . . . . . . 26
	9. Experiments . . . . . . . . . . . . . . . . . . . . . . . . . 26		9. Experiments . . . . . . . . . . . . . . . . . . . . . . . . . 27
	10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27		10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
	11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 27		11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28
	12. References . . . . . . . . . . . . . . . . . . . . . . . . . 27		12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
	12.1. Normative References . . . . . . . . . . . . . . . . . . 27		12.1. Normative References . . . . . . . . . . . . . . . . . . 28
	12.2. Informative References . . . . . . . . . . . . . . . . . 28		12.2. Informative References . . . . . . . . . . . . . . . . . 29
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
	1. Requirements Language		1. Requirements Language
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in BCP		"OPTIONAL" in this document are to be interpreted as described in BCP
	14 [RFC2119] [RFC8174] when, and only when, they appear in all		14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	2. Introduction		2. Introduction
	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
	in this document are the Extract and Expand functions of HKDF		in this document are the Extract and Expand functions of HKDF
	[RFC5869], which is built on HMAC [RFC2104]. These are defined as		[RFC5869], which is built on HMAC [RFC2104]. These are defined as
	follows in terms of the function "HMAC-Hash(key, value)" for a		follows in terms of the function "HMAC-Hash(key, value)" for a
	negotiated "Hash" function such as SHA-256; the symbol | denotes		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
	skipping to change at page 5, line 14 ¶		skipping to change at page 5, line 14 ¶
	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, PK_A }		A -> B: Init1 = { INIT1_MAGIC, sym_cipher_list, N_A, Pub_A }
	B -> A: Init2 = { INIT2_MAGIC, sym_cipher, N_B, PK_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 symmetric ciphers (AEAD algorithms)		o "sym_cipher_list": a list of identifiers of symmetric ciphers
	acceptable to host A. These are specified in Table 5 in		(AEAD algorithms) acceptable to host A. These are specified 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 "PK_A", "PK_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, "PK_B".		host B's public key, "Pub_B".
	The two sides then compute a pseudo-random key ("PRK"), from which		The two sides then compute a pseudo-random key "PRK", from which all
	all session keys 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_keylen + 12)		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_keylen + 12)		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 a resumed session, as described more thoroughly below in		In a resumed session, as described more thoroughly below in
	Section 3.5, each host uses the keys in the same way as it did in the		Section 3.5, each host uses the keys in the same way as it did in the
	original session, regardless of its role in the current session: for		original session, regardless of its role in the current session: for
	example, if a host played role "A" in the first session, it will use		example, if a host played role "A" in the first session, it will use
	keys "k_ab[j]" to encrypt in each derived session.		keys "k_ab[j]" to encrypt in each derived session.
	The value "ae_keylen" depends on the authenticated-encryption		The values "ae_key_len" and "ae_nonce_len" depend on the
	algorithm selected, and is given under "Key Length" in Table 5 in		authenticated-encryption algorithm selected, and are given in Table 3
	Section 7. The algorithm uses the first "ae_keylen" bytes of each		in Section 6. The algorithm uses the first "ae_key_len" bytes of
	traffic key as an authenticated-encryption key, and the following 12		each traffic key as an authenticated-encryption key, and the
	bytes as a "nonce randomizer".		following "ae_nonce_len" bytes as a "nonce randomizer".
	After host B sends "Init2" or host A receives it, that host may		Implementations SHOULD provide an interface allowing the user to
			specify, for a particular connection, the set of AEAD algorithms to
			advertize in "sym_cipher_list" (when playing role "A") and also the
			order of preference to use when selecting an algorithm from those
			offered (when playing role "B"). A companion document
			[I-D.ietf-tcpinc-api] describes recommended interfaces for this
			purpose.
			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. The value 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.
			An attacker who can force either side of a connection to reuse a
			session secret with the same nonce will completely break the security
			of tcpcrypt. Reuse of session secrets is possible in the event of
			virtual machine cloning or reuse of system-level hibernation state.
			Implementations SHOULD provide an API through which to set the
			resumption nonce length, and MUST default to eight bytes if they
			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 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 the 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
			and "v = 1", but the suboption data is less than 9 bytes in length,
			it MUST behave as if the same TEP had been sent with "v = 0". That
			is, the suboption MUST be interpreted as an offer to negotiate fresh
			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 "ss[i]" to compute "mk[0]", implementations SHOULD		After using the session secret "ss[i]" to compute "mk[0]",
	compute and cache "ss[i+1]" for possible use by a later session, then		implementations SHOULD compute and cache "ss[i+1]" for possible use
	erase "ss[i]" from memory. Hosts SHOULD retain "ss[i+1]" until it is		by a later session, then erase "ss[i]" from memory. Hosts MAY retain
	used or the memory needs to be reclaimed. Hosts SHOULD NOT write a		"ss[i+1]" until it is used or the memory needs to be reclaimed.
	cached "ss[i+1]" value to non-volatile storage.		Hosts 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 pre-session		negotiate resumption with the same host and for the same original
	key "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 a given pre-session key "ss[0]" is only		choose to implement session resumption such that all session secrets
	used for either passive or active opens at the same host, not both.		derived from a given "ss[0]" are used for either passive or active
			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 pre-session key "ss[0]", or with keys		sessions derived from the same original session secret "ss[0]", or
	"k_ba[j]". Thus, which keys a host uses to send segments is not		with keys "k_ba[j]". Thus, which keys a host uses to send segments
	affected by the role it plays in the current connection: it depends		is not affected by the role it plays in the current connection: it
	only on whether the host played the "A" or "B" role in the initial		depends only on whether the host played the "A" or "B" role in the
	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
	that during the connection no session secrets will be cached and all		specify two policies for the duration of the connection: 1) that
	resumption requests will be ignored in favor of fresh key exchange.		resumption requests will be ignored, and thus fresh key exchange will
	And for an established connection, an application must be able to		be necessary; and 2) that no session secrets will be cached. (These
	cause any cache state that was used in or resulted from establishing		policies can be specified independently or as a unit.) And for an
	the connection to be flushed. A companion document		established connection, an application MUST have a means to cause any
	[I-D.ietf-tcpinc-api] describes recommended interfaces for this		cache state that was used in or resulted from establishing the
	purpose.		connection to be flushed. A companion document [I-D.ietf-tcpinc-api]
			describes recommended interfaces for this purpose.
	3.6. Data Encryption and Authentication		3.6. Data Encryption and Authentication
	Following key exchange (or its omission via session resumption), all		Following key exchange (or its omission via session resumption), all
	further communication in a tcpcrypt-enabled connection is carried out		further communication in a tcpcrypt-enabled connection is carried out
	within delimited _encryption frames_ that are encrypted and		within delimited _encryption frames_ that are encrypted and
	authenticated using the agreed keys.		authenticated using the agreed 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, and 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.		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
			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 an "offset" field		frame, but not explicitly transmitted. It contains a 64-bit "offset"
	whose integer value is the zero-indexed byte offset of the beginning		field whose integer value is the zero-indexed byte offset of the
	of the current encryption frame in the underlying TCP datastream.		beginning of the current encryption frame in the underlying TCP
	(That is, the offset in the framing stream, not the plaintext		datastream. (That is, the offset in the framing stream, not the
	application stream.) Because it is strictly necessary for the		plaintext application stream.) The offset is then left-padded with
	security of the AEAD algorithms specified in this document, an		zero-valued bytes to form a value of length "ae_nonce_len". Because
	implementation MUST NOT ever transmit distinct frames with the same		it is strictly necessary for the security of the AEAD algorithms
	frame ID value under the same encryption key. In particular, a		specified in this document, an implementation MUST NOT ever transmit
	retransmitted TCP segment MUST contain the same payload bytes for the		distinct frames with the same frame ID value under the same
	same TCP sequence numbers, and a host MUST NOT transmit more than		encryption key. In particular, a retransmitted TCP segment MUST
	2^64 bytes in the underlying TCP datastream (which would cause the		contain the same payload bytes for the same TCP sequence numbers, and
	"offset" field to wrap) before re-keying.		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-
			keying as decribed in Section 3.8.
	With reference to the "AEAD Interface" described in Section 2 of		With reference to the "AEAD Interface" described in Section 2 of
	[RFC5116], tcpcrypt invokes the AEAD algorithm with values taken from		[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		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.		host's role as described in Section 3.3.
	First, the traffic key is divided into two parts:		First, the traffic key is divided into two parts:
	byte 0 ae_keylen ae_keylen + 11		ae_key_len + ae_nonce_len - 1
	| | |		|
	v v v		byte 0 ae_key_len |
	+----+----+--...--+----+----+----+--...--+----+		| | |
	| K | NR |		v v v
	+----+----+--...--+----+----+----+--...--+----+		+----+----+--...--+----+----+----+--...--+----+
			| K | NR |
			+----+----+--...--+----+----+----+--...--+----+
	\_____________________________________________/		\_____________________________________________/
	traffic key		traffic key
	The first "ae_keylen" 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 12 bytes provide a "nonce randomizer" value		"K", while the remaining "ae_nonce_len" bytes provide a "nonce
	"NR". The frame ID is then combined via bitwise exclusive-or with		randomizer" value "NR". The frame ID is then combined via bitwise
	the nonce randomizer to yield "N", the AEAD nonce for the frame:		exclusive-or with the nonce randomizer 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 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 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.		implementation MAY instead drop these segments (and "renege" if they
			have been SACKed, according to [RFC2018] Section 8).
	3.7. TCP Header Protection		3.7. TCP Header Protection
	The "ciphertext" field of the encryption frame contains protected		The "ciphertext" field of the encryption frame contains protected
	versions of certain TCP header values.		versions of certain TCP header values.
	When the "URGp" bit is set, the "urgent" value indicates an offset		When the "URGp" bit is set, the "urgent" value indicates an offset
	from the current frame's beginning offset; the sum of these offsets		from the current frame's beginning offset; the sum of these offsets
	gives the index of the last byte of urgent data in the application		gives the index of the last byte of urgent data in the application
	datastream.		datastream.
	skipping to change at page 14, line 30 ¶		skipping to change at page 15, line 20 ¶
	tcpcrypt means setting FIN on the segment containing the last byte of		tcpcrypt means setting FIN on the segment containing the last byte of
	the last frame. However, a receiver MUST report the end-of-file		the last frame. However, a receiver MUST report the end-of-file
	condition to the connection's local user when and only when it		condition to the connection's local user when and only when it
	receives a frame with the "FINp" bit set. If a host receives a		receives a frame with the "FINp" bit set. If a host receives a
	segment with the TCP FIN flag set but the received datastream		segment with the TCP FIN flag set but the received datastream
	including this segment does not contain a frame with "FINp" set, the		including this segment does not contain a frame with "FINp" set, the
	host SHOULD abort the connection and raise an error condition		host SHOULD abort the connection and raise an error condition
	distinct from the end-of-file condition. But if there are		distinct from the end-of-file condition. But if there are
	unacknowledged segments whose retransmission could potentially result		unacknowledged segments whose retransmission could potentially result
	in a valid frame, the host MAY instead drop the segment with the TCP		in a valid frame, the host MAY instead drop the segment with the TCP
	FIN flag set.		FIN flag set (and "renege" if it has been SACKed, according to
			[RFC2018] Section 8).
	3.8. Re-Keying		3.8. Re-Keying
	Re-keying allows hosts to wipe from memory keys that could decrypt		Re-keying allows hosts to wipe from memory keys that could decrypt
	previously transmitted segments. It also allows the use of AEAD		previously transmitted segments. It also allows the use of AEAD
	ciphers that can securely encrypt only a bounded number of messages		ciphers that can securely encrypt only a bounded number of messages
	under a given key.		under a given key.
	As described above in Section 3.3, a master key "mk[j]" is used to		As described above in Section 3.3, a master key "mk[j]" is used to
	generate two encryption keys "k_ab[j]" and "k_ba[j]". We refer to		generate two encryption keys "k_ab[j]" and "k_ba[j]". We refer to
	skipping to change at page 15, line 4 ¶		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 16, line 36 ¶		skipping to change at page 17, line 27 ¶
	8		8
	+--------+-----+----+-----+----+---...---+-----+-----+		+--------+-----+----+-----+----+---...---+-----+-----+
	|nciphers|sym_ |sym_ | |sym_ |		|nciphers|sym_ |sym_ | |sym_ |
	| = K |cipher[0] |cipher[1] | |cipher[K-1]|		| = K |cipher[0] |cipher[1] | |cipher[K-1]|
	+--------+-----+----+-----+----+---...---+-----+-----+		+--------+-----+----+-----+----+---...---+-----+-----+
	2*K + 9 2*K + 9 + N_A_LEN		2*K + 9 2*K + 9 + N_A_LEN
	| |		| |
	v v		v v
	+-------+---...---+-------+-------+---...---+-------+		+-------+---...---+-------+-------+---...---+-------+
	| N_A | PK_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" and the length of "PK_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 "PK_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 "PK_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 |
	| = M | |		| = M | |
	+-------+-------+-------+-------+-------+-------+		+-------+-------+-------+-------+-------+-------+
	10 10 + N_B_LEN		10 10 + N_B_LEN
	| |		| |
	v v		v v
	+-------+---...---+-------+-------+---...---+-------+		+-------+---...---+-------+-------+---...---+-------+
	| N_B | PK_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 from the symmetric-cipher identifiers in the previously-		selection from the symmetric-cipher identifiers in the previously-
	received "Init1" message. The length "N_B_LEN" and the length of		received "Init1" message. The length "N_B_LEN" and the length of
	"PK_B" are both determined by the negotiated 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 "PK_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 "PK_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 |
	+-------+-------+-------+-------+---...---+-------+		+-------+-------+-------+-------+---...---+-------+
	skipping to change at page 18, line 44 ¶		skipping to change at page 19, line 36 ¶
	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 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 19, line 43 ¶		skipping to change at page 20, line 34 ¶
	+-------+-------+-------+		+-------+-------+-------+
	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		byte 0 ae_nonce_len - 8 ae_nonce_len - 1
	+------+------+------+------+		| | |
	0 | FRAME_ID_MAGIC |		v v v
	+------+------+------+------+		+-----+--...--+-----+-----+--...--+-----+
	4 | |		| 0 | | 0 | offset |
	+ offset +		+-----+--...--+-----+-----+--...--+-----+
	8 | |
	+------+------+------+------+
	The 4-byte magic constant is defined in Section 4.3. The 8-byte		The 8-byte "offset" field contains an integer in big-endian format.
	"offset" field contains an integer in big-endian format. Its value		Its value is specified in Section 3.6. Zero-valued bytes are
	is specified in Section 3.6.		prepended to the "offset" field to form a structure of length
			"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 |
	| 0x44415441 | FRAME_ID_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
	keys:		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 [ieee1363]. The named		secret value derivation primitive defined in [IEEE-1363]. The named
	curves are defined in [nist-dss]. When the public-key values "PK_A"		curves are defined in [NIST-DSS]. When the public-key values "Pub_A"
	and "PK_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 [ieee1363], and are prefixed		Primitive" described in Section E.2.3 of [IEEE-1363], and are
	by a two-byte length in big-endian format:		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 to the algorithm in [ieee1363] 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 perform the
	functions X25519 and X448, respectively, to perform the Diffie-Helman		Diffie-Helman protocol using the functions X25519 and X448,
	protocol as described in [RFC7748]. When using these ciphers,		respectively. Implementations SHOULD compute these functions using
	public-key values "PK_A" and "PK_B" are transmitted directly with no		the algorithms described in [RFC7748]. When they do so,
	length prefix: 32 bytes for Curve25519, and 56 bytes for Curve448.		implementations MUST check whether the computed Diffie-Hellman shared
			secret is the all-zero value and abort if so, as described in
			Section 6 of [RFC7748]. Alternative implementations of these
			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].
	Implementations are required to implement certain TEPs, according to		For these schemes, public-key values "Pub_A" and "Pub_B" are
	Table 2 below. Note that system administrators may configure which		transmitted directly with no length prefix: 32 bytes for ECDHE-
	TEPs a host will negotiate, independent of these requirements.		Curve25519, and 56 bytes for ECDHE-Curve448.
			Table 2 below specifies the requirement levels of the four TEPs
			specified in this document. In particular, all implementations of
			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
	Specifiers and key-lengths for AEAD algorithms are given in Table 5		This document uses "sym-cipher" identifiers in the messages "Init1"
	in Section 7. The algorithms "AEAD_AES_128_GCM" and		and "Init2" (see Section 3.3) to negotiate the use of AEAD
	"AEAD_AES_256_GCM" are specified in [RFC5116]. The algorithm		algorithms; the values of these identifiers are given in Table 5 in
	"AEAD_CHACHA20_POLY1305" is specified in [RFC7539].		Section 7. The algorithms "AEAD_AES_128_GCM" and "AEAD_AES_256_GCM"
			are specified in [RFC5116]. The algorithm "AEAD_CHACHA20_POLY1305"
			is specified in [RFC7539].
	Implementations are required to support certain algorithms according		Implementations MUST support certain AEAD algorithms according to
	to Table 3 below. Note that system administrators may configure		Table 3 below. Note that system administrators MAY configure which
	which algorithms a host will negotiate, independent of these		algorithms a host will negotiate independent of these requirements.
	requirements.
	+-------------+------------------------+		Lastly, this document uses the lengths "ae_key_len" and
	| Requirement | AEAD Algorithm |		"ae_nonce_len" to specify aspects of encryption and data formats.
	+-------------+------------------------+		These values depend on the negotiated AEAD algorithm, also according
	| MUST | AEAD_AES_128_GCM |		to the table below.
	| SHOULD | AEAD_AES_256_GCM |
	| SHOULD | AEAD_CHACHA20_POLY1305 |
	+-------------+------------------------+
	Table 3: Requirements for implementation of AEAD algorithms		+------------------------+-------------+------------+--------------+
			| AEAD Algorithm | Requirement | ae_key_len | ae_nonce_len |
			+------------------------+-------------+------------+--------------+
			| AEAD_AES_128_GCM | REQUIRED | 16 bytes | 12 bytes |
			| AEAD_AES_256_GCM | RECOMMENDED | 32 bytes | 12 bytes |
			| AEAD_CHACHA20_POLY1305 | RECOMMENDED | 32 bytes | 12 bytes |
			+------------------------+-------------+------------+--------------+
			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
	various key-agreement schemes used by these tcpcrypt variants are		various key-agreement schemes used by these tcpcrypt variants are
	defined in Section 5.		defined in Section 5.
	skipping to change at page 22, line 35 ¶		skipping to change at page 23, line 46 ¶
	| Value | Meaning | Reference |		| Value | Meaning | Reference |
	+-------+---------------------------+-----------+		+-------+---------------------------+-----------+
	| 0x21 | TCPCRYPT_ECDHE_P256 | [RFC-TBD] |		| 0x21 | TCPCRYPT_ECDHE_P256 | [RFC-TBD] |
	| 0x22 | TCPCRYPT_ECDHE_P521 | [RFC-TBD] |		| 0x22 | TCPCRYPT_ECDHE_P521 | [RFC-TBD] |
	| 0x23 | TCPCRYPT_ECDHE_Curve25519 | [RFC-TBD] |		| 0x23 | TCPCRYPT_ECDHE_Curve25519 | [RFC-TBD] |
	| 0x24 | TCPCRYPT_ECDHE_Curve448 | [RFC-TBD] |		| 0x24 | TCPCRYPT_ECDHE_Curve448 | [RFC-TBD] |
	+-------+---------------------------+-----------+		+-------+---------------------------+-----------+
	Table 4: TEP identifiers for use with tcpcrypt		Table 4: TEP identifiers for use with tcpcrypt
	In Section 4.1, this document defines "sym_cipher" specifiers in the		In Section 6, this document defines the use of several AEAD
			algorithms for encrypting application data. To name these
			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 inclusive, for which IANA is to maintain a new
	"tcpcrypt AEAD Algorithm" registry under the "Transmission Control		"tcpcrypt AEAD Algorithm" 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. The AEAD algorithms named there		registry are given in Table 5 below. Future assignments are to be
	are defined in Section 6. Future assignments are to be made upon		made upon satisfying either of two policies defined in [RFC8126]:
	satisfying either of two policies defined in [RFC8126]: "IETF Review"		"IETF Review" or (for non-IETF stream specifications) "Expert Review
	or (for non-IETF stream specifications) "Expert Review with RFC		with RFC Required." IANA will furthermore provide early allocation
	Required." IANA will furthermore provide early allocation [RFC7120]		[RFC7120] to facilitate testing before RFCs are finalized.
	to facilitate testing before RFCs are finalized.
	+--------+------------------------+------------+-----------+		+--------+------------------------+---------------------+
	| Value | AEAD Algorithm | Key Length | Reference |		| Value | AEAD Algorithm | Reference |
	+--------+------------------------+------------+-----------+		+--------+------------------------+---------------------+
	| 0x0001 | AEAD_AES_128_GCM | 16 bytes | [RFC-TBD] |		| 0x0001 | AEAD_AES_128_GCM | [RFC-TBD] Section 6 |
	| 0x0002 | AEAD_AES_256_GCM | 32 bytes | [RFC-TBD] |		| 0x0002 | AEAD_AES_256_GCM | [RFC-TBD] Section 6 |
	| 0x0010 | AEAD_CHACHA20_POLY1305 | 32 bytes | [RFC-TBD] |		| 0x0010 | AEAD_CHACHA20_POLY1305 | [RFC-TBD] Section 6 |
	+--------+------------------------+------------+-----------+		+--------+------------------------+---------------------+
	Table 5: Authenticated-encryption algorithms corresponding to		Table 5: Authenticated-encryption algorithms for use with tcpcrypt
	sym_cipher specifiers in Init1 and Init2 messages.
	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 gain 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 keys 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 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.
	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 session 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
	skipping to change at page 25, line 28 ¶		skipping to change at page 26, line 30 ¶
	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.
	The IETF's appraisal of best current practice on this matter		The IETF's appraisal of best current practice on this matter
	[RFC7696] says, "Ideally, two independent sets of mandatory-to-		[RFC7696] says, "Ideally, two independent sets of mandatory-to-
	implement algorithms will be specified, allowing for a primary suite		implement algorithms will be specified, allowing for a primary suite
	and a secondary suite. This approach ensures that the secondary		and a secondary suite. This approach ensures that the secondary
	suite is widely deployed if a flaw is found in the primary one."		suite is widely deployed if a flaw is found in the primary one."
	To meet that ideal, it might appear natural to also mandate ECDHE		To meet that ideal, it might appear natural to also mandate ECDHE
	using P-256, as this scheme is well-studied, widely implemented, and		using P-256. However, implementing the Diffie-Hellman function using
	sufficiently different from the Curve25519-based scheme that it is		NIST elliptic curves (including those specified for use with
	unlikely they will both suffer from a single (non-quantum)		tcpcrypt, P-256 and P-521) appears to be very difficult to achieve
	cryptanalytic advance.		without introducing vulnerability to side-channel attacks
			[NIST-fail]. Although well-trusted implementations are available as
	However, implementing the Diffie-Hellman function using NIST elliptic		part of large cryptographic libraries, these can be difficult to
	curves (including those specified for use with tcpcrypt, P-256 and		extract for use in operating-system kernels where tcpcrypt is usually
	P-521) appears to be very difficult to achieve without introducing		best implemented. In contrast, the characteristics of Curve25519
	vulnerability to side-channel attacks [nist-ecc]. Although well-		together with its recent popularity has led to many safe and
	trusted implementations are available as part of large cryptographic		efficient implementations, including some that fit naturally into the
	libraries, these may be difficult to extract for use in operating-		kernel environment.
	system kernels where tcpcrypt is usually best implemented. In
	contrast, the characteristics of Curve25519 together with its recent
	popularity has led to many safe and efficient implementations,
	including some that fit naturally into the kernel environment.
	[RFC7696] insists that, "The selected algorithms need to be resistant		[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 27, line 34 ¶		skipping to change at page 28, line 33 ¶
	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-19 (work in progress), June 2018.
	[ieee1363]		[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
			Selective Acknowledgment Options", RFC 2018,
			DOI 10.17487/RFC2018, October 1996,
			<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 28, line 45 ¶		skipping to change at page 29, line 50 ¶
	[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		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-06 (work in progress),
	September 2017.		June 2018.
	[nist-ecc]		[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.
End of changes. 127 change blocks.
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