< draft-ietf-curdle-gss-keyex-sha2-09.txt		draft-ietf-curdle-gss-keyex-sha2-10.txt >
	Internet Engineering Task Force S. Sorce		Internet Engineering Task Force S. Sorce
	Internet-Draft H. Kario		Internet-Draft H. Kario
	Updates: 4462 (if approved) Red Hat, Inc.		Updates: 4462 (if approved) Red Hat, Inc.
	Intended status: Standards Track Jun 11, 2019		Intended status: Standards Track Jul 22, 2019
	Expires: December 13, 2019		Expires: January 23, 2020
	GSS-API Key Exchange with SHA2		GSS-API Key Exchange with SHA2
	draft-ietf-curdle-gss-keyex-sha2-09		draft-ietf-curdle-gss-keyex-sha2-10
	Abstract		Abstract
	This document specifies additions and amendments to RFC4462. It		This document specifies additions and amendments to RFC4462. It
	defines a new key exchange method that uses SHA-2 for integrity and		defines a new key exchange method that uses SHA-2 for integrity and
	deprecates weak DH groups. The purpose of this specification is to		deprecates weak DH groups. The purpose of this specification is to
	modernize the cryptographic primitives used by GSS Key Exchanges.		modernize the cryptographic primitives used by GSS Key Exchanges.
	Status of This Memo		Status of This Memo
	skipping to change at page 1, line 34 ¶		skipping to change at page 1, line 34 ¶
	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 https://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 December 13, 2019.		This Internet-Draft will expire on January 23, 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 27 ¶		skipping to change at page 2, line 27 ¶
	8.1. New Finite Field DH mechanisms . . . . . . . . . . . . . 10		8.1. New Finite Field DH mechanisms . . . . . . . . . . . . . 10
	8.2. New Elliptic Curve DH mechanisms . . . . . . . . . . . . 10		8.2. New Elliptic Curve DH mechanisms . . . . . . . . . . . . 10
	8.3. GSSAPI Delegation . . . . . . . . . . . . . . . . . . . . 10		8.3. GSSAPI Delegation . . . . . . . . . . . . . . . . . . . . 10
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
	9.1. Normative References . . . . . . . . . . . . . . . . . . 11		9.1. Normative References . . . . . . . . . . . . . . . . . . 11
	9.2. Informative References . . . . . . . . . . . . . . . . . 12		9.2. Informative References . . . . . . . . . . . . . . . . . 12
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
	1. Introduction		1. Introduction
	SSH GSS-API Methods [RFC4462] allows the use of GSSAPI for		SSH GSS-API Methods [RFC4462] allows the use of GSSAPI [RFC2743] for
	authentication and key exchange in SSH. It defines three exchange		authentication and key exchange in SSH. It defines three exchange
	methods all based on DH groups and SHA-1. This document updates		methods all based on DH groups and SHA-1. This document updates
	RFC4462 with new methods intended to support environments that desire		RFC4462 with new methods intended to support environments that desire
	to use the SHA-2 cryptographic hash functions.		to use the SHA-2 cryptographic hash functions.
	2. Rationale		2. Rationale
	Due to security concerns with SHA-1 [RFC6194] and with MODP groups		Due to security concerns with SHA-1 [RFC6194] and with MODP groups
	with less than 2048 bits [NIST-SP-800-131Ar1] we propose the use of		with less than 2048 bits [NIST-SP-800-131Ar1] we propose the use of
	the SHA-2 [RFC6234] based hashes with DH group14, group15, group16,		hashes based on SHA-2 [RFC6234] with DH group14, group15, group16,
	group17 and group18 [RFC3526]. Additionally we add support for key		group17 and group18 [RFC3526]. Additionally we add support for key
	exchange based on Elliptic Curve Diffie Hellman with the NIST P-256,		exchange based on Elliptic Curve Diffie Hellman with the NIST P-256,
	P-384 and P-521 as well as the X25519 and X448 curves. Following the		P-384 and P-521 [SEC2v2] as well as the X25519 and X448 [RFC7748]
	practice of [RFC8268] only SHA-256 and SHA-512 hashes are used for DH		curves. Following the practice of [RFC8268] only SHA-256 and SHA-512
	groups. For NIST curves the same curve-to-hashing algorithm pairing		hashes are used for DH groups. For NIST curves the same curve-to-
	used in [RFC5656] is adopted for consistency.		hashing algorithm pairing used in [RFC5656] is adopted for
			consistency.
	3. Document Conventions		3. Document Conventions
	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 [RFC2119] RFC8174 [RFC8174] when, and only when, they		14 RFC2119 [RFC2119] RFC8174 [RFC8174] when, and only when, they
	appear in all capitals, as shown here.		appear in all capitals, as shown here.
	4. New Diffie-Hellman Key Exchange methods		4. New Diffie-Hellman Key Exchange methods
	This document adopts the same naming convention defined in [RFC4462]		This document adopts the same naming convention defined in [RFC4462]
	to define families of methods that cover any GSS-API mechanism used		to define families of methods that cover any GSS-API mechanism used
	with a specific Diffie-Hellman group and SHA-2 Hash combination.		with a specific Diffie-Hellman group and SHA-2 Hash combination.
	The following new key exchange algorithms are defined:
	+--------------------------+--------------------------------+		+--------------------------+--------------------------------+
	| Key Exchange Method Name | Implementation Recommendations |		| Key Exchange Method Name | Implementation Recommendations |
	+--------------------------+--------------------------------+		+--------------------------+--------------------------------+
	| gss-group14-sha256-* | SHOULD/RECOMMENDED |		| gss-group14-sha256-* | SHOULD/RECOMMENDED |
	| gss-group15-sha512-* | MAY/OPTIONAL |		| gss-group15-sha512-* | MAY/OPTIONAL |
	| gss-group16-sha512-* | SHOULD/RECOMMENDED |		| gss-group16-sha512-* | SHOULD/RECOMMENDED |
	| gss-group17-sha512-* | MAY/OPTIONAL |		| gss-group17-sha512-* | MAY/OPTIONAL |
	| gss-group18-sha512-* | MAY/OPTIONAL |		| gss-group18-sha512-* | MAY/OPTIONAL |
	+--------------------------+--------------------------------+		+--------------------------+--------------------------------+
	Each key exchange method is implicitly registered by this document.		Table 1: New key exchange algorithms
	The IESG is considered to be the owner of all these key exchange
	methods; this does NOT imply that the IESG is considered to be the
	owner of the underlying GSS-API mechanism.
	Each method in any family of methods specifies GSS-API-authenticated		Each key exchange method prefix is registered by this document. The
	Diffie-Hellman key exchanges as described in Section 2.1 of		IESG is the change controller of all these key exchange methods; this
	[RFC4462]. The method name for each method is the concatenation of		does NOT imply that the IESG is considered to be in control of the
	the family name prefix with the Base64 encoding of the MD5 hash		corresponding GSS-API mechanism.
	[RFC1321] of the ASN.1 DER encoding [ISO-IEC-8825-1] of the
	underlying GSS-API mechanism's OID. Base64 encoding is described in
	Section 6.8 of [RFC2045].
	Family method refences		Each method in any family of methods (Table 2) specifies GSS-API-
			authenticated Diffie-Hellman key exchanges as described in
			Section 2.1 of [RFC4462]. The method name for each method (Table 1)
			is the concatenation of the family name prefix with the Base64
			encoding of the MD5 hash [RFC1321] of the ASN.1 DER encoding
			[ISO-IEC-8825-1] of the corresponding GSS-API mechanism's OID.
			Base64 encoding is described in Section 4 of [RFC4648].
	+---------------------+-------------+-------------+-----------------+		+---------------------+-------------+-------------+-----------------+
	| Family Name prefix | Hash | Group | Reference |		| Family Name prefix | Hash | Group | Reference |
	| | Function | | |		| | Function | | |
	+---------------------+-------------+-------------+-----------------+		+---------------------+-------------+-------------+-----------------+
	| gss-group14-sha256- | SHA-256 | 2048-bit | Section 3 of |		| gss-group14-sha256- | SHA-256 | 2048-bit | Section 3 of |
	| | | MODP | [RFC3526] |		| | | MODP | [RFC3526] |
	| gss-group15-sha512- | SHA-512 | 3072-bit | Section 4 of |		| gss-group15-sha512- | SHA-512 | 3072-bit | Section 4 of |
	| | | MODP | [RFC3526] |		| | | MODP | [RFC3526] |
	| gss-group16-sha512- | SHA-512 | 4096-bit | Section 5 of |		| gss-group16-sha512- | SHA-512 | 4096-bit | Section 5 of |
	| | | MODP | [RFC3526] |		| | | MODP | [RFC3526] |
	| gss-group17-sha512- | SHA-512 | 6144-bit | Section 6 of |		| gss-group17-sha512- | SHA-512 | 6144-bit | Section 6 of |
	| | | MODP | [RFC3526] |		| | | MODP | [RFC3526] |
	| gss-group18-sha512- | SHA-512 | 8192-bit | Section 7 of |		| gss-group18-sha512- | SHA-512 | 8192-bit | Section 7 of |
	| | | MODP | [RFC3526] |		| | | MODP | [RFC3526] |
	+---------------------+-------------+-------------+-----------------+		+---------------------+-------------+-------------+-----------------+
			Table 2: Family method references
	5. New Elliptic Curve Diffie-Hellman Key Exchange methods		5. New Elliptic Curve Diffie-Hellman Key Exchange methods
	In [RFC5656] new SSH key exchange algorithms based on Elliptic Curve		In [RFC5656] new SSH key exchange algorithms based on Elliptic Curve
	Cryptography are introduced. We reuse much of section 4 of [RFC5656]		Cryptography are introduced. We reuse much of section 4 of [RFC5656]
	to define GSS-API-authenticated ECDH Key Exchanges.		to define GSS-API-authenticated ECDH Key Exchanges.
	Additionally we utilize also the curves defined in		Additionally, we also utilize the curves defined in
	[I-D.ietf-curdle-ssh-curves] to complement the 3 classic NIST defined		[I-D.ietf-curdle-ssh-curves] to complement the three classic NIST-
	curves required by [RFC5656].		defined curves required by [RFC5656].
	5.1. Generic GSS-API Key Exchange with ECDH		5.1. Generic GSS-API Key Exchange with ECDH
	This section reuses much of the scheme defined in Section 2.1 of		This section reuses much of the scheme defined in Section 2.1 of
	[RFC4462] and combines it with the scheme defined in Section 4 of		[RFC4462] and combines it with the scheme defined in Section 4 of
	[RFC5656]; in particular, all checks and verification steps		[RFC5656]; in particular, all checks and verification steps
	prescribed in Section 4 of [RFC5656] apply here as well.		prescribed in Section 4 of [RFC5656] apply here as well.
	Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 perform the		Key-agreement schemes ECDHE-Curve25519 and ECDHE-Curve448 perform the
	Diffie-Helman protocol using the functions X25519 and X448,		Diffie-Helman protocol using the functions X25519 and X448,
	respectively. Implementations SHOULD compute these functions using		respectively. Implementations MUST compute these functions using the
	the algorithms described in [RFC7748]. When they do so,		algorithms described in [RFC7748]. When they do so, implementations
	implementations MUST check whether the computed Diffie-Hellman shared		MUST check whether the computed Diffie-Hellman shared secret is the
	secret is the all-zero value and abort if so, as described in		all-zero value and abort if so, as described in Section 6 of
	Section 6 of [RFC7748]. Alternative implementations of these		[RFC7748]. Alternative implementations of these functions SHOULD
	functions SHOULD abort when either input forces the shared secret to		abort when either input forces the shared secret to one of a small
	one of a small set of values, as discussed in Section 7 of [RFC7748].		set of values, as discussed in Section 7 of [RFC7748].
	This section defers to [RFC7546] as the source of information on GSS-		This section defers to [RFC7546] as the source of information on GSS-
	API context establishment operations, Section 3 being the most		API context establishment operations, Section 3 being the most
	relevant. All Security Considerations described in [RFC7546] apply		relevant. All Security Considerations described in [RFC7546] apply
	here too.		here too.
	The parties generate each an ephemeral key pair, according to		The parties each generate an ephemeral key pair, according to
	Section 3.2.1 of [SEC1v2]. Keys are verified upon receipt by the		Section 3.2.1 of [SEC1v2]. Keys are verified upon receipt by the
	parties according to Section 3.2.3.1 of [SEC1v2].		parties according to Section 3.2.3.1 of [SEC1v2].
	For NIST Curves the keys use the uncompressed point representation		For NIST Curves the keys use the uncompressed point representation
	and must be converted using the algorithm in Section 2.3.4 of		and MUST be converted using the algorithm in Section 2.3.4 of
	[SEC1v2]. If the conversion fails or the point is trasmitted using		[SEC1v2]. If the conversion fails or the point is transmitted using
	the compressed representation, the key exchange MUST fail.		the compressed representation, the key exchange MUST fail.
	A GSS Context is established according to Section 4 of [RFC5656]; The		A GSS Context is established according to Section 4 of [RFC5656]; The
	client initiates the establishment using GSS_Init_sec_context() and		client initiates the establishment using GSS_Init_sec_context() and
	the server responds to it using GSS_Accept_sec_context(). For the		the server responds to it using GSS_Accept_sec_context(). For the
	negotiation, the client MUST set mutual_req_flag and integ_req_flag		negotiation, the client MUST set mutual_req_flag and integ_req_flag
	to "true". In addition, deleg_req_flag MAY be set to "true" to		to "true". In addition, deleg_req_flag MAY be set to "true" to
	request access delegation, if requested by the user. Since the key		request access delegation, if requested by the user. Since the key
	exchange process authenticates only the host, the setting of		exchange process authenticates only the host, the setting of
	anon_req_flag is immaterial to this process. If the client does not		anon_req_flag is immaterial to this process. If the client does not
	skipping to change at page 5, line 18 ¶		skipping to change at page 5, line 18 ¶
	then anon_req_flag SHOULD be set to "true". Otherwise, this flag MAY		then anon_req_flag SHOULD be set to "true". Otherwise, this flag MAY
	be set to true if the client wishes to hide its identity. This key		be set to true if the client wishes to hide its identity. This key
	exchange process will exchange only a single message token once the		exchange process will exchange only a single message token once the
	context has been established, therefore the replay_det_req_flag and		context has been established, therefore the replay_det_req_flag and
	sequence_req_flag SHOULD be set to "false".		sequence_req_flag SHOULD be set to "false".
	The client MUST include its public key with the first message it		The client MUST include its public key with the first message it
	sends to the server during this process; if the server receives more		sends to the server during this process; if the server receives more
	than one key or none at all, the key exchange MUST fail.		than one key or none at all, the key exchange MUST fail.
	During GSS Context estalishment multiple tokens may be exchanged by		During GSS Context establishment multiple tokens may be exchanged by
	the client and the server. When the GSS Context is established		the client and the server. When the GSS Context is established
	(major_status is GSS_S_COMPLETE) the parties check that mutual_state		(major_status is GSS_S_COMPLETE) the parties check that mutual_state
	and integ_avail are both "true". If not the key exchange MUST fail.		and integ_avail are both "true". If not the key exchange MUST fail.
	Once a party receives the peer's public key it proceeds to compute a		Once a party receives the peer's public key it proceeds to compute a
	shared secret K. For NIST Curves the computation is done according		shared secret K. For NIST Curves the computation is done according
	to Section 3.3.1 of [SEC1v2] and the resulting value z is converted		to Section 3.3.1 of [SEC1v2] and the resulting value z is converted
	to the octet string K using the conversion defined in Section 2.3.5		to the octet string K using the conversion defined in Section 2.3.5
	of [SEC1v2]. For curve25519 and curve448 the algorithms in Section 6		of [SEC1v2]. For curve25519 and curve448 the algorithms in Section 6
	of [RFC7748] are used instead.		of [RFC7748] are used instead.
	skipping to change at page 6, line 40 ¶		skipping to change at page 6, line 40 ¶
	Calls GSS_VerifyMIC( MIC, H )		Calls GSS_VerifyMIC( MIC, H )
	This is implemented with the following messages:		This is implemented with the following messages:
	The client sends:		The client sends:
	byte SSH_MSG_KEXGSS_INIT		byte SSH_MSG_KEXGSS_INIT
	string output_token (from GSS_Init_sec_context())		string output_token (from GSS_Init_sec_context())
	string Q_C, client's ephemeral public key octet string		string Q_C, client's ephemeral public key octet string
	The server may responds with:		The server may respond with:
	byte SSH_MSG_KEXGSS_HOSTKEY		byte SSH_MSG_KEXGSS_HOSTKEY
	string server public host key and certificates (K_S)		string server public host key and certificates (K_S)
	The server sends:		The server sends:
	byte SSH_MSG_KEXGSS_CONTINUE		byte SSH_MSG_KEXGSS_CONTINUE
	string output_token (from GSS_Accept_sec_context())		string output_token (from GSS_Accept_sec_context())
	Each time the client receives the message described above, it makes		Each time the client receives the message described above, it makes
	skipping to change at page 8, line 12 ¶		skipping to change at page 8, line 12 ¶
	GSS_S_COMPLETE, a protocol error has occurred and the key exchange		GSS_S_COMPLETE, a protocol error has occurred and the key exchange
	MUST fail.		MUST fail.
	If the client receives a SSH_MSG_KEXGSS_COMPLETE message and a call		If the client receives a SSH_MSG_KEXGSS_COMPLETE message and a call
	to GSS_Init_sec_context() does not result in a major_status code of		to GSS_Init_sec_context() does not result in a major_status code of
	GSS_S_COMPLETE, a protocol error has occurred and the key exchange		GSS_S_COMPLETE, a protocol error has occurred and the key exchange
	MUST fail.		MUST fail.
	5.2. ECDH Key Exchange Methods		5.2. ECDH Key Exchange Methods
	The following new key exchange methods are defined:
	+--------------------------+--------------------------------+		+--------------------------+--------------------------------+
	| Key Exchange Method Name | Implementation Recommendations |		| Key Exchange Method Name | Implementation Recommendations |
	+--------------------------+--------------------------------+		+--------------------------+--------------------------------+
	| gss-nistp256-sha256-* | SHOULD/RECOMMENDED |		| gss-nistp256-sha256-* | SHOULD/RECOMMENDED |
	| gss-nistp384-sha384-* | MAY/OPTIONAL |		| gss-nistp384-sha384-* | MAY/OPTIONAL |
	| gss-nistp521-sha512-* | MAY/OPTIONAL |		| gss-nistp521-sha512-* | MAY/OPTIONAL |
	| gss-curve25519-sha256-* | SHOULD/RECOMMENDED |		| gss-curve25519-sha256-* | SHOULD/RECOMMENDED |
	| gss-curve448-sha512-* | MAY/OPTIONAL |		| gss-curve448-sha512-* | MAY/OPTIONAL |
	+--------------------------+--------------------------------+		+--------------------------+--------------------------------+
	Each key exchange method is implicitly registered by this document.		Table 3: New key exchange methods
	The IESG is considered to be the owner of all these key exchange
	methods; this does NOT imply that the IESG is considered to be the
	owner of the underlying GSS-API mechanism.
	Each method in any family of methods specifies GSS-API-authenticated		Each key exchange method prefix is registered by this document. The
	Elliptic Curve Diffie-Hellman key exchanges as described in		IESG is the change controller of all these key exchange methods; this
	Section 5.1. The method name for each method is the concatenation of		does NOT imply that the IESG is considered to be in control of the
	the family method name with the Base64 encoding of the MD5 hash		corresponding GSS-API mechanism.
	[RFC1321] of the ASN.1 DER encoding [ISO-IEC-8825-1] of the
	underlying GSS-API mechanism's OID. Base64 encoding is described in
	Section 6.8 of [RFC2045].
	Family method refences		Each method in any family of methods (Table 4) specifies GSS-API-
			authenticated Elliptic Curve Diffie-Hellman key exchanges as
			described in Section 5.1. The method name for each method (Table 3)
			is the concatenation of the family method name with the Base64
			encoding of the MD5 hash [RFC1321] of the ASN.1 DER encoding
			[ISO-IEC-8825-1] of the corresponding GSS-API mechanism's OID.
			Base64 encoding is described in Section 4 of [RFC4648].
	+------------------------+----------+---------------+---------------+		+------------------------+----------+---------------+---------------+
	| Family Name prefix | Hash | Parameters / | Definition |		| Family Name prefix | Hash | Parameters / | Definition |
	| | Function | Function Name | |		| | Function | Function Name | |
	+------------------------+----------+---------------+---------------+		+------------------------+----------+---------------+---------------+
	| gss-nistp256-sha256- | SHA-256 | secp256r1 | Section 2.4.2 |		| gss-nistp256-sha256- | SHA-256 | secp256r1 | Section 2.4.2 |
	| | | | of [SEC2v2] |		| | | | of [SEC2v2] |
	| gss-nistp384-sha384- | SHA-384 | secp384r1 | Section 2.5.1 |		| gss-nistp384-sha384- | SHA-384 | secp384r1 | Section 2.5.1 |
	| | | | of [SEC2v2] |		| | | | of [SEC2v2] |
	| gss-nistp521-sha512- | SHA-512 | secp521r1 | Section 2.6.1 |		| gss-nistp521-sha512- | SHA-512 | secp521r1 | Section 2.6.1 |
	| | | | of [SEC2v2] |		| | | | of [SEC2v2] |
	| gss-curve25519-sha256- | SHA-256 | X22519 | Section 5 of |		| gss-curve25519-sha256- | SHA-256 | X22519 | Section 5 of |
	| | | | [RFC7748] |		| | | | [RFC7748] |
	| gss-curve448-sha512- | SHA-512 | X448 | Section 5 of |		| gss-curve448-sha512- | SHA-512 | X448 | Section 5 of |
	| | | | [RFC7748] |		| | | | [RFC7748] |
	+------------------------+----------+---------------+---------------+		+------------------------+----------+---------------+---------------+
			Table 4: Family method refences
	6. Deprecated Algorithms		6. Deprecated Algorithms
	Because they have small key lengths and are no longer strong in the		Because they have small key lengths and are no longer strong in the
	face of brute-force attacks, the algorithms in the following table		face of brute-force attacks, the algorithms in the following table
	are considered deprecated and SHOULD NOT be used.		are considered deprecated and SHOULD NOT be used.
	Deprecated Algorithms		Deprecated Algorithms
	+--------------------------+--------------------------------+		+--------------------------+--------------------------------+
	| Key Exchange Method Name | Implementation Recommendations |		| Key Exchange Method Name | Implementation Recommendations |
	skipping to change at page 10, line 47 ¶		skipping to change at page 10, line 47 ¶
	Although a new cryptographic primitive is used with these methods the		Although a new cryptographic primitive is used with these methods the
	actual key exchange closely follows the key exchange defined in		actual key exchange closely follows the key exchange defined in
	[RFC5656]; therefore all the original Security Considerations as well		[RFC5656]; therefore all the original Security Considerations as well
	as those expressed in [RFC5656] apply.		as those expressed in [RFC5656] apply.
	8.3. GSSAPI Delegation		8.3. GSSAPI Delegation
	Some GSSAPI mechanisms can act on a request to delegate credentials		Some GSSAPI mechanisms can act on a request to delegate credentials
	to the target host when the deleg_req_flag is set. In this case,		to the target host when the deleg_req_flag is set. In this case,
	extra care must be taken to ensure that the acceptor being		extra care must be taken to ensure that the acceptor being
	authenticated matches the target the user intended. Some mechanisms		authenticated matches the target the user intended. Some mechanism
	implementations (like commonly used krb5 libraries) may use insecure		implementations (such as commonly used krb5 libraries) may use
	DNS resolution to canonicalize the target name; in these cases		insecure DNS resolution to canonicalize the target name; in these
	spoofing a DNS response that points to an attacker-controlled machine		cases spoofing a DNS response that points to an attacker-controlled
	may results in the user silently delegating credentials to the		machine may result in the user silently delegating credentials to the
	attacker, who can then impersonate the user at will.		attacker, who can then impersonate the user at will.
	9. References		9. References
	9.1. Normative References		9.1. Normative References
	[I-D.ietf-curdle-ssh-curves]		[I-D.ietf-curdle-ssh-curves]
	Adamantiadis, A., Josefsson, S., and M. Baushke, "Secure		Adamantiadis, A., Josefsson, S., and M. Baushke, "Secure
	Shell (SSH) Key Exchange Method using Curve25519 and		Shell (SSH) Key Exchange Method using Curve25519 and
	Curve448", draft-ietf-curdle-ssh-curves-08 (work in		Curve448", draft-ietf-curdle-ssh-curves-08 (work in
	progress), June 2018.		progress), June 2018.
	[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,		[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
	DOI 10.17487/RFC1321, April 1992,		DOI 10.17487/RFC1321, April 1992,
	<https://www.rfc-editor.org/info/rfc1321>.		<https://www.rfc-editor.org/info/rfc1321>.
	[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
	Extensions (MIME) Part One: Format of Internet Message
	Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
	<https://www.rfc-editor.org/info/rfc2045>.
	[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,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
			[RFC2743] Linn, J., "Generic Security Service Application Program
			Interface Version 2, Update 1", RFC 2743,
			DOI 10.17487/RFC2743, January 2000,
			<https://www.rfc-editor.org/info/rfc2743>.
	[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)		[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
	Diffie-Hellman groups for Internet Key Exchange (IKE)",		Diffie-Hellman groups for Internet Key Exchange (IKE)",
	RFC 3526, DOI 10.17487/RFC3526, May 2003,		RFC 3526, DOI 10.17487/RFC3526, May 2003,
	<https://www.rfc-editor.org/info/rfc3526>.		<https://www.rfc-editor.org/info/rfc3526>.
	[RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch,		[RFC4462] Hutzelman, J., Salowey, J., Galbraith, J., and V. Welch,
	"Generic Security Service Application Program Interface		"Generic Security Service Application Program Interface
	(GSS-API) Authentication and Key Exchange for the Secure		(GSS-API) Authentication and Key Exchange for the Secure
	Shell (SSH) Protocol", RFC 4462, DOI 10.17487/RFC4462, May		Shell (SSH) Protocol", RFC 4462, DOI 10.17487/RFC4462, May
	2006, <https://www.rfc-editor.org/info/rfc4462>.		2006, <https://www.rfc-editor.org/info/rfc4462>.
			[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
			Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
			<https://www.rfc-editor.org/info/rfc4648>.
	[RFC5656] Stebila, D. and J. Green, "Elliptic Curve Algorithm		[RFC5656] Stebila, D. and J. Green, "Elliptic Curve Algorithm
	Integration in the Secure Shell Transport Layer",		Integration in the Secure Shell Transport Layer",
	RFC 5656, DOI 10.17487/RFC5656, December 2009,		RFC 5656, DOI 10.17487/RFC5656, December 2009,
	<https://www.rfc-editor.org/info/rfc5656>.		<https://www.rfc-editor.org/info/rfc5656>.
	[RFC7546] Kaduk, B., "Structure of the Generic Security Service		[RFC7546] Kaduk, B., "Structure of the Generic Security Service
	(GSS) Negotiation Loop", RFC 7546, DOI 10.17487/RFC7546,		(GSS) Negotiation Loop", RFC 7546, DOI 10.17487/RFC7546,
	May 2015, <https://www.rfc-editor.org/info/rfc7546>.		May 2015, <https://www.rfc-editor.org/info/rfc7546>.
	[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves		[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
End of changes. 27 change blocks.
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