rfc9987v1.txt		rfc9987.txt
	skipping to change at line 247 ¶		skipping to change at line 247 ¶
	Otherwise, an agent MAY refuse to load a key that has already been		Otherwise, an agent MAY refuse to load a key that has already been
	loaded.		loaded.
	An agent MAY support only a subset of the key types defined here and		An agent MAY support only a subset of the key types defined here and
	MAY support additional key types as described below. If an agent		MAY support additional key types as described below. If an agent
	does not recognise the type name in a request to add a key, then it		does not recognise the type name in a request to add a key, then it
	MUST respond with an SSH_AGENT_FAILURE reply.		MUST respond with an SSH_AGENT_FAILURE reply.
	5.2.1. DSA Keys		5.2.1. DSA Keys
	Digital Signature Algorithm (DSA) keys have key type "ssh-dss" and		Digital Signature Algorithm (DSA) keys have key type name "ssh-dss"
	are defined in [RFC4253]. They may be added to the agent using the		and are defined in [RFC4253]. They may be added to the agent using
	following message. The "constraints" field is only present for the		the following message. The "constraints" field is only present for
	SSH_AGENTC_ADD_ID_CONSTRAINED message.		the SSH_AGENTC_ADD_ID_CONSTRAINED message.
	byte SSH_AGENTC_ADD_IDENTITY or		byte SSH_AGENTC_ADD_IDENTITY or
	SSH_AGENTC_ADD_ID_CONSTRAINED		SSH_AGENTC_ADD_ID_CONSTRAINED
	string "ssh-dss"		string "ssh-dss"
	mpint p		mpint p
	mpint q		mpint q
	mpint g		mpint g
	mpint y		mpint y
	mpint x		mpint x
	string comment		string comment
	skipping to change at line 305 ¶		skipping to change at line 305 ¶
	byte SSH_AGENTC_ADD_IDENTITY or		byte SSH_AGENTC_ADD_IDENTITY or
	SSH_AGENTC_ADD_ID_CONSTRAINED		SSH_AGENTC_ADD_ID_CONSTRAINED
	string "ssh-ed25519" or "ssh-ed448"		string "ssh-ed25519" or "ssh-ed448"
	string ENC(A)		string ENC(A)
	string k || ENC(A)		string k || ENC(A)
	string comment		string comment
	constraint[] constraints		constraint[] constraints
	The first value is the EdDSA public key ENC(A). The second value is		The first value is the EdDSA public key ENC(A). The second value is
	a concatenation of the private key k and the public ENC(A) key (this		a concatenation of the private key k and the public ENC(A) key (this
	redundant repetition of the public key is to maintain compatibility		repetition of the public key is to maintain compatibility with widely
	with widely deployed implementations). The contents and		deployed implementations). The contents and interpretation of the
	interpretation of the ENC(A) and k values are defined by Section 3.2		ENC(A) and k values are defined by Section 3.2 of [RFC8032].
	of [RFC8032].
	5.2.4. RSA Keys		5.2.4. RSA Keys
	RSA keys have key type "ssh-rsa" and are defined in [RFC4253]. They		RSA keys have key type name "ssh-rsa" and are defined in [RFC4253].
	may be added to the agent using the following message. The		They may be added to the agent using the following message. The
	"constraints" field is only present for the		"constraints" field is only present for the
	SSH_AGENTC_ADD_ID_CONSTRAINED message.		SSH_AGENTC_ADD_ID_CONSTRAINED message.
	byte SSH_AGENTC_ADD_IDENTITY or		byte SSH_AGENTC_ADD_IDENTITY or
	SSH_AGENTC_ADD_ID_CONSTRAINED		SSH_AGENTC_ADD_ID_CONSTRAINED
	string "ssh-rsa"		string "ssh-rsa"
	mpint n		mpint n
	mpint e		mpint e
	mpint d		mpint d
	mpint iqmp		mpint iqmp
	skipping to change at line 487 ¶		skipping to change at line 486 ¶
	byte SSH_AGENTC_REMOVE_SMARTCARD_KEY		byte SSH_AGENTC_REMOVE_SMARTCARD_KEY
	string token id		string token id
	string PIN		string PIN
	Where "token id" is an opaque identifier for the hardware token and		Where "token id" is an opaque identifier for the hardware token and
	"PIN" is an optional password or PIN (not typically used), both		"PIN" is an optional password or PIN (not typically used), both
	encoded using UTF-8. Requesting deletion of token-hosted keys SHOULD		encoded using UTF-8. Requesting deletion of token-hosted keys SHOULD
	cause the agent to remove all keys it loaded from the device matching		cause the agent to remove all keys it loaded from the device matching
	"token id". Similarly to SSH_AGENTC_REMOVE_ALL_IDENTITIES, agents		"token id". Similarly to SSH_AGENTC_REMOVE_ALL_IDENTITIES, agents
	SHOULD honour this request regardless of local policy to allow fast		SHOULD honour this request regardless of local policy to allow fast
	and complete removal of keys. Note: this operation affects the agent		and complete removal of keys. Removing a token-hosted key affects
	only; it SHOULD NOT cause the keys be deleted from the token itself.		the agent only; it SHOULD NOT cause the keys be deleted from the
			token itself.
	An agent MUST reply with SSH_AGENT_SUCCESS if the keys were deleted		An agent MUST reply with SSH_AGENT_SUCCESS if the keys were deleted
	or SSH_AGENT_FAILURE if none were found.		or SSH_AGENT_FAILURE if none were found.
	5.5. Requesting a List of Keys		5.5. Requesting a List of Keys
	A client may request a list of keys from an agent using the following		A client may request a list of keys from an agent using the following
	message:		message:
	byte SSH_AGENTC_REQUEST_IDENTITIES		byte SSH_AGENTC_REQUEST_IDENTITIES
	skipping to change at line 654 ¶		skipping to change at line 654 ¶
	In both cases, it is common to expose the name or address of the		In both cases, it is common to expose the name or address of the
	listening endpoint via an environment variable named "SSH_AUTH_SOCK".		listening endpoint via an environment variable named "SSH_AUTH_SOCK".
	Clients of an agent will use this variable to locate and connect to		Clients of an agent will use this variable to locate and connect to
	the listening agent. Alternatively, agents MAY use an implicit		the listening agent. Alternatively, agents MAY use an implicit
	mechanism for clients to locate their endpoint, such as a default		mechanism for clients to locate their endpoint, such as a default
	per-user location.		per-user location.
	7. Forwarding Access to an Agent		7. Forwarding Access to an Agent
	The agent protocol may be forwarded over an SSH connection, using the		Using the connection protocol described in [RFC4254], the agent
	[RFC4254] connection protocol, allowing agent forwarding to be		protocol may be forwarded over an SSH connection. This allows agent
	requested for any session channel, using a model that is similar to		forwarding to be requested for any session channel using a model that
	the connection protocol's support for X11 Forwarding (Section 6.3 of		is similar to the connection protocol's support for X11 Forwarding
	[RFC4254]). This feature is OPTIONAL for the SSH protocol and agent		(Section 6.3 of [RFC4254]). This feature is OPTIONAL for the SSH
	implementations.		protocol and agent implementations.
	7.1. Advertising Agent Forwarding Support		7.1. Advertising Agent Forwarding Support
	Support for agent forwarding may be advertised by an SSH server using		Support for agent forwarding may be advertised by an SSH server using
	the extension mechanism described in [RFC8308] using the name "agent-		the extension mechanism described in [RFC8308] using the name "agent-
	forward" in the SSH_MSG_EXT_INFO message.		forward" in the SSH_MSG_EXT_INFO message.
	string "agent-forward"		string "agent-forward"
	string "0" (version)		string "0" (version)
	skipping to change at line 734 ¶		skipping to change at line 734 ¶
	As above, the "agent-connect" open type name SHOULD only be used if		As above, the "agent-connect" open type name SHOULD only be used if
	support was explicitly advertised as per Section 7.1.		support was explicitly advertised as per Section 7.1.
	An SSH client SHOULD be prepared to handle multiple concurrent		An SSH client SHOULD be prepared to handle multiple concurrent
	forwarded connections to a client-side agent; otherwise, requests to		forwarded connections to a client-side agent; otherwise, requests to
	access the agent from the remote side that happen to overlap prior		access the agent from the remote side that happen to overlap prior
	requests may fail. Overlapping requests may occur because the SSH		requests may fail. Overlapping requests may occur because the SSH
	connection protocol [RFC4254] allows multiple user sessions over a		connection protocol [RFC4254] allows multiple user sessions over a
	single transport (see [RFC4253]), which may each request use of the		single transport (see [RFC4253]), which may each request use of the
	agentcw independently and potentially concurrently.		agent independently and potentially concurrently.
	An SSH client MAY accept agent connection requests (subject to		An SSH client MAY accept agent connection requests (subject to
	authorisation) without a prior agent forwarding request having been		authorisation) without a prior agent forwarding request having been
	made to support the situation where agent forwarding without opening		made to support the situation where agent forwarding without opening
	a session is desired. Similarly, an SSH client MAY continue to		a session is desired. Similarly, an SSH client MAY continue to
	accept agent connection requests after the session for which agent		accept agent connection requests after the session for which agent
	forwarding was requested has closed.		forwarding was requested has closed.
	An SSH client MUST refuse unauthorised agent connection requests,		An SSH client MUST refuse unauthorised agent connection requests,
	when agent forwarding is neither requested nor desired by the SSH		when agent forwarding is neither requested nor desired by the SSH
	skipping to change at line 1167 ¶		skipping to change at line 1167 ¶
	Forwarding access to a local agent over an SSH connection (Section 7)		Forwarding access to a local agent over an SSH connection (Section 7)
	inherently creates a transitive trust relationship. SSH		inherently creates a transitive trust relationship. SSH
	implementations SHOULD NOT forward use of an agent by default, and		implementations SHOULD NOT forward use of an agent by default, and
	users SHOULD NOT forward use of an agent to hosts that are not fully		users SHOULD NOT forward use of an agent to hosts that are not fully
	trusted, as doing so could expose access to the user's keys to		trusted, as doing so could expose access to the user's keys to
	attackers on remote hosts. Agents SHOULD implement additional		attackers on remote hosts. Agents SHOULD implement additional
	controls over key visibility and use for forwarded agent connections;		controls over key visibility and use for forwarded agent connections;
	otherwise, the user has only an all-or-nothing choice about whether		otherwise, the user has only an all-or-nothing choice about whether
	to forward an agent.		to forward an agent.
	Implementation of token/smartcard-hosted keys requires some care,		Implementation of keys hosted by a token or smartcard requires some
	too. On some systems, tokens may be invoked by providing a path to a		care, too. On some systems, tokens may be invoked by providing a
	shared library that must be loaded to make use of keys hosted on the		path to a shared library that must be loaded to make use of keys
	device (a path to a library for a particular PKCS#11 module, for		hosted on the device (a path to a library for a particular PKCS#11
	example). Loading a shared library on most platforms implies		module, for example). Loading a shared library on most platforms
	automatic execution of code in that library in the address space of		implies automatic execution of code in that library in the address
	the process that loads it. To avoid the loading of potentially		space of the process that loads it. To avoid the loading of
	hostile code, agents that support loading token-hosted keys via a		potentially hostile code, agents that support loading token-hosted
	library path SHOULD ensure that only trusted token provider libraries		keys via a library path SHOULD ensure that only trusted token
	are loadable. Additionally, agents SHOULD ensure that loaded token		provider libraries are loadable. Additionally, agents SHOULD ensure
	library code cannot gain access to other keys loaded in the agent and		that loaded token library code cannot gain access to other keys
	MAY disallow remote clients from loading token keys entirely.		loaded in the agent and MAY disallow remote clients from loading
	Protection for existing keys from a token library code may be		token keys entirely. Protection for existing keys from a token
	achieved by loading the token library into a separate process to the		library code may be achieved by loading the token library into a
	agent and arranging for the agent to invoke token operations to this		separate process to the agent and arranging for the agent to invoke
	process via IPC.		token operations to this process via IPC.
	Finally, with respect to the agent locking functionality in		Finally, with respect to the agent locking functionality in
	Section 5.7, an agent SHOULD take countermeasures against brute-force		Section 5.7, an agent SHOULD take countermeasures against brute-force
	guessing attacks on the passphrase. This may take the form of		guessing attacks on the passphrase. This may take the form of
	enforced delays when an unlock attempt is made with an incorrect		enforced delays when an unlock attempt is made with an incorrect
	password (potentially increasing for subsequent failures), a lockout		password (potentially increasing for subsequent failures), a lockout
	period where the agent refuses to accept further requests after some		period where the agent refuses to accept further requests after some
	threshold of failed unlock attempts has been made, and/or deletion of		threshold of failed unlock attempts has been made, and/or deletion of
	all keys held by the agent after a threshold of failed unlock		all keys held by the agent after a threshold of failed unlock
	attempts.		attempts.
	11. References		11. References
	11.1. Normative References		11.1. Normative References
			[FIPS.186-4]
			NIST, "Digital Signature Standard (DSS)", NIST FIPS 186-4,
			DOI 10.6028/NIST.FIPS.186-4, June 2013,
			<https://doi.org/10.6028/NIST.FIPS.186-4>.
			[FIPS.186-5]
			NIST, "Digital Signature Standard (DSS)", NIST FIPS 186-5,
			DOI 10.6028/NIST.FIPS.186-5, February 2023,
			<https://doi.org/10.6028/NIST.FIPS.186-5>.
	[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>.
	[RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)		[RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
	Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,		Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251,
	January 2006, <https://www.rfc-editor.org/info/rfc4251>.		January 2006, <https://www.rfc-editor.org/info/rfc4251>.
	[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)		[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
	skipping to change at line 1243 ¶		skipping to change at line 1253 ¶
	[RFC8332] Bider, D., "Use of RSA Keys with SHA-256 and SHA-512 in		[RFC8332] Bider, D., "Use of RSA Keys with SHA-256 and SHA-512 in
	the Secure Shell (SSH) Protocol", RFC 8332,		the Secure Shell (SSH) Protocol", RFC 8332,
	DOI 10.17487/RFC8332, March 2018,		DOI 10.17487/RFC8332, March 2018,
	<https://www.rfc-editor.org/info/rfc8332>.		<https://www.rfc-editor.org/info/rfc8332>.
	[RFC8709] Harris, B. and L. Velvindron, "Ed25519 and Ed448 Public		[RFC8709] Harris, B. and L. Velvindron, "Ed25519 and Ed448 Public
	Key Algorithms for the Secure Shell (SSH) Protocol",		Key Algorithms for the Secure Shell (SSH) Protocol",
	RFC 8709, DOI 10.17487/RFC8709, February 2020,		RFC 8709, DOI 10.17487/RFC8709, February 2020,
	<https://www.rfc-editor.org/info/rfc8709>.		<https://www.rfc-editor.org/info/rfc8709>.
	[FIPS.186-4]
	NIST, "Digital Signature Standard (DSS)", NIST FIPS 186-4,
	DOI 10.6028/NIST.FIPS.186-4, June 2013,
	<https://doi.org/10.6028/NIST.FIPS.186-4>.
	[FIPS.186-5]
	NIST, "Digital Signature Standard (DSS)", NIST FIPS 186-5,
	DOI 10.6028/NIST.FIPS.186-5, February 2023,
	<https://doi.org/10.6028/NIST.FIPS.186-5>.
	11.2. Informative References		11.2. Informative References
	[RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)		[IANA-PUBKEYS]
	Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,		IANA, "Public Key Algorithm Names",
	January 2006, <https://www.rfc-editor.org/info/rfc4252>.		<https://www.iana.org/assignments/ssh-parameters/>.
	[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for		[IANA-SSH] IANA, "Secure Shell (SSH) Protocol Parameters",
	Writing an IANA Considerations Section in RFCs", BCP 26,		<https://www.iana.org/assignments/ssh-parameters/>.
	RFC 8126, DOI 10.17487/RFC8126, June 2017,
	<https://www.rfc-editor.org/info/rfc8126>.
	[IANA-SSH-CHANREQ]		[IANA-SSH-CHANREQ]
	IANA, "Connection Protocol Channel Types",		IANA, "Connection Protocol Channel Types",
	<https://www.iana.org/assignments/ssh-parameters/>.		<https://www.iana.org/assignments/ssh-parameters/>.
	[IANA-SSH] IANA, "Secure Shell (SSH) Protocol Parameters",
	<https://www.iana.org/assignments/ssh-parameters/>.
	[IANA-SSH-CHANTYPE]		[IANA-SSH-CHANTYPE]
	IANA, "Extension Names",		IANA, "Extension Names",
	<https://www.iana.org/assignments/ssh-parameters/>.		<https://www.iana.org/assignments/ssh-parameters/>.
	[IANA-SSH-EXT]		[IANA-SSH-EXT]
	IANA, "Connection Protocol Channel Request Names",		IANA, "Connection Protocol Channel Request Names",
	<https://www.iana.org/assignments/ssh-parameters/>.		<https://www.iana.org/assignments/ssh-parameters/>.
	[IANA-PUBKEYS]		[RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
	IANA, "Public Key Algorithm Names",		Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
	<https://www.iana.org/assignments/ssh-parameters/>.		January 2006, <https://www.rfc-editor.org/info/rfc4252>.
			[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
			Writing an IANA Considerations Section in RFCs", BCP 26,
			RFC 8126, DOI 10.17487/RFC8126, June 2017,
			<https://www.rfc-editor.org/info/rfc8126>.
	Acknowledgments		Acknowledgments
	This protocol was designed and first implemented by Markus Friedl,		This protocol was designed and first implemented by Markus Friedl,
	based on a similar protocol for an agent to support the legacy SSH		based on a similar protocol for an agent to support the legacy SSH
	version 1 by Tatu Ylonen.		version 1 by Tatu Ylonen.
	Thanks to Simon Tatham, Niels Möller, James Spencer, Simon Josefsson,		Thanks to Simon Tatham, Niels Möller, James Spencer, Simon Josefsson,
	Matt Johnston, Jakub Jelen, Rich Salz, Caspar Schutijser, Florian		Matt Johnston, Jakub Jelen, Rich Salz, Caspar Schutijser, Florian
	Obser, Martin Thomson, Deb Cooley, and Tero Kivinen who reviewed and		Obser, Martin Thomson, Deb Cooley, and Tero Kivinen who reviewed and
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