diff options
Diffstat (limited to 'usr.bin')
| -rw-r--r-- | usr.bin/ssh/PROTOCOL | 5 | ||||
| -rw-r--r-- | usr.bin/ssh/PROTOCOL.agent | 516 |
2 files changed, 520 insertions, 1 deletions
diff --git a/usr.bin/ssh/PROTOCOL b/usr.bin/ssh/PROTOCOL index 64b194cd333..859e61f6760 100644 --- a/usr.bin/ssh/PROTOCOL +++ b/usr.bin/ssh/PROTOCOL @@ -9,6 +9,9 @@ http://www.openssh.com/txt/draft-ietf-secsh-filexfer-02.txt Features from newer versions of the draft are not supported, unless explicitly implemented as extensions described below. +The protocol used by OpenSSH's ssh-agent is described in the file +PROTOCOL.agent + 1. transport: Protocol 2 MAC algorithm "umac-64@openssh.com" This is a new transport-layer MAC method using the UMAC algorithm @@ -237,4 +240,4 @@ The values of the f_flag bitmask are as follows: This extension is advertised in the SSH_FXP_VERSION hello with version "2". -$OpenBSD: PROTOCOL,v 1.8 2008/06/28 07:25:07 djm Exp $ +$OpenBSD: PROTOCOL,v 1.9 2008/06/28 14:08:30 djm Exp $ diff --git a/usr.bin/ssh/PROTOCOL.agent b/usr.bin/ssh/PROTOCOL.agent new file mode 100644 index 00000000000..982a5dbefc3 --- /dev/null +++ b/usr.bin/ssh/PROTOCOL.agent @@ -0,0 +1,516 @@ +This describes the protocol used by OpenSSH's ssh-agent. + +OpenSSH's agent supports managing keys for the standard SSH protocol +2 as well as the legacy SSH protocol 1. Support for these key types +is almost completely disjoint - in all but a few cases, operations on +protocol 2 keys cannot see or affect protocol 1 keys and vice-versa. + +Protocol 1 and protocol 2 keys are separated because of the differing +cryptographic usage: protocol 1 private RSA keys are used to decrypt +challenges that were encrypted with the corresponding public key, +whereas protocol 2 RSA private keys are used to sign challenges with +a private key for verification with the corresponding public key. It +is considered unsound practice to use the same key for signing and +encryption. + +With a couple of exceptions, the protocol message names used in this +document indicate which type of key the message relates to. SSH_* +messages refer to protocol 1 keys only. SSH2_* messages refer to +protocol 2 keys. Furthermore, the names also indicate whether message +is a request to the agent (*_AGENTC_*) or a reply from the agent +(*_AGENT_*). Section 3 below contains the mapping of the protocol +message names to their integer values. + +1. Data types + +Because of it support for legacy SSH protocol 1 keys, OpenSSH's agent +protocol makes use of some data types not defined in RFC 4251. + +1.1 uint16 + +The "uint16" data type is a simple MSB-first 16 bit unsigned integer +encoded in two bytes. + +1.2 mpint1 + +The "mpint1" type represents an arbitrary precision integer (bignum). +Its format is as follows: + + uint16 bits + byte[(bits + 7) / 8] bignum + +"bignum" contains an unsigned arbitrary precision integer encoded as +eight bits per byte in big-endian (MSB first) format. + +Note the difference between the "mpint1" encoding an the the "mpint" +encoding defined in RFC 4251. Also note that the length of the encoded +integer is specified in bits, not bytes and that the byte length of of +the integer must be calculated by rounding up the number of bits to the +nearest eight. + +2. Protocol Messages + +All protocol messages are prefixed with their length in bytes, encoded +as a 32 bit unsigned integer. Specifically: + + uint32 message_length + byte[message_length] message + +The following message description refer only to the content the +"message" field. + +2.1 Generic server responses + +The following generic messages may be sent by the server in response to +requests from the client. On success the agent may reply either with: + + byte SSH_AGENT_SUCCESS + +or a request-specific success message. + +On failure, the agent may reply with: + + byte SSH_AGENT_FAILURE + +SSH_AGENT_FAILURE messages are also sent in reply to unknown request +types. + +2.2 Adding keys to the agent + +Keys are added to the agent using the SSH_AGENTC_ADD_RSA_IDENTITY and +SSH2_AGENTC_ADD_IDENTITY requests for protocol 1 and protocol 2 keys +respectively. + +Two variants of these requests are SSH_AGENTC_ADD_RSA_ID_CONSTRAINED +and SSH2_AGENTC_ADD_ID_CONSTRAINED - these add keys with optional +"constraints" on their usage. + +OpenSSH may be built with support for keys hosted on a smartcard +or other hardware security module. These keys may added +to the agent using the SSH_AGENTC_ADD_SMARTCARD_KEY and +SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED requests + +2.2.1 Key constraints + +The OpenSSH agent supports some basic optional constraints on key usage. +At present there are two constraints defined. + +The first constraint limits the validity duration of a key. It is +encoded as: + + byte SSH_AGENT_CONSTRAIN_LIFETIME + uint32 seconds + +Where "seconds" contains the number of seconds that the key shall remain +valid measured from the moment that the agent receives it. After the +validity period has expired, OpenSSH's agent will erase these keys from +memory. + +The second constraint requires the agent to seek explicit user +confirmation before performing private key operations with the loaded +key. This constraint is encoded as: + + byte SSH_AGENT_CONSTRAIN_CONFIRM + +Zero or more constraints may be specified when adding a key with one +of the *_CONSTRAINED requests. Multiple constraints are appended +consecutively to the end of the request: + + byte constraint1_type + .... constraint1_date + byte constraint2_type + .... constraint2_date + .... + byte constraintN_type + .... constraintN_date + +Such a sequence of zero or more constraints will be referred to below +as "constraint[]". Agents may determine whether there are constraints +by checking whether additional data exists in the an "add key" request +after the key data itself. OpenSSH will refuse to add a key if it +contains unknown constraints. + +2.2.2 Add protocol 1 key + +A client may add a protocol 1 key to an agent with the following +request: + + byte SSH_AGENTC_ADD_RSA_IDENTITY or + SSH_AGENTC_ADD_RSA_ID_CONSTRAINED + uint32 ignored + mpint1 rsa_n + mpint1 rsa_e + mpint1 rsa_d + mpint1 rsa_iqmp + mpint1 rsa_q + mpint1 rsa_p + string key_comment + constraint[] key_constraints + +Note that there is some redundancy in the key parameters; a key could be +fully specified using just rsa_q, rsa_p and rsa_e at the cost of extra +computation. + +"key_constraints" may only be present if the request type is +SSH_AGENTC_ADD_RSA_IDENTITY. + +The agent will reply with a SSH_AGENT_SUCCESS if the key has been +successfully added or a SSH_AGENT_FAILURE if an error occurred. + +2.2.3 Add protocol 2 key + +The OpenSSH agent supports DSA and RSA keys for protocol 2. DSA keys may +be added using the following request + + byte SSH2_AGENTC_ADD_IDENTITY or + SSH2_AGENTC_ADD_ID_CONSTRAINED + string "ssh-dss" + mpint dsa_p + mpint dsa_q + mpint dsa_g + mpint dsa_public_key + mpint dsa_private_key + string key_comment + constraint[] key_constraints + +RSA keys may be added with this request: + + byte SSH2_AGENTC_ADD_IDENTITY or + SSH2_AGENTC_ADD_ID_CONSTRAINED + string "ssh-rsa" + mpint rsa_n + mpint rsa_e + mpint rsa_d + mpint rsa_iqmp + mpint rsa_p + mpint rsa_q + string key_comment + constraint[] key_constraints + +Note that the 'rsa_p' and 'rsa_q' parameters are send in the reverse +order to the protocol 1 add keys message. As with the corresponding +protocol 1 "add key" request, the private key is overspecified to avoid +redundant processing. + +For both DSA and RSA key add requests, "key_constraints" may only be +present if the request type is SSH2_AGENTC_ADD_ID_CONSTRAINED. + +The agent will reply with a SSH_AGENT_SUCCESS if the key has been +successfully added or a SSH_AGENT_FAILURE if an error occurred. + +2.2.4 Loading keys from a smartcard + +The OpenSSH agent may have optional smartcard support built in to it. If +so, it supports an operation to load keys from a smartcard. Technically, +only the public components of the keys are loaded into the agent so +this operation really arranges for future private key operations to be +delegated to the smartcard. + + byte SSH_AGENTC_ADD_SMARTCARD_KEY or + SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED + string reader_id + string pin + constraint[] key_constraints + +"reader_id" the an identifier to a smartcard reader and "pin" +is a PIN or passphrase used to unlock the private key(s) on the +device. "key_constraints" may only be present if the request type is +SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED. + +This operation may load all SSH keys that are unlocked using the +"pin" on the specified reader. The type of key loaded (protocol 1 +or protocol 2) will be specified by the smartcard itself, it is not +client-specified. + +The agent will reply with a SSH_AGENT_SUCCESS if one or more keys have +been successfully loaded or a SSH_AGENT_FAILURE if an error occurred. +The agent will also return SSH_AGENT_FAILURE if it does not support +smartcards. + +2.3 Removing multiple keys + +A client may request that an agent delete all protocol 1 keys using the +following request: + + byte SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES + +This message requests the deletion of all protocol 2 keys: + + byte SSH2_AGENTC_REMOVE_ALL_IDENTITIES + +On success, the agent will delete all keys of the requested type and +reply with a SSH_AGENT_SUCCESS message. If an error occurred, the agent +will reply with SSH_AGENT_FAILURE. + +Note that, to delete all keys (both protocol 1 and 2), a client +must send both a SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES and a +SSH2_AGENTC_REMOVE_ALL_IDENTITIES request. + +2.4 Removing specific keys + +2.4.1 Removing a protocol 1 key + +Removal of a protocol 1 key may be requested with the following message: + + byte SSH_AGENTC_REMOVE_RSA_IDENTITY + uint32 key_bits + mpint1 rsa_e + mpint1 rsa_n + +Note that key_bits is strictly redundant, as it may be inferred by the +length of rsa_n. + +The agent will delete any private key matching the specified public key +and return SSH_AGENT_SUCCESS. If no such key was found, the agent will +return SSH_AGENT_FAILURE. + +2.4.2 Removing a protocol 2 key + +Protocol 2 keys may be removed with the following request: + + byte SSH2_AGENTC_REMOVE_IDENTITY + byte[n] key_blob + +Where "key_blob" is encoded as per RFC 4253 section 6.6 "Public Key +Algorithms" for either of the supported key types: "ssh-dss" or +"ssh-rsa". + +The agent will delete any private key matching the specified public key +and return SSH_AGENT_SUCCESS. If no such key was found, the agent will +return SSH_AGENT_FAILURE. + +2.4.3 Removing keys loaded from a smartcard + +A client may request that a server remove one or more smartcard-hosted +keys using this message: + + byte SSH_AGENTC_REMOVE_SMARTCARD_KEY + string reader_id + string pin + +"reader_id" the an identifier to a smartcard reader and "pin" is a PIN +or passphrase used to unlock the private key(s) on the device. + +When this message is received, and if the agent supports +smartcard-hosted keys, it will delete all keys that are hosted on the +specified smartcard that may be accessed with the given "pin". + +The agent will reply with a SSH_AGENT_SUCCESS if one or more keys have +been successfully removed or a SSH_AGENT_FAILURE if an error occurred. +The agent will also return SSH_AGENT_FAILURE if it does not support +smartcards. + +2.5 Requesting a list of known keys + +An agent may be requested to list which keys it holds. Different +requests exist for protocol 1 and protocol 2 keys. + +2.5.1 Requesting a list of protocol 1 keys + +To request a list of protocol 1 keys that are held in the agent, a +client may send the following message: + + byte SSH_AGENTC_REQUEST_RSA_IDENTITIES + +The agent will reply with the following message: + + byte SSH_AGENT_RSA_IDENTITIES_ANSWER + uint32 num_keys + +Followed by zero or more consecutive keys, encoded as: + + uint32 bits + mpint1 rsa_e + mpint1 rsa_n + string key_comment + +2.5.2 Requesting a list of protocol 2 keys + +A client may send the following message to request a list of keys +protocol 2 keys that are stored in the agent: + + byte SSH2_AGENTC_REQUEST_IDENTITIES + +The agent will reply with the following message header: + + byte SSH2_AGENT_IDENTITIES_ANSWER + uint32 num_keys + +Followed by zero or more consecutive keys, encoded as: + + byte[n] key_blob + string key_comment + +Where "key_blob" is encoded as per RFC 4253 section 6.6 "Public Key +Algorithms" for either of the supported key types: "ssh-dss" or +"ssh-rsa". + +2.6 Private key operations + +The purpose of the agent is to perform private key operations, such as +signing and encryption without requiring a passphrase to unlock the +key and without allowing the private key itself to be exposed. There +are separate requests for the protocol 1 and protocol 2 private key +operations. + +2.6.1 Protocol 1 private key challenge + +The private key operation used in version 1 of the SSH protocol is +decrypting a challenge that has been encrypted with a public key. +It may be requested using this message: + + byte SSH_AGENTC_RSA_CHALLENGE + uint32 ignored + mpint1 rsa_e + mpint1 rsa_n + mpint1 encrypted_challenge + byte[16] session_id + uint32 response_type /* must be 1 */ + +"rsa_e" and "rsa_n" are used to identify which private key to use. +"encrypted_challenge" is a challenge blob that has (presumably) +been encrypted with the public key and must be in the range +1 <= encrypted_challenge < 2^256. "session_id" is the SSH protocol 1 +session ID (computed from the server host key, the server semi-ephemeral +key and the session cookie.) + +"ignored" and "response_type" exist for compatibility with legacy +implementations. "response_type" must be equal to 1; other response +types are not supported. + +On receiving this request, the server decrypts the "encrypted_challenge" +using private key matching the supplied (rsa_e, rsa_n) values. For +the response derivation, the decrypted challenge is represented as an +unsigned, big-endian integer encoded in a 32 byte buffer (i.e. values +smaller than 2^248 will have leading 0 bytes). + +The response value is then calculated as: + + response = MD5(decrypted_challenge || session_id) + +and returned in the following message + + byte SSH_AGENT_RSA_RESPONSE + byte[16] response + +If the agent cannot find the key specified by the supplied (rsa_e, +rsa_n) then it will return SSH_AGENT_FAILURE. + +2.6.2 Protocol 2 private key signature request + +A client may use the following message to request signing of data using +a protocol 2 key: + + byte SSH2_AGENTC_SIGN_REQUEST + string key_blob + string data + uint32 flags + +Where "key_blob" is encoded as per RFC 4253 section 6.6 "Public Key +Algorithms" for either of the supported key types: "ssh-dss" or +"ssh-rsa". "flags" is a bit-mask, but at present only one possible value +is defined (see below for its meaning): + + SSH_AGENT_OLD_SIGNATURE 1 + +Upon receiving this request, the agent will look up the private key that +corresponds to the public key contained in key_blob. It will use this +private key to sign the "data" and produce a signature blob using the +key type-specific method described in RFC 4253 section 6.6 "Public Key +Algorithms". + +An exception to this is for "ssh-dss" keys where the "flags" word +contains the value SSH_AGENT_OLD_SIGNATURE. In this case, a legacy +signature encoding is used in lieu of the standard one. In this case, +the DSA signature blob is encoded as: + + byte[40] signature + +The signature will be returned in the response message: + + byte SSH2_AGENT_SIGN_RESPONSE + string signature_blob + +If the agent cannot find the key specified by the supplied key_blob then +it will return SSH_AGENT_FAILURE. + +2.7 Locking or unlocking an agent + +The agent supports temporary locking with a passphrase to suspend +processing of sensitive operations until it has been unlocked with the +same passphrase. To lock an agent, a client send the following request: + + byte SSH_AGENTC_LOCK + string passphrase + +Upon receipt of this message and if the agent is not already locked, +it will suspend processing requests and return a SSH_AGENT_SUCCESS +reply. If the agent is already locked, it will return SSH_AGENT_FAILURE. + +While locked, the agent will refuse all requests except +SSH_AGENTC_UNLOCK, SSH_AGENTC_REQUEST_RSA_IDENTITIES and +SSH2_AGENTC_REQUEST_IDENTITIES. The "request identities" requests are +treated specially by a locked agent: it will always return an empty list +of keys. + +To unlock an agent, a client may request: + + byte SSH_AGENTC_UNLOCK + string passphrase + +If the passphrase matches and the agent is locked, then it will resume +processing all requests and return SSH_AGENT_SUCCESS. If the agent +is not locked or the passphrase does not match then it will return +SSH_AGENT_FAILURE. + +Locking and unlocking affects both protocol 1 and protocol 2 keys. + +3. Protocol message numbers + +3.1 Requests from client to agent for protocol 1 key operations + + SSH_AGENTC_REQUEST_RSA_IDENTITIES 1 + SSH_AGENTC_RSA_CHALLENGE 3 + SSH_AGENTC_ADD_RSA_IDENTITY 7 + SSH_AGENTC_REMOVE_RSA_IDENTITY 8 + SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES 9 + SSH_AGENTC_ADD_RSA_ID_CONSTRAINED 24 + +3.2 Requests from client to agent for protocol 2 key operations + + SSH2_AGENTC_REQUEST_IDENTITIES 11 + SSH2_AGENTC_SIGN_REQUEST 13 + SSH2_AGENTC_ADD_IDENTITY 17 + SSH2_AGENTC_REMOVE_IDENTITY 18 + SSH2_AGENTC_REMOVE_ALL_IDENTITIES 19 + SSH2_AGENTC_ADD_ID_CONSTRAINED 25 + +3.3 Key-type independent requests from client to agent + + SSH_AGENTC_ADD_SMARTCARD_KEY 20 + SSH_AGENTC_REMOVE_SMARTCARD_KEY 21 + SSH_AGENTC_LOCK 22 + SSH_AGENTC_UNLOCK 23 + SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED 26 + +3.4 Generic replies from agent to client + + SSH_AGENT_FAILURE 5 + SSH_AGENT_SUCCESS 6 + +3.5 Replies from agent to client for protocol 1 key operations + + SSH_AGENT_RSA_IDENTITIES_ANSWER 2 + SSH_AGENT_RSA_RESPONSE 4 + +3.6 Replies from agent to client for protocol 2 key operations + + SSH2_AGENT_IDENTITIES_ANSWER 12 + SSH2_AGENT_SIGN_RESPONSE 14 + +3.7 Key constraint identifiers + + SSH_AGENT_CONSTRAIN_LIFETIME 1 + SSH_AGENT_CONSTRAIN_CONFIRM 2 + +$OpenBSD: PROTOCOL.agent,v 1.1 2008/06/28 14:08:30 djm Exp $ |