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Annotation of src/usr.bin/ssh/PROTOCOL, Revision 1.43

1.1 djm 1: This documents OpenSSH's deviations and extensions to the published SSH
2: protocol.
3:
1.2 djm 4: Note that OpenSSH's sftp and sftp-server implement revision 3 of the SSH
5: filexfer protocol described in:
1.1 djm 6:
7: http://www.openssh.com/txt/draft-ietf-secsh-filexfer-02.txt
8:
1.14 djm 9: Newer versions of the draft will not be supported, though some features
10: are individually implemented as extensions described below.
1.1 djm 11:
1.9 djm 12: The protocol used by OpenSSH's ssh-agent is described in the file
13: PROTOCOL.agent
14:
1.16 djm 15: 1. Transport protocol changes
16:
17: 1.1. transport: Protocol 2 MAC algorithm "umac-64@openssh.com"
1.1 djm 18:
19: This is a new transport-layer MAC method using the UMAC algorithm
20: (rfc4418). This method is identical to the "umac-64" method documented
21: in:
22:
23: http://www.openssh.com/txt/draft-miller-secsh-umac-01.txt
24:
1.16 djm 25: 1.2. transport: Protocol 2 compression algorithm "zlib@openssh.com"
1.1 djm 26:
27: This transport-layer compression method uses the zlib compression
28: algorithm (identical to the "zlib" method in rfc4253), but delays the
29: start of compression until after authentication has completed. This
1.2 djm 30: avoids exposing compression code to attacks from unauthenticated users.
1.1 djm 31:
32: The method is documented in:
33:
34: http://www.openssh.com/txt/draft-miller-secsh-compression-delayed-00.txt
35:
1.31 djm 36: 1.3. transport: New public key algorithms "ssh-rsa-cert-v01@openssh.com",
37: "ssh-dsa-cert-v01@openssh.com",
1.16 djm 38: "ecdsa-sha2-nistp256-cert-v01@openssh.com",
39: "ecdsa-sha2-nistp384-cert-v01@openssh.com" and
40: "ecdsa-sha2-nistp521-cert-v01@openssh.com"
1.15 djm 41:
1.16 djm 42: OpenSSH introduces new public key algorithms to support certificate
1.26 djm 43: authentication for users and host keys. These methods are documented
44: in the file PROTOCOL.certkeys
1.15 djm 45:
1.16 djm 46: 1.4. transport: Elliptic Curve cryptography
47:
48: OpenSSH supports ECC key exchange and public key authentication as
49: specified in RFC5656. Only the ecdsa-sha2-nistp256, ecdsa-sha2-nistp384
50: and ecdsa-sha2-nistp521 curves over GF(p) are supported. Elliptic
51: curve points encoded using point compression are NOT accepted or
52: generated.
53:
1.18 markus 54: 1.5 transport: Protocol 2 Encrypt-then-MAC MAC algorithms
55:
56: OpenSSH supports MAC algorithms, whose names contain "-etm", that
57: perform the calculations in a different order to that defined in RFC
58: 4253. These variants use the so-called "encrypt then MAC" ordering,
59: calculating the MAC over the packet ciphertext rather than the
60: plaintext. This ordering closes a security flaw in the SSH transport
61: protocol, where decryption of unauthenticated ciphertext provided a
62: "decryption oracle" that could, in conjunction with cipher flaws, reveal
63: session plaintext.
64:
65: Specifically, the "-etm" MAC algorithms modify the transport protocol
66: to calculate the MAC over the packet ciphertext and to send the packet
67: length unencrypted. This is necessary for the transport to obtain the
68: length of the packet and location of the MAC tag so that it may be
69: verified without decrypting unauthenticated data.
70:
71: As such, the MAC covers:
72:
1.19 djm 73: mac = MAC(key, sequence_number || packet_length || encrypted_packet)
1.18 markus 74:
1.19 djm 75: where "packet_length" is encoded as a uint32 and "encrypted_packet"
76: contains:
1.18 markus 77:
78: byte padding_length
79: byte[n1] payload; n1 = packet_length - padding_length - 1
80: byte[n2] random padding; n2 = padding_length
81:
1.20 markus 82: 1.6 transport: AES-GCM
83:
84: OpenSSH supports the AES-GCM algorithm as specified in RFC 5647.
85: Because of problems with the specification of the key exchange
86: the behaviour of OpenSSH differs from the RFC as follows:
87:
88: AES-GCM is only negotiated as the cipher algorithms
89: "aes128-gcm@openssh.com" or "aes256-gcm@openssh.com" and never as
90: an MAC algorithm. Additionally, if AES-GCM is selected as the cipher
91: the exchanged MAC algorithms are ignored and there doesn't have to be
92: a matching MAC.
93:
1.22 djm 94: 1.7 transport: chacha20-poly1305@openssh.com authenticated encryption
95:
96: OpenSSH supports authenticated encryption using ChaCha20 and Poly1305
97: as described in PROTOCOL.chacha20poly1305.
98:
1.23 djm 99: 1.8 transport: curve25519-sha256@libssh.org key exchange algorithm
100:
101: OpenSSH supports the use of ECDH in Curve25519 for key exchange as
102: described at:
103: http://git.libssh.org/users/aris/libssh.git/plain/doc/curve25519-sha256@libssh.org.txt?h=curve25519
104:
1.16 djm 105: 2. Connection protocol changes
106:
107: 2.1. connection: Channel write close extension "eow@openssh.com"
1.1 djm 108:
109: The SSH connection protocol (rfc4254) provides the SSH_MSG_CHANNEL_EOF
110: message to allow an endpoint to signal its peer that it will send no
111: more data over a channel. Unfortunately, there is no symmetric way for
112: an endpoint to request that its peer should cease sending data to it
113: while still keeping the channel open for the endpoint to send data to
114: the peer.
115:
1.2 djm 116: This is desirable, since it saves the transmission of data that would
1.1 djm 117: otherwise need to be discarded and it allows an endpoint to signal local
118: processes of the condition, e.g. by closing the corresponding file
119: descriptor.
120:
121: OpenSSH implements a channel extension message to perform this
1.10 djm 122: signalling: "eow@openssh.com" (End Of Write). This message is sent by
123: an endpoint when the local output of a session channel is closed or
124: experiences a write error. The message is formatted as follows:
1.1 djm 125:
126: byte SSH_MSG_CHANNEL_REQUEST
127: uint32 recipient channel
128: string "eow@openssh.com"
129: boolean FALSE
130:
131: On receiving this message, the peer SHOULD cease sending data of
132: the channel and MAY signal the process from which the channel data
133: originates (e.g. by closing its read file descriptor).
134:
135: As with the symmetric SSH_MSG_CHANNEL_EOF message, the channel does
136: remain open after a "eow@openssh.com" has been sent and more data may
137: still be sent in the other direction. This message does not consume
138: window space and may be sent even if no window space is available.
139:
1.12 djm 140: NB. due to certain broken SSH implementations aborting upon receipt
141: of this message (in contravention of RFC4254 section 5.4), this
142: message is only sent to OpenSSH peers (identified by banner).
1.38 djm 143: Other SSH implementations may be listed to receive this message
1.12 djm 144: upon request.
145:
1.16 djm 146: 2.2. connection: disallow additional sessions extension
147: "no-more-sessions@openssh.com"
1.6 djm 148:
149: Most SSH connections will only ever request a single session, but a
150: attacker may abuse a running ssh client to surreptitiously open
151: additional sessions under their control. OpenSSH provides a global
152: request "no-more-sessions@openssh.com" to mitigate this attack.
153:
154: When an OpenSSH client expects that it will never open another session
155: (i.e. it has been started with connection multiplexing disabled), it
156: will send the following global request:
157:
158: byte SSH_MSG_GLOBAL_REQUEST
159: string "no-more-sessions@openssh.com"
160: char want-reply
161:
162: On receipt of such a message, an OpenSSH server will refuse to open
163: future channels of type "session" and instead immediately abort the
164: connection.
165:
166: Note that this is not a general defence against compromised clients
167: (that is impossible), but it thwarts a simple attack.
168:
1.12 djm 169: NB. due to certain broken SSH implementations aborting upon receipt
170: of this message, the no-more-sessions request is only sent to OpenSSH
171: servers (identified by banner). Other SSH implementations may be
1.38 djm 172: listed to receive this message upon request.
1.12 djm 173:
1.16 djm 174: 2.3. connection: Tunnel forward extension "tun@openssh.com"
1.7 djm 175:
1.8 djm 176: OpenSSH supports layer 2 and layer 3 tunnelling via the "tun@openssh.com"
1.7 djm 177: channel type. This channel type supports forwarding of network packets
1.28 djm 178: with datagram boundaries intact between endpoints equipped with
1.7 djm 179: interfaces like the BSD tun(4) device. Tunnel forwarding channels are
180: requested by the client with the following packet:
181:
182: byte SSH_MSG_CHANNEL_OPEN
183: string "tun@openssh.com"
184: uint32 sender channel
185: uint32 initial window size
186: uint32 maximum packet size
187: uint32 tunnel mode
188: uint32 remote unit number
189:
190: The "tunnel mode" parameter specifies whether the tunnel should forward
191: layer 2 frames or layer 3 packets. It may take one of the following values:
192:
193: SSH_TUNMODE_POINTOPOINT 1 /* layer 3 packets */
194: SSH_TUNMODE_ETHERNET 2 /* layer 2 frames */
195:
196: The "tunnel unit number" specifies the remote interface number, or may
1.37 dtucker 197: be 0x7fffffff to allow the server to automatically choose an interface. A
1.13 djm 198: server that is not willing to open a client-specified unit should refuse
199: the request with a SSH_MSG_CHANNEL_OPEN_FAILURE error. On successful
200: open, the server should reply with SSH_MSG_CHANNEL_OPEN_SUCCESS.
1.7 djm 201:
202: Once established the client and server may exchange packet or frames
203: over the tunnel channel by encapsulating them in SSH protocol strings
204: and sending them as channel data. This ensures that packet boundaries
205: are kept intact. Specifically, packets are transmitted using normal
206: SSH_MSG_CHANNEL_DATA packets:
207:
208: byte SSH_MSG_CHANNEL_DATA
209: uint32 recipient channel
210: string data
211:
212: The contents of the "data" field for layer 3 packets is:
213:
214: uint32 packet length
215: uint32 address family
216: byte[packet length - 4] packet data
217:
218: The "address family" field identifies the type of packet in the message.
219: It may be one of:
220:
221: SSH_TUN_AF_INET 2 /* IPv4 */
222: SSH_TUN_AF_INET6 24 /* IPv6 */
223:
224: The "packet data" field consists of the IPv4/IPv6 datagram itself
225: without any link layer header.
226:
1.13 djm 227: The contents of the "data" field for layer 2 packets is:
1.7 djm 228:
229: uint32 packet length
230: byte[packet length] frame
231:
1.8 djm 232: The "frame" field contains an IEEE 802.3 Ethernet frame, including
1.7 djm 233: header.
234:
1.24 millert 235: 2.4. connection: Unix domain socket forwarding
236:
237: OpenSSH supports local and remote Unix domain socket forwarding
238: using the "streamlocal" extension. Forwarding is initiated as per
239: TCP sockets but with a single path instead of a host and port.
240:
241: Similar to direct-tcpip, direct-streamlocal is sent by the client
242: to request that the server make a connection to a Unix domain socket.
243:
244: byte SSH_MSG_CHANNEL_OPEN
245: string "direct-streamlocal@openssh.com"
246: uint32 sender channel
247: uint32 initial window size
248: uint32 maximum packet size
249: string socket path
1.30 djm 250: string reserved
251: uint32 reserved
1.24 millert 252:
253: Similar to forwarded-tcpip, forwarded-streamlocal is sent by the
254: server when the client has previously send the server a streamlocal-forward
255: GLOBAL_REQUEST.
256:
257: byte SSH_MSG_CHANNEL_OPEN
258: string "forwarded-streamlocal@openssh.com"
259: uint32 sender channel
260: uint32 initial window size
261: uint32 maximum packet size
262: string socket path
263: string reserved for future use
264:
265: The reserved field is not currently defined and is ignored on the
266: remote end. It is intended to be used in the future to pass
267: information about the socket file, such as ownership and mode.
268: The client currently sends the empty string for this field.
269:
270: Similar to tcpip-forward, streamlocal-forward is sent by the client
271: to request remote forwarding of a Unix domain socket.
272:
273: byte SSH2_MSG_GLOBAL_REQUEST
274: string "streamlocal-forward@openssh.com"
275: boolean TRUE
276: string socket path
277:
278: Similar to cancel-tcpip-forward, cancel-streamlocal-forward is sent
279: by the client cancel the forwarding of a Unix domain socket.
280:
281: byte SSH2_MSG_GLOBAL_REQUEST
282: string "cancel-streamlocal-forward@openssh.com"
283: boolean FALSE
284: string socket path
285:
1.27 djm 286: 2.5. connection: hostkey update and rotation "hostkeys-00@openssh.com"
287: and "hostkeys-prove-00@openssh.com"
1.25 djm 288:
289: OpenSSH supports a protocol extension allowing a server to inform
1.26 djm 290: a client of all its protocol v.2 host keys after user-authentication
1.25 djm 291: has completed.
292:
293: byte SSH_MSG_GLOBAL_REQUEST
1.27 djm 294: string "hostkeys-00@openssh.com"
1.41 djm 295: char 0 /* want-reply */
1.25 djm 296: string[] hostkeys
297:
1.26 djm 298: Upon receiving this message, a client should check which of the
1.32 djm 299: supplied host keys are present in known_hosts.
300:
301: Note that the server may send key types that the client does not
1.37 dtucker 302: support. The client should disregard such keys if they are received.
1.32 djm 303:
304: If the client identifies any keys that are not present for the host,
305: it should send a "hostkeys-prove@openssh.com" message to request the
306: server prove ownership of the private half of the key.
1.26 djm 307:
308: byte SSH_MSG_GLOBAL_REQUEST
1.27 djm 309: string "hostkeys-prove-00@openssh.com"
1.26 djm 310: char 1 /* want-reply */
311: string[] hostkeys
312:
313: When a server receives this message, it should generate a signature
314: using each requested key over the following:
315:
1.27 djm 316: string "hostkeys-prove-00@openssh.com"
1.26 djm 317: string session identifier
318: string hostkey
319:
320: These signatures should be included in the reply, in the order matching
321: the hostkeys in the request:
322:
323: byte SSH_MSG_REQUEST_SUCCESS
324: string[] signatures
325:
326: When the client receives this reply (and not a failure), it should
327: validate the signatures and may update its known_hosts file, adding keys
328: that it has not seen before and deleting keys for the server host that
329: are no longer offered.
330:
331: These extensions let a client learn key types that it had not previously
332: encountered, thereby allowing it to potentially upgrade from weaker
333: key algorithms to better ones. It also supports graceful key rotation:
334: a server may offer multiple keys of the same type for a period (to
335: give clients an opportunity to learn them using this extension) before
336: removing the deprecated key from those offered.
1.25 djm 337:
1.36 djm 338: 2.6. connection: SIGINFO support for "signal" channel request
339:
340: The SSH channels protocol (RFC4254 section 6.9) supports sending a
341: signal to a session attached to a channel. OpenSSH supports one
342: extension signal "INFO@openssh.com" that allows sending SIGINFO on
343: BSD-derived systems.
344:
1.43 ! djm 345: 3. Authentication protocol changes
1.16 djm 346:
1.43 ! djm 347: 3.1. Host-bound public key authentication
! 348:
! 349: This is trivial change to the traditional "publickey" authentication
! 350: method. The authentication request is identical to the original method
! 351: but for the name and one additional field:
! 352:
! 353: byte SSH2_MSG_USERAUTH_REQUEST
! 354: string username
! 355: string "ssh-connection"
! 356: string "publickey-hostbound-v00@openssh.com"
! 357: bool has_signature
! 358: string pkalg
! 359: string public key
! 360: string server host key
! 361:
! 362: Because the entire SSH2_MSG_USERAUTH_REQUEST message is included in
! 363: the signed data, this ensures that a binding between the destination
! 364: user, the server identity and the session identifier is visible to the
! 365: signer. OpenSSH uses this binding via signed data to implement per-key
! 366: restrictions in ssh-agent.
! 367:
! 368: A server may advertise this method using the SSH2_MSG_EXT_INFO
! 369: mechanism (RFC8308), with the following message:
! 370:
! 371: string "publickey-hostbound@openssh.com"
! 372: string "0" (version)
! 373:
! 374: Clients should prefer host-bound authentication when advertised by
! 375: server.
! 376:
! 377: 4. SFTP protocol changes
! 378:
! 379: 4.1. sftp: Reversal of arguments to SSH_FXP_SYMLINK
1.1 djm 380:
381: When OpenSSH's sftp-server was implemented, the order of the arguments
1.8 djm 382: to the SSH_FXP_SYMLINK method was inadvertently reversed. Unfortunately,
1.1 djm 383: the reversal was not noticed until the server was widely deployed. Since
384: fixing this to follow the specification would cause incompatibility, the
385: current order was retained. For correct operation, clients should send
386: SSH_FXP_SYMLINK as follows:
387:
388: uint32 id
389: string targetpath
390: string linkpath
391:
1.43 ! djm 392: 4.2. sftp: Server extension announcement in SSH_FXP_VERSION
1.1 djm 393:
394: OpenSSH's sftp-server lists the extensions it supports using the
395: standard extension announcement mechanism in the SSH_FXP_VERSION server
396: hello packet:
397:
398: uint32 3 /* protocol version */
399: string ext1-name
400: string ext1-version
401: string ext2-name
402: string ext2-version
403: ...
404: string extN-name
405: string extN-version
406:
407: Each extension reports its integer version number as an ASCII encoded
408: string, e.g. "1". The version will be incremented if the extension is
409: ever changed in an incompatible way. The server MAY advertise the same
410: extension with multiple versions (though this is unlikely). Clients MUST
1.8 djm 411: check the version number before attempting to use the extension.
1.1 djm 412:
1.43 ! djm 413: 4.3. sftp: Extension request "posix-rename@openssh.com"
1.1 djm 414:
415: This operation provides a rename operation with POSIX semantics, which
416: are different to those provided by the standard SSH_FXP_RENAME in
417: draft-ietf-secsh-filexfer-02.txt. This request is implemented as a
418: SSH_FXP_EXTENDED request with the following format:
419:
420: uint32 id
421: string "posix-rename@openssh.com"
422: string oldpath
423: string newpath
424:
425: On receiving this request the server will perform the POSIX operation
426: rename(oldpath, newpath) and will respond with a SSH_FXP_STATUS message.
427: This extension is advertised in the SSH_FXP_VERSION hello with version
428: "1".
429:
1.43 ! djm 430: 4.4. sftp: Extension requests "statvfs@openssh.com" and
1.2 djm 431: "fstatvfs@openssh.com"
1.1 djm 432:
433: These requests correspond to the statvfs and fstatvfs POSIX system
434: interfaces. The "statvfs@openssh.com" request operates on an explicit
435: pathname, and is formatted as follows:
436:
437: uint32 id
438: string "statvfs@openssh.com"
439: string path
440:
1.8 djm 441: The "fstatvfs@openssh.com" operates on an open file handle:
1.1 djm 442:
443: uint32 id
1.2 djm 444: string "fstatvfs@openssh.com"
1.1 djm 445: string handle
446:
447: These requests return a SSH_FXP_STATUS reply on failure. On success they
448: return the following SSH_FXP_EXTENDED_REPLY reply:
449:
450: uint32 id
1.4 dtucker 451: uint64 f_bsize /* file system block size */
452: uint64 f_frsize /* fundamental fs block size */
1.1 djm 453: uint64 f_blocks /* number of blocks (unit f_frsize) */
454: uint64 f_bfree /* free blocks in file system */
455: uint64 f_bavail /* free blocks for non-root */
456: uint64 f_files /* total file inodes */
457: uint64 f_ffree /* free file inodes */
458: uint64 f_favail /* free file inodes for to non-root */
1.3 djm 459: uint64 f_fsid /* file system id */
1.4 dtucker 460: uint64 f_flag /* bit mask of f_flag values */
461: uint64 f_namemax /* maximum filename length */
1.1 djm 462:
463: The values of the f_flag bitmask are as follows:
464:
465: #define SSH_FXE_STATVFS_ST_RDONLY 0x1 /* read-only */
466: #define SSH_FXE_STATVFS_ST_NOSUID 0x2 /* no setuid */
467:
1.11 djm 468: Both the "statvfs@openssh.com" and "fstatvfs@openssh.com" extensions are
469: advertised in the SSH_FXP_VERSION hello with version "2".
1.3 djm 470:
1.43 ! djm 471: 4.5. sftp: Extension request "hardlink@openssh.com"
1.17 djm 472:
473: This request is for creating a hard link to a regular file. This
474: request is implemented as a SSH_FXP_EXTENDED request with the
475: following format:
476:
477: uint32 id
478: string "hardlink@openssh.com"
479: string oldpath
480: string newpath
481:
482: On receiving this request the server will perform the operation
483: link(oldpath, newpath) and will respond with a SSH_FXP_STATUS message.
484: This extension is advertised in the SSH_FXP_VERSION hello with version
485: "1".
486:
1.43 ! djm 487: 4.6. sftp: Extension request "fsync@openssh.com"
1.21 djm 488:
489: This request asks the server to call fsync(2) on an open file handle.
490:
491: uint32 id
492: string "fsync@openssh.com"
493: string handle
494:
495: One receiving this request, a server will call fsync(handle_fd) and will
496: respond with a SSH_FXP_STATUS message.
497:
498: This extension is advertised in the SSH_FXP_VERSION hello with version
499: "1".
500:
1.43 ! djm 501: 4.7. sftp: Extension request "lsetstat@openssh.com"
1.39 djm 502:
503: This request is like the "setstat" command, but sets file attributes on
504: symlinks. It is implemented as a SSH_FXP_EXTENDED request with the
505: following format:
506:
507: uint32 id
508: string "lsetstat@openssh.com"
509: string path
510: ATTRS attrs
511:
512: See the "setstat" command for more details.
513:
514: This extension is advertised in the SSH_FXP_VERSION hello with version
515: "1".
516:
1.43 ! djm 517: 4.8. sftp: Extension request "limits@openssh.com"
1.40 djm 518:
519: This request is used to determine various limits the server might impose.
520: Clients should not attempt to exceed these limits as the server might sever
521: the connection immediately.
522:
523: uint32 id
524: string "limits@openssh.com"
525:
526: The server will respond with a SSH_FXP_EXTENDED_REPLY reply:
527:
528: uint32 id
529: uint64 max-packet-length
530: uint64 max-read-length
531: uint64 max-write-length
532: uint64 max-open-handles
533:
534: The 'max-packet-length' applies to the total number of bytes in a
535: single SFTP packet. Servers SHOULD set this at least to 34000.
536:
537: The 'max-read-length' is the largest length in a SSH_FXP_READ packet.
538: Even if the client requests a larger size, servers will usually respond
539: with a shorter SSH_FXP_DATA packet. Servers SHOULD set this at least to
540: 32768.
541:
542: The 'max-write-length' is the largest length in a SSH_FXP_WRITE packet
543: the server will accept. Servers SHOULD set this at least to 32768.
544:
545: The 'max-open-handles' is the maximum number of active handles that the
546: server allows (e.g. handles created by SSH_FXP_OPEN and SSH_FXP_OPENDIR
547: packets). Servers MAY count internal file handles against this limit
548: (e.g. system logging or stdout/stderr), so clients SHOULD NOT expect to
549: open this many handles in practice.
550:
551: If the server doesn't enforce a specific limit, then the field may be
552: set to 0. This implies the server relies on the OS to enforce limits
553: (e.g. available memory or file handles), and such limits might be
554: dynamic. The client SHOULD take care to not try to exceed reasonable
555: limits.
556:
557: This extension is advertised in the SSH_FXP_VERSION hello with version
558: "1".
559:
1.43 ! djm 560: 4.9. sftp: Extension request "expand-path@openssh.com"
1.42 djm 561:
562: This request supports canonicalisation of relative paths and
563: those that need tilde-expansion, i.e. "~", "~/..." and "~user/..."
564: These paths are expanded using shell-like rules and the resultant
565: path is canonicalised similarly to SSH2_FXP_REALPATH.
566:
567: It is implemented as a SSH_FXP_EXTENDED request with the following
568: format:
569:
570: uint32 id
571: string "expand-path@openssh.com"
572: string path
573:
574: Its reply is the same format as that of SSH2_FXP_REALPATH.
575:
576: This extension is advertised in the SSH_FXP_VERSION hello with version
577: "1".
578:
1.43 ! djm 579: 5. Miscellaneous changes
1.34 djm 580:
1.43 ! djm 581: 5.1 Public key format
1.34 djm 582:
583: OpenSSH public keys, as generated by ssh-keygen(1) and appearing in
584: authorized_keys files, are formatted as a single line of text consisting
585: of the public key algorithm name followed by a base64-encoded key blob.
1.35 djm 586: The public key blob (before base64 encoding) is the same format used for
587: the encoding of public keys sent on the wire: as described in RFC4253
588: section 6.6 for RSA and DSA keys, RFC5656 section 3.1 for ECDSA keys
589: and the "New public key formats" section of PROTOCOL.certkeys for the
590: OpenSSH certificate formats.
1.34 djm 591:
1.43 ! djm 592: 5.2 Private key format
1.34 djm 593:
594: OpenSSH private keys, as generated by ssh-keygen(1) use the format
595: described in PROTOCOL.key by default. As a legacy option, PEM format
596: (RFC7468) private keys are also supported for RSA, DSA and ECDSA keys
597: and were the default format before OpenSSH 7.8.
598:
1.43 ! djm 599: 5.3 KRL format
1.34 djm 600:
601: OpenSSH supports a compact format for Key Revocation Lists (KRLs). This
602: format is described in the PROTOCOL.krl file.
603:
1.43 ! djm 604: 5.4 Connection multiplexing
1.34 djm 605:
606: OpenSSH's connection multiplexing uses messages as described in
607: PROTOCOL.mux over a Unix domain socket for communications between a
608: master instance and later clients.
609:
1.43 ! djm 610: 5.5. Agent protocol extensions
! 611:
! 612: OpenSSH extends the usual agent protocol. These changes are documented
! 613: in the PROTOCOL.agent file.
! 614:
! 615: $OpenBSD: PROTOCOL,v 1.42 2021/08/09 23:47:44 djm Exp $