Annotation of src/usr.bin/ssh/PROTOCOL, Revision 1.49
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:
1.45 dtucker 105: This is identical to curve25519-sha256 as later published in RFC8731.
106:
1.49 ! djm 107: 1.9 transport: ping facility
! 108:
! 109: OpenSSH implements a transport level ping message SSH2_MSG_PING
! 110: and a corresponding SSH2_MSG_PONG reply.
! 111:
! 112: #define SSH2_MSG_PING 192
! 113: #define SSH2_MSG_PONG 193
! 114:
! 115: The ping message is simply:
! 116:
! 117: byte SSH_MSG_PING
! 118: string data
! 119:
! 120: The reply copies the data (which may be the empty string) from the
! 121: ping:
! 122:
! 123: byte SSH_MSG_PONG
! 124: string data
! 125:
! 126: Replies are sent in order. They are sent immediately except when rekeying
! 127: is in progress, in which case they are queued until rekeying completes.
! 128:
! 129: The server advertises support for these messages using the
! 130: SSH2_MSG_EXT_INFO mechanism (RFC8308), with the following message:
! 131:
! 132: string "ping@openssh.com"
! 133: string "0" (version)
! 134:
! 135: The ping/reply message is implemented at the transport layer rather
! 136: than as a named global or channel request to allow pings with very
! 137: short packet lengths, which would not be possible with other
! 138: approaches.
! 139:
1.16 djm 140: 2. Connection protocol changes
141:
142: 2.1. connection: Channel write close extension "eow@openssh.com"
1.1 djm 143:
144: The SSH connection protocol (rfc4254) provides the SSH_MSG_CHANNEL_EOF
145: message to allow an endpoint to signal its peer that it will send no
146: more data over a channel. Unfortunately, there is no symmetric way for
147: an endpoint to request that its peer should cease sending data to it
148: while still keeping the channel open for the endpoint to send data to
149: the peer.
150:
1.2 djm 151: This is desirable, since it saves the transmission of data that would
1.1 djm 152: otherwise need to be discarded and it allows an endpoint to signal local
153: processes of the condition, e.g. by closing the corresponding file
154: descriptor.
155:
156: OpenSSH implements a channel extension message to perform this
1.10 djm 157: signalling: "eow@openssh.com" (End Of Write). This message is sent by
158: an endpoint when the local output of a session channel is closed or
159: experiences a write error. The message is formatted as follows:
1.1 djm 160:
161: byte SSH_MSG_CHANNEL_REQUEST
162: uint32 recipient channel
163: string "eow@openssh.com"
164: boolean FALSE
165:
166: On receiving this message, the peer SHOULD cease sending data of
167: the channel and MAY signal the process from which the channel data
168: originates (e.g. by closing its read file descriptor).
169:
170: As with the symmetric SSH_MSG_CHANNEL_EOF message, the channel does
171: remain open after a "eow@openssh.com" has been sent and more data may
172: still be sent in the other direction. This message does not consume
173: window space and may be sent even if no window space is available.
174:
1.12 djm 175: NB. due to certain broken SSH implementations aborting upon receipt
176: of this message (in contravention of RFC4254 section 5.4), this
177: message is only sent to OpenSSH peers (identified by banner).
1.38 djm 178: Other SSH implementations may be listed to receive this message
1.12 djm 179: upon request.
180:
1.16 djm 181: 2.2. connection: disallow additional sessions extension
182: "no-more-sessions@openssh.com"
1.6 djm 183:
184: Most SSH connections will only ever request a single session, but a
185: attacker may abuse a running ssh client to surreptitiously open
186: additional sessions under their control. OpenSSH provides a global
187: request "no-more-sessions@openssh.com" to mitigate this attack.
188:
189: When an OpenSSH client expects that it will never open another session
190: (i.e. it has been started with connection multiplexing disabled), it
191: will send the following global request:
192:
193: byte SSH_MSG_GLOBAL_REQUEST
194: string "no-more-sessions@openssh.com"
195: char want-reply
196:
197: On receipt of such a message, an OpenSSH server will refuse to open
198: future channels of type "session" and instead immediately abort the
199: connection.
200:
201: Note that this is not a general defence against compromised clients
202: (that is impossible), but it thwarts a simple attack.
203:
1.12 djm 204: NB. due to certain broken SSH implementations aborting upon receipt
205: of this message, the no-more-sessions request is only sent to OpenSSH
206: servers (identified by banner). Other SSH implementations may be
1.38 djm 207: listed to receive this message upon request.
1.12 djm 208:
1.16 djm 209: 2.3. connection: Tunnel forward extension "tun@openssh.com"
1.7 djm 210:
1.8 djm 211: OpenSSH supports layer 2 and layer 3 tunnelling via the "tun@openssh.com"
1.7 djm 212: channel type. This channel type supports forwarding of network packets
1.28 djm 213: with datagram boundaries intact between endpoints equipped with
1.7 djm 214: interfaces like the BSD tun(4) device. Tunnel forwarding channels are
215: requested by the client with the following packet:
216:
217: byte SSH_MSG_CHANNEL_OPEN
218: string "tun@openssh.com"
219: uint32 sender channel
220: uint32 initial window size
221: uint32 maximum packet size
222: uint32 tunnel mode
223: uint32 remote unit number
224:
225: The "tunnel mode" parameter specifies whether the tunnel should forward
226: layer 2 frames or layer 3 packets. It may take one of the following values:
227:
228: SSH_TUNMODE_POINTOPOINT 1 /* layer 3 packets */
229: SSH_TUNMODE_ETHERNET 2 /* layer 2 frames */
230:
231: The "tunnel unit number" specifies the remote interface number, or may
1.37 dtucker 232: be 0x7fffffff to allow the server to automatically choose an interface. A
1.13 djm 233: server that is not willing to open a client-specified unit should refuse
234: the request with a SSH_MSG_CHANNEL_OPEN_FAILURE error. On successful
235: open, the server should reply with SSH_MSG_CHANNEL_OPEN_SUCCESS.
1.7 djm 236:
237: Once established the client and server may exchange packet or frames
238: over the tunnel channel by encapsulating them in SSH protocol strings
239: and sending them as channel data. This ensures that packet boundaries
240: are kept intact. Specifically, packets are transmitted using normal
241: SSH_MSG_CHANNEL_DATA packets:
242:
243: byte SSH_MSG_CHANNEL_DATA
244: uint32 recipient channel
245: string data
246:
247: The contents of the "data" field for layer 3 packets is:
248:
249: uint32 packet length
250: uint32 address family
251: byte[packet length - 4] packet data
252:
253: The "address family" field identifies the type of packet in the message.
254: It may be one of:
255:
256: SSH_TUN_AF_INET 2 /* IPv4 */
257: SSH_TUN_AF_INET6 24 /* IPv6 */
258:
259: The "packet data" field consists of the IPv4/IPv6 datagram itself
260: without any link layer header.
261:
1.13 djm 262: The contents of the "data" field for layer 2 packets is:
1.7 djm 263:
264: uint32 packet length
265: byte[packet length] frame
266:
1.8 djm 267: The "frame" field contains an IEEE 802.3 Ethernet frame, including
1.7 djm 268: header.
269:
1.24 millert 270: 2.4. connection: Unix domain socket forwarding
271:
272: OpenSSH supports local and remote Unix domain socket forwarding
273: using the "streamlocal" extension. Forwarding is initiated as per
274: TCP sockets but with a single path instead of a host and port.
275:
276: Similar to direct-tcpip, direct-streamlocal is sent by the client
277: to request that the server make a connection to a Unix domain socket.
278:
279: byte SSH_MSG_CHANNEL_OPEN
280: string "direct-streamlocal@openssh.com"
281: uint32 sender channel
282: uint32 initial window size
283: uint32 maximum packet size
284: string socket path
1.30 djm 285: string reserved
286: uint32 reserved
1.24 millert 287:
288: Similar to forwarded-tcpip, forwarded-streamlocal is sent by the
289: server when the client has previously send the server a streamlocal-forward
290: GLOBAL_REQUEST.
291:
292: byte SSH_MSG_CHANNEL_OPEN
293: string "forwarded-streamlocal@openssh.com"
294: uint32 sender channel
295: uint32 initial window size
296: uint32 maximum packet size
297: string socket path
298: string reserved for future use
299:
300: The reserved field is not currently defined and is ignored on the
301: remote end. It is intended to be used in the future to pass
302: information about the socket file, such as ownership and mode.
303: The client currently sends the empty string for this field.
304:
305: Similar to tcpip-forward, streamlocal-forward is sent by the client
306: to request remote forwarding of a Unix domain socket.
307:
308: byte SSH2_MSG_GLOBAL_REQUEST
309: string "streamlocal-forward@openssh.com"
310: boolean TRUE
311: string socket path
312:
313: Similar to cancel-tcpip-forward, cancel-streamlocal-forward is sent
314: by the client cancel the forwarding of a Unix domain socket.
315:
316: byte SSH2_MSG_GLOBAL_REQUEST
317: string "cancel-streamlocal-forward@openssh.com"
318: boolean FALSE
319: string socket path
320:
1.27 djm 321: 2.5. connection: hostkey update and rotation "hostkeys-00@openssh.com"
322: and "hostkeys-prove-00@openssh.com"
1.25 djm 323:
324: OpenSSH supports a protocol extension allowing a server to inform
1.26 djm 325: a client of all its protocol v.2 host keys after user-authentication
1.25 djm 326: has completed.
327:
328: byte SSH_MSG_GLOBAL_REQUEST
1.27 djm 329: string "hostkeys-00@openssh.com"
1.41 djm 330: char 0 /* want-reply */
1.25 djm 331: string[] hostkeys
332:
1.26 djm 333: Upon receiving this message, a client should check which of the
1.32 djm 334: supplied host keys are present in known_hosts.
335:
336: Note that the server may send key types that the client does not
1.37 dtucker 337: support. The client should disregard such keys if they are received.
1.32 djm 338:
339: If the client identifies any keys that are not present for the host,
340: it should send a "hostkeys-prove@openssh.com" message to request the
341: server prove ownership of the private half of the key.
1.26 djm 342:
343: byte SSH_MSG_GLOBAL_REQUEST
1.27 djm 344: string "hostkeys-prove-00@openssh.com"
1.26 djm 345: char 1 /* want-reply */
346: string[] hostkeys
347:
348: When a server receives this message, it should generate a signature
349: using each requested key over the following:
350:
1.27 djm 351: string "hostkeys-prove-00@openssh.com"
1.26 djm 352: string session identifier
353: string hostkey
354:
355: These signatures should be included in the reply, in the order matching
356: the hostkeys in the request:
357:
358: byte SSH_MSG_REQUEST_SUCCESS
359: string[] signatures
360:
361: When the client receives this reply (and not a failure), it should
362: validate the signatures and may update its known_hosts file, adding keys
363: that it has not seen before and deleting keys for the server host that
364: are no longer offered.
365:
366: These extensions let a client learn key types that it had not previously
367: encountered, thereby allowing it to potentially upgrade from weaker
368: key algorithms to better ones. It also supports graceful key rotation:
369: a server may offer multiple keys of the same type for a period (to
370: give clients an opportunity to learn them using this extension) before
371: removing the deprecated key from those offered.
1.25 djm 372:
1.36 djm 373: 2.6. connection: SIGINFO support for "signal" channel request
374:
375: The SSH channels protocol (RFC4254 section 6.9) supports sending a
376: signal to a session attached to a channel. OpenSSH supports one
377: extension signal "INFO@openssh.com" that allows sending SIGINFO on
378: BSD-derived systems.
379:
1.43 djm 380: 3. Authentication protocol changes
1.16 djm 381:
1.43 djm 382: 3.1. Host-bound public key authentication
383:
384: This is trivial change to the traditional "publickey" authentication
385: method. The authentication request is identical to the original method
386: but for the name and one additional field:
387:
388: byte SSH2_MSG_USERAUTH_REQUEST
389: string username
390: string "ssh-connection"
391: string "publickey-hostbound-v00@openssh.com"
392: bool has_signature
393: string pkalg
394: string public key
395: string server host key
396:
397: Because the entire SSH2_MSG_USERAUTH_REQUEST message is included in
398: the signed data, this ensures that a binding between the destination
399: user, the server identity and the session identifier is visible to the
400: signer. OpenSSH uses this binding via signed data to implement per-key
401: restrictions in ssh-agent.
402:
403: A server may advertise this method using the SSH2_MSG_EXT_INFO
404: mechanism (RFC8308), with the following message:
405:
406: string "publickey-hostbound@openssh.com"
407: string "0" (version)
408:
409: Clients should prefer host-bound authentication when advertised by
410: server.
411:
412: 4. SFTP protocol changes
413:
414: 4.1. sftp: Reversal of arguments to SSH_FXP_SYMLINK
1.1 djm 415:
416: When OpenSSH's sftp-server was implemented, the order of the arguments
1.8 djm 417: to the SSH_FXP_SYMLINK method was inadvertently reversed. Unfortunately,
1.1 djm 418: the reversal was not noticed until the server was widely deployed. Since
419: fixing this to follow the specification would cause incompatibility, the
420: current order was retained. For correct operation, clients should send
421: SSH_FXP_SYMLINK as follows:
422:
423: uint32 id
424: string targetpath
425: string linkpath
426:
1.43 djm 427: 4.2. sftp: Server extension announcement in SSH_FXP_VERSION
1.1 djm 428:
429: OpenSSH's sftp-server lists the extensions it supports using the
430: standard extension announcement mechanism in the SSH_FXP_VERSION server
431: hello packet:
432:
433: uint32 3 /* protocol version */
434: string ext1-name
435: string ext1-version
436: string ext2-name
437: string ext2-version
438: ...
439: string extN-name
440: string extN-version
441:
442: Each extension reports its integer version number as an ASCII encoded
443: string, e.g. "1". The version will be incremented if the extension is
444: ever changed in an incompatible way. The server MAY advertise the same
445: extension with multiple versions (though this is unlikely). Clients MUST
1.8 djm 446: check the version number before attempting to use the extension.
1.1 djm 447:
1.43 djm 448: 4.3. sftp: Extension request "posix-rename@openssh.com"
1.1 djm 449:
450: This operation provides a rename operation with POSIX semantics, which
451: are different to those provided by the standard SSH_FXP_RENAME in
452: draft-ietf-secsh-filexfer-02.txt. This request is implemented as a
453: SSH_FXP_EXTENDED request with the following format:
454:
455: uint32 id
456: string "posix-rename@openssh.com"
457: string oldpath
458: string newpath
459:
460: On receiving this request the server will perform the POSIX operation
461: rename(oldpath, newpath) and will respond with a SSH_FXP_STATUS message.
462: This extension is advertised in the SSH_FXP_VERSION hello with version
463: "1".
464:
1.43 djm 465: 4.4. sftp: Extension requests "statvfs@openssh.com" and
1.2 djm 466: "fstatvfs@openssh.com"
1.1 djm 467:
468: These requests correspond to the statvfs and fstatvfs POSIX system
469: interfaces. The "statvfs@openssh.com" request operates on an explicit
470: pathname, and is formatted as follows:
471:
472: uint32 id
473: string "statvfs@openssh.com"
474: string path
475:
1.8 djm 476: The "fstatvfs@openssh.com" operates on an open file handle:
1.1 djm 477:
478: uint32 id
1.2 djm 479: string "fstatvfs@openssh.com"
1.1 djm 480: string handle
481:
482: These requests return a SSH_FXP_STATUS reply on failure. On success they
483: return the following SSH_FXP_EXTENDED_REPLY reply:
484:
485: uint32 id
1.4 dtucker 486: uint64 f_bsize /* file system block size */
487: uint64 f_frsize /* fundamental fs block size */
1.1 djm 488: uint64 f_blocks /* number of blocks (unit f_frsize) */
489: uint64 f_bfree /* free blocks in file system */
490: uint64 f_bavail /* free blocks for non-root */
491: uint64 f_files /* total file inodes */
492: uint64 f_ffree /* free file inodes */
493: uint64 f_favail /* free file inodes for to non-root */
1.3 djm 494: uint64 f_fsid /* file system id */
1.4 dtucker 495: uint64 f_flag /* bit mask of f_flag values */
496: uint64 f_namemax /* maximum filename length */
1.1 djm 497:
498: The values of the f_flag bitmask are as follows:
499:
500: #define SSH_FXE_STATVFS_ST_RDONLY 0x1 /* read-only */
501: #define SSH_FXE_STATVFS_ST_NOSUID 0x2 /* no setuid */
502:
1.11 djm 503: Both the "statvfs@openssh.com" and "fstatvfs@openssh.com" extensions are
504: advertised in the SSH_FXP_VERSION hello with version "2".
1.3 djm 505:
1.43 djm 506: 4.5. sftp: Extension request "hardlink@openssh.com"
1.17 djm 507:
508: This request is for creating a hard link to a regular file. This
509: request is implemented as a SSH_FXP_EXTENDED request with the
510: following format:
511:
512: uint32 id
513: string "hardlink@openssh.com"
514: string oldpath
515: string newpath
516:
517: On receiving this request the server will perform the operation
518: link(oldpath, newpath) and will respond with a SSH_FXP_STATUS message.
519: This extension is advertised in the SSH_FXP_VERSION hello with version
520: "1".
521:
1.43 djm 522: 4.6. sftp: Extension request "fsync@openssh.com"
1.21 djm 523:
524: This request asks the server to call fsync(2) on an open file handle.
525:
526: uint32 id
527: string "fsync@openssh.com"
528: string handle
529:
1.44 djm 530: On receiving this request, a server will call fsync(handle_fd) and will
1.21 djm 531: respond with a SSH_FXP_STATUS message.
532:
533: This extension is advertised in the SSH_FXP_VERSION hello with version
534: "1".
535:
1.43 djm 536: 4.7. sftp: Extension request "lsetstat@openssh.com"
1.39 djm 537:
538: This request is like the "setstat" command, but sets file attributes on
539: symlinks. It is implemented as a SSH_FXP_EXTENDED request with the
540: following format:
541:
542: uint32 id
543: string "lsetstat@openssh.com"
544: string path
545: ATTRS attrs
546:
547: See the "setstat" command for more details.
548:
549: This extension is advertised in the SSH_FXP_VERSION hello with version
550: "1".
551:
1.43 djm 552: 4.8. sftp: Extension request "limits@openssh.com"
1.40 djm 553:
554: This request is used to determine various limits the server might impose.
555: Clients should not attempt to exceed these limits as the server might sever
556: the connection immediately.
557:
558: uint32 id
559: string "limits@openssh.com"
560:
561: The server will respond with a SSH_FXP_EXTENDED_REPLY reply:
562:
563: uint32 id
564: uint64 max-packet-length
565: uint64 max-read-length
566: uint64 max-write-length
567: uint64 max-open-handles
568:
569: The 'max-packet-length' applies to the total number of bytes in a
570: single SFTP packet. Servers SHOULD set this at least to 34000.
571:
572: The 'max-read-length' is the largest length in a SSH_FXP_READ packet.
573: Even if the client requests a larger size, servers will usually respond
574: with a shorter SSH_FXP_DATA packet. Servers SHOULD set this at least to
575: 32768.
576:
577: The 'max-write-length' is the largest length in a SSH_FXP_WRITE packet
578: the server will accept. Servers SHOULD set this at least to 32768.
579:
580: The 'max-open-handles' is the maximum number of active handles that the
581: server allows (e.g. handles created by SSH_FXP_OPEN and SSH_FXP_OPENDIR
582: packets). Servers MAY count internal file handles against this limit
583: (e.g. system logging or stdout/stderr), so clients SHOULD NOT expect to
584: open this many handles in practice.
585:
586: If the server doesn't enforce a specific limit, then the field may be
587: set to 0. This implies the server relies on the OS to enforce limits
588: (e.g. available memory or file handles), and such limits might be
589: dynamic. The client SHOULD take care to not try to exceed reasonable
590: limits.
591:
592: This extension is advertised in the SSH_FXP_VERSION hello with version
593: "1".
594:
1.43 djm 595: 4.9. sftp: Extension request "expand-path@openssh.com"
1.42 djm 596:
597: This request supports canonicalisation of relative paths and
598: those that need tilde-expansion, i.e. "~", "~/..." and "~user/..."
599: These paths are expanded using shell-like rules and the resultant
600: path is canonicalised similarly to SSH2_FXP_REALPATH.
601:
602: It is implemented as a SSH_FXP_EXTENDED request with the following
603: format:
604:
605: uint32 id
606: string "expand-path@openssh.com"
607: string path
608:
609: Its reply is the same format as that of SSH2_FXP_REALPATH.
610:
611: This extension is advertised in the SSH_FXP_VERSION hello with version
612: "1".
613:
1.44 djm 614: 4.10. sftp: Extension request "copy-data"
615:
616: This request asks the server to copy data from one open file handle and
617: write it to a different open file handle. This avoids needing to transfer
618: the data across the network twice (a download followed by an upload).
619:
620: byte SSH_FXP_EXTENDED
621: uint32 id
622: string "copy-data"
623: string read-from-handle
624: uint64 read-from-offset
625: uint64 read-data-length
626: string write-to-handle
627: uint64 write-to-offset
628:
629: The server will copy read-data-length bytes starting from
630: read-from-offset from the read-from-handle and write them to
631: write-to-handle starting from write-to-offset, and then respond with a
632: SSH_FXP_STATUS message.
633:
634: It's equivalent to issuing a series of SSH_FXP_READ requests on
635: read-from-handle and a series of requests of SSH_FXP_WRITE on
636: write-to-handle.
637:
638: If read-from-handle and write-to-handle are the same, the server will
639: fail the request and respond with a SSH_FX_INVALID_PARAMETER message.
640:
641: If read-data-length is 0, then the server will read data from the
642: read-from-handle until EOF is reached.
643:
644: This extension is advertised in the SSH_FXP_VERSION hello with version
645: "1".
646:
647: This request is identical to the "copy-data" request documented in:
648:
649: https://tools.ietf.org/html/draft-ietf-secsh-filexfer-extensions-00#section-7
650:
1.46 djm 651: 4.11. sftp: Extension request "home-directory"
652:
653: This request asks the server to expand the specified user's home directory.
654: An empty username implies the current user. This can be used by the client
655: to expand ~/ type paths locally.
656:
657: byte SSH_FXP_EXTENDED
658: uint32 id
659: string "home-directory"
660: string username
661:
662: This extension is advertised in the SSH_FXP_VERSION hello with version
663: "1".
664:
665: This provides similar information as the "expand-path@openssh.com" extension.
666:
667: This request is identical to the "home-directory" request documented in:
668:
669: https://datatracker.ietf.org/doc/html/draft-ietf-secsh-filexfer-extensions-00#section-5
670:
1.47 djm 671: 4.12. sftp: Extension request "users-groups-by-id@openssh.com"
672:
1.48 dtucker 673: This request asks the server to return user and/or group names that
1.47 djm 674: correspond to one or more IDs (e.g. as returned from a SSH_FXP_STAT
675: request). This may be used by the client to provide usernames in
676: directory listings.
677:
678: byte SSH_FXP_EXTENDED
679: uint32 id
680: string "users-groups-by-id@openssh.com"
681: string uids
682: string gids
683:
684: Where "uids" and "gids" consists of one or more integer user or group
685: identifiers:
686:
687: uint32 id-0
688: ...
689:
690: The server will reply with a SSH_FXP_EXTENDED_REPLY:
691:
692: byte SSH_FXP_EXTENDED_REPLY
693: string usernames
694: string groupnames
695:
696: Where "username" and "groupnames" consists of names in identical request
697: order to "uids" and "gids" respectively:
698:
699: string name-0
700: ...
701:
702: If a name cannot be identified for a given user or group ID, an empty
703: string will be returned in its place.
704:
705: It is acceptable for either "uids" or "gids" to be an empty set, in
706: which case the respective "usernames" or "groupnames" list will also
707: be empty.
708:
709: This extension is advertised in the SSH_FXP_VERSION hello with version
710: "1".
711:
1.43 djm 712: 5. Miscellaneous changes
1.34 djm 713:
1.43 djm 714: 5.1 Public key format
1.34 djm 715:
716: OpenSSH public keys, as generated by ssh-keygen(1) and appearing in
717: authorized_keys files, are formatted as a single line of text consisting
718: of the public key algorithm name followed by a base64-encoded key blob.
1.35 djm 719: The public key blob (before base64 encoding) is the same format used for
720: the encoding of public keys sent on the wire: as described in RFC4253
721: section 6.6 for RSA and DSA keys, RFC5656 section 3.1 for ECDSA keys
722: and the "New public key formats" section of PROTOCOL.certkeys for the
723: OpenSSH certificate formats.
1.34 djm 724:
1.43 djm 725: 5.2 Private key format
1.34 djm 726:
727: OpenSSH private keys, as generated by ssh-keygen(1) use the format
728: described in PROTOCOL.key by default. As a legacy option, PEM format
729: (RFC7468) private keys are also supported for RSA, DSA and ECDSA keys
730: and were the default format before OpenSSH 7.8.
731:
1.43 djm 732: 5.3 KRL format
1.34 djm 733:
734: OpenSSH supports a compact format for Key Revocation Lists (KRLs). This
735: format is described in the PROTOCOL.krl file.
736:
1.43 djm 737: 5.4 Connection multiplexing
1.34 djm 738:
739: OpenSSH's connection multiplexing uses messages as described in
740: PROTOCOL.mux over a Unix domain socket for communications between a
741: master instance and later clients.
742:
1.43 djm 743: 5.5. Agent protocol extensions
744:
745: OpenSSH extends the usual agent protocol. These changes are documented
746: in the PROTOCOL.agent file.
747:
1.49 ! djm 748: $OpenBSD: PROTOCOL,v 1.48 2022/11/07 01:53:01 dtucker Exp $