Annotation of src/usr.bin/ssh/PROTOCOL, Revision 1.47
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:
1.16 djm 107: 2. Connection protocol changes
108:
109: 2.1. connection: Channel write close extension "eow@openssh.com"
1.1 djm 110:
111: The SSH connection protocol (rfc4254) provides the SSH_MSG_CHANNEL_EOF
112: message to allow an endpoint to signal its peer that it will send no
113: more data over a channel. Unfortunately, there is no symmetric way for
114: an endpoint to request that its peer should cease sending data to it
115: while still keeping the channel open for the endpoint to send data to
116: the peer.
117:
1.2 djm 118: This is desirable, since it saves the transmission of data that would
1.1 djm 119: otherwise need to be discarded and it allows an endpoint to signal local
120: processes of the condition, e.g. by closing the corresponding file
121: descriptor.
122:
123: OpenSSH implements a channel extension message to perform this
1.10 djm 124: signalling: "eow@openssh.com" (End Of Write). This message is sent by
125: an endpoint when the local output of a session channel is closed or
126: experiences a write error. The message is formatted as follows:
1.1 djm 127:
128: byte SSH_MSG_CHANNEL_REQUEST
129: uint32 recipient channel
130: string "eow@openssh.com"
131: boolean FALSE
132:
133: On receiving this message, the peer SHOULD cease sending data of
134: the channel and MAY signal the process from which the channel data
135: originates (e.g. by closing its read file descriptor).
136:
137: As with the symmetric SSH_MSG_CHANNEL_EOF message, the channel does
138: remain open after a "eow@openssh.com" has been sent and more data may
139: still be sent in the other direction. This message does not consume
140: window space and may be sent even if no window space is available.
141:
1.12 djm 142: NB. due to certain broken SSH implementations aborting upon receipt
143: of this message (in contravention of RFC4254 section 5.4), this
144: message is only sent to OpenSSH peers (identified by banner).
1.38 djm 145: Other SSH implementations may be listed to receive this message
1.12 djm 146: upon request.
147:
1.16 djm 148: 2.2. connection: disallow additional sessions extension
149: "no-more-sessions@openssh.com"
1.6 djm 150:
151: Most SSH connections will only ever request a single session, but a
152: attacker may abuse a running ssh client to surreptitiously open
153: additional sessions under their control. OpenSSH provides a global
154: request "no-more-sessions@openssh.com" to mitigate this attack.
155:
156: When an OpenSSH client expects that it will never open another session
157: (i.e. it has been started with connection multiplexing disabled), it
158: will send the following global request:
159:
160: byte SSH_MSG_GLOBAL_REQUEST
161: string "no-more-sessions@openssh.com"
162: char want-reply
163:
164: On receipt of such a message, an OpenSSH server will refuse to open
165: future channels of type "session" and instead immediately abort the
166: connection.
167:
168: Note that this is not a general defence against compromised clients
169: (that is impossible), but it thwarts a simple attack.
170:
1.12 djm 171: NB. due to certain broken SSH implementations aborting upon receipt
172: of this message, the no-more-sessions request is only sent to OpenSSH
173: servers (identified by banner). Other SSH implementations may be
1.38 djm 174: listed to receive this message upon request.
1.12 djm 175:
1.16 djm 176: 2.3. connection: Tunnel forward extension "tun@openssh.com"
1.7 djm 177:
1.8 djm 178: OpenSSH supports layer 2 and layer 3 tunnelling via the "tun@openssh.com"
1.7 djm 179: channel type. This channel type supports forwarding of network packets
1.28 djm 180: with datagram boundaries intact between endpoints equipped with
1.7 djm 181: interfaces like the BSD tun(4) device. Tunnel forwarding channels are
182: requested by the client with the following packet:
183:
184: byte SSH_MSG_CHANNEL_OPEN
185: string "tun@openssh.com"
186: uint32 sender channel
187: uint32 initial window size
188: uint32 maximum packet size
189: uint32 tunnel mode
190: uint32 remote unit number
191:
192: The "tunnel mode" parameter specifies whether the tunnel should forward
193: layer 2 frames or layer 3 packets. It may take one of the following values:
194:
195: SSH_TUNMODE_POINTOPOINT 1 /* layer 3 packets */
196: SSH_TUNMODE_ETHERNET 2 /* layer 2 frames */
197:
198: The "tunnel unit number" specifies the remote interface number, or may
1.37 dtucker 199: be 0x7fffffff to allow the server to automatically choose an interface. A
1.13 djm 200: server that is not willing to open a client-specified unit should refuse
201: the request with a SSH_MSG_CHANNEL_OPEN_FAILURE error. On successful
202: open, the server should reply with SSH_MSG_CHANNEL_OPEN_SUCCESS.
1.7 djm 203:
204: Once established the client and server may exchange packet or frames
205: over the tunnel channel by encapsulating them in SSH protocol strings
206: and sending them as channel data. This ensures that packet boundaries
207: are kept intact. Specifically, packets are transmitted using normal
208: SSH_MSG_CHANNEL_DATA packets:
209:
210: byte SSH_MSG_CHANNEL_DATA
211: uint32 recipient channel
212: string data
213:
214: The contents of the "data" field for layer 3 packets is:
215:
216: uint32 packet length
217: uint32 address family
218: byte[packet length - 4] packet data
219:
220: The "address family" field identifies the type of packet in the message.
221: It may be one of:
222:
223: SSH_TUN_AF_INET 2 /* IPv4 */
224: SSH_TUN_AF_INET6 24 /* IPv6 */
225:
226: The "packet data" field consists of the IPv4/IPv6 datagram itself
227: without any link layer header.
228:
1.13 djm 229: The contents of the "data" field for layer 2 packets is:
1.7 djm 230:
231: uint32 packet length
232: byte[packet length] frame
233:
1.8 djm 234: The "frame" field contains an IEEE 802.3 Ethernet frame, including
1.7 djm 235: header.
236:
1.24 millert 237: 2.4. connection: Unix domain socket forwarding
238:
239: OpenSSH supports local and remote Unix domain socket forwarding
240: using the "streamlocal" extension. Forwarding is initiated as per
241: TCP sockets but with a single path instead of a host and port.
242:
243: Similar to direct-tcpip, direct-streamlocal is sent by the client
244: to request that the server make a connection to a Unix domain socket.
245:
246: byte SSH_MSG_CHANNEL_OPEN
247: string "direct-streamlocal@openssh.com"
248: uint32 sender channel
249: uint32 initial window size
250: uint32 maximum packet size
251: string socket path
1.30 djm 252: string reserved
253: uint32 reserved
1.24 millert 254:
255: Similar to forwarded-tcpip, forwarded-streamlocal is sent by the
256: server when the client has previously send the server a streamlocal-forward
257: GLOBAL_REQUEST.
258:
259: byte SSH_MSG_CHANNEL_OPEN
260: string "forwarded-streamlocal@openssh.com"
261: uint32 sender channel
262: uint32 initial window size
263: uint32 maximum packet size
264: string socket path
265: string reserved for future use
266:
267: The reserved field is not currently defined and is ignored on the
268: remote end. It is intended to be used in the future to pass
269: information about the socket file, such as ownership and mode.
270: The client currently sends the empty string for this field.
271:
272: Similar to tcpip-forward, streamlocal-forward is sent by the client
273: to request remote forwarding of a Unix domain socket.
274:
275: byte SSH2_MSG_GLOBAL_REQUEST
276: string "streamlocal-forward@openssh.com"
277: boolean TRUE
278: string socket path
279:
280: Similar to cancel-tcpip-forward, cancel-streamlocal-forward is sent
281: by the client cancel the forwarding of a Unix domain socket.
282:
283: byte SSH2_MSG_GLOBAL_REQUEST
284: string "cancel-streamlocal-forward@openssh.com"
285: boolean FALSE
286: string socket path
287:
1.27 djm 288: 2.5. connection: hostkey update and rotation "hostkeys-00@openssh.com"
289: and "hostkeys-prove-00@openssh.com"
1.25 djm 290:
291: OpenSSH supports a protocol extension allowing a server to inform
1.26 djm 292: a client of all its protocol v.2 host keys after user-authentication
1.25 djm 293: has completed.
294:
295: byte SSH_MSG_GLOBAL_REQUEST
1.27 djm 296: string "hostkeys-00@openssh.com"
1.41 djm 297: char 0 /* want-reply */
1.25 djm 298: string[] hostkeys
299:
1.26 djm 300: Upon receiving this message, a client should check which of the
1.32 djm 301: supplied host keys are present in known_hosts.
302:
303: Note that the server may send key types that the client does not
1.37 dtucker 304: support. The client should disregard such keys if they are received.
1.32 djm 305:
306: If the client identifies any keys that are not present for the host,
307: it should send a "hostkeys-prove@openssh.com" message to request the
308: server prove ownership of the private half of the key.
1.26 djm 309:
310: byte SSH_MSG_GLOBAL_REQUEST
1.27 djm 311: string "hostkeys-prove-00@openssh.com"
1.26 djm 312: char 1 /* want-reply */
313: string[] hostkeys
314:
315: When a server receives this message, it should generate a signature
316: using each requested key over the following:
317:
1.27 djm 318: string "hostkeys-prove-00@openssh.com"
1.26 djm 319: string session identifier
320: string hostkey
321:
322: These signatures should be included in the reply, in the order matching
323: the hostkeys in the request:
324:
325: byte SSH_MSG_REQUEST_SUCCESS
326: string[] signatures
327:
328: When the client receives this reply (and not a failure), it should
329: validate the signatures and may update its known_hosts file, adding keys
330: that it has not seen before and deleting keys for the server host that
331: are no longer offered.
332:
333: These extensions let a client learn key types that it had not previously
334: encountered, thereby allowing it to potentially upgrade from weaker
335: key algorithms to better ones. It also supports graceful key rotation:
336: a server may offer multiple keys of the same type for a period (to
337: give clients an opportunity to learn them using this extension) before
338: removing the deprecated key from those offered.
1.25 djm 339:
1.36 djm 340: 2.6. connection: SIGINFO support for "signal" channel request
341:
342: The SSH channels protocol (RFC4254 section 6.9) supports sending a
343: signal to a session attached to a channel. OpenSSH supports one
344: extension signal "INFO@openssh.com" that allows sending SIGINFO on
345: BSD-derived systems.
346:
1.43 djm 347: 3. Authentication protocol changes
1.16 djm 348:
1.43 djm 349: 3.1. Host-bound public key authentication
350:
351: This is trivial change to the traditional "publickey" authentication
352: method. The authentication request is identical to the original method
353: but for the name and one additional field:
354:
355: byte SSH2_MSG_USERAUTH_REQUEST
356: string username
357: string "ssh-connection"
358: string "publickey-hostbound-v00@openssh.com"
359: bool has_signature
360: string pkalg
361: string public key
362: string server host key
363:
364: Because the entire SSH2_MSG_USERAUTH_REQUEST message is included in
365: the signed data, this ensures that a binding between the destination
366: user, the server identity and the session identifier is visible to the
367: signer. OpenSSH uses this binding via signed data to implement per-key
368: restrictions in ssh-agent.
369:
370: A server may advertise this method using the SSH2_MSG_EXT_INFO
371: mechanism (RFC8308), with the following message:
372:
373: string "publickey-hostbound@openssh.com"
374: string "0" (version)
375:
376: Clients should prefer host-bound authentication when advertised by
377: server.
378:
379: 4. SFTP protocol changes
380:
381: 4.1. sftp: Reversal of arguments to SSH_FXP_SYMLINK
1.1 djm 382:
383: When OpenSSH's sftp-server was implemented, the order of the arguments
1.8 djm 384: to the SSH_FXP_SYMLINK method was inadvertently reversed. Unfortunately,
1.1 djm 385: the reversal was not noticed until the server was widely deployed. Since
386: fixing this to follow the specification would cause incompatibility, the
387: current order was retained. For correct operation, clients should send
388: SSH_FXP_SYMLINK as follows:
389:
390: uint32 id
391: string targetpath
392: string linkpath
393:
1.43 djm 394: 4.2. sftp: Server extension announcement in SSH_FXP_VERSION
1.1 djm 395:
396: OpenSSH's sftp-server lists the extensions it supports using the
397: standard extension announcement mechanism in the SSH_FXP_VERSION server
398: hello packet:
399:
400: uint32 3 /* protocol version */
401: string ext1-name
402: string ext1-version
403: string ext2-name
404: string ext2-version
405: ...
406: string extN-name
407: string extN-version
408:
409: Each extension reports its integer version number as an ASCII encoded
410: string, e.g. "1". The version will be incremented if the extension is
411: ever changed in an incompatible way. The server MAY advertise the same
412: extension with multiple versions (though this is unlikely). Clients MUST
1.8 djm 413: check the version number before attempting to use the extension.
1.1 djm 414:
1.43 djm 415: 4.3. sftp: Extension request "posix-rename@openssh.com"
1.1 djm 416:
417: This operation provides a rename operation with POSIX semantics, which
418: are different to those provided by the standard SSH_FXP_RENAME in
419: draft-ietf-secsh-filexfer-02.txt. This request is implemented as a
420: SSH_FXP_EXTENDED request with the following format:
421:
422: uint32 id
423: string "posix-rename@openssh.com"
424: string oldpath
425: string newpath
426:
427: On receiving this request the server will perform the POSIX operation
428: rename(oldpath, newpath) and will respond with a SSH_FXP_STATUS message.
429: This extension is advertised in the SSH_FXP_VERSION hello with version
430: "1".
431:
1.43 djm 432: 4.4. sftp: Extension requests "statvfs@openssh.com" and
1.2 djm 433: "fstatvfs@openssh.com"
1.1 djm 434:
435: These requests correspond to the statvfs and fstatvfs POSIX system
436: interfaces. The "statvfs@openssh.com" request operates on an explicit
437: pathname, and is formatted as follows:
438:
439: uint32 id
440: string "statvfs@openssh.com"
441: string path
442:
1.8 djm 443: The "fstatvfs@openssh.com" operates on an open file handle:
1.1 djm 444:
445: uint32 id
1.2 djm 446: string "fstatvfs@openssh.com"
1.1 djm 447: string handle
448:
449: These requests return a SSH_FXP_STATUS reply on failure. On success they
450: return the following SSH_FXP_EXTENDED_REPLY reply:
451:
452: uint32 id
1.4 dtucker 453: uint64 f_bsize /* file system block size */
454: uint64 f_frsize /* fundamental fs block size */
1.1 djm 455: uint64 f_blocks /* number of blocks (unit f_frsize) */
456: uint64 f_bfree /* free blocks in file system */
457: uint64 f_bavail /* free blocks for non-root */
458: uint64 f_files /* total file inodes */
459: uint64 f_ffree /* free file inodes */
460: uint64 f_favail /* free file inodes for to non-root */
1.3 djm 461: uint64 f_fsid /* file system id */
1.4 dtucker 462: uint64 f_flag /* bit mask of f_flag values */
463: uint64 f_namemax /* maximum filename length */
1.1 djm 464:
465: The values of the f_flag bitmask are as follows:
466:
467: #define SSH_FXE_STATVFS_ST_RDONLY 0x1 /* read-only */
468: #define SSH_FXE_STATVFS_ST_NOSUID 0x2 /* no setuid */
469:
1.11 djm 470: Both the "statvfs@openssh.com" and "fstatvfs@openssh.com" extensions are
471: advertised in the SSH_FXP_VERSION hello with version "2".
1.3 djm 472:
1.43 djm 473: 4.5. sftp: Extension request "hardlink@openssh.com"
1.17 djm 474:
475: This request is for creating a hard link to a regular file. This
476: request is implemented as a SSH_FXP_EXTENDED request with the
477: following format:
478:
479: uint32 id
480: string "hardlink@openssh.com"
481: string oldpath
482: string newpath
483:
484: On receiving this request the server will perform the operation
485: link(oldpath, newpath) and will respond with a SSH_FXP_STATUS message.
486: This extension is advertised in the SSH_FXP_VERSION hello with version
487: "1".
488:
1.43 djm 489: 4.6. sftp: Extension request "fsync@openssh.com"
1.21 djm 490:
491: This request asks the server to call fsync(2) on an open file handle.
492:
493: uint32 id
494: string "fsync@openssh.com"
495: string handle
496:
1.44 djm 497: On receiving this request, a server will call fsync(handle_fd) and will
1.21 djm 498: respond with a SSH_FXP_STATUS message.
499:
500: This extension is advertised in the SSH_FXP_VERSION hello with version
501: "1".
502:
1.43 djm 503: 4.7. sftp: Extension request "lsetstat@openssh.com"
1.39 djm 504:
505: This request is like the "setstat" command, but sets file attributes on
506: symlinks. It is implemented as a SSH_FXP_EXTENDED request with the
507: following format:
508:
509: uint32 id
510: string "lsetstat@openssh.com"
511: string path
512: ATTRS attrs
513:
514: See the "setstat" command for more details.
515:
516: This extension is advertised in the SSH_FXP_VERSION hello with version
517: "1".
518:
1.43 djm 519: 4.8. sftp: Extension request "limits@openssh.com"
1.40 djm 520:
521: This request is used to determine various limits the server might impose.
522: Clients should not attempt to exceed these limits as the server might sever
523: the connection immediately.
524:
525: uint32 id
526: string "limits@openssh.com"
527:
528: The server will respond with a SSH_FXP_EXTENDED_REPLY reply:
529:
530: uint32 id
531: uint64 max-packet-length
532: uint64 max-read-length
533: uint64 max-write-length
534: uint64 max-open-handles
535:
536: The 'max-packet-length' applies to the total number of bytes in a
537: single SFTP packet. Servers SHOULD set this at least to 34000.
538:
539: The 'max-read-length' is the largest length in a SSH_FXP_READ packet.
540: Even if the client requests a larger size, servers will usually respond
541: with a shorter SSH_FXP_DATA packet. Servers SHOULD set this at least to
542: 32768.
543:
544: The 'max-write-length' is the largest length in a SSH_FXP_WRITE packet
545: the server will accept. Servers SHOULD set this at least to 32768.
546:
547: The 'max-open-handles' is the maximum number of active handles that the
548: server allows (e.g. handles created by SSH_FXP_OPEN and SSH_FXP_OPENDIR
549: packets). Servers MAY count internal file handles against this limit
550: (e.g. system logging or stdout/stderr), so clients SHOULD NOT expect to
551: open this many handles in practice.
552:
553: If the server doesn't enforce a specific limit, then the field may be
554: set to 0. This implies the server relies on the OS to enforce limits
555: (e.g. available memory or file handles), and such limits might be
556: dynamic. The client SHOULD take care to not try to exceed reasonable
557: limits.
558:
559: This extension is advertised in the SSH_FXP_VERSION hello with version
560: "1".
561:
1.43 djm 562: 4.9. sftp: Extension request "expand-path@openssh.com"
1.42 djm 563:
564: This request supports canonicalisation of relative paths and
565: those that need tilde-expansion, i.e. "~", "~/..." and "~user/..."
566: These paths are expanded using shell-like rules and the resultant
567: path is canonicalised similarly to SSH2_FXP_REALPATH.
568:
569: It is implemented as a SSH_FXP_EXTENDED request with the following
570: format:
571:
572: uint32 id
573: string "expand-path@openssh.com"
574: string path
575:
576: Its reply is the same format as that of SSH2_FXP_REALPATH.
577:
578: This extension is advertised in the SSH_FXP_VERSION hello with version
579: "1".
580:
1.44 djm 581: 4.10. sftp: Extension request "copy-data"
582:
583: This request asks the server to copy data from one open file handle and
584: write it to a different open file handle. This avoids needing to transfer
585: the data across the network twice (a download followed by an upload).
586:
587: byte SSH_FXP_EXTENDED
588: uint32 id
589: string "copy-data"
590: string read-from-handle
591: uint64 read-from-offset
592: uint64 read-data-length
593: string write-to-handle
594: uint64 write-to-offset
595:
596: The server will copy read-data-length bytes starting from
597: read-from-offset from the read-from-handle and write them to
598: write-to-handle starting from write-to-offset, and then respond with a
599: SSH_FXP_STATUS message.
600:
601: It's equivalent to issuing a series of SSH_FXP_READ requests on
602: read-from-handle and a series of requests of SSH_FXP_WRITE on
603: write-to-handle.
604:
605: If read-from-handle and write-to-handle are the same, the server will
606: fail the request and respond with a SSH_FX_INVALID_PARAMETER message.
607:
608: If read-data-length is 0, then the server will read data from the
609: read-from-handle until EOF is reached.
610:
611: This extension is advertised in the SSH_FXP_VERSION hello with version
612: "1".
613:
614: This request is identical to the "copy-data" request documented in:
615:
616: https://tools.ietf.org/html/draft-ietf-secsh-filexfer-extensions-00#section-7
617:
1.46 djm 618: 4.11. sftp: Extension request "home-directory"
619:
620: This request asks the server to expand the specified user's home directory.
621: An empty username implies the current user. This can be used by the client
622: to expand ~/ type paths locally.
623:
624: byte SSH_FXP_EXTENDED
625: uint32 id
626: string "home-directory"
627: string username
628:
629: This extension is advertised in the SSH_FXP_VERSION hello with version
630: "1".
631:
632: This provides similar information as the "expand-path@openssh.com" extension.
633:
634: This request is identical to the "home-directory" request documented in:
635:
636: https://datatracker.ietf.org/doc/html/draft-ietf-secsh-filexfer-extensions-00#section-5
637:
1.47 ! djm 638: 4.12. sftp: Extension request "users-groups-by-id@openssh.com"
! 639:
! 640: This request asks the server to returns user and/or group names that
! 641: correspond to one or more IDs (e.g. as returned from a SSH_FXP_STAT
! 642: request). This may be used by the client to provide usernames in
! 643: directory listings.
! 644:
! 645: byte SSH_FXP_EXTENDED
! 646: uint32 id
! 647: string "users-groups-by-id@openssh.com"
! 648: string uids
! 649: string gids
! 650:
! 651: Where "uids" and "gids" consists of one or more integer user or group
! 652: identifiers:
! 653:
! 654: uint32 id-0
! 655: ...
! 656:
! 657: The server will reply with a SSH_FXP_EXTENDED_REPLY:
! 658:
! 659: byte SSH_FXP_EXTENDED_REPLY
! 660: string usernames
! 661: string groupnames
! 662:
! 663: Where "username" and "groupnames" consists of names in identical request
! 664: order to "uids" and "gids" respectively:
! 665:
! 666: string name-0
! 667: ...
! 668:
! 669: If a name cannot be identified for a given user or group ID, an empty
! 670: string will be returned in its place.
! 671:
! 672: It is acceptable for either "uids" or "gids" to be an empty set, in
! 673: which case the respective "usernames" or "groupnames" list will also
! 674: be empty.
! 675:
! 676: This extension is advertised in the SSH_FXP_VERSION hello with version
! 677: "1".
! 678:
1.43 djm 679: 5. Miscellaneous changes
1.34 djm 680:
1.43 djm 681: 5.1 Public key format
1.34 djm 682:
683: OpenSSH public keys, as generated by ssh-keygen(1) and appearing in
684: authorized_keys files, are formatted as a single line of text consisting
685: of the public key algorithm name followed by a base64-encoded key blob.
1.35 djm 686: The public key blob (before base64 encoding) is the same format used for
687: the encoding of public keys sent on the wire: as described in RFC4253
688: section 6.6 for RSA and DSA keys, RFC5656 section 3.1 for ECDSA keys
689: and the "New public key formats" section of PROTOCOL.certkeys for the
690: OpenSSH certificate formats.
1.34 djm 691:
1.43 djm 692: 5.2 Private key format
1.34 djm 693:
694: OpenSSH private keys, as generated by ssh-keygen(1) use the format
695: described in PROTOCOL.key by default. As a legacy option, PEM format
696: (RFC7468) private keys are also supported for RSA, DSA and ECDSA keys
697: and were the default format before OpenSSH 7.8.
698:
1.43 djm 699: 5.3 KRL format
1.34 djm 700:
701: OpenSSH supports a compact format for Key Revocation Lists (KRLs). This
702: format is described in the PROTOCOL.krl file.
703:
1.43 djm 704: 5.4 Connection multiplexing
1.34 djm 705:
706: OpenSSH's connection multiplexing uses messages as described in
707: PROTOCOL.mux over a Unix domain socket for communications between a
708: master instance and later clients.
709:
1.43 djm 710: 5.5. Agent protocol extensions
711:
712: OpenSSH extends the usual agent protocol. These changes are documented
713: in the PROTOCOL.agent file.
714:
1.47 ! djm 715: $OpenBSD: PROTOCOL,v 1.46 2022/08/12 05:20:28 djm Exp $
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