Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

1 files changed, 15 insertions, 8 deletions

diff --git a/usr.bin/ssh/PROTOCOL b/usr.bin/ssh/PROTOCOL
index 9b74b94754f..5fc31eade32 100644
--- a/usr.bin/ssh/PROTOCOL
+++ b/usr.bin/ssh/PROTOCOL
@@ -31,7 +31,14 @@ The method is documented in:
 
 http://www.openssh.com/txt/draft-miller-secsh-compression-delayed-00.txt
 
-3. connection: Channel write close extension "eow@openssh.com"
+3. transport: New public key algorithms "ssh-rsa-cert-v00@openssh.com" and
+   "ssh-dsa-cert-v00@openssh.com"
+
+OpenSSH introduces two new public key algorithms to support certificate
+authentication for users and hostkeys. These methods are documented in
+the file PROTOCOL.certkeys
+
+4. connection: Channel write close extension "eow@openssh.com"
 
 The SSH connection protocol (rfc4254) provides the SSH_MSG_CHANNEL_EOF
 message to allow an endpoint to signal its peer that it will send no
@@ -70,7 +77,7 @@ message is only sent to OpenSSH peers (identified by banner).
 Other SSH implementations may be whitelisted to receive this message
 upon request.
 
-4. connection: disallow additional sessions extension
+5. connection: disallow additional sessions extension
    "no-more-sessions@openssh.com"
 
 Most SSH connections will only ever request a single session, but a
@@ -98,7 +105,7 @@ of this message, the no-more-sessions request is only sent to OpenSSH
 servers (identified by banner). Other SSH implementations may be
 whitelisted to receive this message upon request.
 
-5. connection: Tunnel forward extension "tun@openssh.com"
+6. connection: Tunnel forward extension "tun@openssh.com"
 
 OpenSSH supports layer 2 and layer 3 tunnelling via the "tun@openssh.com"
 channel type. This channel type supports forwarding of network packets
@@ -159,7 +166,7 @@ The contents of the "data" field for layer 2 packets is:
 The "frame" field contains an IEEE 802.3 Ethernet frame, including
 header.
 
-6. sftp: Reversal of arguments to SSH_FXP_SYMLINK
+7. sftp: Reversal of arguments to SSH_FXP_SYMLINK
 
 When OpenSSH's sftp-server was implemented, the order of the arguments
 to the SSH_FXP_SYMLINK method was inadvertently reversed. Unfortunately,
@@ -172,7 +179,7 @@ SSH_FXP_SYMLINK as follows:
 	string		targetpath
 	string		linkpath
 
-7. sftp: Server extension announcement in SSH_FXP_VERSION
+8. sftp: Server extension announcement in SSH_FXP_VERSION
 
 OpenSSH's sftp-server lists the extensions it supports using the
 standard extension announcement mechanism in the SSH_FXP_VERSION server
@@ -193,7 +200,7 @@ ever changed in an incompatible way. The server MAY advertise the same
 extension with multiple versions (though this is unlikely). Clients MUST
 check the version number before attempting to use the extension.
 
-8. sftp: Extension request "posix-rename@openssh.com"
+9. sftp: Extension request "posix-rename@openssh.com"
 
 This operation provides a rename operation with POSIX semantics, which
 are different to those provided by the standard SSH_FXP_RENAME in
@@ -210,7 +217,7 @@ rename(oldpath, newpath) and will respond with a SSH_FXP_STATUS message.
 This extension is advertised in the SSH_FXP_VERSION hello with version
 "1".
 
-9. sftp: Extension requests "statvfs@openssh.com" and
+10. sftp: Extension requests "statvfs@openssh.com" and
          "fstatvfs@openssh.com"
 
 These requests correspond to the statvfs and fstatvfs POSIX system
@@ -251,4 +258,4 @@ The values of the f_flag bitmask are as follows:
 Both the "statvfs@openssh.com" and "fstatvfs@openssh.com" extensions are
 advertised in the SSH_FXP_VERSION hello with version "2".
 
-$OpenBSD: PROTOCOL,v 1.14 2010/01/09 00:57:10 djm Exp $
+$OpenBSD: PROTOCOL,v 1.15 2010/02/26 20:29:54 djm Exp $