1 files changed, 68 insertions, 25 deletions

diff --git a/sshd.0 b/sshd.0
index 6e37c9fc1..34eaafc92 100644
--- a/sshd.0
+++ b/sshd.0
@@ -4,9 +4,9 @@ NAME
      sshd - OpenSSH SSH daemon
 
 SYNOPSIS
-     sshd [-46DdeiqTt] [-b bits] [-C connection_spec] [-f config_file]
-          [-g login_grace_time] [-h host_key_file] [-k key_gen_time]
-          [-o option] [-p port] [-u len]
+     sshd [-46DdeiqTt] [-b bits] [-C connection_spec]
+          [-c host_certificate_file] [-f config_file] [-g login_grace_time]
+          [-h host_key_file] [-k key_gen_time] [-o option] [-p port] [-u len]
 
 DESCRIPTION
      sshd (OpenSSH Daemon) is the daemon program for ssh(1).  Together these
@@ -44,14 +44,20 @@ DESCRIPTION
              are required and may be supplied in any order, either with multi-
              ple -C options or as a comma-separated list.
 
+     -c host_certificate_file
+             Specifies a path to a certificate file to identify sshd during
+             key exchange.  The certificate file must match a host key file
+             specified using the -h option or the HostKey configuration direc-
+             tive.
+
      -D      When this option is specified, sshd will not detach and does not
              become a daemon.  This allows easy monitoring of sshd.
 
-     -d      Debug mode.  The server sends verbose debug output to the system
-             log, and does not put itself in the background.  The server also
-             will not fork and will only process one connection.  This option
-             is only intended for debugging for the server.  Multiple -d op-
-             tions increase the debugging level.  Maximum is 3.
+     -d      Debug mode.  The server sends verbose debug output to standard
+             error, and does not put itself in the background.  The server al-
+             so will not fork and will only process one connection.  This op-
+             tion is only intended for debugging for the server.  Multiple -d
+             options increase the debugging level.  Maximum is 3.
 
      -e      When this option is specified, sshd will send the output to the
              standard error instead of the system log.
@@ -133,11 +139,11 @@ DESCRIPTION
              AllowUsers or DenyUsers.
 
 AUTHENTICATION
-     The OpenSSH SSH daemon supports SSH protocols 1 and 2.  Both protocols
-     are supported by default, though this can be changed via the Protocol op-
-     tion in sshd_config(5).  Protocol 2 supports both RSA and DSA keys; pro-
-     tocol 1 only supports RSA keys.  For both protocols, each host has a
-     host-specific key, normally 2048 bits, used to identify the host.
+     The OpenSSH SSH daemon supports SSH protocols 1 and 2.  The default is to
+     use protocol 2 only, though this can be changed via the Protocol option
+     in sshd_config(5).  Protocol 2 supports both RSA and DSA keys; protocol 1
+     only supports RSA keys.  For both protocols, each host has a host-specif-
+     ic key, normally 2048 bits, used to identify the host.
 
      Forward security for protocol 1 is provided through an additional server
      key, normally 768 bits, generated when the server starts.  This key is
@@ -280,6 +286,15 @@ AUTHORIZED_KEYS FILE FORMAT
      lowing option specifications are supported (note that option keywords are
      case-insensitive):
 
+     cert-authority
+             Specifies that the listed key is a certification authority (CA)
+             that is trusted to validate signed certificates for user authen-
+             tication.
+
+             Certificates may encode access restrictions similar to these key
+             options.  If both certificate restrictions and key options are
+             present, the most restrictive union of the two is applied.
+
      command="command"
              Specifies that the command is executed whenever this key is used
              for authentication.  The command supplied by the user (if any) is
@@ -294,7 +309,9 @@ AUTHORIZED_KEYS FILE FORMAT
              explicitly prohibited.  The command originally supplied by the
              client is available in the SSH_ORIGINAL_COMMAND environment vari-
              able.  Note that this option applies to shell, command or subsys-
-             tem execution.
+             tem execution.  Also note that this command may be superseded by
+             either a sshd_config(5) ForceCommand directive or a command em-
+             bedded in a certificate.
 
      environment="NAME=value"
              Specifies that the string is to be added to the environment when
@@ -373,8 +390,15 @@ SSH_KNOWN_HOSTS FILE FORMAT
      matically: whenever the user connects from an unknown host, its key is
      added to the per-user file.
 
-     Each line in these files contains the following fields: hostnames, bits,
-     exponent, modulus, comment.  The fields are separated by spaces.
+     Each line in these files contains the following fields: markers (option-
+     al), hostnames, bits, exponent, modulus, comment.  The fields are sepa-
+     rated by spaces.
+
+     The marker is optional, but if it is present then it must be one of
+     ``@cert-authority'', to indicate that the line contains a certification
+     authority (CA) key, or ``@revoked'', to indicate that the key contained
+     on the line is revoked and must not ever be accepted.  Only one marker
+     should be used on a key line.
 
      Hostnames is a comma-separated list of patterns (`*' and `?' act as wild-
      cards); each pattern in turn is matched against the canonical host name
@@ -398,17 +422,32 @@ SSH_KNOWN_HOSTS FILE FORMAT
      Lines starting with `#' and empty lines are ignored as comments.
 
      When performing host authentication, authentication is accepted if any
-     matching line has the proper key.  It is thus permissible (but not recom-
-     mended) to have several lines or different host keys for the same names.
-     This will inevitably happen when short forms of host names from different
-     domains are put in the file.  It is possible that the files contain con-
-     flicting information; authentication is accepted if valid information can
-     be found from either file.
+     matching line has the proper key; either one that matches exactly or, if
+     the server has presented a certificate for authentication, the key of the
+     certification authority that signed the certificate.  For a key to be
+     trusted as a certification authority, it must use the ``@cert-authority''
+     marker described above.
+
+     The known hosts file also provides a facility to mark keys as revoked,
+     for example when it is known that the associated private key has been
+     stolen.  Revoked keys are specified by including the ``@revoked'' marker
+     at the beginning of the key line, and are never accepted for authentica-
+     tion or as certification authorities, but instead will produce a warning
+     from ssh(1) when they are encountered.
+
+     It is permissible (but not recommended) to have several lines or differ-
+     ent host keys for the same names.  This will inevitably happen when short
+     forms of host names from different domains are put in the file.  It is
+     possible that the files contain conflicting information; authentication
+     is accepted if valid information can be found from either file.
 
      Note that the lines in these files are typically hundreds of characters
      long, and you definitely don't want to type in the host keys by hand.
-     Rather, generate them by a script or by taking /etc/ssh/ssh_host_key.pub
-     and adding the host names at the front.
+     Rather, generate them by a script, ssh-keyscan(1) or by taking
+     /etc/ssh/ssh_host_key.pub and adding the host names at the front.
+     ssh-keygen(1) also offers some basic automated editing for
+     ~/.ssh/known_hosts including removing hosts matching a host name and con-
+     verting all host names to their hashed representations.
 
      An example ssh_known_hosts file:
 
@@ -418,6 +457,10 @@ SSH_KNOWN_HOSTS FILE FORMAT
         # A hashed hostname
         |1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
         AAAA1234.....=
+        # A revoked key
+        @revoked * ssh-rsa AAAAB5W...
+        # A CA key, accepted for any host in *.mydomain.com or *.mydomain.org
+        @cert-authority *.mydomain.org,*.mydomain.com ssh-rsa AAAAB5W...
 
 FILES
      ~/.hushlogin
@@ -571,4 +614,4 @@ CAVEATS
      System security is not improved unless rshd, rlogind, and rexecd are dis-
      abled (thus completely disabling rlogin and rsh into the machine).
 
-OpenBSD 4.6                     March 26, 2009                               9
+OpenBSD 4.6                      March 5, 2010                              10