NAME    [Toc]    [Back]

     ssh-keyscan - gather ssh public keys

SYNOPSIS    [Toc]    [Back]

     ssh-keyscan [-v46] [-p port]  [-T  timeout]  [-t  type]  [-f
file]
                 [host | addrlist namelist] [...]

DESCRIPTION    [Toc]    [Back]

     ssh-keyscan  is  a utility for gathering the public ssh host
keys of a number
 of hosts.  It was designed to aid in building and  verifying
     ssh_known_hosts  files.   ssh-keyscan provides a minimal interface suitable
     for use by shell and perl scripts.

     ssh-keyscan uses non-blocking socket I/O to contact as  many
hosts as possible
 in parallel, so it is very efficient.  The keys from a
domain of
     1,000 hosts can be collected in tens of seconds,  even  when
some of those
     hosts  are  down  or do not run ssh.  For scanning, one does
not need login
     access to the machines that are being scanned, nor does  the
scanning process
 involve any encryption.

     The options are as follows:

     -p port
             Port to connect to on the remote host.

     -T timeout
             Set the timeout for connection attempts.  If timeout
seconds have
             elapsed since a connection was initiated to  a  host
or since the
             last time anything was read from that host, then the
connection
             is closed and the host in  question  considered  unavailable.  Default
 is 5 seconds.

     -t type
             Specifies  the  type  of  the  key to fetch from the
scanned hosts.
             The possible values are ``rsa1'' for  protocol  version 1 and
             ``rsa'' or ``dsa'' for protocol version 2.  Multiple
values may
             be specified by separating them  with  commas.   The
default is
             ``rsa1''.

     -f filename
             Read  hosts  or  addrlist  namelist  pairs from this
file, one per
             line.  If -  is  supplied  instead  of  a  filename,
ssh-keyscan will
             read hosts or addrlist namelist pairs from the standard input.

     -v      Verbose mode.  Causes ssh-keyscan to print debugging
messages
             about its progress.

     -4      Forces ssh-keyscan to use IPv4 addresses only.

     -6      Forces ssh-keyscan to use IPv6 addresses only.

SECURITY    [Toc]    [Back]

     If  a  ssh_known_hosts file is constructed using ssh-keyscan
without verifying
 the keys, users will  be  vulnerable  to  man  in  the
middle attacks.
     On the other hand, if the security model allows such a risk,
ssh-keyscan
     can help in the detection of tampered keyfiles or man in the
middle attacks
  which  have  begun after the ssh_known_hosts file was
created.

FILES    [Toc]    [Back]

     Input format:

     1.2.3.4,1.2.4.4                 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4

     Output format for rsa1 keys:

     host-or-namelist bits exponent modulus

     Output format for rsa and dsa keys:

     host-or-namelist keytype base64-encoded-key

     Where keytype is either ``ssh-rsa'' or ``ssh-dss''.

     /etc/ssh/ssh_known_hosts

EXAMPLES    [Toc]    [Back]

     Print the rsa1 host key for machine hostname:

     $ ssh-keyscan hostname

     Find  all  hosts  from  the file ssh_hosts which have new or
different keys
     from those in the sorted file ssh_known_hosts:

     $ ssh-keyscan -t rsa,dsa -f ssh_hosts |              sort -u
- ssh_known_hosts | diff ssh_known_hosts -

SEE ALSO    [Toc]    [Back]

     ssh(1), sshd(8)

AUTHORS    [Toc]    [Back]

     David  Mazieres  <[email protected]> wrote the initial version,
and
     Wayne Davison <[email protected]>  added  support
for protocol
     version 2.

BUGS    [Toc]    [Back]

     It  generates "Connection closed by remote host" messages on
the consoles
     of all the machines it scans if the  server  is  older  than
version 2.9.
     This is because it opens a connection to the ssh port, reads
the public
     key, and drops the connection as soon as it gets the key.

OpenBSD     3.6                         January      1,      1996