ssh security Post: 67733

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ssh-keysign

ssh-keysign(1M)                                                                                                                    ssh-keysign(1M)

NAME

       ssh-keysign - ssh helper program for host-based authentication

SYNOPSIS

       ssh-keysign

       ssh-keysign  is  used  by ssh(1) to access the local host keys and generate the digital signature required during host-based authentication
       with SSH protocol version 2. This signature is of data that includes, among other items, the name of the client host and the  name  of  the
       client user.

       ssh-keysign  is  disabled  by  default and can be enabled only in the global client configuration file /etc/ssh/ssh_config by setting Host-
       basedAuthentication to yes.

       ssh-keysign is not intended to be invoked by the user, but from ssh. See ssh(1) and sshd(1M) for more information about host-based  authen-
       tication.

       /etc/ssh/ssh_config

           Controls whether ssh-keysign is enabled.

       /etc/ssh/ssh_host_dsa_key
       /etc/ssh/ssh_host_rsa_key

           These  files  contain the private parts of the host keys used to generate the digital signature. They should be owned by root, readable
           only by root, and not accessible to others. Because they are readable only by root, ssh-keysign must  be  set-uid  root  if  host-based
           authentication is used.

       ssh-keysign will not sign host-based authentication data under the following conditions:

         o  If the HostbasedAuthentication client configuration parameter is not set to yes in /etc/ssh/ssh_config. This setting cannot be overri-
            den in users' ~/.ssh/ssh_config files.

         o  If the client hostname and username in /etc/ssh/ssh_config do not match the canonical hostname of  the  client  where  ssh-keysign  is
            invoked and the name of the user invoking ssh-keysign.

       In  spite of ssh-keysign's restrictions on the contents of the host-based authentication data, there remains the ability of users to use it
       as an avenue for obtaining the client's private host keys. For this reason host-based authentication is turned off by default.

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWsshu                     |
       +-----------------------------+-----------------------------+
       |Interface Stability          |Evolving                     |
       +-----------------------------+-----------------------------+

       ssh(1), sshd(1M), ssh_config(4), attributes(5)

AUTHORS

       Markus Friedl, markus@openbsd.org

HISTORY

       ssh-keysign first appeared in Ox 3.2.

                                                                    9 Jun 2004                                                     ssh-keysign(1M)