secsh-agent, ssh-agent -- authentication agent

SYNOPSIS

secsh-agent [-c|-s] [-d] [command [args...]]

secsh-agent [-c|-s] -k

ssh-agent [-c|-s] [-d] [command [args...]]

ssh-agent [-c|-s] -k

secsh-agent is a program to hold private keys used for public key authentication (RSA, DSA). The idea is that secsh-agent is started in the beginning of an X-session or a login session, and all other windows or programs are started as clients to the secsh-agent program. Through use of environment variables, the agent can be located and automatically used for authentication when logging in to other machines using secsh.

If a command line is given, this is executed as a subprocess of the agent. When the command dies, so does the agent.

The agent initially does not have any private keys. Keys are added using secsh-add. When executed without arguments, secsh-add adds the $USERPROFILE/.ssh/identity file. If the identity has a passphrase, secsh-add asks for the passphrase (using a small X11 application if running under X11, or from the terminal if running without X). It then sends the identity to the agent. Several identities can be stored in the agent; the agent can automatically use any of these identities. secsh-add -l displays the identities currently held by the agent.

The idea is that the agent is run in the user's local PC, laptop, or terminal. Authentication data need not be stored on any other machine, and authentication passphrases never go over the network. However, the connection to the agent is forwarded over SSH remote logins, and the user can thus use the privileges given by the identities anywhere in the network in a secure way.

There are two main ways to get an agent setup: Either the agent starts a new subcommand into which some environment variables are exported, or the agent prints the needed shell commands (either sh or csh syntax can be generated) which can be evalled in the calling shell. Later secsh looks at these variables and uses them to establish a connection to the agent.

A unix-domain socket is created ($TMPDIR/ssh-XXXXXXXX/agent.<pid>), and the name of this socket is stored in the SSH_AUTH_SOCK environment variable. The socket is made accessible only to the current user. This method is easily abused by root or another instance of the same user.

The SSH_AGENT_PID environment variable holds the agent's PID.

The agent exits automatically when the command given on the command line terminates.

You can also call secsh-agent as ssh-agent.

Options

-c: Generates C-shell commands on stdout. This is the default if SHELL looks like it's a csh style of shell.
-s: Generate Bourne shell commands on stdout. This is the default if SHELL does not look like it's a csh style of shell.
-k: Kills the current agent (given by the SSH_AGENT_PID environment variable).
-d: Enables debug mode. When this option is specified, secsh-agent will not fork.

FILES

$USERPROFILE/.ssh/identity: Contains the protocol version 1 RSA authentication identity of the user. This file should not be readable by anyone but the user. Note that secsh-add ignores this file if it is accessible by others. It is possible to specify a passphrase when generating the key; that passphrase will be used to encrypt the private part of this file. This is the default file added by secsh-add when no other files have been specified.
$USERPROFILE/.ssh/id_dsa: Contains the protocol version 2 DSA authentication identity of the user.
$USERPROFILE/.ssh/id_rsa: Contains the protocol version 2 RSA authentication identity of the user.
$TMPDIR/ssh-XXXXXXXX/agent.<pid>: Unix-domain sockets used to contain the connection to the authentication agent. These sockets should only be readable by the owner. The sockets should get automatically removed when the agent exits.

AUTHORS

OpenSSH is a derivative of the original and free ssh 1.2.12 release by Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo de Raadt and Dug Song removed many bugs, re-added newer features and created OpenSSH. Markus Friedl contributed the support for SSH protocol versions 1.5 and 2.0.

PORTABILITY

All UNIX systems. Windows 2000. Windows XP. Windows Server 2003. Windows Vista.

NOTES

The secsh-add utility, by default, loads keys from the $USERPROFILE directory on Windows NT/2000/XP/2003/Vista platforms instead of ~/. This was done because the ~/ directory might not be available for the case of a domain machine that cannot contact a domain controller. Note that the secure shell service continues to use the ~/.ssh directory to store configuration files.

The authentication agent only works when connecting to secure shell servers that are based upon OpenSSH. The agent does not work when connecting to ssh.com-based servers.

AVAILABILITY

MKS Toolkit for System Administrators
MKS Toolkit for Developers
MKS Toolkit for Interoperability
MKS Toolkit for Professional Developers
MKS Toolkit for Enterprise Developers
MKS Toolkit for Enterprise Developers 64-Bit Edition

secsh-agent, ssh-agent
authentication agent

Command