NAME

SYNOPSIS

DESCRIPTION

The safesh utility automatically creates one DSA key (called an identity) for each host you connect to, and stores this in a separate agent for each host. It is also capable of adding keys for other hosts to this agent, so you can use it for restricted forwarding of authentication. Because each host uses its own ssh-agent(1), the hosts you forward authentication to can only get at the authentication for the hosts you specifically say it should be able to get at.

When run, safesh:

1. Normalizes the hostname you are talking about, using the $HOME/.safesh/map file.
2. Checks if the user and host has an SSH DSA key in $HOME/.safesh, and creates one using ssh-keygen(1) if it does not. The DSA key is stored in $HOME/.safesh/$USER@$HOST-$PORT/dsa_id. You will be asked for a passphrase when the key is created. Note that if you use the same passphrase for all safesh keys, you will only be asked for the passphrase once per host you connect to. If you use different passphrases, you will be asked once per forwarded key for each host you connect to (after a machine startup).
3. Checks if you have the ssh-agent(1) for this host running, and starts it if not.
4. Checks what keys you are supposed to have active when connecting to this host (the key for the host and any keys listed in $HOME/.safesh/$USER@$HOST-$PORT/extra_keys), and which of these are missing from the active agent.
5. If any identities were missing from the agent, it executes ssh-add(1) to add them to the agent.
6. Executes ssh(1) with either $USER@$HOST or the extra command line supplied by the user.

BASIC CONCEPT DESCRIPTION

SIMPLE HOWTO

1. Do “safeshinstall <[user@]hostname>”.

   This will ask for a passphrase (three times), create a directory $HOME/.safesh/<user>@<hostname>-22, which contains authentication data for your user at ⟨hostname⟩, and add the contents of $HOME/.safesh/<user>@<hostname>-22/id_dsa.pub to $HOME/.ssh/authorized_keys2 on the host you connect to. The latter will result in ssh(1) asking for authentication in the fashion you already use (most likely by asking for your password).

2. Log in with “safesh <hostname>” from now on.

   This will ask you for a passphrase if you have not logged into that host this session, and otherwise just let right in.

UTILITY COMMANDS

The scpsh utility is for supporting use of scp(1) with safesh. The scpsh [user@]host command will start a new interactive shell (using the SHELL environment variable to determine which it should be), with the environment variables for using ssh-agent(1) to authenticate to [user@]host already set. This allows use of scp(1) without having to type passwords to authenticate.

The cvs-safesh utility makes it easy to use safesh along with cvs(1) and other programs that use rsh(1) or ssh(1) with the format “ssh <user@host> <command>” or “ssh <host> <command>”. To use with cvs(1), just set CVS_RSH to “cvs-safesh” instead of “ssh”.

FILES

$HOME/.safesh/

Directory containing information for safesh.

$HOME/.safesh/map

Mapping file for safesh, describing how to map host names to their canonical form. This is usually used to map short names to their long form. The format of the file is one mapping per line, what it is mapped from as the first word, what it is mapped to as the second.

It is also possible to use this to map domain names to their safe form by having the name of the host as the first parameter, and the name of the host with a period (‘.’) at the end as the second parameter, e.g., “freefall.freebsd.org freefall.freebsd.org.”.

$HOME/.safesh/$USER@$HOST-$PORT/

Directory with data for a particular hostname. Automatically generated on first connect to a host with safesh.

$HOME/.safesh/$USER@$HOST-$PORT/dsa_id

Private key for use to authenticate as $USER@$HOST. Automatically generated on first connect to a host with safesh.

$HOME/.safesh/$USER@$HOST-$PORT/dsa_id.pub

Public key for use by $HOST to authenticate $USER. To connect to $HOST as $USER using safesh without giving a password, add the contents of this file to the end of $HOME/.ssh/authorized_keys2. Automatically generated on first connect to a host with safesh.

$HOME/.safesh/$USER@$HOST-$PORT/$AUTHTARGET

Private key for use when $HOST authenticates towards $AUTHTARGET. This is used in preference to $HOME/.safesh/$AUTHTARGET/dsa_id for authentication forwarding through $HOST to $AUTHTARGET. The file is only used if $AUTHTARGET is listed in $HOME/.safesh/$USER@$HOST-$PORT/extra_keys. This file is not generated automatically by safesh. It is only present if you have generated it using ssh-keygen(1). Note that it is usually more than useless (can pose a security risk) to copy a key used for other authentication to this location.

The use of explict authentication files for authentication forwarding is primarily for protection against the case where the machine you run safesh on is compromised. Using this file, you can use a separate passphrase from the one used for the key for connecting directly to $AUTHTARGET; that key need not even exist. By using IP restrictions in the authorized_keys file for the key, you can make sure that the host safesh runs on cannot connect to $AUTHTARGET using the authentication forwarding key. The use of a separate forwarding key can also be used in combination with a modified SSH to log which key was used where, and thus track key propagation.

$HOME/.safesh/$USER@$HOST-$PORT/$AUTHTARGET.pub

Public key corresponding to the private key described above.

$HOME/.safesh/$USER@$HOST-$PORT/extra_keys

List of extra keys to make available for this host. Each line in the file is first attempted matched against the host/user/port database in $HOME/.safesh/. Username and/or port is added if just the hostname is specified extra_keys, and the hostname is always normalized using the map file. If a key exists in $HOME/.safesh/, safesh attempts to add that. Otherwise, it first tries to look for the line as a file relative to /, then relative to $HOME. If it does not find either of these, safesh will exit with an error message. If it finds one, it will add it using ssh-add(1).

$HOME/.safesh/$USER@$HOST-$PORT/activeagent-$YOURHOST.sh

Bourne shell (see sh(1), bash(1), zsh(1)) script for setting up the environment variables for a particular ssh-agent(1) process used for this host. Only valid if safesh has been run against that host as this user since the machine safesh runs on was last booted. Note that this file must be source'd, not just run as a shell script.

$HOME/.safesh/$USER@$HOST-$PORT/activeagent-$YOURHOST.csh

CSH (see csh(1), tcsh(1)) script for setting up the environment variables for a particular ssh-agent(1) process used for this host. Only valid if safesh has been run against that host as this user since the machine safesh runs on was last booted. Note that this file must be source'd, not just run as a shell script.

AUTHORS

SEE ALSO

KNOWN ISSUES

The ssh-agent(1) processes that are started by safesh will hang around until next reboot unless you put the “killall ssh-agent” command in .logout or similar. This allows any login to your account to use your authentication towards machines you have connected to (including anybody with root on the box), persisting after you log out. You must always assume that root can grab your authentication at the moment you run do it, so this is only an issue in that the authentication stays available longer. This is not resolvable without rewriting ssh-agent(1).

MISSING FEATURES

Two-step secure SSH with an untrusted host in the middle

It is possible to use the port forwarding capability of ssh(1) to forward authentication through another server, without allowing the other server to indepently authenticate to a third party, and without allowing it to see what is going on in your connection. This is based on just forwarding a tunnel through the untrusted host, and doing direct authentication to the server on the other side. With the present version of OpenSSH, this has the problem of leaving the actual port forwarding open while the tunnel is open, allowing other users to set up their own tunnels, and weakening another side of the security model.

Read out fingerprints

The safesh utility should make it trivial to retrieve the fingerprint for:

1. The host it is running on.

   This must presently be done with “ssh-keygen -l /etc/ssh/ssh_host_key.pub” (to get the fingerprint for SSH 1) and “ssh-keygen -l -f /etc/ssh/ssh_host_dsa_key” (for SSH 2).

2. Other hosts, as registered in the known_host file on the host it is running on.

   This must presently be done by manual inspection.

Merge known_hosts

The safesh utility should make it trivial to merge known_hosts and known_hosts2 with ones from another host, including retrieving and uploading known_hosts as appropriate.

Manage .ssh/authorized_keys2

The safesh utility should be able to automatically remove keys from the authorized_keys2 file on other machines, to make everything about the safesh process self-contained.

Manage setup of key limitations

When managing authorized_keys2, it is also reasonable to manage key limitation in this. IP restrictions (“from=”) should be handled to make it easy to create setups where the local machine does not have direct access to a target. Command restrictions etc. would be good to have just for completeness.

Emulate the entire ssh(1) syntax

Presently, the safesh utility has a fairly weird syntax. This is because it is a fairly quick hack, just made to be usable. Later, it would be nice to rewrite it to be fully compatible with ssh(1). This would allow use as a drop-in replacement.

Description of the trust/threat/security model

It would be nice to have a complete description of the normal SSH threat model as well as the safesh threat model, in order to make people fully conscious of their own model.

Emulate scp(1)

The scp(1) utility is very useful, and the only way to use it with safesh at the moment is through a subshell created by scpsh. An ideal safesh implementation would include wrapping of scp(1), too.

VARIABLE REPLACEMENT IN DESCRIPTIONS

$HOME

Path to your home directory.

$HOST

The name of the host you are running safesh towards. This is the machine you are ssh(1)'ing into.

$YOURHOST

The name of the host you are running safesh on, as output by hostname(1). This is the name of the machine you are ssh(1)'ing from. The use of $YOURHOST makes safesh safe to use with NFS-mounted home directories.

$AUTHTARGET

The authentication target for an authentication forwarding. This is not the same as $HOST. $AUTHTARGET is a machine you are ssh(1)'ing to from $HOST. The format of $AUTHTARGET is ⟨user⟩ @ ⟨somehost⟩-⟨someport⟩, where ⟨⟨user⟩⟩ defaults to the username you run safesh as, and ⟨⟨someport⟩⟩ default to 22 (and it is not possible to set anything else at this time).

$USER

The username used on $HOST; defaults to the same as the username you have on $YOURHOST, but will be different if you do “safesh user@host” instead of just “safesh host”.

$PORT

The port used on $HOST. Presently always 22.