freebsd-ports/security/safesh/src/safesh.1

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.\" Copyright (c) 2002 Eivind Eklund
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.Dd January 26, 2002
.Dt SAFESH 1
.Sh NAME
.Nm safesh
.Nd safe key manager for OpenSSH
.Sh SYNOPSIS
.Nm
.Oo Ar user@ Oc Ns Ar host
.Oo
.Fl Fl
.Ar ssh-parameters ...
.Oc
.Nm safeshinstall
.Oo Ar user@ Oc Ns Ar host
.Nm cvs-safesh
.Oo Ar user@ Oc Ns Ar host
.Op Ar command
.Nm scpsh
.Oo Ar user@ Oc Ns Ar host
.Sh DESCRIPTION
NOTE: This text often refers to
.Va $VARIABLE
in description.
What each of the references will be replaced with when
.Nm
runs is described at the end of the manpage.
.Pp
The
.Nm
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
.Xr 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.
.Pp
When run,
.Nm :
.Bl -enum
.It
Normalizes the hostname you are talking about, using the
.Pa $HOME/.safesh/map
file.
.It
Checks if the user and host has an SSH DSA key in
.Pa $HOME/.safesh ,
and creates one using
.Xr ssh-keygen 1
if it does not.
The DSA key is stored in
.Pa $HOME/.safesh/$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
.Nm
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).
.It
Checks if you have the
.Xr ssh-agent 1
for this host running, and starts it if not.
.It
Checks what keys you are supposed to have active when connecting to this host
(the key for the host and any keys listed in
.Pa $HOME/.safesh/$USER@$HOST-$PORT/extra_keys ) ,
and which of these are missing from the active agent.
.It
If any identities were missing from the agent, it executes
.Xr ssh-add 1
to add them to the agent.
.It
Executes
.Xr ssh 1
with either
.Ar $USER@$HOST
or the extra command line supplied by the user.
.El
.Sh BASIC CONCEPT DESCRIPTION
The
.Nm
utility
is an authentication manager for OpenSSH.
It is an attempt at making it easy to use the built-in authentication features
of OpenSSH securely.
By default, the SSH security model is that all hosts the
user connects to are trusted, and are given complete access, including the
ability to authenticate as the user towards other hosts if the user is running
.Xr ssh-agent 1 .
OpenSSH has improved this security model somewhat by not forwarding SSH
authentication by default, but still allows the host that you connect to
to grab your credentials and authenticate as you to anybody else when you
do authentication forwarding to it.
.Sh SIMPLE HOWTO
Starting to make use of
.Nm
is trivial:
.Bl -enum
.It
Do
.Dq Li "safeshinstall <[user@]hostname>" .
.Pp
This will ask for a passphrase (three times), create a directory
.Pa $HOME/.safesh/<user>@<hostname>-22 ,
which contains authentication
data for your user at
.Aq Ar hostname ,
and add the contents of
.Pa $HOME/.safesh/<user>@<hostname>-22/id_dsa.pub
to
.Pa $HOME/.ssh/authorized_keys2
on the host you connect to.
The latter will result in
.Xr ssh 1
asking for authentication in the fashion you already use (most likely by
asking for your password).
.It
Log in with
.Dq Li "safesh <hostname>"
from now on.
.Pp
This will ask you for a passphrase if you have not logged into that host this
session, and otherwise just let right in.
.El
.Sh UTILITY COMMANDS
The
.Nm
utility
ships with two utility hacks to work around the fact that it is not a complete
.Xr ssh 1
replacement,
.Nm scpsh
and
.Nm cvs-safesh .
.Pp
The
.Nm scpsh
utility
is for supporting use of
.Xr scp 1
with
.Nm .
The
.Nm scpsh
.Oo Ar user@ Oc Ns Ar host
command
will start a new interactive shell (using the
.Ev SHELL
environment variable to determine which it should be), with the environment
variables for using
.Xr ssh-agent 1
to authenticate to
.Oo Ar user@ Oc Ns Ar host
already set.
This allows use of
.Xr scp 1
without having to type passwords to authenticate.
.Pp
The
.Nm cvs-safesh
utility
makes it easy to use
.Nm
along with
.Xr cvs 1
and other programs that use
.Xr rsh 1
or
.Xr ssh 1
with the format
.Dq Li "ssh <user@host> <command>"
or
.Dq Li "ssh <host> <command>" .
To use with
.Xr cvs 1 ,
just set
.Ev CVS_RSH
to
.Dq Li cvs-safesh
instead of
.Dq Li ssh .
.Sh FILES
.Bl -tag -width ".Pa $HOME/.safesh"
.It Pa $HOME/.safesh/
Directory containing information for
.Nm .
.It Pa $HOME/.safesh/map
Mapping file for
.Nm ,
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.
.Pp
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
.Pq Ql .\&
at the end as the second parameter,
e.g.,
.Dq Li freefall.freebsd.org freefall.freebsd.org. .
.It Pa $HOME/.safesh/$USER@$HOST-$PORT/
Directory with data for a particular hostname.
Automatically generated on first connect to a host with
.Nm .
.It Pa $HOME/.safesh/$USER@$HOST-$PORT/dsa_id
Private key for use to authenticate as
.Ar $USER@$HOST .
Automatically generated on first connect to a host with
.Nm .
.It Pa $HOME/.safesh/$USER@$HOST-$PORT/dsa_id.pub
Public key for use by
.Ar $HOST
to authenticate
.Ar $USER .
To connect to
.Ar $HOST
as
.Ar $USER
using
.Nm
without giving a password, add the contents of this file
to the end of
.Pa $HOME/.ssh/authorized_keys2 .
Automatically generated on first connect to a host with
.Nm .
.It Pa $HOME/.safesh/$USER@$HOST-$PORT/$AUTHTARGET
Private key for use when
.Ar $HOST
authenticates towards
.Ar $AUTHTARGET .
This is used in preference to
.Pa $HOME/.safesh/$AUTHTARGET/dsa_id
for authentication forwarding through
.Ar $HOST
to
.Ar $AUTHTARGET .
The file is only used if
.Ar $AUTHTARGET
is listed in
.Pa $HOME/.safesh/$USER@$HOST-$PORT/extra_keys .
This file is not generated automatically by
.Nm .
It is only present if you have generated it using
.Xr 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.
.Pp
The use of explict authentication files for authentication forwarding is
primarily for protection against the case where the machine you run
.Nm
on is compromised.
Using this file, you can use a separate passphrase from the one used for the
key for connecting directly to
.Ar $AUTHTARGET ;
that key need not even exist.
By using IP restrictions in the
.Pa authorized_keys
file for the key, you can make
sure that the host
.Nm
runs on cannot connect to
.Ar $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.
.It Pa $HOME/.safesh/$USER@$HOST-$PORT/$AUTHTARGET.pub
Public key corresponding to the private key described above.
.It Pa $HOME/.safesh/$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
.Pa $HOME/.safesh/ .
Username and/or port is added if just the hostname is specified
.Pa extra_keys ,
and the hostname is always normalized using the map file.
If a key exists in
.Pa $HOME/.safesh/ ,
.Nm
attempts to add that.
Otherwise, it first tries to look for the line as a file relative to
.Pa / ,
then relative to
.Pa $HOME .
If it does not find either of these,
.Nm
will exit with an error message.
If it finds one, it will add it using
.Xr ssh-add 1 .
.It Pa $HOME/.safesh/$USER@$HOST-$PORT/activeagent-$YOURHOST.sh
Bourne shell (see
.Xr sh 1 ,
.Xr bash 1 ,
.Xr zsh 1 )
script for setting up the environment variables for a particular
.Xr ssh-agent 1
process used for this host.
Only valid if
.Nm
has been run against that host as this user since the machine
.Nm
runs on was last booted.
Note that this file must be source'd, not just run as a shell script.
.It Pa $HOME/.safesh/$USER@$HOST-$PORT/activeagent-$YOURHOST.csh
CSH (see
.Xr csh 1 ,
.Xr tcsh 1 )
script for setting up the environment variables for a particular
.Xr ssh-agent 1
process used for this host.
Only valid if
.Nm
has been run against that host as this user since the machine
.Nm
runs on was last booted.
Note that this file must be source'd, not just run as a shell script.
.El
.Sh AUTHORS
The
.Nm
utility
was written by
.An Eivind Eklund Aq eivind@FreeBSD.org .
.Sh SEE ALSO
.Xr ssh 1 ,
.Xr ssh-add 1 ,
.Xr ssh-agent 1 ,
.Xr ssh-keygen 1
.Sh KNOWN ISSUES
The
.Nm
utility
does not handle whitespace in filenames specified in
.Pa extra_keys
correctly.
.Pp
The
.Xr ssh-agent 1
processes that are started by
.Nm
will hang around until next reboot unless
you put the
.Dq Li "killall ssh-agent"
command in
.Pa .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
.Xr ssh-agent 1 .
.Sh MISSING FEATURES
.Bl -tag -width 4n
.It Em Two-step secure SSH with an untrusted host in the middle
It is possible to use the port forwarding capability of
.Xr 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.
.It Em Read out fingerprints
The
.Nm
utility
should make it trivial to retrieve the fingerprint for:
.Bl -enum
.It
The host it is running on.
.Pp
This must presently be done with
.Dq Li "ssh-keygen -l /etc/ssh/ssh_host_key.pub"
(to get the fingerprint for SSH 1) and
.Dq Li "ssh-keygen -l -f /etc/ssh/ssh_host_dsa_key"
(for SSH 2).
.It
Other hosts, as registered in the
.Pa known_host
file on the host it is running
on.
.Pp
This must presently be done by manual inspection.
.El
.It Em Merge Pa known_hosts
The
.Nm
utility
should make it trivial to merge
.Pa known_hosts
and
.Pa known_hosts2
with ones from
another host, including retrieving and uploading
.Pa known_hosts
as appropriate.
.It Em Manage Pa .ssh/authorized_keys2
The
.Nm
utility
should be able to automatically remove keys from the
.Pa authorized_keys2
file
on other machines, to make everything about the
.Nm
process self-contained.
.It Em Manage setup of key limitations
When managing
.Pa authorized_keys2 ,
it is also reasonable to manage key limitation
in this.
IP restrictions
.Pq Qq Li 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.
.It Em Emulate the entire Xr ssh 1 Em syntax
Presently, the
.Nm
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
.Xr ssh 1 .
This would allow use as a drop-in replacement.
.It Em 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
.Nm
threat model, in order to make people fully conscious of their own model.
.It Em Emulate Xr scp 1
The
.Xr scp 1
utility
is very useful, and the only way to use it with
.Nm
at the moment is through a subshell created by
.Nm scpsh .
An ideal
.Nm
implementation would include wrapping of
.Xr scp 1 ,
too.
.El
.Sh VARIABLE REPLACEMENT IN DESCRIPTIONS
.Bl -tag -width ".Va $AUTHTARGET"
.It Va $HOME
Path to your home directory.
.It Va $HOST
The name of the host you are running
.Nm
towards.
This is the machine you are
.Xr ssh 1 Ns 'ing
into.
.It Va $YOURHOST
The name of the host you are running
.Nm
on, as output by
.Xr hostname 1 .
This is the name of the machine you are
.Xr ssh 1 Ns 'ing
from.
The use of
.Va $YOURHOST
makes
.Nm
safe to use with NFS-mounted home directories.
.It Va $AUTHTARGET
The authentication target for an authentication forwarding.
This is
.Em not
the same as
.Va $HOST .
.Va $AUTHTARGET
is a machine you are
.Xr ssh 1 Ns 'ing
to
.Em from
.Va $HOST .
The format of
.Va $AUTHTARGET
is
.Sm off
.Ao Ar user Ac @ Ao Ar somehost Ac - Aq Ar someport ,
.Sm on
where
.Aq Aq user
defaults to the username you run
.Nm
as, and
.Aq Aq someport
default to 22 (and it is not possible to set anything
else at this time).
.It Va $USER
The username used on
.Va $HOST ;
defaults to the same as the
username you have on
.Va $YOURHOST ,
but will be different if you do
.Dq Li "safesh user@host"
instead of just
.Dq Li "safesh host" .
.It Va $PORT
The port used on
.Va $HOST .
Presently always 22.
.El