'\" te
.\" Copyright (c) 2003, Sun Microsystems, Inc. All Rights Reserved
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
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.TH SSH-KEYSIGN 1M "Jun 9, 2004"
.SH NAME
ssh-keysign \- ssh helper program for host-based authentication
.SH SYNOPSIS
.LP
.nf
\fBssh-keysign\fR
.fi

.SH DESCRIPTION
.LP
\fBssh-keysign\fR is used by \fBssh\fR(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.
.sp
.LP
\fBssh-keysign\fR is disabled by default and can be enabled only in the global
client configuration file \fB/etc/ssh/ssh_config\fR by setting
\fBHostbasedAuthentication\fR to \fByes\fR.
.sp
.LP
\fBssh-keysign\fR is not intended to be invoked by the user, but from
\fBssh\fR. See \fBssh\fR(1) and \fBsshd\fR(1M) for more information about
host-based authentication.
.SH FILES
.ne 2
.na
\fB\fB/etc/ssh/ssh_config\fR\fR
.ad
.RS 29n
Controls whether \fBssh-keysign\fR is enabled.
.RE

.sp
.ne 2
.na
\fB\fB/etc/ssh/ssh_host_dsa_key\fR\fR
.ad
.br
.na
\fB\fB/etc/ssh/ssh_host_rsa_key\fR\fR
.ad
.RS 29n
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, \fBssh-keysign\fR
must be \fBset-uid\fR root if host-based authentication is used.
.RE

.SH SECURITY
.LP
ssh-keysign will not sign host-based authentication data under the following
conditions:
.RS +4
.TP
.ie t \(bu
.el o
If the \fBHostbasedAuthentication\fR client configuration parameter is not set
to \fByes\fR in \fB/etc/ssh/ssh_config\fR. This setting cannot be overriden in
users' \fB~/.ssh/ssh_config\fR files.
.RE
.RS +4
.TP
.ie t \(bu
.el o
If the client hostname and username in \fB/etc/ssh/ssh_config\fR do not match
the canonical hostname of the client where \fBssh-keysign\fR is invoked and the
name of the user invoking \fBssh-keysign\fR.
.RE
.sp
.LP
In spite of \fBssh-keysign\fR'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.
.SH ATTRIBUTES
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Evolving
.TE

.SH SEE ALSO
.LP
\fBssh\fR(1), \fBsshd\fR(1M), \fBssh_config\fR(4), \fBattributes\fR(5)
.SH AUTHORS
.LP
Markus Friedl, \fBmarkus@openbsd.org\fR
.SH HISTORY
.LP
\fBssh-keysign\fR first appeared in Ox 3.2.