'\" te
.\" Copyright (c) 2003, Sun Microsystems, Inc. All Rights Reserved
.TH ssh-keysign 1M "9 Jun 2004" "SunOS 5.11" "System Administration Commands"
.SH NAME
ssh-keysign \- ssh helper program for host-based authentication
.SH SYNOPSIS
.LP
.nf
\fBssh-keysign\fR 
.fi

.SH DESCRIPTION
.sp
.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
.sp
.ne 2
.mk
.na
\fB\fB/etc/ssh/ssh_config\fR\fR
.ad
.RS 29n
.rt  
Controls whether \fBssh-keysign\fR is enabled.
.RE

.sp
.ne 2
.mk
.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
.rt  
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
.sp
.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
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
tab() box;
cw(2.75i) |cw(2.75i) 
lw(2.75i) |lw(2.75i) 
.
ATTRIBUTE TYPEATTRIBUTE VALUE
_
Availabilitynetwork/ssh
_
Interface StabilityCommitted
.TE

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