.\" $OpenBSD: ssh-keysign.8,v 1.17 2022/03/31 17:27:27 naddy Exp $
.\"
.\" Copyright (c) 2002 Markus Friedl.  All rights reserved.
.\"
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.Dd $Mdocdate: March 31 2022 $
.Dt SSH-KEYSIGN 8
.Os
.Sh NAME
.Nm ssh-keysign
.Nd OpenSSH helper for host-based authentication
.Sh SYNOPSIS
.Nm
.Sh DESCRIPTION
.Nm
is used by
.Xr ssh 1
to access the local host keys and generate the digital signature
required during host-based authentication.
.Pp
.Nm
is disabled by default and can only be enabled in the
global client configuration file
.Pa /etc/ssh/ssh_config
by setting
.Cm EnableSSHKeysign
to
.Dq yes .
.Pp
.Nm
is not intended to be invoked by the user, but from
.Xr ssh 1 .
See
.Xr ssh 1
and
.Xr sshd 8
for more information about host-based authentication.
.Sh FILES
.Bl -tag -width Ds -compact
.It Pa /etc/ssh/ssh_config
Controls whether
.Nm
is enabled.
.Pp
.It Pa /etc/ssh/ssh_host_dsa_key
.It Pa /etc/ssh/ssh_host_ecdsa_key
.It Pa /etc/ssh/ssh_host_ed25519_key
.It Pa /etc/ssh/ssh_host_rsa_key
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.
Since they are readable only by root,
.Nm
must be set-uid root if host-based authentication is used.
.Pp
.It Pa /etc/ssh/ssh_host_dsa_key-cert.pub
.It Pa /etc/ssh/ssh_host_ecdsa_key-cert.pub
.It Pa /etc/ssh/ssh_host_ed25519_key-cert.pub
.It Pa /etc/ssh/ssh_host_rsa_key-cert.pub
If these files exist, they are assumed to contain public certificate
information corresponding with the private keys above.
.El
.Sh SEE ALSO
.Xr ssh 1 ,
.Xr ssh-keygen 1 ,
.Xr ssh_config 5 ,
.Xr sshd 8
.Sh HISTORY
.Nm
first appeared in
.Ox 3.2 .
.Sh AUTHORS
.An Markus Friedl Aq Mt markus@openbsd.org