Add support for certificate key types for users and hosts.

OpenSSH certificate key types are not X.509 certificates, but a much
simpler format that encodes a public key, identity information and
some validity constraints and signs it with a CA key. CA keys are
regular SSH keys. This certificate style avoids the attack surface
of X.509 certificates and is very easy to deploy.

Certified host keys allow automatic acceptance of new host keys
when a CA certificate is marked as trusted in ~/.ssh/known_hosts.
see VERIFYING HOST KEYS in ssh(1) for details.

Certified user keys allow authentication of users when the signing
CA key is marked as trusted in authorized_keys. See "AUTHORIZED_KEYS
FILE FORMAT" in sshd(8) for details.

Certificates are minted using ssh-keygen(1), documentation is in
the "CERTIFICATES" section of that manpage.

Documentation on the format of certificates is in the file
PROTOCOL.certkeys

feedback and ok markus@

1 files changed, 10 insertions, 2 deletions

diff --git a/usr.bin/ssh/sshd_config.5 b/usr.bin/ssh/sshd_config.5
index 042d2f3c279..3b492a3dbc2 100644
--- a/usr.bin/ssh/sshd_config.5
+++ b/usr.bin/ssh/sshd_config.5
@@ -34,8 +34,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: sshd_config.5,v 1.116 2010/01/09 23:04:13 dtucker Exp $
-.Dd $Mdocdate: January 9 2010 $
+.\" $OpenBSD: sshd_config.5,v 1.117 2010/02/26 20:29:54 djm Exp $
+.Dd $Mdocdate: February 26 2010 $
 .Dt SSHD_CONFIG 5
 .Os
 .Sh NAME
@@ -412,6 +412,14 @@ uses the name supplied by the client rather than
 attempting to resolve the name from the TCP connection itself.
 The default is
 .Dq no .
+.It Cm HostCertificate
+Specifies a file containing a public host certificate.
+The certificate's public key must match a private host key already specified
+by
+.Cm HostKey .
+The default behaviour of
+.Xr sshd 8
+is not to load any certificates.
 .It Cm HostKey
 Specifies a file containing a private host key
 used by SSH.