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, 13 insertions, 7 deletions

diff --git a/usr.bin/ssh/kexgexs.c b/usr.bin/ssh/kexgexs.c
index 9ac43b88ece..b751a7eeea3 100644
--- a/usr.bin/ssh/kexgexs.c
+++ b/usr.bin/ssh/kexgexs.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: kexgexs.c,v 1.12 2009/06/21 07:37:15 dtucker Exp $ */
+/* $OpenBSD: kexgexs.c,v 1.13 2010/02/26 20:29:54 djm Exp $ */
 /*
  * Copyright (c) 2000 Niels Provos.  All rights reserved.
  * Copyright (c) 2001 Markus Friedl.  All rights reserved.
@@ -49,18 +49,24 @@ void
 kexgex_server(Kex *kex)
 {
 	BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
-	Key *server_host_key;
+	Key *server_host_public, *server_host_private;
 	DH *dh;
 	u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
 	u_int sbloblen, klen, slen, hashlen;
 	int omin = -1, min = -1, omax = -1, max = -1, onbits = -1, nbits = -1;
 	int type, kout;
 
-	if (kex->load_host_key == NULL)
+	if (kex->load_host_public_key == NULL ||
+	    kex->load_host_private_key == NULL)
 		fatal("Cannot load hostkey");
-	server_host_key = kex->load_host_key(kex->hostkey_type);
-	if (server_host_key == NULL)
+	server_host_public = kex->load_host_public_key(kex->hostkey_type);
+	if (server_host_public == NULL)
 		fatal("Unsupported hostkey type %d", kex->hostkey_type);
+	server_host_private = kex->load_host_private_key(kex->hostkey_type);
+	if (server_host_private == NULL)
+		fatal("Missing private key for hostkey type %d",
+		    kex->hostkey_type);
+
 
 	type = packet_read();
 	switch (type) {
@@ -146,7 +152,7 @@ kexgex_server(Kex *kex)
 	memset(kbuf, 0, klen);
 	xfree(kbuf);
 
-	key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
+	key_to_blob(server_host_public, &server_host_key_blob, &sbloblen);
 
 	if (type == SSH2_MSG_KEX_DH_GEX_REQUEST_OLD)
 		omin = min = omax = max = -1;
@@ -176,7 +182,7 @@ kexgex_server(Kex *kex)
 	}
 
 	/* sign H */
-	if (PRIVSEP(key_sign(server_host_key, &signature, &slen, hash,
+	if (PRIVSEP(key_sign(server_host_private, &signature, &slen, hash,
 	    hashlen)) < 0)
 		fatal("kexgex_server: key_sign failed");