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, 52 insertions, 19 deletions

diff --git a/usr.bin/ssh/ssh.c b/usr.bin/ssh/ssh.c
index f3c73641735..48192bff4f5 100644
--- a/usr.bin/ssh/ssh.c
+++ b/usr.bin/ssh/ssh.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh.c,v 1.334 2010/02/08 22:03:05 jmc Exp $ */
+/* $OpenBSD: ssh.c,v 1.335 2010/02/26 20:29:54 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1287,34 +1287,35 @@ load_public_identity_files(void)
 	int i = 0;
 	Key *public;
 	struct passwd *pw;
+	u_int n_ids;
+	char *identity_files[SSH_MAX_IDENTITY_FILES];
+	Key *identity_keys[SSH_MAX_IDENTITY_FILES];
 #ifdef ENABLE_PKCS11
 	Key **keys;
 	int nkeys;
+#endif /* PKCS11 */
 
+	n_ids = 0;
+	bzero(identity_files, sizeof(identity_files));
+	bzero(identity_keys, sizeof(identity_keys));
+
+#ifdef ENABLE_PKCS11
 	if (options.pkcs11_provider != NULL &&
 	    options.num_identity_files < SSH_MAX_IDENTITY_FILES &&
 	    (pkcs11_init(!options.batch_mode) == 0) &&
 	    (nkeys = pkcs11_add_provider(options.pkcs11_provider, NULL,
 	    &keys)) > 0) {
-		int count = 0;
 		for (i = 0; i < nkeys; i++) {
-			count++;
-			memmove(&options.identity_files[1],
-			    &options.identity_files[0],
-			    sizeof(char *) * (SSH_MAX_IDENTITY_FILES - 1));
-			memmove(&options.identity_keys[1],
-			    &options.identity_keys[0],
-			    sizeof(Key *) * (SSH_MAX_IDENTITY_FILES - 1));
-			options.num_identity_files++;
-			options.identity_keys[0] = keys[i];
-			options.identity_files[0] =
+			if (n_ids >= SSH_MAX_IDENTITY_FILES) {
+				key_free(keys[i]);
+				continue;
+			}
+			identity_keys[n_ids] = keys[i];
+			identity_files[n_ids] =
 			    xstrdup(options.pkcs11_provider); /* XXX */
+			n_ids++;
 		}
-		if (options.num_identity_files > SSH_MAX_IDENTITY_FILES)
-			options.num_identity_files = SSH_MAX_IDENTITY_FILES;
-		i = count;
 		xfree(keys);
-		/* XXX leaks some keys */
 	}
 #endif /* ENABLE_PKCS11 */
 	if ((pw = getpwuid(original_real_uid)) == NULL)
@@ -1324,7 +1325,11 @@ load_public_identity_files(void)
 	if (gethostname(thishost, sizeof(thishost)) == -1)
 		fatal("load_public_identity_files: gethostname: %s",
 		    strerror(errno));
-	for (; i < options.num_identity_files; i++) {
+	for (i = 0; i < options.num_identity_files; i++) {
+		if (n_ids >= SSH_MAX_IDENTITY_FILES) {
+			xfree(options.identity_files[i]);
+			continue;
+		}
 		cp = tilde_expand_filename(options.identity_files[i],
 		    original_real_uid);
 		filename = percent_expand(cp, "d", pwdir,
@@ -1335,9 +1340,37 @@ load_public_identity_files(void)
 		debug("identity file %s type %d", filename,
 		    public ? public->type : -1);
 		xfree(options.identity_files[i]);
-		options.identity_files[i] = filename;
-		options.identity_keys[i] = public;
+		identity_files[n_ids] = filename;
+		identity_keys[n_ids] = public;
+
+		if (++n_ids >= SSH_MAX_IDENTITY_FILES)
+			continue;
+
+		/* Try to add the certificate variant too */
+		xasprintf(&cp, "%s-cert", filename);
+		public = key_load_public(cp, NULL);
+		debug("identity file %s type %d", cp,
+		    public ? public->type : -1);
+		if (public == NULL) {
+			xfree(cp);
+			continue;
+		}
+		if (!key_is_cert(public)) {
+			debug("%s: key %s type %s is not a certificate",
+			    __func__, cp, key_type(public));
+			key_free(public);
+			xfree(cp);
+			continue;
+		}
+		identity_keys[n_ids] = public;
+		/* point to the original path, most likely the private key */
+		identity_files[n_ids] = xstrdup(filename);
+		n_ids++;
 	}
+	options.num_identity_files = n_ids;
+	memcpy(options.identity_files, identity_files, sizeof(identity_files));
+	memcpy(options.identity_keys, identity_keys, sizeof(identity_keys));
+
 	bzero(pwname, strlen(pwname));
 	xfree(pwname);
 	bzero(pwdir, strlen(pwdir));