- djm@cvs.openbsd.org 2010/03/04 10:36:03

[auth-rh-rsa.c auth-rsa.c auth.c auth.h auth2-hostbased.c auth2-pubkey.c]
     [authfile.c authfile.h hostfile.c hostfile.h servconf.c servconf.h]
     [ssh-keygen.c ssh.1 sshconnect.c sshd_config.5]
     Add a TrustedUserCAKeys option to sshd_config to specify CA keys that
     are trusted to authenticate users (in addition than doing it per-user
     in authorized_keys).

     Add a RevokedKeys option to sshd_config and a @revoked marker to
     known_hosts to allow keys to me revoked and banned for user or host
     authentication.

     feedback and ok markus@

ChangeLog

@@ -22,6 +22,19 @@
      [key.c]
      use buffer_get_string_ptr_ret() where we are checking the return
      value explicitly instead of the fatal()-causing buffer_get_string_ptr()
+   - djm@cvs.openbsd.org 2010/03/04 10:36:03
+     [auth-rh-rsa.c auth-rsa.c auth.c auth.h auth2-hostbased.c auth2-pubkey.c]
+     [authfile.c authfile.h hostfile.c hostfile.h servconf.c servconf.h]
+     [ssh-keygen.c ssh.1 sshconnect.c sshd_config.5]
+     Add a TrustedUserCAKeys option to sshd_config to specify CA keys that
+     are trusted to authenticate users (in addition than doing it per-user
+     in authorized_keys).
+     
+     Add a RevokedKeys option to sshd_config and a @revoked marker to
+     known_hosts to allow keys to me revoked and banned for user or host
+     authentication.
+     
+     feedback and ok markus@
 
 20100303
  - (djm) [PROTOCOL.certkeys] Add RCS Ident

auth-rh-rsa.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth-rh-rsa.c,v 1.42 2006/08/03 03:34:41 deraadt Exp $ */
+/* $OpenBSD: auth-rh-rsa.c,v 1.43 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -44,6 +44,9 @@ auth_rhosts_rsa_key_allowed(struct passwd *pw, char *cuser, char *chost,
 {
 	HostStatus host_status;
 
+	if (auth_key_is_revoked(client_host_key))
+		return 0;
+
 	/* Check if we would accept it using rhosts authentication. */
 	if (!auth_rhosts(pw, cuser))
 		return 0;

auth-rsa.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth-rsa.c,v 1.73 2008/07/02 12:03:51 dtucker Exp $ */
+/* $OpenBSD: auth-rsa.c,v 1.74 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -94,6 +94,9 @@ auth_rsa_verify_response(Key *key, BIGNUM *challenge, u_char response[16])
 	MD5_CTX md;
 	int len;
 
+	if (auth_key_is_revoked(key))
+		return 0;
+
 	/* don't allow short keys */
 	if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
 		error("auth_rsa_verify_response: RSA modulus too small: %d < minimum %d bits",

auth.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth.c,v 1.84 2010/02/09 06:18:46 djm Exp $ */
+/* $OpenBSD: auth.c,v 1.85 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -69,6 +69,7 @@
 #ifdef GSSAPI
 #include "ssh-gss.h"
 #endif
+#include "authfile.h"
 #include "monitor_wrap.h"
 
 /* import */
@@ -582,6 +583,34 @@ getpwnamallow(const char *user)
 	return (NULL);
 }
 
+/* Returns 1 if key is revoked by revoked_keys_file, 0 otherwise */
+int
+auth_key_is_revoked(Key *key)
+{
+	char *key_fp;
+
+	if (options.revoked_keys_file == NULL)
+		return 0;
+
+	switch (key_in_file(key, options.revoked_keys_file, 0)) {
+	case 0:
+		/* key not revoked */
+		return 0;
+	case -1:
+		/* Error opening revoked_keys_file: refuse all keys */
+		error("Revoked keys file is unreadable: refusing public key "
+		    "authentication");
+		return 1;
+	case 1:
+		/* Key revoked */
+		key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
+		error("%s key %s is revoked", key_type(key), key_fp);
+		xfree(key_fp);
+		return 1;
+	}
+	fatal("key_in_file returned junk");
+}
+
 void
 auth_debug_add(const char *fmt,...)
 {

auth.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth.h,v 1.64 2010/02/26 20:29:54 djm Exp $ */
+/* $OpenBSD: auth.h,v 1.65 2010/03/04 10:36:03 djm Exp $ */
 
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
@@ -171,6 +171,7 @@ char	*authorized_keys_file(struct passwd *);
 char	*authorized_keys_file2(struct passwd *);
 
 FILE	*auth_openkeyfile(const char *, struct passwd *, int);
+int	 auth_key_is_revoked(Key *);
 
 HostStatus
 check_key_in_hostfiles(struct passwd *, Key *, const char *,

auth2-hostbased.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-hostbased.c,v 1.12 2008/07/17 08:51:07 djm Exp $ */
+/* $OpenBSD: auth2-hostbased.c,v 1.13 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -145,6 +145,9 @@ hostbased_key_allowed(struct passwd *pw, const char *cuser, char *chost,
 	HostStatus host_status;
 	int len;
 
+	if (auth_key_is_revoked(key))
+		return 0;
+
 	resolvedname = get_canonical_hostname(options.use_dns);
 	ipaddr = get_remote_ipaddr();
 

auth2-pubkey.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.20 2010/02/26 20:29:54 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.21 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -56,6 +56,7 @@
 #endif
 #include "monitor_wrap.h"
 #include "misc.h"
+#include "authfile.h"
 
 /* import */
 extern ServerOptions options;
@@ -276,6 +277,47 @@ user_key_allowed2(struct passwd *pw, Key *key, char *file)
 	return found_key;
 }
 
+/* Authenticate a certificate key against TrustedUserCAKeys */
+static int
+user_cert_trusted_ca(struct passwd *pw, Key *key)
+{
+	char *key_fp, *ca_fp;
+	const char *reason;
+	int ret = 0;
+
+	if (!key_is_cert(key) || options.trusted_user_ca_keys == NULL)
+		return 0;
+
+	key_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
+	ca_fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
+
+	if (key_in_file(key->cert->signature_key,
+	    options.trusted_user_ca_keys, 1) != 1) {
+		debug2("%s: CA %s %s is not listed in %s", __func__,
+		    key_type(key->cert->signature_key), ca_fp,
+		    options.trusted_user_ca_keys);
+		goto out;
+	}
+	if (key_cert_check_authority(key, 0, 1, pw->pw_name, &reason) != 0) {
+		error("%s", reason);
+		auth_debug_add("%s", reason);
+		goto out;
+	}
+	if (auth_cert_constraints(&key->cert->constraints, pw) != 0)
+		goto out;
+
+	verbose("%s certificate %s allowed by trusted %s key %s",
+	    key_type(key), key_fp, key_type(key->cert->signature_key), ca_fp);
+	ret = 1;
+
+ out:
+	if (key_fp != NULL)
+		xfree(key_fp);
+	if (ca_fp != NULL)
+		xfree(ca_fp);
+	return ret;
+}
+
 /* check whether given key is in .ssh/authorized_keys* */
 int
 user_key_allowed(struct passwd *pw, Key *key)
@@ -283,6 +325,15 @@ user_key_allowed(struct passwd *pw, Key *key)
 	int success;
 	char *file;
 
+	if (auth_key_is_revoked(key))
+		return 0;
+	if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))
+		return 0;
+
+	success = user_cert_trusted_ca(pw, key);
+	if (success)
+		return success;
+
 	file = authorized_keys_file(pw);
 	success = user_key_allowed2(pw, key, file);
 	xfree(file);

authfile.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: authfile.c,v 1.79 2010/01/12 00:16:47 dtucker Exp $ */
+/* $OpenBSD: authfile.c,v 1.80 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -692,3 +692,65 @@ key_load_public(const char *filename, char **commentp)
 	key_free(pub);
 	return NULL;
 }
+
+/*
+ * Returns 1 if the specified "key" is listed in the file "filename",
+ * 0 if the key is not listed or -1 on error.
+ * If strict_type is set then the key type must match exactly,
+ * otherwise a comparison that ignores certficiate data is performed.
+ */
+int
+key_in_file(Key *key, const char *filename, int strict_type)
+{
+	FILE *f;
+	char line[SSH_MAX_PUBKEY_BYTES];
+	char *cp;
+	u_long linenum = 0;
+	int ret = 0;
+	Key *pub;
+	int (*key_compare)(const Key *, const Key *) = strict_type ?
+	    key_equal : key_equal_public;
+
+	if ((f = fopen(filename, "r")) == NULL) {
+		if (errno == ENOENT) {
+			debug("%s: keyfile \"%s\" missing", __func__, filename);
+			return 0;
+		} else {
+			error("%s: could not open keyfile \"%s\": %s", __func__,
+			    filename, strerror(errno));
+			return -1;
+		}
+	}
+
+	while (read_keyfile_line(f, filename, line, sizeof(line),
+		    &linenum) != -1) {
+		cp = line;
+
+		/* Skip leading whitespace. */
+		for (; *cp && (*cp == ' ' || *cp == '\t'); cp++)
+			;
+
+		/* Skip comments and empty lines */
+		switch (*cp) {
+		case '#':
+		case '\n':
+		case '\0':
+			continue;
+		}
+
+		pub = key_new(KEY_UNSPEC);
+		if (key_read(pub, &cp) != 1) {
+			key_free(pub);
+			continue;
+		}
+		if (key_compare(key, pub)) {
+			ret = 1;
+			key_free(pub);
+			break;
+		}
+		key_free(pub);
+	}
+	fclose(f);
+	return ret;
+}
+

authfile.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: authfile.h,v 1.13 2006/04/25 08:02:27 dtucker Exp $ */
+/* $OpenBSD: authfile.h,v 1.14 2010/03/04 10:36:03 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -22,5 +22,6 @@ Key	*key_load_private(const char *, const char *, char **);
 Key	*key_load_private_type(int, const char *, const char *, char **, int *);
 Key	*key_load_private_pem(int, int, const char *, char **);
 int	 key_perm_ok(int, const char *);
+int	 key_in_file(Key *, const char *, int);
 
 #endif

hostfile.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: hostfile.c,v 1.47 2010/02/26 20:29:54 djm Exp $ */
+/* $OpenBSD: hostfile.c,v 1.48 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -183,6 +183,41 @@ hostfile_check_key(int bits, const Key *key, const char *host, const char *filen
 	return 1;
 }
 
+static enum { MRK_ERROR, MRK_NONE, MRK_REVOKE, MRK_CA }
+check_markers(char **cpp)
+{
+	char marker[32], *sp, *cp = *cpp;
+	int ret = MRK_NONE;
+
+	while (*cp == '@') {
+		/* Only one marker is allowed */
+		if (ret != MRK_NONE)
+			return MRK_ERROR;
+		/* Markers are terminated by whitespace */
+		if ((sp = strchr(cp, ' ')) == NULL &&
+		    (sp = strchr(cp, '\t')) == NULL)
+			return MRK_ERROR;
+		/* Extract marker for comparison */
+		if (sp <= cp + 1 || sp >= cp + sizeof(marker))
+			return MRK_ERROR;
+		memcpy(marker, cp, sp - cp);
+		marker[sp - cp] = '\0';
+		if (strcmp(marker, CA_MARKER) == 0)
+			ret = MRK_CA;
+		else if (strcmp(marker, REVOKE_MARKER) == 0)
+			ret = MRK_REVOKE;
+		else
+			return MRK_ERROR;
+
+		/* Skip past marker and any whitespace that follows it */
+		cp = sp;
+		for (; *cp == ' ' || *cp == '\t'; cp++)
+			;
+	}
+	*cpp = cp;
+	return ret;
+}
+
 /*
  * Checks whether the given host (which must be in all lowercase) is already
  * in the list of our known hosts. Returns HOST_OK if the host is known and
@@ -195,17 +230,21 @@ hostfile_check_key(int bits, const Key *key, const char *host, const char *filen
 
 static HostStatus
 check_host_in_hostfile_by_key_or_type(const char *filename,
-    const char *host, const Key *key, int keytype, Key *found, int *numret)
+    const char *host, const Key *key, int keytype, Key *found,
+    int want_revocation, int *numret)
 {
 	FILE *f;
 	char line[8192];
-	int linenum = 0, want_cert = key_is_cert(key);
+	int want, have, linenum = 0, want_cert = key_is_cert(key);
 	u_int kbits;
 	char *cp, *cp2, *hashed_host;
 	HostStatus end_return;
 
 	debug3("check_host_in_hostfile: host %s filename %s", host, filename);
 
+	if (want_revocation && (key == NULL || keytype != 0 || found != NULL))
+		fatal("%s: invalid arguments", __func__);
+
 	/* Open the file containing the list of known hosts. */
 	f = fopen(filename, "r");
 	if (!f)
@@ -229,21 +268,18 @@ check_host_in_hostfile_by_key_or_type(const char *filename,
 		if (!*cp || *cp == '#' || *cp == '\n')
 			continue;
 
-		/*
+		if (want_revocation)
-		 * Ignore CA keys when looking for raw keys.
+			want = MRK_REVOKE;
-		 * Ignore raw keys when looking for CA keys.
+		else if (want_cert)
-		 */
+			want = MRK_CA;
-		if (strncasecmp(cp, CA_MARKER, sizeof(CA_MARKER) - 1) == 0 &&
+		else
-		    (cp[sizeof(CA_MARKER) - 1] == ' ' ||
+			want = MRK_NONE;
-		    cp[sizeof(CA_MARKER) - 1] == '\t')) {
+
-			if (want_cert) {
+		if ((have = check_markers(&cp)) == MRK_ERROR) {
-				/* Skip the marker and following whitespace */
+			verbose("%s: invalid marker at %s:%d",
-				cp += sizeof(CA_MARKER);
+			    __func__, filename, linenum);
-				for (; *cp == ' ' || *cp == '\t'; cp++)
+			continue;
-					;
+		} else if (want != have)
-			} else
-				continue;
-		} else if (want_cert)
 			continue;
 
 		/* Find the end of the host name portion. */
@@ -267,6 +303,9 @@ check_host_in_hostfile_by_key_or_type(const char *filename,
 		/* Got a match.  Skip host name. */
 		cp = cp2;
 
+		if (want_revocation)
+			found = key_new(KEY_UNSPEC);
+
 		/*
 		 * Extract the key from the line.  This will skip any leading
 		 * whitespace.  Ignore badly formatted lines.
@@ -289,6 +328,24 @@ check_host_in_hostfile_by_key_or_type(const char *filename,
 		if (!hostfile_check_key(kbits, found, host, filename, linenum))
 			continue;
 
+		if (want_revocation) {
+			if (key_is_cert(key) &&
+			    key_equal_public(key->cert->signature_key, found)) {
+				verbose("check_host_in_hostfile: revoked CA "
+				    "line %d", linenum);
+				key_free(found);
+				return HOST_REVOKED;
+			}
+			if (key_equal_public(key, found)) {
+				verbose("check_host_in_hostfile: revoked key "
+				    "line %d", linenum);
+				key_free(found);
+				return HOST_REVOKED;
+			}
+			key_free(found);
+			continue;
+		}
+
 		/* Check if the current key is the same as the given key. */
 		if (want_cert && key_equal(key->cert->signature_key, found)) {
 			/* Found CA cert for key */
@@ -325,8 +382,11 @@ check_host_in_hostfile(const char *filename, const char *host, const Key *key,
 {
 	if (key == NULL)
 		fatal("no key to look up");
-	return (check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
+	if (check_host_in_hostfile_by_key_or_type(filename, host,
-	    found, numret));
+	    key, 0, NULL, 1, NULL) == HOST_REVOKED)
+		return HOST_REVOKED;
+	return check_host_in_hostfile_by_key_or_type(filename, host, key, 0,
+	    found, 0, numret);
 }
 
 int
@@ -334,7 +394,7 @@ lookup_key_in_hostfile_by_type(const char *filename, const char *host,
     int keytype, Key *found, int *numret)
 {
 	return (check_host_in_hostfile_by_key_or_type(filename, host, NULL,
-	    keytype, found, numret) == HOST_FOUND);
+	    keytype, found, 0, numret) == HOST_FOUND);
 }
 
 /*

hostfile.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: hostfile.h,v 1.17 2010/02/26 20:29:54 djm Exp $ */
+/* $OpenBSD: hostfile.h,v 1.18 2010/03/04 10:36:03 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -15,7 +15,7 @@
 #define HOSTFILE_H
 
 typedef enum {
-	HOST_OK, HOST_NEW, HOST_CHANGED, HOST_FOUND
+	HOST_OK, HOST_NEW, HOST_CHANGED, HOST_REVOKED, HOST_FOUND
 }       HostStatus;
 
 int	 hostfile_read_key(char **, u_int *, Key *);
@@ -29,6 +29,7 @@ int	lookup_key_in_hostfile_by_type(const char *, const char *,
 #define HASH_DELIM	'|'
 
 #define CA_MARKER	"@cert-authority"
+#define REVOKE_MARKER	"@revoked"
 
 char	*host_hash(const char *, const char *, u_int);
 

servconf.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: servconf.c,v 1.203 2010/02/26 20:29:54 djm Exp $ */
+/* $OpenBSD: servconf.c,v 1.204 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -129,6 +129,8 @@ initialize_server_options(ServerOptions *options)
 	options->adm_forced_command = NULL;
 	options->chroot_directory = NULL;
 	options->zero_knowledge_password_authentication = -1;
+	options->revoked_keys_file = NULL;
+	options->trusted_user_ca_keys = NULL;
 }
 
 void
@@ -308,6 +310,7 @@ typedef enum {
 	sMatch, sPermitOpen, sForceCommand, sChrootDirectory,
 	sUsePrivilegeSeparation, sAllowAgentForwarding,
 	sZeroKnowledgePasswordAuthentication, sHostCertificate,
+	sRevokedKeys, sTrustedUserCAKeys,
 	sDeprecated, sUnsupported
 } ServerOpCodes;
 
@@ -427,6 +430,8 @@ static struct {
 	{ "forcecommand", sForceCommand, SSHCFG_ALL },
 	{ "chrootdirectory", sChrootDirectory, SSHCFG_ALL },
 	{ "hostcertificate", sHostCertificate, SSHCFG_GLOBAL },
+	{ "revokedkeys", sRevokedKeys, SSHCFG_ALL },
+	{ "trustedusercakeys", sTrustedUserCAKeys, SSHCFG_ALL },
 	{ NULL, sBadOption, 0 }
 };
 
@@ -1323,6 +1328,14 @@ process_server_config_line(ServerOptions *options, char *line,
 			*charptr = xstrdup(arg);
 		break;
 
+	case sTrustedUserCAKeys:
+		charptr = &options->trusted_user_ca_keys;
+		goto parse_filename;
+
+	case sRevokedKeys:
+		charptr = &options->revoked_keys_file;
+		goto parse_filename;
+
 	case sDeprecated:
 		logit("%s line %d: Deprecated option %s",
 		    filename, linenum, arg);
@@ -1437,6 +1450,8 @@ copy_set_server_options(ServerOptions *dst, ServerOptions *src, int preauth)
 		return;
 	M_CP_STROPT(adm_forced_command);
 	M_CP_STROPT(chroot_directory);
+	M_CP_STROPT(trusted_user_ca_keys);
+	M_CP_STROPT(revoked_keys_file);
 }
 
 #undef M_CP_INTOPT
@@ -1656,6 +1671,8 @@ dump_config(ServerOptions *o)
 	dump_cfg_string(sAuthorizedKeysFile2, o->authorized_keys_file2);
 	dump_cfg_string(sForceCommand, o->adm_forced_command);
 	dump_cfg_string(sChrootDirectory, o->chroot_directory);
+	dump_cfg_string(sTrustedUserCAKeys, o->trusted_user_ca_keys);
+	dump_cfg_string(sRevokedKeys, o->revoked_keys_file);
 
 	/* string arguments requiring a lookup */
 	dump_cfg_string(sLogLevel, log_level_name(o->log_level));

servconf.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: servconf.h,v 1.91 2010/02/26 20:29:54 djm Exp $ */
+/* $OpenBSD: servconf.h,v 1.92 2010/03/04 10:36:03 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -154,6 +154,8 @@ typedef struct {
 	int	num_permitted_opens;
 
 	char   *chroot_directory;
+	char   *revoked_keys_file;
+	char   *trusted_user_ca_keys;
 }       ServerOptions;
 
 void	 initialize_server_options(ServerOptions *);

ssh-keygen.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: ssh-keygen.c,v 1.180 2010/03/02 23:20:57 djm Exp $ */
+/* $OpenBSD: ssh-keygen.c,v 1.181 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1994 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland

ssh.1

@@ -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: ssh.1,v 1.296 2010/02/26 22:09:28 jmc Exp $
+.\" $OpenBSD: ssh.1,v 1.297 2010/03/04 10:36:03 djm Exp $
-.Dd $Mdocdate: February 26 2010 $
+.Dd $Mdocdate: March 4 2010 $
 .Dt SSH 1
 .Os
 .Sh NAME
@@ -1121,6 +1121,22 @@ See the
 section of
 .Xr ssh-keygen 1
 for more details.
+.Pp
+Keys may be also be marked as revoked using the
+.Dq @revoked
+marker.
+Revoked keys will always trigger a warning when encountered and the host
+that presented them will be treated as untrusted.
+For example:
+.Pp
+.Dl @revoked * ssh-rsa AAAAB5W...
+.Pp
+Revoking a key revokes it for direct use and as a certification authority.
+Do not use both the
+.Dq @cert-authority and
+.Dq @revoked
+markers on the same line.
+.Pp
 .Sh SSH-BASED VIRTUAL PRIVATE NETWORKS
 .Nm
 contains support for Virtual Private Network (VPN) tunnelling

sshconnect.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: sshconnect.c,v 1.219 2010/02/26 20:29:54 djm Exp $ */
+/* $OpenBSD: sshconnect.c,v 1.220 2010/03/04 10:36:03 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -859,6 +859,25 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
 			logit("Warning: Permanently added '%.200s' (%s) to the "
 			    "list of known hosts.", hostp, type);
 		break;
+	case HOST_REVOKED:
+		error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
+		error("@       WARNING: REVOKED HOST KEY DETECTED!               @");
+		error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
+		error("The %s host key for %s is marked as revoked.", type, host);
+		error("This could mean that a stolen key is being used to");
+		error("impersonate this host.");
+
+		/*
+		 * If strict host key checking is in use, the user will have
+		 * to edit the key manually and we can only abort.
+		 */
+		if (options.strict_host_key_checking) {
+			error("%s host key for %.200s was revoked and you have "
+			    "requested strict checking.", type, host);
+			goto fail;
+		}
+		goto continue_unsafe;
+
 	case HOST_CHANGED:
 		if (want_cert) {
 			/*
@@ -908,6 +927,7 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
 			goto fail;
 		}
 
+ continue_unsafe:
 		/*
 		 * If strict host key checking has not been requested, allow
 		 * the connection but without MITM-able authentication or
@@ -1007,7 +1027,7 @@ check_host_key(char *hostname, struct sockaddr *hostaddr, u_short port,
 	return 0;
 
 fail:
-	if (want_cert) {
+	if (want_cert && host_status != HOST_REVOKED) {
 		/*
 		 * No matching certificate. Downgrade cert to raw key and
 		 * search normally.

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 1.117 2010/02/26 20:29:54 djm Exp $
+.\" $OpenBSD: sshd_config.5,v 1.118 2010/03/04 10:36:03 djm Exp $
-.Dd $Mdocdate: February 26 2010 $
+.Dd $Mdocdate: March 4 2010 $
 .Dt SSHD_CONFIG 5
 .Os
 .Sh NAME
@@ -814,6 +814,11 @@ Specifies whether public key authentication is allowed.
 The default is
 .Dq yes .
 Note that this option applies to protocol version 2 only.
+.It Cm RevokedKeys
+Specifies a list of revoked public keys.
+Keys listed in this file will be refused for public key authentication.
+Note that if this file is not readable, then public key authentication will
+be refused for all users.
 .It Cm RhostsRSAAuthentication
 Specifies whether rhosts or /etc/hosts.equiv authentication together
 with successful RSA host authentication is allowed.
@@ -889,6 +894,22 @@ This avoids infinitely hanging sessions.
 .Pp
 To disable TCP keepalive messages, the value should be set to
 .Dq no .
+.It Cm TrustedUserCAKeys
+Specifies a file containing public keys of certificate authorities that are
+trusted sign user certificates for authentication.
+Keys are listed one per line, empty lines and comments starting with
+.Ql #
+are allowed.
+If a certificate is presented for authentication and has its signing CA key
+listed in this file, then it may be used for authentication for any user
+listed in the certificate's principals list.
+Note that certificates that lack a list of principals will not be permitted
+for authentication using
+.Cm TrustedUserCAKeys .
+For more details in certificates, please see the
+.Sx CERTIFICATES
+section in
+.Xr ssh-keygen 1 .
 .It Cm UseDNS
 Specifies whether
 .Xr sshd 8