- djm@cvs.openbsd.org 2005/03/01 10:40:27

[hostfile.c hostfile.h readconf.c readconf.h ssh.1 ssh_config.5]
     [sshconnect.c sshd.8]
     add support for hashing host names and addresses added to known_hosts
     files, to improve privacy of which hosts user have been visiting; ok
     markus@ deraadt@

ChangeLog

@@ -27,6 +27,12 @@
      Patch originally by Dan Astorian, but worked on by several people
      Adds GatewayPorts=clientspecified option on server to allow remote 
      forwards to bind to client-specified ports.
+   - djm@cvs.openbsd.org 2005/03/01 10:40:27
+     [hostfile.c hostfile.h readconf.c readconf.h ssh.1 ssh_config.5]
+     [sshconnect.c sshd.8]
+     add support for hashing host names and addresses added to known_hosts
+     files, to improve privacy of which hosts user have been visiting; ok 
+     markus@ deraadt@
 
 20050226
  - (dtucker) [openbsd-compat/bsd-openpty.c openbsd-compat/inet_ntop.c]
@@ -2203,4 +2209,4 @@
    - (djm) Trim deprecated options from INSTALL. Mention UsePAM
    - (djm) Fix quote handling in sftp; Patch from admorten AT umich.edu
 
-$Id: ChangeLog,v 1.3672 2005/03/01 10:24:33 djm Exp $
+$Id: ChangeLog,v 1.3673 2005/03/01 10:47:37 djm Exp $

hostfile.c

@@ -36,13 +36,102 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: hostfile.c,v 1.32 2003/11/10 16:23:41 jakob Exp $");
+RCSID("$OpenBSD: hostfile.c,v 1.33 2005/03/01 10:40:26 djm Exp $");
+
+#include <resolv.h>
+#include <openssl/hmac.h>
+#include <openssl/sha.h>
 
 #include "packet.h"
 #include "match.h"
 #include "key.h"
 #include "hostfile.h"
 #include "log.h"
+#include "xmalloc.h"
+
+static int
+extract_salt(const char *s, u_int l, char *salt, size_t salt_len)
+{
+	char *p, *b64salt;
+	u_int b64len;
+	int ret;
+
+	if (l < sizeof(HASH_MAGIC) - 1) {
+		debug2("extract_salt: string too short");
+		return (-1);
+	}
+	if (strncmp(s, HASH_MAGIC, sizeof(HASH_MAGIC) - 1) != 0) {
+		debug2("extract_salt: invalid magic identifier");
+		return (-1);
+	}
+	s += sizeof(HASH_MAGIC) - 1;
+	l -= sizeof(HASH_MAGIC) - 1;
+	if ((p = memchr(s, HASH_DELIM, l)) == NULL) {
+		debug2("extract_salt: missing salt termination character");
+		return (-1);
+	}
+
+	b64len = p - s;
+	/* Sanity check */
+	if (b64len == 0 || b64len > 1024) {
+		debug2("extract_salt: bad encoded salt length %u", b64len);
+		return (-1);
+	}
+	b64salt = xmalloc(1 + b64len);
+	memcpy(b64salt, s, b64len);
+	b64salt[b64len] = '\0';
+
+	ret = __b64_pton(b64salt, salt, salt_len);
+	xfree(b64salt);
+	if (ret == -1) {
+		debug2("extract_salt: salt decode error");
+		return (-1);
+	}
+	if (ret != SHA_DIGEST_LENGTH) {
+		debug2("extract_salt: expected salt len %u, got %u",
+		    salt_len, ret);
+		return (-1);
+	}
+	
+	return (0);
+}
+
+char *
+host_hash(const char *host, const char *name_from_hostfile, u_int src_len)
+{
+	const EVP_MD *md = EVP_sha1();
+	HMAC_CTX mac_ctx;
+	char salt[256], result[256], uu_salt[512], uu_result[512];
+	static char encoded[1024];
+	u_int i, len;
+
+	len = EVP_MD_size(md);
+
+	if (name_from_hostfile == NULL) {
+		/* Create new salt */
+		for (i = 0; i < len; i++)
+			salt[i] = arc4random();
+	} else {
+		/* Extract salt from known host entry */
+		if (extract_salt(name_from_hostfile, src_len, salt,
+		    sizeof(salt)) == -1)
+			return (NULL);
+	}
+
+	HMAC_Init(&mac_ctx, salt, len, md);
+	HMAC_Update(&mac_ctx, host, strlen(host));
+	HMAC_Final(&mac_ctx, result, NULL);
+	HMAC_cleanup(&mac_ctx);
+
+	if (__b64_ntop(salt, len, uu_salt, sizeof(uu_salt)) == -1 || 
+	    __b64_ntop(result, len, uu_result, sizeof(uu_result)) == -1)
+		fatal("host_hash: __b64_ntop failed");
+
+	snprintf(encoded, sizeof(encoded), "%s%s%c%s", HASH_MAGIC, uu_salt,
+	    HASH_DELIM, uu_result);
+
+	return (encoded);
+}
 
 /*
  * Parses an RSA (number of bits, e, n) or DSA key from a string.  Moves the
@@ -104,7 +193,7 @@ check_host_in_hostfile_by_key_or_type(const char *filename,
 	char line[8192];
 	int linenum = 0;
 	u_int kbits;
-	char *cp, *cp2;
+	char *cp, *cp2, *hashed_host;
 	HostStatus end_return;
 
 	debug3("check_host_in_hostfile: filename %s", filename);
@@ -137,8 +226,18 @@ check_host_in_hostfile_by_key_or_type(const char *filename,
 			;
 
 		/* Check if the host name matches. */
-		if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1)
+		if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
-			continue;
+			if (*cp != HASH_DELIM)
+				continue;
+			hashed_host = host_hash(host, cp, (u_int) (cp2 - cp));
+			if (hashed_host == NULL) {
+				debug("Invalid hashed host line %d of %s",
+				    linenum, filename);
+				continue;
+			}
+			if (strncmp(hashed_host, cp, (u_int) (cp2 - cp)) != 0)
+				continue;
+		}
 
 		/* Got a match.  Skip host name. */
 		cp = cp2;
@@ -211,16 +310,28 @@ lookup_key_in_hostfile_by_type(const char *filename, const char *host,
  */
 
 int
-add_host_to_hostfile(const char *filename, const char *host, const Key *key)
+add_host_to_hostfile(const char *filename, const char *host, const Key *key, 
+    int store_hash)
 {
 	FILE *f;
 	int success = 0;
+	char *hashed_host;
+
 	if (key == NULL)
 		return 1;	/* XXX ? */
 	f = fopen(filename, "a");
 	if (!f)
 		return 0;
-	fprintf(f, "%s ", host);
+
+	if (store_hash) {
+		if ((hashed_host = host_hash(host, NULL, 0)) == NULL) {
+			error("add_host_to_hostfile: host_hash failed");
+			fclose(f);
+			return 0;
+		}
+	}
+	fprintf(f, "%s ", store_hash ? hashed_host : host);
+
 	if (key_write(key, f)) {
 		success = 1;
 	} else {

hostfile.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: hostfile.h,v 1.14 2003/11/10 16:23:41 jakob Exp $	*/
+/*	$OpenBSD: hostfile.h,v 1.15 2005/03/01 10:40:26 djm Exp $	*/
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -21,8 +21,13 @@ typedef enum {
 int	 hostfile_read_key(char **, u_int *, Key *);
 HostStatus check_host_in_hostfile(const char *, const char *,
 	    const Key *, Key *, int *);
-int	add_host_to_hostfile(const char *, const char *, const Key *);
+int	add_host_to_hostfile(const char *, const char *, const Key *, int);
 int	lookup_key_in_hostfile_by_type(const char *, const char *,
 	    int, Key *, int *);
 
+#define HASH_MAGIC	"|1|"
+#define HASH_DELIM	'|'
+
+char	*host_hash(const char *, const char *, u_int);
+
 #endif

readconf.c

@@ -12,7 +12,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: readconf.c,v 1.135 2005/03/01 10:09:52 djm Exp $");
+RCSID("$OpenBSD: readconf.c,v 1.136 2005/03/01 10:40:26 djm Exp $");
 
 #include "ssh.h"
 #include "xmalloc.h"
@@ -106,7 +106,7 @@ typedef enum {
 	oEnableSSHKeysign, oRekeyLimit, oVerifyHostKeyDNS, oConnectTimeout,
 	oAddressFamily, oGssAuthentication, oGssDelegateCreds,
 	oServerAliveInterval, oServerAliveCountMax, oIdentitiesOnly,
-	oSendEnv, oControlPath, oControlMaster,
+	oSendEnv, oControlPath, oControlMaster, oHashKnownHosts,
 	oDeprecated, oUnsupported
 } OpCodes;
 
@@ -197,6 +197,7 @@ static struct {
 	{ "sendenv", oSendEnv },
 	{ "controlpath", oControlPath },
 	{ "controlmaster", oControlMaster },
+	{ "hashknownhosts", oHashKnownHosts },
 	{ NULL, oBadOption }
 };
 
@@ -790,6 +791,10 @@ parse_int:
 		intptr = &options->control_master;
 		goto parse_yesnoask;
 
+	case oHashKnownHosts:
+		intptr = &options->hash_known_hosts;
+		goto parse_flag;
+
 	case oDeprecated:
 		debug("%s line %d: Deprecated option \"%s\"",
 		    filename, linenum, keyword);
@@ -933,6 +938,7 @@ initialize_options(Options * options)
 	options->num_send_env = 0;
 	options->control_path = NULL;
 	options->control_master = -1;
+	options->hash_known_hosts = -1;
 }
 
 /*
@@ -1055,6 +1061,8 @@ fill_default_options(Options * options)
 		options->server_alive_count_max = 3;
 	if (options->control_master == -1)
 		options->control_master = 0;
+	if (options->hash_known_hosts == -1)
+		options->hash_known_hosts = 0;
 	/* options->proxy_command should not be set by default */
 	/* options->user will be set in the main program if appropriate */
 	/* options->hostname will be set in the main program if appropriate */

readconf.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: readconf.h,v 1.65 2005/03/01 10:09:52 djm Exp $	*/
+/*	$OpenBSD: readconf.h,v 1.66 2005/03/01 10:40:27 djm Exp $	*/
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -112,6 +112,8 @@ typedef struct {
 
 	char	*control_path;
 	int	control_master;
+
+	int	hash_known_hosts;
 }       Options;
 
 

ssh.1

@@ -34,7 +34,7 @@
 .\" (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 1.200 2005/03/01 10:09:52 djm Exp $
+.\" $OpenBSD: ssh.1,v 1.201 2005/03/01 10:40:27 djm Exp $
 .Dd September 25, 1999
 .Dt SSH 1
 .Os
@@ -701,6 +701,7 @@ For full details of the options listed below, and their possible values, see
 .It GlobalKnownHostsFile
 .It GSSAPIAuthentication
 .It GSSAPIDelegateCredentials
+.It HashKnownHosts
 .It Host
 .It HostbasedAuthentication
 .It HostKeyAlgorithms

ssh_config.5

@@ -34,7 +34,7 @@
 .\" (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_config.5,v 1.43 2005/03/01 10:09:52 djm Exp $
+.\" $OpenBSD: ssh_config.5,v 1.44 2005/03/01 10:40:27 djm Exp $
 .Dd September 25, 1999
 .Dt SSH_CONFIG 5
 .Os
@@ -407,6 +407,21 @@ Forward (delegate) credentials to the server.
 The default is
 .Dq no .
 Note that this option applies to protocol version 2 only.
+.It Cm HashKnownHosts
+Indicates that
+.Nm ssh
+should hash host names and addresses when they are added to
+.Pa $HOME/.ssh/known_hosts .
+These hashed names may be used normally by
+.Nm ssh
+and
+.Nm sshd ,
+but they do not reveal identifying information should the file's contents
+be disclosed.
+The default is
+.Dq no .
+Note that hashing of names and addresses will not be retrospectively applied 
+to existing known hosts files.
 .It Cm HostbasedAuthentication
 Specifies whether to try rhosts based authentication with public key
 authentication.

sshconnect.c

@@ -13,7 +13,7 @@
  */
 
 #include "includes.h"
-RCSID("$OpenBSD: sshconnect.c,v 1.159 2005/01/05 08:51:32 markus Exp $");
+RCSID("$OpenBSD: sshconnect.c,v 1.160 2005/03/01 10:40:27 djm Exp $");
 
 #include <openssl/bn.h>
 
@@ -678,7 +678,7 @@ check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
 				    "'%.128s' not in list of known hosts.",
 				    type, ip);
 			else if (!add_host_to_hostfile(user_hostfile, ip,
-			    host_key))
+			    host_key, options.hash_known_hosts))
 				logit("Failed to add the %s host key for IP "
 				    "address '%.128s' to the list of known "
 				    "hosts (%.30s).", type, ip, user_hostfile);
@@ -744,7 +744,8 @@ check_host_key(char *host, struct sockaddr *hostaddr, Key *host_key,
 		 * If not in strict mode, add the key automatically to the
 		 * local known_hosts file.
 		 */
-		if (!add_host_to_hostfile(user_hostfile, hostp, host_key))
+		if (!add_host_to_hostfile(user_hostfile, hostp, host_key,
+		    options.hash_known_hosts))
 			logit("Failed to add the host to the list of known "
 			    "hosts (%.500s).", user_hostfile);
 		else

sshd.8

@@ -34,7 +34,7 @@
 .\" (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.8,v 1.204 2005/02/25 10:55:13 jmc Exp $
+.\" $OpenBSD: sshd.8,v 1.205 2005/03/01 10:40:27 djm Exp $
 .Dd September 25, 1999
 .Dt SSHD 8
 .Os
@@ -553,6 +553,14 @@ to indicate negation: if the host name matches a negated
 pattern, it is not accepted (by that line) even if it matched another
 pattern on the line.
 .Pp
+Alternately, hostnames may be stored in a hashed form which hides host names
+and addresses should the file's contents be disclosed. Hashed hostnames start
+with a 
+.Ql \&|
+character.
+Only one hashed hostname may appear on a single line and none of the above
+negation or wildcard operators may be applied.
+.Pp
 Bits, exponent, and modulus are taken directly from the RSA host key; they
 can be obtained, e.g., from
 .Pa /etc/ssh/ssh_host_key.pub .
@@ -584,6 +592,11 @@ and adding the host names at the front.
 closenet,...,130.233.208.41 1024 37 159...93 closenet.hut.fi
 cvs.openbsd.org,199.185.137.3 ssh-rsa AAAA1234.....=
 .Ed
+.Bd -literal
+# A hashed hostname
+|1|JfKTdBh7rNbXkVAQCRp4OQoPfmI=|USECr3SWf1JUPsms5AqfD5QfxkM= ssh-rsa
+AAAA1234.....=
+.Ed
 .Sh FILES
 .Bl -tag -width Ds
 .It Pa /etc/ssh/sshd_config