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@

1 files changed, 117 insertions, 6 deletions

diff --git a/usr.bin/ssh/hostfile.c b/usr.bin/ssh/hostfile.c
index 88c05491278..2e1c8bcd0c4 100644
--- a/usr.bin/ssh/hostfile.c
+++ b/usr.bin/ssh/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)
-			continue;
+		if (match_hostname(host, cp, (u_int) (cp2 - cp)) != 1) {
+			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 {