- jakob@cvs.openbsd.org 2003/05/14 18:16:20
[key.c key.h readconf.c readconf.h ssh_config.5 sshconnect.c]
[dns.c dns.h README.dns ssh-keygen.1 ssh-keygen.c]
add experimental support for verifying hos keys using DNS as described
in draft-ietf-secsh-dns-xx.txt. more information in README.dns.
ok markus@ and henning@
diff --git a/dns.c b/dns.c
new file mode 100644
index 0000000..9b7a0e7
--- /dev/null
+++ b/dns.c
@@ -0,0 +1,293 @@
+/* $OpenBSD: dns.c,v 1.4 2003/05/14 23:29:22 jakob Exp $ */
+
+/*
+ * Copyright (c) 2003 Wesley Griffin. All rights reserved.
+ * Copyright (c) 2003 Jakob Schlyter. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+
+#include "includes.h"
+
+#ifdef DNS
+#include <openssl/bn.h>
+#ifdef LWRES
+#include <lwres/netdb.h>
+#include <dns/result.h>
+#else /* LWRES */
+#include <netdb.h>
+#endif /* LWRES */
+
+#include "xmalloc.h"
+#include "key.h"
+#include "dns.h"
+#include "log.h"
+#include "uuencode.h"
+
+extern char *__progname;
+RCSID("$OpenBSD: dns.c,v 1.4 2003/05/14 23:29:22 jakob Exp $");
+
+#ifndef LWRES
+static const char *errset_text[] = {
+ "success", /* 0 ERRSET_SUCCESS */
+ "out of memory", /* 1 ERRSET_NOMEMORY */
+ "general failure", /* 2 ERRSET_FAIL */
+ "invalid parameter", /* 3 ERRSET_INVAL */
+ "name does not exist", /* 4 ERRSET_NONAME */
+ "data does not exist", /* 5 ERRSET_NODATA */
+};
+
+static const char *
+dns_result_totext(unsigned int error)
+{
+ switch (error) {
+ case ERRSET_SUCCESS:
+ return errset_text[ERRSET_SUCCESS];
+ case ERRSET_NOMEMORY:
+ return errset_text[ERRSET_NOMEMORY];
+ case ERRSET_FAIL:
+ return errset_text[ERRSET_FAIL];
+ case ERRSET_INVAL:
+ return errset_text[ERRSET_INVAL];
+ case ERRSET_NONAME:
+ return errset_text[ERRSET_NONAME];
+ case ERRSET_NODATA:
+ return errset_text[ERRSET_NODATA];
+ default:
+ return "unknown error";
+ }
+}
+#endif /* LWRES */
+
+
+/*
+ * Read SSHFP parameters from key buffer.
+ */
+static int
+dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
+ u_char **digest, u_int *digest_len, Key *key)
+{
+ int success = 0;
+
+ switch (key->type) {
+ case KEY_RSA:
+ *algorithm = SSHFP_KEY_RSA;
+ break;
+ case KEY_DSA:
+ *algorithm = SSHFP_KEY_DSA;
+ break;
+ default:
+ *algorithm = SSHFP_KEY_RESERVED;
+ }
+
+ if (*algorithm) {
+ *digest_type = SSHFP_HASH_SHA1;
+ *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
+ success = 1;
+ } else {
+ *digest_type = SSHFP_HASH_RESERVED;
+ *digest = NULL;
+ *digest_len = 0;
+ success = 0;
+ }
+
+ return success;
+}
+
+/*
+ * Read SSHFP parameters from rdata buffer.
+ */
+static int
+dns_read_rdata(u_int8_t *algorithm, u_int8_t *digest_type,
+ u_char **digest, u_int *digest_len, u_char *rdata, int rdata_len)
+{
+ int success = 0;
+
+ *algorithm = SSHFP_KEY_RESERVED;
+ *digest_type = SSHFP_HASH_RESERVED;
+
+ if (rdata_len >= 2) {
+ *algorithm = rdata[0];
+ *digest_type = rdata[1];
+ *digest_len = rdata_len - 2;
+
+ if (*digest_len > 0) {
+ *digest = (u_char *) xmalloc(*digest_len);
+ memcpy(*digest, rdata + 2, *digest_len);
+ } else {
+ *digest = NULL;
+ }
+
+ success = 1;
+ }
+
+ return success;
+}
+
+
+/*
+ * Verify the given hostname, address and host key using DNS.
+ * Returns 0 if key verifies or -1 if key does NOT verify
+ */
+int
+verify_host_key_dns(const char *hostname, struct sockaddr *address,
+ Key *hostkey)
+{
+ int counter;
+ int result;
+ struct rrsetinfo *fingerprints = NULL;
+ int failures = 0;
+
+ u_int8_t hostkey_algorithm;
+ u_int8_t hostkey_digest_type;
+ u_char *hostkey_digest;
+ u_int hostkey_digest_len;
+
+ u_int8_t dnskey_algorithm;
+ u_int8_t dnskey_digest_type;
+ u_char *dnskey_digest;
+ u_int dnskey_digest_len;
+
+
+ debug3("verify_hostkey_dns");
+ if (hostkey == NULL)
+ fatal("No key to look up!");
+
+ result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
+ DNS_RDATATYPE_SSHFP, 0, &fingerprints);
+ if (result) {
+ verbose("DNS lookup error: %s", dns_result_totext(result));
+ return DNS_VERIFY_ERROR;
+ }
+
+#ifdef DNSSEC
+ /* Only accept validated answers */
+ if (!fingerprints->rri_flags & RRSET_VALIDATED) {
+ error("Ignored unvalidated fingerprint from DNS.");
+ return DNS_VERIFY_ERROR;
+ }
+#endif
+
+ debug("found %d fingerprints in DNS", fingerprints->rri_nrdatas);
+
+ /* Initialize host key parameters */
+ if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
+ &hostkey_digest, &hostkey_digest_len, hostkey)) {
+ error("Error calculating host key fingerprint.");
+ return DNS_VERIFY_ERROR;
+ }
+
+ for (counter = 0 ; counter < fingerprints->rri_nrdatas ; counter++) {
+ /*
+ * Extract the key from the answer. Ignore any badly
+ * formatted fingerprints.
+ */
+ if (!dns_read_rdata(&dnskey_algorithm, &dnskey_digest_type,
+ &dnskey_digest, &dnskey_digest_len,
+ fingerprints->rri_rdatas[counter].rdi_data,
+ fingerprints->rri_rdatas[counter].rdi_length)) {
+ verbose("Error parsing fingerprint from DNS.");
+ continue;
+ }
+
+ /* Check if the current key is the same as the given key */
+ if (hostkey_algorithm == dnskey_algorithm &&
+ hostkey_digest_type == dnskey_digest_type) {
+
+ if (hostkey_digest_len == dnskey_digest_len &&
+ memcmp(hostkey_digest, dnskey_digest,
+ hostkey_digest_len) == 0) {
+
+ /* Matching algoritm and digest. */
+ freerrset(fingerprints);
+#ifdef DNSSEC
+ debug("matching host key fingerprint found in DNS");
+ return DNS_VERIFY_OK;
+#else
+ logit("Matching host key fingerprint found in DNS.");
+ return DNS_VERIFY_ERROR;
+#endif
+ } else {
+ /* Correct algorithm but bad digest */
+ debug("verify_hostkey_dns: failed");
+ failures++;
+ }
+ }
+ }
+
+ freerrset(fingerprints);
+
+ if (failures) {
+ error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
+ error("@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @");
+ error("@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@");
+ error("IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!");
+ error("Someone could be eavesdropping on you right now (man-in-the-middle attack)!");
+ error("It is also possible that the %s host key has just been changed.",
+ key_type(hostkey));
+ error("Please contact your system administrator.");
+ return DNS_VERIFY_FAILED;
+ }
+
+ debug("fingerprints found in DNS, but none of them matched");
+
+ return DNS_VERIFY_ERROR;
+}
+
+
+/*
+ * Export the fingerprint of a key as a DNS resource record
+ */
+int
+export_dns_rr(const char *hostname, Key *key, FILE *f, int generic)
+{
+ u_int8_t rdata_pubkey_algorithm = 0;
+ u_int8_t rdata_digest_type = SSHFP_HASH_SHA1;
+ u_char *rdata_digest;
+ u_int rdata_digest_len;
+
+ int i;
+ int success = 0;
+
+ if (dns_read_key(&rdata_pubkey_algorithm, &rdata_digest_type,
+ &rdata_digest, &rdata_digest_len, key)) {
+
+ if (generic)
+ fprintf(f, "%s IN TYPE%d \\# %d %02x %02x ", hostname,
+ DNS_RDATATYPE_SSHFP, 2 + rdata_digest_len,
+ rdata_pubkey_algorithm, rdata_digest_type);
+ else
+ fprintf(f, "%s IN SSHFP %d %d ", hostname,
+ rdata_pubkey_algorithm, rdata_digest_type);
+
+ for (i = 0; i < rdata_digest_len; i++)
+ fprintf(f, "%02x", rdata_digest[i]);
+ fprintf(f, "\n");
+ success = 1;
+ } else {
+ error("dns_export_rr: unsupported algorithm");
+ }
+
+ return success;
+}
+
+#endif /* DNS */