- 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@

1 files changed, 293 insertions, 0 deletions

diff --git a/dns.c b/dns.c
new file mode 100644
index 00000000..9b7a0e7a
--- /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 */