- djm@cvs.openbsd.org 2012/05/23 03:28:28

     [dns.c dns.h key.c key.h ssh-keygen.c]
     add support for RFC6594 SSHFP DNS records for ECDSA key types.
     patch from bugzilla-m67 AT nulld.me in bz#1978; ok + tweak markus@

1 files changed, 69 insertions, 34 deletions

diff --git a/dns.c b/dns.c
index 131cb3d8b..9e3084ba5 100644
--- a/dns.c
+++ b/dns.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: dns.c,v 1.27 2010/08/31 11:54:45 djm Exp $ */
+/* $OpenBSD: dns.c,v 1.28 2012/05/23 03:28:28 djm Exp $ */
 
 /*
  * Copyright (c) 2003 Wesley Griffin. All rights reserved.
@@ -78,27 +78,46 @@ dns_read_key(u_int8_t *algorithm, u_int8_t *digest_type,
     u_char **digest, u_int *digest_len, Key *key)
 {
         int success = 0;
+        enum fp_type fp_type = 0;
 
         switch (key->type) {
         case KEY_RSA:
                 *algorithm = SSHFP_KEY_RSA;
+                if (!*digest_type)
+                        *digest_type = SSHFP_HASH_SHA1;
                 break;
         case KEY_DSA:
                 *algorithm = SSHFP_KEY_DSA;
+                if (!*digest_type)
+                        *digest_type = SSHFP_HASH_SHA1;
+                break;
+        case KEY_ECDSA:
+                *algorithm = SSHFP_KEY_ECDSA;
+                if (!*digest_type)
+                        *digest_type = SSHFP_HASH_SHA256;
                 break;
-        /* XXX KEY_ECDSA */
         default:
                 *algorithm = SSHFP_KEY_RESERVED; /* 0 */
+                *digest_type = SSHFP_HASH_RESERVED; /* 0 */
+        }
+
+        switch (*digest_type) {
+        case SSHFP_HASH_SHA1:
+                fp_type = SSH_FP_SHA1;
+                break;
+        case SSHFP_HASH_SHA256:
+                fp_type = SSH_FP_SHA256;
+                break;
+        default:
+                *digest_type = SSHFP_HASH_RESERVED; /* 0 */
         }
 
-        if (*algorithm) {
-                *digest_type = SSHFP_HASH_SHA1;
-                *digest = key_fingerprint_raw(key, SSH_FP_SHA1, digest_len);
+        if (*algorithm && *digest_type) {
+                *digest = key_fingerprint_raw(key, fp_type, digest_len);
                 if (*digest == NULL)
                         fatal("dns_read_key: null from key_fingerprint_raw()");
                 success = 1;
         } else {
-                *digest_type = SSHFP_HASH_RESERVED;
                 *digest = NULL;
                 *digest_len = 0;
                 success = 0;
@@ -180,7 +199,7 @@ verify_host_key_dns(const char *hostname, struct sockaddr *address,
         struct rrsetinfo *fingerprints = NULL;
 
         u_int8_t hostkey_algorithm;
-        u_int8_t hostkey_digest_type;
+        u_int8_t hostkey_digest_type = SSHFP_HASH_RESERVED;
         u_char *hostkey_digest;
         u_int hostkey_digest_len;
 
@@ -216,7 +235,7 @@ verify_host_key_dns(const char *hostname, struct sockaddr *address,
                     fingerprints->rri_nrdatas);
         }
 
-        /* Initialize host key parameters */
+        /* Initialize default host key parameters */
         if (!dns_read_key(&hostkey_algorithm, &hostkey_digest_type,
             &hostkey_digest, &hostkey_digest_len, hostkey)) {
                 error("Error calculating host key fingerprint.");
@@ -240,16 +259,27 @@ verify_host_key_dns(const char *hostname, struct sockaddr *address,
                         continue;
                 }
 
+                if (hostkey_digest_type != dnskey_digest_type) {
+                        hostkey_digest_type = dnskey_digest_type;
+                        xfree(hostkey_digest);
+
+                        /* Initialize host key parameters */
+                        if (!dns_read_key(&hostkey_algorithm,
+                            &hostkey_digest_type, &hostkey_digest,
+                            &hostkey_digest_len, hostkey)) {
+                                error("Error calculating key fingerprint.");
+                                freerrset(fingerprints);
+                                return -1;
+                        }
+                }
+
                 /* 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) {
-
+                            timingsafe_bcmp(hostkey_digest, dnskey_digest,
+                            hostkey_digest_len) == 0)
                                 *flags |= DNS_VERIFY_MATCH;
-                        }
                 }
                 xfree(dnskey_digest);
         }
@@ -275,31 +305,36 @@ 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_int8_t rdata_digest_type = SSHFP_HASH_RESERVED;
+        u_int8_t dtype;
         u_char *rdata_digest;
-        u_int rdata_digest_len;
-
-        u_int i;
+        u_int i, rdata_digest_len;
         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 (dtype = SSHFP_HASH_SHA1; dtype < SSHFP_HASH_MAX; dtype++) {
+                rdata_digest_type = dtype;
+                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");
+                        xfree(rdata_digest); /* from key_fingerprint_raw() */
+                        success = 1;
+                }
+        }
 
-                for (i = 0; i < rdata_digest_len; i++)
-                        fprintf(f, "%02x", rdata_digest[i]);
-                fprintf(f, "\n");
-                xfree(rdata_digest); /* from key_fingerprint_raw() */
-                success = 1;
-        } else {
-                error("export_dns_rr: unsupported algorithm");
+        /* No SSHFP record was generated at all */
+        if (success == 0) {
+                error("%s: unsupported algorithm and/or digest_type", __func__);
         }
 
         return success;