Implement proposal 228: cross-certification with onion keys

Routers now use TAP and ntor onion keys to sign their identity keys,
and put these signatures in their descriptors.  That allows other
parties to be confident that the onion keys are indeed controlled by
the router that generated the descriptor.

1 files changed, 87 insertions, 0 deletions

diff --git a/src/or/routerkeys.c b/src/or/routerkeys.c
index 6609d89311..9ad5a89479 100644
--- a/src/or/routerkeys.c
+++ b/src/or/routerkeys.c
@@ -435,6 +435,93 @@ get_current_auth_key_cert(void)
   return auth_key_cert;
 }
 
+/** Construct cross-certification for the master identity key with
+ * the ntor onion key. Store the sign of the corresponding ed25519 public key
+ * in *<b>sign_out</b>. */
+tor_cert_t *
+make_ntor_onion_key_crosscert(const curve25519_keypair_t *onion_key,
+      const ed25519_public_key_t *master_id_key, time_t now, time_t lifetime,
+      int *sign_out)
+{
+  tor_cert_t *cert = NULL;
+  ed25519_keypair_t ed_onion_key;
+
+  if (ed25519_keypair_from_curve25519_keypair(&ed_onion_key, sign_out,
+                                              onion_key) < 0)
+    goto end;
+
+  cert = tor_cert_create(&ed_onion_key, CERT_TYPE_ONION_ID, master_id_key,
+      now, lifetime, 0);
+
+ end:
+  memwipe(&ed_onion_key, 0, sizeof(ed_onion_key));
+  return cert;
+}
+
+/** Construct and return an RSA signature for the TAP onion key to
+ * cross-certify the RSA and Ed25519 identity keys. Set <b>len_out</b> to its
+ * length. */
+uint8_t *
+make_tap_onion_key_crosscert(const crypto_pk_t *onion_key,
+                             const ed25519_public_key_t *master_id_key,
+                             const crypto_pk_t *rsa_id_key,
+                             int *len_out)
+{
+  uint8_t signature[PK_BYTES];
+  uint8_t signed_data[DIGEST_LEN + ED25519_PUBKEY_LEN];
+
+  *len_out = 0;
+  crypto_pk_get_digest(rsa_id_key, (char*)signed_data);
+  memcpy(signed_data + DIGEST_LEN, master_id_key->pubkey, ED25519_PUBKEY_LEN);
+
+  int r = crypto_pk_private_sign(onion_key,
+                               (char*)signature, sizeof(signature),
+                               (const char*)signed_data, sizeof(signed_data));
+  if (r < 0)
+    return NULL;
+
+  *len_out = r;
+
+  return tor_memdup(signature, r);
+}
+
+/** Check whether an RSA-TAP cross-certification is correct. Return 0 if it
+ * is, -1 if it isn't. */
+int
+check_tap_onion_key_crosscert(const uint8_t *crosscert,
+                              int crosscert_len,
+                              const crypto_pk_t *onion_pkey,
+                              const ed25519_public_key_t *master_id_pkey,
+                              const uint8_t *rsa_id_digest)
+{
+  uint8_t *cc = tor_malloc(crypto_pk_keysize(onion_pkey));
+  int cc_len =
+    crypto_pk_public_checksig(onion_pkey,
+                              (char*)cc,
+                              crypto_pk_keysize(onion_pkey),
+                              (const char*)crosscert,
+                              crosscert_len);
+  if (cc_len < 0) {
+    goto err;
+  }
+  if (cc_len < DIGEST_LEN + ED25519_PUBKEY_LEN) {
+    log_warn(LD_DIR, "Short signature on cross-certification with TAP key");
+    goto err;
+  }
+  if (tor_memneq(cc, rsa_id_digest, DIGEST_LEN) ||
+      tor_memneq(cc + DIGEST_LEN, master_id_pkey->pubkey,
+                 ED25519_PUBKEY_LEN)) {
+    log_warn(LD_DIR, "Incorrect cross-certification with TAP key");
+    goto err;
+  }
+
+  tor_free(cc);
+  return 0;
+ err:
+  tor_free(cc);
+  return -1;
+}
+
 void
 routerkeys_free_all(void)
 {