Enforce Ed25519 identities (client-side)

This patch makes two absolutely critical changes:
  - If an ed25519 identity is not as expected when creating a channel,
    we call that channel unsuccessful and close it.
  - When a client creating a channel or an extend cell for a circuit, we
    only include the ed25519 identity if we believe that the node on
    the other side supports ed25519 link authentication (from
    #15055).  Otherwise we will insist on nodes without the right
    link protocol authenticating themselves.
  - When deciding to extend to another relay, we only upgrade the
    extend to extend by ed25519 ID when we know the ed25519 ID _and_
    we know that the other side can authenticate.

This patch also tells directory servers, when probing nodes, to
try to check their ed25519 identities too (if they can authenticate
by ed25519 identity).

Also, handle the case where we connect by RSA Id, and learn the
ED25519 ID for the node in doing so.

1 files changed, 56 insertions, 11 deletions

diff --git a/src/or/connection_or.c b/src/or/connection_or.c
index a22c4ad1ef..0caf8a97fd 100644
--- a/src/or/connection_or.c
+++ b/src/or/connection_or.c
@@ -1547,8 +1547,24 @@ connection_or_client_learned_peer_id(or_connection_t *conn,
                                      const ed25519_public_key_t *ed_peer_id)
 {
   const or_options_t *options = get_options();
-
-  if (tor_digest_is_zero(conn->identity_digest)) {
+  channel_tls_t *chan_tls = conn->chan;
+  channel_t *chan = channel_tls_to_base(chan_tls);
+  tor_assert(chan);
+
+  const int expected_rsa_key =
+    ! tor_digest_is_zero(conn->identity_digest);
+  const int expected_ed_key =
+    ! ed25519_public_key_is_zero(&chan->ed25519_identity);
+
+  log_info(LD_HANDSHAKE, "learned peer id for %p (%s): %s, %s",
+           conn,
+           safe_str_client(conn->base_.address),
+           hex_str((const char*)rsa_peer_id, DIGEST_LEN),
+           ed25519_fmt(ed_peer_id));
+
+  if (! expected_rsa_key && ! expected_ed_key) {
+    log_info(LD_HANDSHAKE, "(we had no ID in mind when we made this "
+             "connection.");
     connection_or_set_identity_digest(conn,
                                       (const char*)rsa_peer_id, ed_peer_id);
     tor_free(conn->nickname);
@@ -1565,13 +1581,35 @@ connection_or_client_learned_peer_id(or_connection_t *conn,
                             (const char*)rsa_peer_id, ed_peer_id);
   }
 
-  if (tor_memneq(rsa_peer_id, conn->identity_digest, DIGEST_LEN)) {
+  const int rsa_mismatch = expected_rsa_key &&
+    tor_memneq(rsa_peer_id, conn->identity_digest, DIGEST_LEN);
+  /* It only counts as an ed25519 mismatch if we wanted an ed25519 identity
+   * and didn't get it. It's okay if we get one that we didn't ask for. */
+  const int ed25519_mismatch =
+    expected_ed_key &&
+    (ed_peer_id == NULL ||
+     ! ed25519_pubkey_eq(&chan->ed25519_identity, ed_peer_id));
+
+  if (rsa_mismatch || ed25519_mismatch) {
     /* I was aiming for a particular digest. I didn't get it! */
-    char seen[HEX_DIGEST_LEN+1];
-    char expected[HEX_DIGEST_LEN+1];
-    base16_encode(seen, sizeof(seen), (const char*)rsa_peer_id, DIGEST_LEN);
-    base16_encode(expected, sizeof(expected), conn->identity_digest,
+    char seen_rsa[HEX_DIGEST_LEN+1];
+    char expected_rsa[HEX_DIGEST_LEN+1];
+    char seen_ed[ED25519_BASE64_LEN+1];
+    char expected_ed[ED25519_BASE64_LEN+1];
+    base16_encode(seen_rsa, sizeof(seen_rsa),
+                  (const char*)rsa_peer_id, DIGEST_LEN);
+    base16_encode(expected_rsa, sizeof(expected_rsa), conn->identity_digest,
                   DIGEST_LEN);
+    if (ed_peer_id) {
+      ed25519_public_to_base64(seen_ed, ed_peer_id);
+    } else {
+      strlcpy(seen_ed, "no ed25519 key", sizeof(seen_ed));
+    }
+    if (! ed25519_public_key_is_zero(&chan->ed25519_identity)) {
+      ed25519_public_to_base64(expected_ed, &chan->ed25519_identity);
+    } else {
+      strlcpy(expected_ed, "no ed25519 key", sizeof(expected_ed));
+    }
     const int using_hardcoded_fingerprints =
       !networkstatus_get_reasonably_live_consensus(time(NULL),
                                                    usable_consensus_flavor());
@@ -1606,9 +1644,11 @@ connection_or_client_learned_peer_id(or_connection_t *conn,
     }
 
     log_fn(severity, LD_HANDSHAKE,
-           "Tried connecting to router at %s:%d, but identity key was not "
-           "as expected: wanted %s but got %s.%s",
-           conn->base_.address, conn->base_.port, expected, seen, extra_log);
+           "Tried connecting to router at %s:%d, but RSA identity key was not "
+           "as expected: wanted %s + %s but got %s + %s.%s",
+           conn->base_.address, conn->base_.port,
+           expected_rsa, expected_ed, seen_rsa, seen_ed, extra_log);
+
     entry_guard_register_connect_status(conn->identity_digest, 0, 1,
                                         time(NULL));
     control_event_or_conn_status(conn, OR_CONN_EVENT_FAILED,
@@ -1621,7 +1661,12 @@ connection_or_client_learned_peer_id(or_connection_t *conn,
     return -1;
   }
 
-  /* XXXX 15056 -- use the Ed25519 key */
+  if (!expected_ed_key && ed_peer_id) {
+    log_info(LD_HANDSHAKE, "(we had no Ed25519 ID in mind when we made this "
+             "connection.");
+    connection_or_set_identity_digest(conn,
+                                      (const char*)rsa_peer_id, ed_peer_id);
+  }
 
   if (authdir_mode_tests_reachability(options)) {
     dirserv_orconn_tls_done(&conn->base_.addr, conn->base_.port,