router: Keep RSA onion public key in ASN.1 format

The OpenSSL "RSA" object is currently 408 bytes compares to the ASN.1 encoding
which is 140 for a 1024 RSA key.

We save 268 bytes per descriptor (routerinfo_t) *and* microdescriptor
(microdesc_t). Scaling this to 6000 relays, and considering client usually
only have microdescriptors, we save 1.608 MB of RAM which is considerable for
mobile client.

This commit makes it that we keep the RSA onion public key (used for TAP
handshake) in ASN.1 format instead of an OpenSSL RSA object.

Changes is done in both routerinfo_t and microdesc_t.

Closes #27246

Signed-off-by: David Goulet <dgoulet@torproject.org>

7 files changed, 55 insertions, 11 deletions

diff --git a/src/feature/nodelist/microdesc.c b/src/feature/nodelist/microdesc.c
index d9630b4f1d..aa5e6b1dbe 100644
--- a/src/feature/nodelist/microdesc.c
+++ b/src/feature/nodelist/microdesc.c
@@ -874,7 +874,7 @@ microdesc_free_(microdesc_t *md, const char *fname, int lineno)
   //tor_assert(md->held_by_nodes == 0);
 
   if (md->onion_pkey)
-    crypto_pk_free(md->onion_pkey);
+    tor_free(md->onion_pkey);
   tor_free(md->onion_curve25519_pkey);
   tor_free(md->ed25519_identity_pkey);
   if (md->body && md->saved_location != SAVED_IN_CACHE)
diff --git a/src/feature/nodelist/microdesc_st.h b/src/feature/nodelist/microdesc_st.h
index e9dc3e0174..40b562f265 100644
--- a/src/feature/nodelist/microdesc_st.h
+++ b/src/feature/nodelist/microdesc_st.h
@@ -53,8 +53,10 @@ struct microdesc_t {
 
   /* Fields in the microdescriptor. */
 
-  /** As routerinfo_t.onion_pkey */
-  crypto_pk_t *onion_pkey;
+  /* Public RSA key for onions in ASN.1 encoded. */
+  char *onion_pkey;
+  size_t onion_pkey_len;
+
   /** As routerinfo_t.onion_curve25519_pkey */
   struct curve25519_public_key_t *onion_curve25519_pkey;
   /** Ed25519 identity key, if included. */
diff --git a/src/feature/nodelist/nodelist.c b/src/feature/nodelist/nodelist.c
index 75a08fe752..1a123f1ce7 100644
--- a/src/feature/nodelist/nodelist.c
+++ b/src/feature/nodelist/nodelist.c
@@ -1761,6 +1761,37 @@ node_get_curve25519_onion_key(const node_t *node)
     return NULL;
 }
 
+/* Return a newly allocacted RSA onion public key taken from the given node.
+ *
+ * Return NULL if node is NULL or no RSA onion public key can be found. It is
+ * the caller responsability to free the returned object. */
+crypto_pk_t *
+node_get_rsa_onion_key(const node_t *node)
+{
+  crypto_pk_t *pk = NULL;
+  const char *onion_pkey;
+  size_t onion_pkey_len;
+
+  if (!node) {
+    goto end;
+  }
+
+  if (node->ri) {
+    onion_pkey = node->ri->onion_pkey;
+    onion_pkey_len = node->ri->onion_pkey_len;
+  } else if (node->rs && node->md) {
+    onion_pkey = node->md->onion_pkey;
+    onion_pkey_len = node->md->onion_pkey_len;
+  } else {
+    /* No descriptor or microdescriptor. */
+    goto end;
+  }
+  pk = router_get_rsa_onion_pkey(onion_pkey, onion_pkey_len);
+
+ end:
+  return pk;
+}
+
 /** Refresh the country code of <b>ri</b>.  This function MUST be called on
  * each router when the GeoIP database is reloaded, and on all new routers. */
 void
diff --git a/src/feature/nodelist/nodelist.h b/src/feature/nodelist/nodelist.h
index ed3a542971..cf7658cf9d 100644
--- a/src/feature/nodelist/nodelist.h
+++ b/src/feature/nodelist/nodelist.h
@@ -95,6 +95,7 @@ void node_get_pref_ipv6_dirport(const node_t *node, tor_addr_port_t *ap_out);
 int node_has_curve25519_onion_key(const node_t *node);
 const struct curve25519_public_key_t *node_get_curve25519_onion_key(
                                   const node_t *node);
+crypto_pk_t *node_get_rsa_onion_key(const node_t *node);
 
 MOCK_DECL(smartlist_t *, nodelist_get_list, (void));
 
diff --git a/src/feature/nodelist/routerinfo_st.h b/src/feature/nodelist/routerinfo_st.h
index ca8fd40e3b..18ea0fade3 100644
--- a/src/feature/nodelist/routerinfo_st.h
+++ b/src/feature/nodelist/routerinfo_st.h
@@ -27,7 +27,10 @@ struct routerinfo_t {
   tor_addr_t ipv6_addr;
   uint16_t ipv6_orport;
 
-  crypto_pk_t *onion_pkey; /**< Public RSA key for onions. */
+  /* Public RSA key for onions in ASN.1 encoded. */
+  char *onion_pkey;
+  size_t onion_pkey_len;
+
   crypto_pk_t *identity_pkey;  /**< Public RSA key for signing. */
   /** Public curve25519 key for onions */
   struct curve25519_public_key_t *onion_curve25519_pkey;
diff --git a/src/feature/nodelist/routerlist.c b/src/feature/nodelist/routerlist.c
index 8b54329da9..bcc5c1f074 100644
--- a/src/feature/nodelist/routerlist.c
+++ b/src/feature/nodelist/routerlist.c
@@ -3217,7 +3217,7 @@ routerinfo_free_(routerinfo_t *router)
   tor_free(router->protocol_list);
   tor_free(router->contact_info);
   if (router->onion_pkey)
-    crypto_pk_free(router->onion_pkey);
+    tor_free(router->onion_pkey);
   tor_free(router->onion_curve25519_pkey);
   if (router->identity_pkey)
     crypto_pk_free(router->identity_pkey);
@@ -5498,7 +5498,8 @@ router_differences_are_cosmetic(const routerinfo_t *r1, const routerinfo_t *r2)
       r1->ipv6_orport != r2->ipv6_orport ||
       r1->dir_port != r2->dir_port ||
       r1->purpose != r2->purpose ||
-      !crypto_pk_eq_keys(r1->onion_pkey, r2->onion_pkey) ||
+      r1->onion_pkey_len != r2->onion_pkey_len ||
+      !tor_memeq(r1->onion_pkey, r2->onion_pkey, r1->onion_pkey_len) ||
       !crypto_pk_eq_keys(r1->identity_pkey, r2->identity_pkey) ||
       strcasecmp(r1->platform, r2->platform) ||
       (r1->contact_info && !r2->contact_info) || /* contact_info is optional */
diff --git a/src/feature/nodelist/routerparse.c b/src/feature/nodelist/routerparse.c
index 166806e9c1..587966210e 100644
--- a/src/feature/nodelist/routerparse.c
+++ b/src/feature/nodelist/routerparse.c
@@ -1535,6 +1535,7 @@ router_parse_entry_from_string(const char *s, const char *end,
   /* Do not set this to '1' until we have parsed everything that we intend to
    * parse that's covered by the hash. */
   int can_dl_again = 0;
+  crypto_pk_t *rsa_pubkey = NULL;
 
   tor_assert(!allow_annotations || !prepend_annotations);
 
@@ -1717,8 +1718,9 @@ router_parse_entry_from_string(const char *s, const char *end,
              "Relay's onion key had invalid exponent.");
     goto err;
   }
-  router->onion_pkey = tok->key;
-  tok->key = NULL; /* Prevent free */
+  router_set_rsa_onion_pkey(tok->key, &router->onion_pkey,
+                            &router->onion_pkey_len);
+  crypto_pk_free(tok->key);
 
   if ((tok = find_opt_by_keyword(tokens, K_ONION_KEY_NTOR))) {
     curve25519_public_key_t k;
@@ -1890,10 +1892,12 @@ router_parse_entry_from_string(const char *s, const char *end,
         goto err;
       }
 
+      rsa_pubkey = router_get_rsa_onion_pkey(router->onion_pkey,
+                                             router->onion_pkey_len);
       if (check_tap_onion_key_crosscert(
                       (const uint8_t*)cc_tap_tok->object_body,
                       (int)cc_tap_tok->object_size,
-                      router->onion_pkey,
+                      rsa_pubkey,
                       &cert->signing_key,
                       (const uint8_t*)router->cache_info.identity_digest)<0) {
         log_warn(LD_DIR, "Incorrect TAP cross-verification");
@@ -2058,6 +2062,7 @@ router_parse_entry_from_string(const char *s, const char *end,
   routerinfo_free(router);
   router = NULL;
  done:
+  crypto_pk_free(rsa_pubkey);
   tor_cert_free(ntor_cc_cert);
   if (tokens) {
     SMARTLIST_FOREACH(tokens, directory_token_t *, t, token_clear(t));
@@ -4752,8 +4757,9 @@ microdescs_parse_from_string(const char *s, const char *eos,
                "Relay's onion key had invalid exponent.");
       goto next;
     }
-    md->onion_pkey = tok->key;
-    tok->key = NULL;
+    router_set_rsa_onion_pkey(tok->key, &md->onion_pkey,
+                              &md->onion_pkey_len);
+    crypto_pk_free(tok->key);
 
     if ((tok = find_opt_by_keyword(tokens, K_ONION_KEY_NTOR))) {
       curve25519_public_key_t k;