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>

1 files changed, 31 insertions, 0 deletions

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