Reject 128-byte keys that are not 1024-bit

When we added the check for key size, we required that the keys be
128 bytes.  But RSA_size (which defers to BN_num_bytes) will return
128 for keys of length 1017..1024.  This patch adds a new
crypto_pk_num_bits() that returns the actual number of significant
bits in the modulus, and uses that to enforce key sizes.

Also, credit the original bug3318 in the changes file.

changes/bug3318

@@ -1,3 +1,7 @@
   o Minor bugfixes:
     - Fix a log message that said "bits" while displaying a value in
-      bytes. Fixes bug 3318; bugfix on 0.2.0.1-alpha.
+      bytes. Found by wanoskarnet. Fixes bug 3318; bugfix on
+      0.2.0.1-alpha.
+    - When checking for 1024-bit keys, check for 1024 bits, not 128
+      bytes. This allows Tor to correctly discard keys of length
+      1017 through 1023. Bugfix on 0.0.9pre5.

src/common/crypto.c

@@ -777,6 +777,17 @@ crypto_pk_keysize(crypto_pk_env_t *env)
   return (size_t) RSA_size(env->key);
 }
 
+/** Return the size of the public key modulus of <b>env</b>, in bits. */
+int
+crypto_pk_num_bits(crypto_pk_env_t *env)
+{
+  tor_assert(env);
+  tor_assert(env->key);
+  tor_assert(env->key->n);
+
+  return BN_num_bits(env->key->n);
+}
+
 /** Increase the reference count of <b>env</b>, and return it.
  */
 crypto_pk_env_t *

src/common/crypto.h

@@ -119,6 +119,7 @@ int crypto_pk_write_private_key_to_filename(crypto_pk_env_t *env,
 int crypto_pk_check_key(crypto_pk_env_t *env);
 int crypto_pk_cmp_keys(crypto_pk_env_t *a, crypto_pk_env_t *b);
 size_t crypto_pk_keysize(crypto_pk_env_t *env);
+int crypto_pk_num_bits(crypto_pk_env_t *env);
 crypto_pk_env_t *crypto_pk_dup_key(crypto_pk_env_t *orig);
 crypto_pk_env_t *crypto_pk_copy_full(crypto_pk_env_t *orig);
 int crypto_pk_key_is_private(const crypto_pk_env_t *key);

src/or/routerparse.c

@@ -3765,9 +3765,9 @@ token_check_object(memarea_t *area, const char *kwd,
       break;
     case NEED_KEY_1024: /* There must be a 1024-bit public key. */
     case NEED_SKEY_1024: /* There must be a 1024-bit private key. */
-      if (tok->key && crypto_pk_keysize(tok->key) != PK_BYTES) {
+      if (tok->key && crypto_pk_num_bits(tok->key) != PK_BYTES*8) {
         tor_snprintf(ebuf, sizeof(ebuf), "Wrong size on key for %s: %d bits",
-                     kwd, (int)crypto_pk_keysize(tok->key)*8);
+                     kwd, crypto_pk_num_bits(tok->key));
         RET_ERR(ebuf);
       }
       /* fall through */

src/test/test_crypto.c

@@ -343,7 +343,9 @@ test_crypto_pk(void)
   test_eq(0, crypto_pk_cmp_keys(pk1, pk2));
 
   test_eq(128, crypto_pk_keysize(pk1));
+  test_eq(1024, crypto_pk_num_bits(pk1));
   test_eq(128, crypto_pk_keysize(pk2));
+  test_eq(1024, crypto_pk_num_bits(pk2));
 
   test_eq(128, crypto_pk_public_encrypt(pk2, data1, sizeof(data1),
                                         "Hello whirled.", 15,