crypto_format: Remove the return value from curve25519_public_to_base64()

And fix the documentation on the function: it does produce trailing
"="s as padding.

Also remove all checks for the return value, which were redundant anyway,
because the function never failed.

Part of 29660.

src/feature/hs/hs_descriptor.c

@@ -403,9 +403,7 @@ encode_enc_key(const hs_desc_intro_point_t *ip)
   tor_assert(ip);
 
   /* Base64 encode the encryption key for the "enc-key" field. */
-  if (curve25519_public_to_base64(key_b64, &ip->enc_key) < 0) {
+  curve25519_public_to_base64(key_b64, &ip->enc_key);
-    goto done;
-  }
   if (tor_cert_encode_ed22519(ip->enc_key_cert, &encoded_cert) < 0) {
     goto done;
   }
@@ -421,7 +419,7 @@ encode_enc_key(const hs_desc_intro_point_t *ip)
 }
 
 /* Encode an introduction point onion key. Return a newly allocated string
- * with it. On failure, return NULL. */
+ * with it. Can not fail. */
 static char *
 encode_onion_key(const hs_desc_intro_point_t *ip)
 {
@@ -431,12 +429,9 @@ encode_onion_key(const hs_desc_intro_point_t *ip)
   tor_assert(ip);
 
   /* Base64 encode the encryption key for the "onion-key" field. */
-  if (curve25519_public_to_base64(key_b64, &ip->onion_key) < 0) {
+  curve25519_public_to_base64(key_b64, &ip->onion_key);
-    goto done;
-  }
   tor_asprintf(&encoded, "%s ntor %s", str_ip_onion_key, key_b64);
 
- done:
   return encoded;
 }
 
@@ -797,8 +792,8 @@ get_inner_encrypted_layer_plaintext(const hs_descriptor_t *desc)
 /* Create the middle layer of the descriptor, which includes the client auth
  * data and the encrypted inner layer (provided as a base64 string at
  * <b>layer2_b64_ciphertext</b>). Return a newly-allocated string with the
- * layer plaintext, or NULL if an error occurred. It's the responsibility of
+ * layer plaintext. It's the responsibility of the caller to free the returned
- * the caller to free the returned string. */
+ * string. Can not fail. */
 static char *
 get_outer_encrypted_layer_plaintext(const hs_descriptor_t *desc,
                                     const char *layer2_b64_ciphertext)
@@ -817,10 +812,7 @@ get_outer_encrypted_layer_plaintext(const hs_descriptor_t *desc,
     tor_assert(!tor_mem_is_zero((char *) ephemeral_pubkey->public_key,
                                 CURVE25519_PUBKEY_LEN));
 
-    if (curve25519_public_to_base64(ephemeral_key_base64,
+    curve25519_public_to_base64(ephemeral_key_base64, ephemeral_pubkey);
-                                    ephemeral_pubkey) < 0) {
-      goto done;
-    }
     smartlist_add_asprintf(lines, "%s %s\n",
                            str_desc_auth_key, ephemeral_key_base64);
 
@@ -845,7 +837,6 @@ get_outer_encrypted_layer_plaintext(const hs_descriptor_t *desc,
 
   layer1_str = smartlist_join_strings(lines, "", 0, NULL);
 
- done:
   /* We need to memwipe all lines because it contains the ephemeral key */
   SMARTLIST_FOREACH(lines, char *, a, memwipe(a, 0, strlen(a)));
   SMARTLIST_FOREACH(lines, char *, a, tor_free(a));

src/lib/crypt_ops/crypto_curve25519.h

@@ -76,8 +76,8 @@ STATIC int curve25519_basepoint_impl(uint8_t *output, const uint8_t *secret);
 
 int curve25519_public_from_base64(curve25519_public_key_t *pkey,
                                   const char *input);
-int curve25519_public_to_base64(char *output,
+void curve25519_public_to_base64(char *output,
-                                const curve25519_public_key_t *pkey);
+                                 const curve25519_public_key_t *pkey);
 
 void curve25519_set_impl_params(int use_ed);
 void curve25519_init(void);

src/lib/crypt_ops/crypto_format.c

@@ -131,20 +131,27 @@ crypto_read_tagged_contents_from_file(const char *fname,
   return r;
 }
 
-/** Encode <b>pkey</b> as a base64-encoded string, without trailing "="
+/** Encode <b>pkey</b> as a base64-encoded string, including trailing "="
  * characters, in the buffer <b>output</b>, which must have at least
- * CURVE25519_BASE64_PADDED_LEN+1 bytes available.  Return 0 on success, -1 on
+ * CURVE25519_BASE64_PADDED_LEN+1 bytes available.
- * failure. */
+ * Can not fail.
-int
+ *
+ * Careful! CURVE25519_BASE64_PADDED_LEN is one byte longer than
+ * ED25519_BASE64_LEN.
+ */
+void
 curve25519_public_to_base64(char *output,
                             const curve25519_public_key_t *pkey)
 {
   char buf[128];
-  base64_encode(buf, sizeof(buf),
+  int n = base64_encode(buf, sizeof(buf),
-                (const char*)pkey->public_key, CURVE25519_PUBKEY_LEN, 0);
+                        (const char*)pkey->public_key,
-  buf[CURVE25519_BASE64_PADDED_LEN] = '\0';
+                        CURVE25519_PUBKEY_LEN, 0);
+  /* These asserts should always succeed, unless there is a bug in
+   * base64_encode(). */
+  tor_assert(n == CURVE25519_BASE64_PADDED_LEN);
+  tor_assert(buf[CURVE25519_BASE64_PADDED_LEN] == '\0');
   memcpy(output, buf, CURVE25519_BASE64_PADDED_LEN+1);
-  return 0;
 }
 
 /** Try to decode a base64-encoded curve25519 public key from <b>input</b>

src/test/test_crypto.c

@@ -2075,7 +2075,7 @@ test_crypto_curve25519_encode(void *arg)
 
   curve25519_secret_key_generate(&seckey, 0);
   curve25519_public_key_generate(&key1, &seckey);
-  tt_int_op(0, OP_EQ, curve25519_public_to_base64(buf, &key1));
+  curve25519_public_to_base64(buf, &key1);
   tt_int_op(CURVE25519_BASE64_PADDED_LEN, OP_EQ, strlen(buf));
 
   tt_int_op(0, OP_EQ, curve25519_public_from_base64(&key2, buf));