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@@ -1400,6 +1400,49 @@ encrypted_data_length_is_valid(size_t len)
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return 0;
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}
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+/* Build the KEYS component for the authorized client computation. The format
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+ * of the construction is:
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+ *
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+ * SECRET_SEED = x25519(sk, pk)
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+ * KEYS = KDF(subcredential | SECRET_SEED, 40)
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+ *
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+ * The keys_out parameter will points to the buffer containing the KEYS. The
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+ * caller should wipe and free its content once done with it. This function
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+ * can't fail. */
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+static void
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+build_descriptor_cookie_keys(const uint8_t *subcredential,
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+ size_t subcredential_len,
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+ const curve25519_secret_key_t *sk,
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+ const curve25519_public_key_t *pk,
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+ uint8_t **keys_out)
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+{
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+ uint8_t secret_seed[CURVE25519_OUTPUT_LEN];
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+ uint8_t *keystream;
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+ size_t keystream_len = HS_DESC_CLIENT_ID_LEN + HS_DESC_COOKIE_KEY_LEN;
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+ crypto_xof_t *xof;
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+
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+ tor_assert(subcredential);
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+ tor_assert(sk);
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+ tor_assert(pk);
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+ tor_assert(keys_out);
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+
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+ keystream = tor_malloc_zero(keystream_len);
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+
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+ /* Calculate x25519(sk, pk) to get the secret seed. */
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+ curve25519_handshake(secret_seed, sk, pk);
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+
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+ /* Calculate KEYS = KDF(subcredential | SECRET_SEED, 40) */
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+ xof = crypto_xof_new();
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+ crypto_xof_add_bytes(xof, subcredential, subcredential_len);
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+ crypto_xof_add_bytes(xof, secret_seed, sizeof(secret_seed));
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+ crypto_xof_squeeze_bytes(xof, keystream, keystream_len);
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+ crypto_xof_free(xof);
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+
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+ memwipe(secret_seed, 0, sizeof(secret_seed));
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+
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+ *keys_out = keystream;
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+}
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+
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/* Decrypt the descriptor cookie given the descriptor, the auth client,
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* and the client secret key. On sucess, return 0 and a newly allocated
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* descriptor cookie descriptor_cookie_out. On error or if the client id
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@@ -1412,12 +1455,10 @@ decrypt_descriptor_cookie(const hs_descriptor_t *desc,
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uint8_t **descriptor_cookie_out)
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{
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int ret = -1;
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- uint8_t secret_seed[CURVE25519_OUTPUT_LEN];
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- uint8_t keystream[HS_DESC_CLIENT_ID_LEN + HS_DESC_COOKIE_KEY_LEN];
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- uint8_t *cookie_key = NULL;
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+ uint8_t *keystream = NULL;
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uint8_t *descriptor_cookie = NULL;
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+ const uint8_t *cookie_key = NULL;
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crypto_cipher_t *cipher = NULL;
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- crypto_xof_t *xof = NULL;
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tor_assert(desc);
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tor_assert(client);
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@@ -1429,16 +1470,11 @@ decrypt_descriptor_cookie(const hs_descriptor_t *desc,
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sizeof(*client_auth_sk)));
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tor_assert(!tor_mem_is_zero((char *) desc->subcredential, DIGEST256_LEN));
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- /* Calculate x25519(client_x, hs_Y) */
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- curve25519_handshake(secret_seed, client_auth_sk,
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- &desc->superencrypted_data.auth_ephemeral_pubkey);
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-
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- /* Calculate KEYS = KDF(subcredential | SECRET_SEED, 40) */
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- xof = crypto_xof_new();
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- crypto_xof_add_bytes(xof, desc->subcredential, DIGEST256_LEN);
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- crypto_xof_add_bytes(xof, secret_seed, sizeof(secret_seed));
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- crypto_xof_squeeze_bytes(xof, keystream, sizeof(keystream));
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- crypto_xof_free(xof);
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+ /* Get the KEYS component to derive the CLIENT-ID and COOKIE-KEY. */
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+ build_descriptor_cookie_keys(desc->subcredential, DIGEST256_LEN,
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+ client_auth_sk,
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+ &desc->superencrypted_data.auth_ephemeral_pubkey,
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+ &keystream);
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/* If the client id of auth client is not the same as the calculcated
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* client id, it means that this auth client is invaild according to the
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@@ -1464,8 +1500,8 @@ decrypt_descriptor_cookie(const hs_descriptor_t *desc,
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if (cipher) {
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crypto_cipher_free(cipher);
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}
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- memwipe(secret_seed, 0, sizeof(secret_seed));
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memwipe(keystream, 0, sizeof(keystream));
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+ tor_free(keystream);
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return ret;
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}
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@@ -2864,11 +2900,9 @@ hs_desc_build_authorized_client(const uint8_t *subcredential,
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const uint8_t *descriptor_cookie,
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hs_desc_authorized_client_t *client_out)
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{
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- uint8_t secret_seed[CURVE25519_OUTPUT_LEN];
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- uint8_t keystream[HS_DESC_CLIENT_ID_LEN + HS_DESC_COOKIE_KEY_LEN];
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- uint8_t *cookie_key;
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+ uint8_t *keystream = NULL;
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+ const uint8_t *cookie_key;
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crypto_cipher_t *cipher;
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- crypto_xof_t *xof;
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tor_assert(client_auth_pk);
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tor_assert(auth_ephemeral_sk);
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@@ -2884,18 +2918,11 @@ hs_desc_build_authorized_client(const uint8_t *subcredential,
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tor_assert(!tor_mem_is_zero((char *) subcredential,
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DIGEST256_LEN));
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- /* Calculate x25519(hs_y, client_X) */
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- curve25519_handshake(secret_seed,
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- auth_ephemeral_sk,
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- client_auth_pk);
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-
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- /* Calculate KEYS = KDF(subcredential | SECRET_SEED, 40) */
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- xof = crypto_xof_new();
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- crypto_xof_add_bytes(xof, subcredential, DIGEST256_LEN);
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- crypto_xof_add_bytes(xof, secret_seed, sizeof(secret_seed));
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- crypto_xof_squeeze_bytes(xof, keystream, sizeof(keystream));
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- crypto_xof_free(xof);
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+ /* Get the KEYS part so we can derive the CLIENT-ID and COOKIE-KEY. */
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+ build_descriptor_cookie_keys(subcredential, DIGEST256_LEN,
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+ auth_ephemeral_sk, client_auth_pk, &keystream);
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+ /* Extract the CLIENT-ID and COOKIE-KEY from the KEYS. */
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memcpy(client_out->client_id, keystream, HS_DESC_CLIENT_ID_LEN);
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cookie_key = keystream + HS_DESC_CLIENT_ID_LEN;
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@@ -2910,8 +2937,8 @@ hs_desc_build_authorized_client(const uint8_t *subcredential,
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(const char *) descriptor_cookie,
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HS_DESC_DESCRIPTOR_COOKIE_LEN);
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- memwipe(secret_seed, 0, sizeof(secret_seed));
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memwipe(keystream, 0, sizeof(keystream));
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+ tor_free(keystream);
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crypto_cipher_free(cipher);
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}
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