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hs-v3: Decrypt the descriptor with client private key

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Parse the client authorization section from the descriptor, use the client
private key to decrypt the auth clients, and then use the descriptor cookie to
decrypt the descriptor.

Signed-off-by: David Goulet <dgoulet@torproject.org>
This commit is contained in:
Suphanat Chunhapanya 2018-04-20 02:10:19 +07:00 committed by David Goulet
parent 63576b0166
commit 7acb720027
1 changed files with 137 additions and 5 deletions
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142
src/feature/hs/hs_descriptor.c
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@ -1181,6 +1181,42 @@ desc_encode_v3(const hs_descriptor_t *desc,
/* === DECODING === */
/* Given the token tok for an auth client, decode it as
* hs_desc_authorized_client_t. tok->args MUST contain at least 3 elements
* Return 0 on success else -1 on failure. */
static int
decode_auth_client(const directory_token_t *tok,
hs_desc_authorized_client_t *client)
{
int ret = -1;
tor_assert(tok);
tor_assert(tok->n_args >= 3);
tor_assert(client);
if (base64_decode((char *) client->client_id, sizeof(client->client_id),
tok->args[0], strlen(tok->args[0])) !=
sizeof(client->client_id)) {
goto done;
}
if (base64_decode((char *) client->iv, sizeof(client->iv),
tok->args[1], strlen(tok->args[1])) !=
sizeof(client->iv)) {
goto done;
}
if (base64_decode((char *) client->encrypted_cookie,
sizeof(client->encrypted_cookie),
tok->args[2], strlen(tok->args[2])) !=
sizeof(client->encrypted_cookie)) {
goto done;
}
/* Success. */
ret = 0;
done:
return ret;
}
/* Given an encoded string of the link specifiers, return a newly allocated
* list of decoded link specifiers. Return NULL on error. */
STATIC smartlist_t *
@ -1420,6 +1456,73 @@ encrypted_data_length_is_valid(size_t len)
return 0;
}
/* Decrypt the descriptor cookie given the descriptor, the auth client,
* and the client secret key. On sucess, return 0 and a newly allocated
* descriptor cookie descriptor_cookie_out. On error or if the client id
* is invalid, return -1 and descriptor_cookie_out is set to
* NULL. */
static int
decrypt_descriptor_cookie(const hs_descriptor_t *desc,
const hs_desc_authorized_client_t *client,
const curve25519_secret_key_t *client_sk,
uint8_t **descriptor_cookie_out)
{
int ret = -1;
uint8_t secret_seed[CURVE25519_OUTPUT_LEN];
uint8_t keystream[HS_DESC_CLIENT_ID_LEN + HS_DESC_COOKIE_KEY_LEN];
uint8_t *cookie_key = NULL;
uint8_t *descriptor_cookie = NULL;
crypto_cipher_t *cipher = NULL;
crypto_xof_t *xof = NULL;
tor_assert(desc);
tor_assert(client);
tor_assert(client_sk);
tor_assert(!tor_mem_is_zero(
(char *) &desc->superencrypted_data.auth_ephemeral_pubkey,
sizeof(desc->superencrypted_data.auth_ephemeral_pubkey)));
tor_assert(!tor_mem_is_zero((char *) client_sk,
sizeof(*client_sk)));
/* Calculate x25519(client_x, hs_Y) */
curve25519_handshake(secret_seed, client_sk,
&desc->superencrypted_data.auth_ephemeral_pubkey);
/* Calculate KEYS = KDF(SECRET_SEED, 40) */
xof = crypto_xof_new();
crypto_xof_add_bytes(xof, secret_seed, sizeof(secret_seed));
crypto_xof_squeeze_bytes(xof, keystream, sizeof(keystream));
crypto_xof_free(xof);
/* If the client id of auth client is not the same as the calculcated
* client id, it means that this auth client is invaild according to the
* client secret key client_sk. */
if (tor_memneq(client->client_id, keystream, HS_DESC_CLIENT_ID_LEN)) {
goto done;
}
cookie_key = keystream + HS_DESC_CLIENT_ID_LEN;
/* This creates a cipher for AES. It can't fail. */
cipher = crypto_cipher_new_with_iv_and_bits(cookie_key, client->iv,
HS_DESC_COOKIE_KEY_BIT_SIZE);
descriptor_cookie = tor_malloc_zero(HS_DESC_DESCRIPTOR_COOKIE_LEN);
/* This can't fail. */
crypto_cipher_decrypt(cipher, (char *) descriptor_cookie,
(const char *) client->encrypted_cookie,
sizeof(client->encrypted_cookie));
/* Success. */
ret = 0;
done:
*descriptor_cookie_out = descriptor_cookie;
if (cipher) {
crypto_cipher_free(cipher);
}
memwipe(secret_seed, 0, sizeof(secret_seed));
memwipe(keystream, 0, sizeof(keystream));
return ret;
}
/** Decrypt an encrypted descriptor layer at <b>encrypted_blob</b> of size
* <b>encrypted_blob_size</b>. The descriptor cookie is optional. Use
* the descriptor object <b>desc</b> and <b>descriptor_cookie</b>
@ -1588,18 +1691,30 @@ desc_decrypt_encrypted(const hs_descriptor_t *desc,
{
size_t encrypted_len = 0;
char *encrypted_plaintext = NULL;
uint8_t *descriptor_cookie = NULL;
tor_assert(desc);
tor_assert(desc->superencrypted_data.clients);
tor_assert(decrypted_out);
/* XXX: We need to decrypt the descriptor properly when the client auth
* is enabled. */
(void) client_sk;
/* If the client secret key is provided, try to find a valid descriptor
* cookie. Otherwise, leave it NULL. */
if (client_sk) {
SMARTLIST_FOREACH_BEGIN(desc->superencrypted_data.clients,
hs_desc_authorized_client_t *, client) {
/* If we can decrypt the descriptor cookie successfully, we will use that
* descriptor cookie and break from the loop. */
if (!decrypt_descriptor_cookie(desc, client, client_sk,
&descriptor_cookie)) {
break;
}
} SMARTLIST_FOREACH_END(client);
}
encrypted_len = decrypt_desc_layer(desc,
desc->superencrypted_data.encrypted_blob,
desc->superencrypted_data.encrypted_blob_size,
NULL, 0, &encrypted_plaintext);
descriptor_cookie, 0, &encrypted_plaintext);
if (!encrypted_len) {
log_warn(LD_REND, "Decrypting encrypted desc failed.");
goto err;
@ -1610,6 +1725,10 @@ desc_decrypt_encrypted(const hs_descriptor_t *desc,
/* In case of error, encrypted_plaintext is already NULL, so the
* following line makes sense. */
*decrypted_out = encrypted_plaintext;
if (descriptor_cookie) {
memwipe(descriptor_cookie, 0, HS_DESC_DESCRIPTOR_COOKIE_LEN);
}
tor_free(descriptor_cookie);
/* This makes sense too, because, in case of error, this is zero. */
return encrypted_len;
}
@ -2125,10 +2244,23 @@ desc_decode_superencrypted_v3(const hs_descriptor_t *desc,
}
/* Extract desc auth client items */
if (!superencrypted->clients) {
superencrypted->clients = smartlist_new();
}
SMARTLIST_FOREACH_BEGIN(tokens, const directory_token_t *, token) {
if (token->tp == R3_DESC_AUTH_CLIENT) {
tor_assert(token->n_args >= 3);
/* XXX: Extract each auth client. */
hs_desc_authorized_client_t *client =
tor_malloc_zero(sizeof(hs_desc_authorized_client_t));
if (decode_auth_client(token, client) < 0) {
log_warn(LD_REND, "Descriptor client authorization section can't "
"be decoded.");
tor_free(client);
goto err;
}
smartlist_add(superencrypted->clients, client);
}
} SMARTLIST_FOREACH_END(token);