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hs-v3: Consolidate descriptor cookie computation code

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Both client and service had their own code for this. Consolidate into one
place so we avoid duplication.

Closes #27549

Signed-off-by: David Goulet <dgoulet@torproject.org>
This commit is contained in:
David Goulet 2018-09-18 13:50:12 -04:00 committed by Nick Mathewson
parent 50367d06f2
commit 3a8f32067d
2 changed files with 61 additions and 31 deletions
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3
changes/ticket27549 Normal file
View File

@ -0,0 +1,3 @@
o Code simplification and refactoring (hidden service v3):
- Consolidate the authorized client descriptor cookie computation code
from client and service into one function. Closes ticket 27549.

89
src/feature/hs/hs_descriptor.c
View File

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