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Use a better salted-MAC construction in build_mac()

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This commit is contained in:
Nick Mathewson
2016-11-04 13:15:28 -04:00
parent 1eed6edf36
commit c189cb5cc2
1 changed files with 7 additions and 2 deletions
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src/or/hs_descriptor.c
+7 -2
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@@ -481,8 +481,7 @@ build_secret_key_iv_mac(const hs_descriptor_t *desc,
}
/* Using a key, salt and encrypted payload, build a MAC and put it in mac_out.
* The length of the mac key and salt must be fixed and if not, you can't rely
* on the result to be a valid MAC. We use SHA3-256 for the MAC computation.
* We use SHA3-256 for the MAC computation.
* This function can't fail. */
static void
build_mac(const uint8_t *mac_key, size_t mac_key_len,
@@ -492,6 +491,9 @@ build_mac(const uint8_t *mac_key, size_t mac_key_len,
{
crypto_digest_t *digest;
const uint64_t mac_len_netorder = tor_htonll(mac_key_len);
const uint64_t salt_len_netorder = tor_htonll(salt_len);
tor_assert(mac_key);
tor_assert(salt);
tor_assert(encrypted);
@@ -500,7 +502,10 @@ build_mac(const uint8_t *mac_key, size_t mac_key_len,
digest = crypto_digest256_new(DIGEST_SHA3_256);
/* As specified in section 2.5 of proposal 224, first add the mac key
* then add the salt first and then the encrypted section. */
crypto_digest_add_bytes(digest, (const char *) &mac_len_netorder, 8);
crypto_digest_add_bytes(digest, (const char *) mac_key, mac_key_len);
crypto_digest_add_bytes(digest, (const char *) &salt_len_netorder, 8);
crypto_digest_add_bytes(digest, (const char *) salt, salt_len);
crypto_digest_add_bytes(digest, (const char *) encrypted, encrypted_len);
crypto_digest_get_digest(digest, (char *) mac_out, mac_len);