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/*
* Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file is distributed
* on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied. See the License for the specific language governing
* permissions and limitations under the License.
*/
#include "crypto/s2n_cipher.h"
#include "crypto/s2n_hmac.h"
#include "crypto/s2n_sequence.h"
#include "error/s2n_errno.h"
#include "stuffer/s2n_stuffer.h"
#include "tls/s2n_cipher_suites.h"
#include "tls/s2n_connection.h"
#include "tls/s2n_crypto.h"
#include "tls/s2n_record_read.h"
#include "utils/s2n_blob.h"
#include "utils/s2n_safety.h"
int s2n_record_parse_composite(
const struct s2n_cipher_suite *cipher_suite,
struct s2n_connection *conn,
uint8_t content_type,
uint16_t encrypted_length,
uint8_t *implicit_iv,
struct s2n_hmac_state *mac,
uint8_t *sequence_number,
struct s2n_session_key *session_key)
{
/* Don't reduce encrypted length for explicit IV, composite decrypt expects it */
struct s2n_blob iv = { .data = implicit_iv, .size = cipher_suite->record_alg->cipher->io.comp.record_iv_size };
uint8_t ivpad[S2N_TLS_MAX_IV_LEN];
/* Add the header to the HMAC */
uint8_t *header = s2n_stuffer_raw_read(&conn->header_in, S2N_TLS_RECORD_HEADER_LENGTH);
POSIX_ENSURE_REF(header);
struct s2n_blob en = { .size = encrypted_length, .data = s2n_stuffer_raw_read(&conn->in, encrypted_length) };
POSIX_ENSURE_REF(en.data);
uint16_t payload_length = encrypted_length;
uint8_t mac_digest_size;
POSIX_GUARD(s2n_hmac_digest_size(mac->alg, &mac_digest_size));
POSIX_ENSURE_GTE(payload_length, mac_digest_size);
payload_length -= mac_digest_size;
/* Compute non-payload parts of the MAC(seq num, type, proto vers, fragment length) for composite ciphers.
* Composite "decrypt" will MAC the actual payload data.
*/
/* In the decrypt case, this outputs the MAC digest length:
* https://github.com/openssl/openssl/blob/master/crypto/evp/e_aes_cbc_hmac_sha1.c#L842 */
int mac_size = 0;
POSIX_GUARD(cipher_suite->record_alg->cipher->io.comp.initial_hmac(session_key, sequence_number, content_type, conn->actual_protocol_version, payload_length, &mac_size));
POSIX_ENSURE_GTE(payload_length, mac_size);
payload_length -= mac_size;
/* Adjust payload_length for explicit IV */
if (conn->actual_protocol_version > S2N_TLS10) {
uint32_t out = 0;
POSIX_GUARD(s2n_sub_overflow(payload_length, cipher_suite->record_alg->cipher->io.comp.record_iv_size, &out));
payload_length = out;
}
/* Decrypt stuff! */
POSIX_ENSURE_NE(en.size, 0);
POSIX_ENSURE_EQ(en.size % iv.size, 0);
/* Copy the last encrypted block to be the next IV */
POSIX_CHECKED_MEMCPY(ivpad, en.data + en.size - iv.size, iv.size);
/* This will: Skip the explicit IV(if applicable), decrypt the payload, verify the MAC and padding. */
POSIX_GUARD((cipher_suite->record_alg->cipher->io.comp.decrypt(session_key, &iv, &en, &en)));
POSIX_CHECKED_MEMCPY(implicit_iv, ivpad, iv.size);
/* Subtract the padding length */
POSIX_ENSURE_GT(en.size, 0);
uint32_t out = 0;
POSIX_GUARD(s2n_sub_overflow(payload_length, en.data[en.size - 1] + 1, &out));
payload_length = out;
struct s2n_blob seq = { .data = sequence_number, .size = S2N_TLS_SEQUENCE_NUM_LEN };
POSIX_GUARD(s2n_increment_sequence_number(&seq));
/* O.k., we've successfully read and decrypted the record, now we need to align the stuffer
* for reading the plaintext data.
*/
POSIX_GUARD(s2n_stuffer_reread(&conn->in));
POSIX_GUARD(s2n_stuffer_reread(&conn->header_in));
/* Skip the IV, if any */
if (conn->actual_protocol_version > S2N_TLS10) {
POSIX_GUARD(s2n_stuffer_skip_read(&conn->in, cipher_suite->record_alg->cipher->io.comp.record_iv_size));
}
/* Truncate and wipe the MAC and any padding */
POSIX_GUARD(s2n_stuffer_wipe_n(&conn->in, s2n_stuffer_data_available(&conn->in) - payload_length));
conn->in_status = PLAINTEXT;
return 0;
}
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