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       1                 :            : /*
       2                 :            :  * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
       3                 :            :  *
       4                 :            :  * Licensed under the Apache License, Version 2.0 (the "License").
       5                 :            :  * You may not use this file except in compliance with the License.
       6                 :            :  * A copy of the License is located at
       7                 :            :  *
       8                 :            :  *  http://aws.amazon.com/apache2.0
       9                 :            :  *
      10                 :            :  * or in the "license" file accompanying this file. This file is distributed
      11                 :            :  * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
      12                 :            :  * express or implied. See the License for the specific language governing
      13                 :            :  * permissions and limitations under the License.
      14                 :            :  */
      15                 :            : 
      16                 :            : #include "crypto/s2n_cipher.h"
      17                 :            : #include "crypto/s2n_hmac.h"
      18                 :            : #include "crypto/s2n_sequence.h"
      19                 :            : #include "error/s2n_errno.h"
      20                 :            : #include "stuffer/s2n_stuffer.h"
      21                 :            : #include "tls/s2n_cipher_suites.h"
      22                 :            : #include "tls/s2n_connection.h"
      23                 :            : #include "tls/s2n_crypto.h"
      24                 :            : #include "tls/s2n_record.h"
      25                 :            : #include "tls/s2n_record_read.h"
      26                 :            : #include "utils/s2n_annotations.h"
      27                 :            : #include "utils/s2n_blob.h"
      28                 :            : #include "utils/s2n_safety.h"
      29                 :            : 
      30                 :            : int s2n_record_parse_aead(
      31                 :            :         const struct s2n_cipher_suite *cipher_suite,
      32                 :            :         struct s2n_connection *conn,
      33                 :            :         uint8_t content_type,
      34                 :            :         uint16_t encrypted_length,
      35                 :            :         uint8_t *implicit_iv,
      36                 :            :         struct s2n_hmac_state *mac,
      37                 :            :         uint8_t *sequence_number,
      38                 :            :         struct s2n_session_key *session_key)
      39                 :    3396435 : {
      40                 :    3396435 :     const int is_tls13_record = cipher_suite->record_alg->flags & S2N_TLS13_RECORD_AEAD_NONCE;
      41                 :            :     /* TLS 1.3 record protection uses a different 5 byte associated data than TLS 1.2's */
      42 [ -  + ][ #  # ]:    3396435 :     s2n_stack_blob(aad, is_tls13_record ? S2N_TLS13_AAD_LEN : S2N_TLS_MAX_AAD_LEN, S2N_TLS_MAX_AAD_LEN);
         [ -  + ][ +  + ]
      43                 :            : 
      44                 :    3396435 :     struct s2n_blob en = { 0 };
      45         [ -  + ]:    3396435 :     POSIX_GUARD(s2n_blob_init(&en, s2n_stuffer_raw_read(&conn->in, encrypted_length), encrypted_length));
      46 [ #  # ][ -  + ]:    3396435 :     POSIX_ENSURE_REF(en.data);
      47                 :            :     /* In AEAD mode, the explicit IV is in the record */
      48 [ -  + ][ #  # ]:    3396435 :     POSIX_ENSURE_GTE(en.size, cipher_suite->record_alg->cipher->io.aead.record_iv_size);
      49                 :            : 
      50                 :    3396435 :     uint8_t aad_iv[S2N_TLS_MAX_IV_LEN] = { 0 };
      51                 :    3396435 :     struct s2n_blob iv = { 0 };
      52         [ -  + ]:    3396435 :     POSIX_GUARD(s2n_blob_init(&iv, aad_iv, sizeof(aad_iv)));
      53                 :    3396435 :     struct s2n_stuffer iv_stuffer = { 0 };
      54         [ -  + ]:    3396435 :     POSIX_GUARD(s2n_stuffer_init(&iv_stuffer, &iv));
      55                 :            : 
      56         [ +  + ]:    3396435 :     if (cipher_suite->record_alg->flags & S2N_TLS12_AES_GCM_AEAD_NONCE) {
      57                 :            :         /* Partially explicit nonce. See RFC 5288 Section 3 */
      58         [ -  + ]:    2271064 :         POSIX_GUARD(s2n_stuffer_write_bytes(&iv_stuffer, implicit_iv, cipher_suite->record_alg->cipher->io.aead.fixed_iv_size));
      59         [ -  + ]:    2271064 :         POSIX_GUARD(s2n_stuffer_write_bytes(&iv_stuffer, en.data, cipher_suite->record_alg->cipher->io.aead.record_iv_size));
      60 [ +  + ][ +  - ]:    2271064 :     } else if (cipher_suite->record_alg->flags & S2N_TLS12_CHACHA_POLY_AEAD_NONCE || is_tls13_record) {
      61                 :            :         /* Fully implicit nonce.
      62                 :            :          * This is introduced with ChaChaPoly with RFC 7905 Section 2
      63                 :            :          * and also used for TLS 1.3 record protection (RFC 8446 Section 5.2).
      64                 :            :          *
      65                 :            :          * In these cipher modes, the sequence number (64 bits) is left padded by 4 bytes
      66                 :            :          * to align and xor-ed with the 96-bit IV.
      67                 :            :          **/
      68                 :    1125371 :         uint8_t four_zeroes[4] = { 0 };
      69         [ -  + ]:    1125371 :         POSIX_GUARD(s2n_stuffer_write_bytes(&iv_stuffer, four_zeroes, 4));
      70         [ -  + ]:    1125371 :         POSIX_GUARD(s2n_stuffer_write_bytes(&iv_stuffer, sequence_number, S2N_TLS_SEQUENCE_NUM_LEN));
      71         [ +  + ]:   14629823 :         for (int i = 0; i < cipher_suite->record_alg->cipher->io.aead.fixed_iv_size; i++) {
      72                 :   13504452 :             S2N_INVARIANT(i <= cipher_suite->record_alg->cipher->io.aead.fixed_iv_size);
      73                 :   13504452 :             aad_iv[i] = aad_iv[i] ^ implicit_iv[i];
      74                 :   13504452 :         }
      75                 :    1125371 :     } else {
      76         [ #  # ]:          0 :         POSIX_BAIL(S2N_ERR_INVALID_NONCE_TYPE);
      77                 :          0 :     }
      78                 :            : 
      79                 :            :     /* Set the IV size to the amount of data written */
      80                 :    3396435 :     iv.size = s2n_stuffer_data_available(&iv_stuffer);
      81                 :            : 
      82                 :    3396435 :     uint16_t payload_length = encrypted_length;
      83                 :            :     /* remove the AEAD overhead from the record size */
      84 [ +  + ][ +  - ]:    3396435 :     POSIX_ENSURE_GTE(payload_length, cipher_suite->record_alg->cipher->io.aead.record_iv_size + cipher_suite->record_alg->cipher->io.aead.tag_size);
      85                 :    3396433 :     payload_length -= cipher_suite->record_alg->cipher->io.aead.record_iv_size;
      86                 :    3396433 :     payload_length -= cipher_suite->record_alg->cipher->io.aead.tag_size;
      87                 :            : 
      88         [ +  + ]:    3396433 :     if (is_tls13_record) {
      89         [ -  + ]:      67526 :         POSIX_GUARD_RESULT(s2n_tls13_aead_aad_init(payload_length, cipher_suite->record_alg->cipher->io.aead.tag_size, &aad));
      90                 :    3328907 :     } else {
      91         [ -  + ]:    3328907 :         POSIX_GUARD_RESULT(s2n_aead_aad_init(conn, sequence_number, content_type, payload_length, &aad));
      92                 :    3328907 :     }
      93                 :            : 
      94                 :            :     /* Decrypt stuff! */
      95                 :            :     /* Skip explicit IV for decryption */
      96                 :    3396433 :     en.size -= cipher_suite->record_alg->cipher->io.aead.record_iv_size;
      97                 :    3396433 :     en.data += cipher_suite->record_alg->cipher->io.aead.record_iv_size;
      98                 :            : 
      99                 :            :     /* Check that we have some data to decrypt */
     100 [ #  # ][ -  + ]:    3396433 :     POSIX_ENSURE_NE(en.size, 0);
     101                 :            : 
     102         [ +  + ]:    3396433 :     POSIX_GUARD(cipher_suite->record_alg->cipher->io.aead.decrypt(session_key, &iv, &aad, &en, &en));
     103                 :     203889 :     struct s2n_blob seq = { 0 };
     104         [ -  + ]:     203889 :     POSIX_GUARD(s2n_blob_init(&seq, sequence_number, S2N_TLS_SEQUENCE_NUM_LEN));
     105         [ -  + ]:     203889 :     POSIX_GUARD(s2n_increment_sequence_number(&seq));
     106                 :            : 
     107                 :            :     /* O.k., we've successfully read and decrypted the record, now we need to align the stuffer
     108                 :            :      * for reading the plaintext data.
     109                 :            :      */
     110         [ -  + ]:     203889 :     POSIX_GUARD(s2n_stuffer_reread(&conn->in));
     111         [ -  + ]:     203889 :     POSIX_GUARD(s2n_stuffer_reread(&conn->header_in));
     112                 :            : 
     113                 :            :     /* Skip the IV, if any */
     114         [ +  - ]:     203889 :     if (conn->actual_protocol_version >= S2N_TLS12) {
     115         [ -  + ]:     203889 :         POSIX_GUARD(s2n_stuffer_skip_read(&conn->in, cipher_suite->record_alg->cipher->io.aead.record_iv_size));
     116                 :     203889 :     }
     117                 :            : 
     118                 :            :     /* Truncate and wipe the MAC and any padding */
     119         [ -  + ]:     203889 :     POSIX_GUARD(s2n_stuffer_wipe_n(&conn->in, s2n_stuffer_data_available(&conn->in) - payload_length));
     120                 :     203889 :     conn->in_status = PLAINTEXT;
     121                 :            : 
     122                 :     203889 :     return 0;
     123                 :     203889 : }