LCOV - code coverage report
Current view: top level - src/crypto - chacha20poly1305.cpp (source / functions) Hit Total Coverage
Test: fuzz_coverage.info Lines: 30 63 47.6 %
Date: 2023-10-05 12:38:51 Functions: 5 10 50.0 %
Branches: 8 34 23.5 %

           Branch data     Line data    Source code
       1                 :            : // Copyright (c) 2023 The Bitcoin Core developers
       2                 :            : // Distributed under the MIT software license, see the accompanying
       3                 :            : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       4                 :            : 
       5                 :            : #include <crypto/chacha20poly1305.h>
       6                 :            : 
       7                 :            : #include <crypto/common.h>
       8                 :            : #include <crypto/chacha20.h>
       9                 :            : #include <crypto/poly1305.h>
      10                 :            : #include <span.h>
      11                 :            : #include <support/cleanse.h>
      12                 :            : 
      13                 :            : #include <assert.h>
      14                 :            : #include <cstddef>
      15                 :            : 
      16                 :        670 : AEADChaCha20Poly1305::AEADChaCha20Poly1305(Span<const std::byte> key) noexcept : m_chacha20(key)
      17                 :            : {
      18         [ +  - ]:        670 :     assert(key.size() == KEYLEN);
      19                 :        670 : }
      20                 :            : 
      21                 :          0 : void AEADChaCha20Poly1305::SetKey(Span<const std::byte> key) noexcept
      22                 :            : {
      23         [ #  # ]:          0 :     assert(key.size() == KEYLEN);
      24                 :          0 :     m_chacha20.SetKey(key);
      25                 :          0 : }
      26                 :            : 
      27                 :            : namespace {
      28                 :            : 
      29                 :            : #ifndef HAVE_TIMINGSAFE_BCMP
      30                 :            : #define HAVE_TIMINGSAFE_BCMP
      31                 :            : 
      32                 :          0 : int timingsafe_bcmp(const unsigned char* b1, const unsigned char* b2, size_t n) noexcept
      33                 :            : {
      34                 :          0 :     const unsigned char *p1 = b1, *p2 = b2;
      35                 :          0 :     int ret = 0;
      36         [ #  # ]:          0 :     for (; n > 0; n--)
      37                 :          0 :         ret |= *p1++ ^ *p2++;
      38                 :          0 :     return (ret != 0);
      39                 :            : }
      40                 :            : 
      41                 :            : #endif
      42                 :            : 
      43                 :            : /** Compute poly1305 tag. chacha20 must be set to the right nonce, block 0. Will be at block 1 after. */
      44                 :        360 : void ComputeTag(ChaCha20& chacha20, Span<const std::byte> aad, Span<const std::byte> cipher, Span<std::byte> tag) noexcept
      45                 :            : {
      46                 :            :     static const std::byte PADDING[16] = {{}};
      47                 :            : 
      48                 :            :     // Get block of keystream (use a full 64 byte buffer to avoid the need for chacha20's own buffering).
      49                 :            :     std::byte first_block[ChaCha20Aligned::BLOCKLEN];
      50                 :        360 :     chacha20.Keystream(first_block);
      51                 :            : 
      52                 :            :     // Use the first 32 bytes of the first keystream block as poly1305 key.
      53                 :        360 :     Poly1305 poly1305{Span{first_block}.first(Poly1305::KEYLEN)};
      54                 :            : 
      55                 :            :     // Compute tag:
      56                 :            :     // - Process the padded AAD with Poly1305.
      57                 :        360 :     const unsigned aad_padding_length = (16 - (aad.size() % 16)) % 16;
      58                 :        360 :     poly1305.Update(aad).Update(Span{PADDING}.first(aad_padding_length));
      59                 :            :     // - Process the padded ciphertext with Poly1305.
      60                 :        360 :     const unsigned cipher_padding_length = (16 - (cipher.size() % 16)) % 16;
      61                 :        360 :     poly1305.Update(cipher).Update(Span{PADDING}.first(cipher_padding_length));
      62                 :            :     // - Process the AAD and plaintext length with Poly1305.
      63                 :            :     std::byte length_desc[Poly1305::TAGLEN];
      64   [ +  -  +  - ]:        360 :     WriteLE64(UCharCast(length_desc), aad.size());
      65   [ +  -  +  - ]:        360 :     WriteLE64(UCharCast(length_desc + 8), cipher.size());
      66                 :        360 :     poly1305.Update(length_desc);
      67                 :            : 
      68                 :            :     // Output tag.
      69                 :        360 :     poly1305.Finalize(tag);
      70                 :        360 : }
      71                 :            : 
      72                 :            : } // namespace
      73                 :            : 
      74                 :        360 : void AEADChaCha20Poly1305::Encrypt(Span<const std::byte> plain1, Span<const std::byte> plain2, Span<const std::byte> aad, Nonce96 nonce, Span<std::byte> cipher) noexcept
      75                 :            : {
      76         [ +  - ]:        360 :     assert(cipher.size() == plain1.size() + plain2.size() + EXPANSION);
      77                 :            : 
      78                 :            :     // Encrypt using ChaCha20 (starting at block 1).
      79                 :        360 :     m_chacha20.Seek(nonce, 1);
      80                 :        360 :     m_chacha20.Crypt(plain1, cipher.first(plain1.size()));
      81                 :        360 :     m_chacha20.Crypt(plain2, cipher.subspan(plain1.size()).first(plain2.size()));
      82                 :            : 
      83                 :            :     // Seek to block 0, and compute tag using key drawn from there.
      84                 :        360 :     m_chacha20.Seek(nonce, 0);
      85                 :        360 :     ComputeTag(m_chacha20, aad, cipher.first(cipher.size() - EXPANSION), cipher.last(EXPANSION));
      86                 :        360 : }
      87                 :            : 
      88                 :          0 : bool AEADChaCha20Poly1305::Decrypt(Span<const std::byte> cipher, Span<const std::byte> aad, Nonce96 nonce, Span<std::byte> plain1, Span<std::byte> plain2) noexcept
      89                 :            : {
      90         [ #  # ]:          0 :     assert(cipher.size() == plain1.size() + plain2.size() + EXPANSION);
      91                 :            : 
      92                 :            :     // Verify tag (using key drawn from block 0).
      93                 :          0 :     m_chacha20.Seek(nonce, 0);
      94                 :            :     std::byte expected_tag[EXPANSION];
      95                 :          0 :     ComputeTag(m_chacha20, aad, cipher.first(cipher.size() - EXPANSION), expected_tag);
      96   [ #  #  #  #  :          0 :     if (timingsafe_bcmp(UCharCast(expected_tag), UCharCast(cipher.last(EXPANSION).data()), EXPANSION)) return false;
                   #  # ]
      97                 :            : 
      98                 :            :     // Decrypt (starting at block 1).
      99                 :          0 :     m_chacha20.Crypt(cipher.first(plain1.size()), plain1);
     100                 :          0 :     m_chacha20.Crypt(cipher.subspan(plain1.size()).first(plain2.size()), plain2);
     101                 :          0 :     return true;
     102                 :          0 : }
     103                 :            : 
     104                 :          0 : void AEADChaCha20Poly1305::Keystream(Nonce96 nonce, Span<std::byte> keystream) noexcept
     105                 :            : {
     106                 :            :     // Skip the first output block, as it's used for generating the poly1305 key.
     107                 :          0 :     m_chacha20.Seek(nonce, 1);
     108                 :          0 :     m_chacha20.Keystream(keystream);
     109                 :          0 : }
     110                 :            : 
     111                 :        360 : void FSChaCha20Poly1305::NextPacket() noexcept
     112                 :            : {
     113         [ +  - ]:        360 :     if (++m_packet_counter == m_rekey_interval) {
     114                 :            :         // Generate a full block of keystream, to avoid needing the ChaCha20 buffer, even though
     115                 :            :         // we only need KEYLEN (32) bytes.
     116                 :            :         std::byte one_block[ChaCha20Aligned::BLOCKLEN];
     117         [ #  # ]:          0 :         m_aead.Keystream({0xFFFFFFFF, m_rekey_counter}, one_block);
     118                 :            :         // Switch keys.
     119                 :          0 :         m_aead.SetKey(Span{one_block}.first(KEYLEN));
     120                 :            :         // Wipe the generated keystream (a copy remains inside m_aead, which will be cleaned up
     121                 :            :         // once it cycles again, or is destroyed).
     122         [ #  # ]:          0 :         memory_cleanse(one_block, sizeof(one_block));
     123                 :            :         // Update counters.
     124                 :          0 :         m_packet_counter = 0;
     125                 :          0 :         ++m_rekey_counter;
     126                 :          0 :     }
     127                 :        360 : }
     128                 :            : 
     129                 :        360 : void FSChaCha20Poly1305::Encrypt(Span<const std::byte> plain1, Span<const std::byte> plain2, Span<const std::byte> aad, Span<std::byte> cipher) noexcept
     130                 :            : {
     131         [ +  - ]:        360 :     m_aead.Encrypt(plain1, plain2, aad, {m_packet_counter, m_rekey_counter}, cipher);
     132                 :        360 :     NextPacket();
     133                 :        360 : }
     134                 :            : 
     135                 :          0 : bool FSChaCha20Poly1305::Decrypt(Span<const std::byte> cipher, Span<const std::byte> aad, Span<std::byte> plain1, Span<std::byte> plain2) noexcept
     136                 :            : {
     137         [ #  # ]:          0 :     bool ret = m_aead.Decrypt(cipher, aad, {m_packet_counter, m_rekey_counter}, plain1, plain2);
     138                 :          0 :     NextPacket();
     139                 :          0 :     return ret;
     140                 :            : }

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