Line data    Source code

       1             : // Copyright (c) 2017-2022 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             : #ifndef BITCOIN_CRYPTO_CHACHA20_H
       6             : #define BITCOIN_CRYPTO_CHACHA20_H
       7             : 
       8             : #include <span.h>
       9             : 
      10             : #include <array>
      11             : #include <cstddef>
      12             : #include <cstdlib>
      13             : #include <stdint.h>
      14             : #include <utility>
      15             : 
      16             : // classes for ChaCha20 256-bit stream cipher developed by Daniel J. Bernstein
      17             : // https://cr.yp.to/chacha/chacha-20080128.pdf.
      18             : //
      19             : // The 128-bit input is here implemented as a 96-bit nonce and a 32-bit block
      20             : // counter, as in RFC8439 Section 2.3. When the 32-bit block counter overflows
      21             : // the first 32-bit part of the nonce is automatically incremented, making it
      22             : // conceptually compatible with variants that use a 64/64 split instead.
      23             : 
      24             : /** ChaCha20 cipher that only operates on multiples of 64 bytes. */
      25             : class ChaCha20Aligned
      26             : {
      27             : private:
      28             :     uint32_t input[12];
      29             : 
      30             : public:
      31             :     /** Expected key length in constructor and SetKey. */
      32             :     static constexpr unsigned KEYLEN{32};
      33             : 
      34             :     /** Block size (inputs/outputs to Keystream / Crypt should be multiples of this). */
      35             :     static constexpr unsigned BLOCKLEN{64};
      36             : 
      37             :     /** For safety, disallow initialization without key. */
      38             :     ChaCha20Aligned() noexcept = delete;
      39             : 
      40             :     /** Initialize a cipher with specified 32-byte key. */
      41             :     ChaCha20Aligned(Span<const std::byte> key) noexcept;
      42             : 
      43             :     /** Destructor to clean up private memory. */
      44             :     ~ChaCha20Aligned();
      45             : 
      46             :     /** Set 32-byte key, and seek to nonce 0 and block position 0. */
      47             :     void SetKey(Span<const std::byte> key) noexcept;
      48             : 
      49             :     /** Type for 96-bit nonces used by the Set function below.
      50             :      *
      51             :      * The first field corresponds to the LE32-encoded first 4 bytes of the nonce, also referred
      52             :      * to as the '32-bit fixed-common part' in Example 2.8.2 of RFC8439.
      53             :      *
      54             :      * The second field corresponds to the LE64-encoded last 8 bytes of the nonce.
      55             :      *
      56             :      */
      57             :     using Nonce96 = std::pair<uint32_t, uint64_t>;
      58             : 
      59             :     /** Set the 96-bit nonce and 32-bit block counter.
      60             :      *
      61             :      * Block_counter selects a position to seek to (to byte BLOCKLEN*block_counter). After 256 GiB,
      62             :      * the block counter overflows, and nonce.first is incremented.
      63             :      */
      64             :     void Seek(Nonce96 nonce, uint32_t block_counter) noexcept;
      65             : 
      66             :     /** outputs the keystream into out, whose length must be a multiple of BLOCKLEN. */
      67             :     void Keystream(Span<std::byte> out) noexcept;
      68             : 
      69             :     /** en/deciphers the message <input> and write the result into <output>
      70             :      *
      71             :      * The size of input and output must be equal, and be a multiple of BLOCKLEN.
      72             :      */
      73             :     void Crypt(Span<const std::byte> input, Span<std::byte> output) noexcept;
      74             : };
      75             : 
      76             : /** Unrestricted ChaCha20 cipher. */
      77             : class ChaCha20
      78             : {
      79             : private:
      80             :     ChaCha20Aligned m_aligned;
      81             :     std::array<std::byte, ChaCha20Aligned::BLOCKLEN> m_buffer;
      82      183725 :     unsigned m_bufleft{0};
      83             : 
      84             : public:
      85             :     /** Expected key length in constructor and SetKey. */
      86             :     static constexpr unsigned KEYLEN = ChaCha20Aligned::KEYLEN;
      87             : 
      88             :     /** For safety, disallow initialization without key. */
      89             :     ChaCha20() noexcept = delete;
      90             : 
      91             :     /** Initialize a cipher with specified 32-byte key. */
      92      367450 :     ChaCha20(Span<const std::byte> key) noexcept : m_aligned(key) {}
      93             : 
      94             :     /** Destructor to clean up private memory. */
      95             :     ~ChaCha20();
      96             : 
      97             :     /** Set 32-byte key, and seek to nonce 0 and block position 0. */
      98             :     void SetKey(Span<const std::byte> key) noexcept;
      99             : 
     100             :     /** 96-bit nonce type. */
     101             :     using Nonce96 = ChaCha20Aligned::Nonce96;
     102             : 
     103             :     /** Set the 96-bit nonce and 32-bit block counter. See ChaCha20Aligned::Seek. */
     104           0 :     void Seek(Nonce96 nonce, uint32_t block_counter) noexcept
     105             :     {
     106           0 :         m_aligned.Seek(nonce, block_counter);
     107           0 :         m_bufleft = 0;
     108           0 :     }
     109             : 
     110             :     /** en/deciphers the message <in_bytes> and write the result into <out_bytes>
     111             :      *
     112             :      * The size of in_bytes and out_bytes must be equal.
     113             :      */
     114             :     void Crypt(Span<const std::byte> in_bytes, Span<std::byte> out_bytes) noexcept;
     115             : 
     116             :     /** outputs the keystream to out. */
     117             :     void Keystream(Span<std::byte> out) noexcept;
     118             : };
     119             : 
     120             : /** Forward-secure ChaCha20
     121             :  *
     122             :  * This implements a stream cipher that automatically transitions to a new stream with a new key
     123             :  * and new nonce after a predefined number of encryptions or decryptions.
     124             :  *
     125             :  * See BIP324 for details.
     126             :  */
     127             : class FSChaCha20
     128             : {
     129             : private:
     130             :     /** Internal stream cipher. */
     131             :     ChaCha20 m_chacha20;
     132             : 
     133             :     /** The number of encryptions/decryptions before a rekey happens. */
     134             :     const uint32_t m_rekey_interval;
     135             : 
     136             :     /** The number of encryptions/decryptions since the last rekey. */
     137             :     uint32_t m_chunk_counter{0};
     138             : 
     139             :     /** The number of rekey operations that have happened. */
     140             :     uint64_t m_rekey_counter{0};
     141             : 
     142             : public:
     143             :     /** Length of keys expected by the constructor. */
     144             :     static constexpr unsigned KEYLEN = 32;
     145             : 
     146             :     // No copy or move to protect the secret.
     147             :     FSChaCha20(const FSChaCha20&) = delete;
     148             :     FSChaCha20(FSChaCha20&&) = delete;
     149             :     FSChaCha20& operator=(const FSChaCha20&) = delete;
     150             :     FSChaCha20& operator=(FSChaCha20&&) = delete;
     151             : 
     152             :     /** Construct an FSChaCha20 cipher that rekeys every rekey_interval Crypt() calls. */
     153             :     FSChaCha20(Span<const std::byte> key, uint32_t rekey_interval) noexcept;
     154             : 
     155             :     /** Encrypt or decrypt a chunk. */
     156             :     void Crypt(Span<const std::byte> input, Span<std::byte> output) noexcept;
     157             : };
     158             : 
     159             : #endif // BITCOIN_CRYPTO_CHACHA20_H