1 // Copyright (c) 2016-present 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_SIPHASH_H
6 #define BITCOIN_CRYPTO_SIPHASH_H
7 8 #include <array>
9 #include <cstdint>
10 #include <span>
11 12 class uint256;
13 14 /** Shared SipHash internal state v[0..3], initialized from (k0, k1). */
15 class SipHashState
16 {
17 static constexpr uint64_t C0{0x736f6d6570736575ULL}, C1{0x646f72616e646f6dULL}, C2{0x6c7967656e657261ULL}, C3{0x7465646279746573ULL};
18 19 public:
20 explicit SipHashState(uint64_t k0, uint64_t k1) noexcept : v{C0 ^ k0, C1 ^ k1, C2 ^ k0, C3 ^ k1} {}
21 22 std::array<uint64_t, 4> v{};
23 };
24 25 /** General SipHash-2-4 implementation. */
26 class CSipHasher
27 {
28 SipHashState m_state;
29 uint64_t m_tmp{0};
30 uint8_t m_count{0}; //!< Only the low 8 bits of the input size matter.
31 32 public:
33 /** Construct a SipHash calculator initialized with 128-bit key (k0, k1). */
34 CSipHasher(uint64_t k0, uint64_t k1);
35 /** Hash a 64-bit integer worth of data.
36 * It is treated as if this was the little-endian interpretation of 8 bytes.
37 * This function can only be used when a multiple of 8 bytes have been written so far.
38 */
39 CSipHasher& Write(uint64_t data);
40 /** Hash arbitrary bytes. */
41 CSipHasher& Write(std::span<const unsigned char> data);
42 /** Compute the 64-bit SipHash-2-4 of the data written so far. The object remains untouched. */
43 uint64_t Finalize() const;
44 };
45 46 /**
47 * Optimized SipHash-2-4 implementation for uint256.
48 *
49 * This class caches the initial SipHash v[0..3] state derived from (k0, k1)
50 * and implements a specialized hashing path for uint256 values, with or
51 * without an extra 32-bit word. The internal state is immutable, so
52 * PresaltedSipHasher instances can be reused for multiple hashes with the
53 * same key.
54 */
55 class PresaltedSipHasher
56 {
57 const SipHashState m_state;
58 59 public:
60 explicit PresaltedSipHasher(uint64_t k0, uint64_t k1) noexcept : m_state{k0, k1} {}
61 62 /** Equivalent to CSipHasher(k0, k1).Write(val).Finalize(). */
63 uint64_t operator()(const uint256& val) const noexcept;
64 65 /**
66 * Equivalent to CSipHasher(k0, k1).Write(val).Write(extra).Finalize(),
67 * with `extra` encoded as 4 little-endian bytes.
68 */
69 uint64_t operator()(const uint256& val, uint32_t extra) const noexcept;
70 };
71 72 #endif // BITCOIN_CRYPTO_SIPHASH_H
73