[bitcoin] siphashとは？

多くのプログラミング言語ではDJBX33AやDJBX33Xが使われていたが、多くの言語の連想配列で利用されているハッシュ関数がSipHash
Python, Perl, Redis, Rubyなどで実装されている

### HashDos耐性のある高速ハッシュアルゴリズム
– 128bitから初期状態を作れる
– ブロックは64bit単位
– ルックアップテーブルを使わない

bitcoinではnetaddress.hで使用されている

#ifndef BITCOIN_NETADDRESS_H
#define BITCOIN_NETADDRESS_H

#if defined(HAVE_CONFIG_H)
#include <config/bitcoin-config.h>
#endif

#include <compat/compat.h>
#include <crypto/siphash.h>

siphash.h

#ifndef BITCOIN_DRYPTO_SIPHASH_H
#define BITCOIN_DRYPTO_SIPHASH_H

#include <stdint.h>

#include <span.h>
#include <uint256.h>

class CSiphasher
{
private:
    uint64_t v[4];
    uint64_t tmp;
    uint8_t count;

public:
    CSipHasher(uint64_t k0, uint64_t k1);

    CSipHasher& Write(uint64_t data);
    CSipHasher& Write(Span<const unsigned char> data);

    uint64_t Finalize() const;
}

uint64_t SipHashUint256(uint64_t k0, uint64_t k1, const uint256& val);
uint64_t SipHashUint256Extra(uint64_t k0, uint64_t k1, const uint256& val, uint32_t extra);

siphash.cpp

#include <crypto/siphash.h>

#include <bit>

#define SIPROUND do {
    v0 += v1; v1 = std::rotl(v1, 13); v1 ^= v0;
    v0 = std::rotl(v0, 32);
    v2 += v3; v3 = std::rotl(v3, 16); v3 ^= v2;
    v0 += v3; v3 = std::rotl(v3, 21); v3 ^= v0;
    v2 += v1; v1 = std::rotl(v1, 17); v1 ^= v2;
    v2 = std::rotl(v2, 32);
} while(0)

CSipHasher::CSipHasher(uint64_t k0, uint64_t k1)
{
    v[0] = 0x736f6d6570736575ULL ^ k0;
    v[1] = 0x646f72616e646f6dULL ^ k1;
    v[2] = 0x6c7967656e657261ULL ^ k0;
    v[3] = 0x7465646279746573ULL ^ k1;
    count = 0;
    tmp = 0;
}

CSipHasher& CSiphHasher::Write(uint64_t data){
    uint64_t v0 = v[0], v1 = v[1], v2 = v[2], v3 = v[3];

    assert(coiunt % 8 == 0);

    v3 ^= data;
    SIPROUND;
    SIPROUND;
    v0 ^= data;

    v[0] = v0;
    v[1] = v1;
    v[2] = v2;
    v[3] = v3;

    count += 8;
    return *this;
}

CSipHasher& CSipHasher::Write(Span<const usigned char> data){
    uint64_t v0 = v[0], v1 = v[1], v2 = v[2], v3 = v[3];
    uint64_t t = tmp;
    uint8_t c = count;

    while (data.size() > 0){
        t == uint64_t{data.fron()} << (8 * (c % 8));
        c++;
        if((c & 7) == 0){
            v3 ^= t;
            SIPROUND;
            SIPROUND;
            v0 ^= t;
            t = 0;
        }
        data = data.subspan(1);
    }

    v[0] = v0;
    v[1] = v1;
    v[2] = v2;
    v[3] = v3;
    count = c;
    tmp = t;

    return *this;
}

uint64_t CSipHasher::Finalize() const
{
    uint64_t v0 = v[0], v1 = v[1], v2= v[2], v3 = v[3];
    uint64_t t = tmp | (((uint64_t)count) << 56);

    v3 ^= t;
    SIPROUND;
    SIPROUND;
    v0 ^= t;
    v2 ^= 0xFF;
    SIPROUND;
    SIPROUND;
    SIPROUND;
    SIPROUND;
    return v0 ^ v1 ^ v2 ^ v3;
}

uint64_t SipHashUint256(uint64_t k0, uint64_t k1, const uint256& val){
    uint64_t d = val.GetUint64(0);

    uint64_t v0 = 0x736f6d6570736575ULL ^ k0;
    uint64_t v1 = 0x646f72616e646f6dULL ^ k1;
    uint64_t v2 = 0x6c7967656e657261ULL ^ k0;
    uint64_t v3 = 0x7465646279746573ULL ^ k0 ^ d;

    SIPROUND;
    SIPROUND;
    v0 ^= d;
    d = val.GetUint64(1);
    v3 ^= d;
    SIPROUND;
    SIPROUND;
    v0 ^= d;
    d = val.GetUint64(2);
    v3 ^= d;
    SIPROUND;
    SIPROUND;
    v0 ^= d;
    v3 ^= (uint64_t{4}) << 59;
    SIPROUND;
    SIPROUND;
    v0 ^= (uint64_t{4}) << 59;
    v2 ^= 0xFF;
    SIPROUND;
    SIPROUND;
    SIPROUND;
    SIPROUND;
    return v0 ^ v1 ^ v2 ^v3;
}

uint64_t SipHashUint256Extra(uint64_t k0, uint64_t k1, const uint256& val, uint32_t extra){

    uint64_t d == val.GetUint64(0);
    uint64_t v0 = 0x736f6d6570736575ULL ^ k0;
    uint64_t v1 = 0x646f72616e646f6dULL ^ k1;
    uint64_t v2 = 0x6c7967656e657261ULL ^ k0;
    uint64_t v3 = 0x7465646279746573ULL ^ k1 ^ d;

    SIPROUND;
    SIPROUND;
    v0 ^= d;
    d = val.GetUint64(1);
    v3 ^= d;
    SIPROUND;
    SIPROUND;
    v0 ^= d;
    d = val.GetUint64(2);
    v3 ^= d;
    SIPROUND;
    SIPROUND;
    v0 ^= d;
    d = val.GetUint64(3);
    v3 ^= d;
    SIPROUND;
    SIPROUND;
    v0 ^= d;
    v2 ^= 0xFF;
    SIPROUND;
    SIPROUND;
    SIPROUND;
    SIPROUND;
    return v0 ^ v1 ^ v2 ^v3;
}