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88 lines
2.1 KiB
88 lines
2.1 KiB
#pragma once
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#include <array>
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#include <algorithm>
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#include <cstdint>
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#define ROTL(a,b) (((a) << (b)) | ((a) >> (32 - (b))))
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#define QR(a, b, c, d) ( \
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a += b, d ^= a, d = ROTL(d,16), \
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c += d, b ^= c, b = ROTL(b,12), \
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a += b, d ^= a, d = ROTL(d, 8), \
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c += d, b ^= c, b = ROTL(b, 7))
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//
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// Based on code from RFC 7539
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//
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template<int ROUNDS>
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void chacha_do_rounds(std::array<uint32_t, 16>& out) {
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static_assert(ROUNDS%2 == 0, "ChaPRNG: Rounds count MUST be even.");
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for (int i = 0; i < ROUNDS; i += 2) {
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// Odd round
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QR(out[0], out[4], out[ 8], out[12]); // column 0
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QR(out[1], out[5], out[ 9], out[13]); // column 1
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QR(out[2], out[6], out[10], out[14]); // column 2
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QR(out[3], out[7], out[11], out[15]); // column 3
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// Even round
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QR(out[0], out[5], out[10], out[15]); // diagonal 1 (main diagonal)
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QR(out[1], out[6], out[11], out[12]); // diagonal 2
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QR(out[2], out[7], out[ 8], out[13]); // diagonal 3
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QR(out[3], out[4], out[ 9], out[14]); // diagonal 4
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}
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}
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template<int ROUNDS, bool REMIX = true, bool DIRECT = false>
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std::array<uint32_t, 16> chacha_block(std::array<uint32_t, 16>& in)
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{
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std::array<uint32_t, 16> out;
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int i;
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if constexpr(DIRECT) {
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chacha_do_rounds<ROUNDS>(in);
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return out;
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}else {
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for (i = 0; i < 16; ++i)
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out[i] = in[i];
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chacha_do_rounds<ROUNDS>(out);
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if constexpr(REMIX) {
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for (i = 0; i < 16; ++i)
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out[i] += in[i];
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}
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return out;
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}
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}
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template<int ROUNDS, bool REMIX = true, bool DIRECT = false>
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class ChaPRNG {
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std::array<uint32_t, 16> source;
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std::array<uint32_t, 16> current;
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uint32_t it = 0;
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public:
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ChaPRNG(std::array<uint32_t, 12> seed = {0}) {
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source[0] = 'expa';
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source[1] = 'nd 3';
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source[2] = '2-by';
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source[3] = 'te k';
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std::copy(seed.begin(), seed.end(), source.begin()+4);
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}
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uint32_t operator()() {
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auto spot = it & 0b1111;
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if(spot == 0) {
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source[12]++;
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if constexpr (DIRECT) {
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chacha_block<ROUNDS, REMIX, DIRECT>(source);
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} else {
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current = chacha_block<ROUNDS, REMIX, DIRECT>(source);
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}
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}
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++it;
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if constexpr (DIRECT)
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return source[spot];
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else
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return current[spot];
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}
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};
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