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142 lines
2.8 KiB
142 lines
2.8 KiB
#pragma once
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#include <stdint.h>
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#include <stddef.h>
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#include <gp/integer_math.hpp>
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#include <algorithm>
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#include <array>
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template<typename word_t = uint32_t, size_t r = 20, size_t b = 128, word_t P = 0xb7e15163L, word_t Q = 0x9e3779b9L>
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class RC6 {
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static constexpr size_t word_size = 8*sizeof(word_t);
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constexpr static word_t r_l(const word_t& w, size_t v) {
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return (w << v) | ( w >> (word_size-v));
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}
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constexpr static word_t r_r(const word_t& w, size_t v) {
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return (w >> v) | ( w << (word_size-v));
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}
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class RC6_KeySched {
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using sched_t = std::array<word_t, 2*r+4>;
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public:
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static constexpr size_t c = (b+word_size-1)/word_size;
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static constexpr size_t v_3 = std::max(c, 2*r+4);
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static constexpr size_t v = v_3*3;
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private:
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sched_t S;
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public:
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constexpr RC6_KeySched(std::array<word_t, c> L)
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{
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assert(r_l(r_r(13,13),13) == 13);
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auto it = S.begin();
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*(it++) = P;
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for(; it != S.end(); ++it)
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{
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*it = *(it-1) + Q;
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}
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word_t A = 0;
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word_t B = 0;
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word_t i = 0;
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word_t j = 0;
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for(size_t s = 0; s < v; ++s)
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{
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A = S[i] = r_l( S[i] + A + B, 3 );
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B = L[j] = r_l( L[j] + A + B, (A + B)%(word_size));
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i = s % S.size();
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j = s % L.size();
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}
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}
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const auto cbegin()
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{
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return S.cbegin();
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}
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const auto cend()
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{
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return S.cend();
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}
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const auto crbegin()
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{
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return S.crbegin();
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}
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const auto crend()
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{
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return S.crend();
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}
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};
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RC6_KeySched S;
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public:
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typedef std::array<word_t, RC6_KeySched::c> key_type;
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typedef std::array<word_t, 4> block_type;
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constexpr RC6(const key_type& key)
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: S(key)
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{}
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constexpr block_type encrypt(block_type plaintext) {
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using namespace gp::math;
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auto& A = plaintext[0];
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auto& B = plaintext[1];
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auto& C = plaintext[2];
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auto& D = plaintext[3];
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auto it = S.cbegin();
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B += *(it++);
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D += *(it++);
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for(size_t i = 0; i < r; ++i)
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{
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auto u = r_l( D * ( 2 * D + 1 ), msb(word_size));
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auto t = r_l( B * ( 2 * B + 1 ), msb(word_size));
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A = r_l((A ^ t), u % word_size) + *(it++);
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C = r_l((C ^ u), t % word_size) + *(it++);
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std::rotate(plaintext.begin(), plaintext.begin()+1, plaintext.end());
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}
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A += *(it++);
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C += *(it++);
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assert(it == S.cend());
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return plaintext;
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}
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constexpr block_type decrypt(block_type plaintext) {
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using namespace gp::math;
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auto& A = plaintext[0];
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auto& B = plaintext[1];
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auto& C = plaintext[2];
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auto& D = plaintext[3];
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auto it = S.crbegin();
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C -= *(it++);
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A -= *(it++);
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for(size_t i = 0; i < r; ++i)
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{
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std::rotate(plaintext.begin(), plaintext.end()-1, plaintext.end());
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auto u = r_l( D * ( 2 * D + 1 ), msb(word_size));
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auto t = r_l( B * ( 2 * B + 1 ), msb(word_size));
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C = r_r( (C - *(it++)) , t % word_size) ^ u ;
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A = r_r( (A - *(it++)) , u % word_size) ^ t ;
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}
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D -= *(it++);
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B -= *(it++);
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assert(it == S.crend());
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return plaintext;
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}
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};
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