Реализация алгоритма ГОСТ-28147-89 для ЛР №2 по ИБ

gost.cpp

#include <cassert>
#include <cstring>
#include <climits>
#include <cstdint>

static uint8_t substitutions[8][16] = 
	{
		{4,  10, 9,  2,  13, 8,  0,  14, 6,  11, 1,  12, 7,  15, 5,  3},
		{14, 11, 4,  12, 6,  13, 15, 10, 2,  3,  8,  1,  0,  7,  5,  9},
		{5,  8,  1,  13, 10, 3,  4,  2,  14, 15, 12, 7,  6,  0,  9,  11},
		{7,  13, 10, 1,  0,  8,  9,  15, 14, 4,  6,  12, 11, 2,  5,  3},
		{6,  12, 7,  1,  5,  15, 13, 8,  4,  10, 9,  14, 0,  3,  11, 2},
		{4,  11, 10, 0,  7,  2,  1,  13, 3,  6,  8,  5,  9,  12, 15, 14},
		{13, 11, 4,  1,  3,  15, 5,  9,  0,  10, 14, 7,  6,  8,  2,  12},
		{1,  15, 13, 0,  5,  7,  10, 4,  9,  2,  3,  14, 6,  11, 8,  12}
	};

// http://stackoverflow.com/questions/776508 with template-related modifications
template<class T>
static T rotl(T n, T c)
{
	const T mask = (CHAR_BIT * sizeof(n) - 1);

	assert((c <= mask) && "rotate by type width or more");
	c &= mask;  // avoid undef behaviour with NDEBUG. 0 overhead for most types / compilers
	return (n << c) | (n >> ((-c) & mask));
}

uint64_t do_round(uint64_t in, uint32_t roundKey)
{
	const uint32_t MSBs = in >> 32;
	const uint32_t LSBs = in & 0xffffffff;

	const uint32_t sBoxIn = (LSBs + roundKey) & UINT_MAX;
	const uint32_t sBoxOut
		= (substitutions[0][(sBoxIn >> 28) & 0xf] << 28)
		| (substitutions[1][(sBoxIn >> 24) & 0xf] << 24)
		| (substitutions[2][(sBoxIn >> 20) & 0xf] << 20)
		| (substitutions[3][(sBoxIn >> 16) & 0xf] << 16)
		| (substitutions[4][(sBoxIn >> 12) & 0xf] << 12)
		| (substitutions[5][(sBoxIn >> 8 ) & 0xf] << 8 )
		| (substitutions[6][(sBoxIn >> 4 ) & 0xf] << 4 )
		| (substitutions[7][(sBoxIn      ) & 0xf]      );

	const uint32_t OutMSBs = LSBs;
	const uint32_t OutLSBs = rotl<uint32_t>(sBoxOut, 11) ^ MSBs;

	return (static_cast<uint64_t>(OutMSBs) << 32) | OutLSBs;
}

uint64_t GOST_28147_89(uint64_t message, uint32_t (&key)[8])
{
	uint64_t buffer = message;

	for(size_t round1 = 0; round1 < 3; ++round1)
	{
		for(size_t round2 = 0; round2 < 8; ++round2)
			buffer = do_round(buffer, key[round2]);
	}

	for(size_t round2 = 0; round2 < 8; ++round2)
		buffer = do_round(buffer, key[7 - round2]);

	return buffer;
}