salsa.cpp

// salsa.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"
#include "salsa.h"
#include "misc.h"
#include "argnames.h"

NAMESPACE_BEGIN(CryptoPP)

void Salsa20_TestInstantiations()
{
        Salsa20::Encryption x;
}

void Salsa20_Policy::CipherGetNextIV(byte *IV)
{
        word32 j6 = m_state[6] + 1;
        word32 j7 = m_state[7] + (j6 == 0);

        UnalignedPutWord(LITTLE_ENDIAN_ORDER, IV, j6);
        UnalignedPutWord(LITTLE_ENDIAN_ORDER, IV+4, j7);
}

void Salsa20_Policy::CipherSetKey(const NameValuePairs &params, const byte *key, size_t length)
{
        m_rounds = params.GetIntValueWithDefault(Name::Rounds(), 20);

        if (!(m_rounds == 8 || m_rounds == 12 || m_rounds == 20))
                throw InvalidRounds(StaticAlgorithmName(), m_rounds);

        GetUserKey(LITTLE_ENDIAN_ORDER, m_state+1, 4, key, 16);
        GetUserKey(LITTLE_ENDIAN_ORDER, m_state+11, 4, key + length - 16, 16);

        // m_state[0,5,10,15] forms "expand 16-byte k" or "expand 32-byte k"
        m_state[0] = 0x61707865;
        m_state[5] = (length == 16) ? 0x3120646e : 0x3320646e;
        m_state[10] = (length == 16) ? 0x79622d36 : 0x79622d32;
        m_state[15] = 0x6b206574;
}

void Salsa20_Policy::CipherResynchronize(byte *keystreamBuffer, const byte *IV)
{
        GetUserKey(LITTLE_ENDIAN_ORDER, m_state+6, 4, IV, 8);
}

void Salsa20_Policy::SeekToIteration(lword iterationCount)
{
        m_state[8] = (word32)iterationCount;
        m_state[9] = (word32)SafeRightShift<32>(iterationCount);
}

void Salsa20_Policy::OperateKeystream(KeystreamOperation operation, byte *output, const byte *input, size_t iterationCount)
{
        KeystreamOutput<LittleEndian> keystreamOutput(operation, output, input);

        word32 x0, x1, x2, x3, x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15;
        word32 j0, j1, j2, j3, j4, j5, j6, j7, j8, j9, j10, j11, j12, j13, j14, j15;

        j0 = m_state[0];
        j1 = m_state[1];
        j2 = m_state[2];
        j3 = m_state[3];
        j4 = m_state[4];
        j5 = m_state[5];
        j6 = m_state[6];
        j7 = m_state[7];
        j8 = m_state[8];
        j9 = m_state[9];
        j10 = m_state[10];
        j11 = m_state[11];
        j12 = m_state[12];
        j13 = m_state[13];
        j14 = m_state[14];
        j15 = m_state[15];

        for (size_t iteration = 0; iteration < iterationCount; ++iteration)
        {
                x0 = j0;
                x1 = j1;
                x2 = j2;
                x3 = j3;
                x4 = j4;
                x5 = j5;
                x6 = j6;
                x7 = j7;
                x8 = j8;
                x9 = j9;
                x10 = j10;
                x11 = j11;
                x12 = j12;
                x13 = j13;
                x14 = j14;
                x15 = j15;

                for (int i=m_rounds; i>0; i-=2)
                {
#define QUARTER_ROUND(a, b, c, d)       \
        b = b ^ rotlFixed(a + d, 7);    \
        c = c ^ rotlFixed(b + a, 9);    \
        d = d ^ rotlFixed(c + b, 13);   \
        a = a ^ rotlFixed(d + c, 18);

                        QUARTER_ROUND(x0, x4, x8, x12)
                        QUARTER_ROUND(x5, x9, x13, x1)
                        QUARTER_ROUND(x10, x14, x2, x6)
                        QUARTER_ROUND(x15, x3, x7, x11)

                        QUARTER_ROUND(x0, x1, x2, x3)
                        QUARTER_ROUND(x5, x6, x7, x4)
                        QUARTER_ROUND(x10, x11, x8, x9)
                        QUARTER_ROUND(x15, x12, x13, x14)
                }

                keystreamOutput (x0 + j0)
                                                (x1 + j1)
                                                (x2 + j2)
                                                (x3 + j3)
                                                (x4 + j4)
                                                (x5 + j5)
                                                (x6 + j6)
                                                (x7 + j7)
                                                (x8 + j8)
                                                (x9 + j9)
                                                (x10 + j10)
                                                (x11 + j11)
                                                (x12 + j12)
                                                (x13 + j13)
                                                (x14 + j14)
                                                (x15 + j15);

                if (++j8 == 0)
                        ++j9;
        }

        m_state[8] = j8;
        m_state[9] = j9;
}

NAMESPACE_END

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