/*

* Salsa20 / XSalsa20

* (C) 1999-2010,2014 Jack Lloyd

*

* Botan is released under the Simplified BSD License (see license.txt)

*/

#include <botan/salsa20.h>

#include <botan/exceptn.h>

#include <botan/loadstor.h>

#include <botan/rotate.h>

namespace Botan {

#define SALSA20_QUARTER_ROUND(x1, x2, x3, x4)    \

   do {                                          \

      x2 ^= rotl<7>(x1 + x4);                    \

      x3 ^= rotl<9>(x2 + x1);                    \

      x4 ^= rotl<13>(x3 + x2);                   \

      x1 ^= rotl<18>(x4 + x3);                   \

   } while(0)

/*

* Generate HSalsa20 cipher stream (for XSalsa20 IV setup)

*/

//static

void Salsa20::hsalsa20(uint32_t output[8], const uint32_t input[16])

   {

   uint32_t x00 = input[ 0], x01 = input[ 1], x02 = input[ 2], x03 = input[ 3],

            x04 = input[ 4], x05 = input[ 5], x06 = input[ 6], x07 = input[ 7],

            x08 = input[ 8], x09 = input[ 9], x10 = input[10], x11 = input[11],

            x12 = input[12], x13 = input[13], x14 = input[14], x15 = input[15];

   for(size_t i = 0; i != 10; ++i)

      {

      SALSA20_QUARTER_ROUND(x00, x04, x08, x12);

      SALSA20_QUARTER_ROUND(x05, x09, x13, x01);

      SALSA20_QUARTER_ROUND(x10, x14, x02, x06);

      SALSA20_QUARTER_ROUND(x15, x03, x07, x11);

      SALSA20_QUARTER_ROUND(x00, x01, x02, x03);

      SALSA20_QUARTER_ROUND(x05, x06, x07, x04);

      SALSA20_QUARTER_ROUND(x10, x11, x08, x09);

      SALSA20_QUARTER_ROUND(x15, x12, x13, x14);

      }

   output[0] = x00;

   output[1] = x05;

   output[2] = x10;

   output[3] = x15;

   output[4] = x06;

   output[5] = x07;

   output[6] = x08;

   output[7] = x09;

   }

/*

* Generate Salsa20 cipher stream

*/

//static

void Salsa20::salsa_core(uint8_t output[64], const uint32_t input[16], size_t rounds)

   {

   BOTAN_ASSERT_NOMSG(rounds % 2 == 0);

   uint32_t x00 = input[ 0], x01 = input[ 1], x02 = input[ 2], x03 = input[ 3],

            x04 = input[ 4], x05 = input[ 5], x06 = input[ 6], x07 = input[ 7],

            x08 = input[ 8], x09 = input[ 9], x10 = input[10], x11 = input[11],

            x12 = input[12], x13 = input[13], x14 = input[14], x15 = input[15];

   for(size_t i = 0; i != rounds / 2; ++i)

      {

      SALSA20_QUARTER_ROUND(x00, x04, x08, x12);

      SALSA20_QUARTER_ROUND(x05, x09, x13, x01);

      SALSA20_QUARTER_ROUND(x10, x14, x02, x06);

      SALSA20_QUARTER_ROUND(x15, x03, x07, x11);

      SALSA20_QUARTER_ROUND(x00, x01, x02, x03);

      SALSA20_QUARTER_ROUND(x05, x06, x07, x04);

      SALSA20_QUARTER_ROUND(x10, x11, x08, x09);

      SALSA20_QUARTER_ROUND(x15, x12, x13, x14);

      }

   store_le(x00 + input[ 0], output + 4 *  0);

   store_le(x01 + input[ 1], output + 4 *  1);

   store_le(x02 + input[ 2], output + 4 *  2);

   store_le(x03 + input[ 3], output + 4 *  3);

   store_le(x04 + input[ 4], output + 4 *  4);

   store_le(x05 + input[ 5], output + 4 *  5);

   store_le(x06 + input[ 6], output + 4 *  6);

   store_le(x07 + input[ 7], output + 4 *  7);

   store_le(x08 + input[ 8], output + 4 *  8);

   store_le(x09 + input[ 9], output + 4 *  9);

   store_le(x10 + input[10], output + 4 * 10);

   store_le(x11 + input[11], output + 4 * 11);

   store_le(x12 + input[12], output + 4 * 12);

   store_le(x13 + input[13], output + 4 * 13);

   store_le(x14 + input[14], output + 4 * 14);

   store_le(x15 + input[15], output + 4 * 15);

   }

#undef SALSA20_QUARTER_ROUND

/*

* Combine cipher stream with message

*/

void Salsa20::cipher(const uint8_t in[], uint8_t out[], size_t length)

   {

   verify_key_set(m_state.empty() == false);

   while(length >= m_buffer.size() - m_position)

      {

      const size_t available = m_buffer.size() - m_position;

      xor_buf(out, in, &m_buffer[m_position], available);

      salsa_core(m_buffer.data(), m_state.data(), 20);

      ++m_state[8];

      m_state[9] += (m_state[8] == 0);

      length -= available;

      in += available;

      out += available;

      m_position = 0;

      }

   xor_buf(out, in, &m_buffer[m_position], length);

   m_position += length;

   }

void Salsa20::initialize_state()

   {

   static const uint32_t TAU[] =

      { 0x61707865, 0x3120646e, 0x79622d36, 0x6b206574 };

   static const uint32_t SIGMA[] =

      { 0x61707865, 0x3320646e, 0x79622d32, 0x6b206574 };

   m_state[1] = m_key[0];

   m_state[2] = m_key[1];

   m_state[3] = m_key[2];

   m_state[4] = m_key[3];

   if(m_key.size() == 4)

      {

      m_state[0] = TAU[0];

      m_state[5] = TAU[1];

      m_state[10] = TAU[2];

      m_state[15] = TAU[3];

      m_state[11] = m_key[0];

      m_state[12] = m_key[1];

      m_state[13] = m_key[2];

      m_state[14] = m_key[3];

      }

   else

      {

      m_state[0] = SIGMA[0];

      m_state[5] = SIGMA[1];

      m_state[10] = SIGMA[2];

      m_state[15] = SIGMA[3];

      m_state[11] = m_key[4];

      m_state[12] = m_key[5];

      m_state[13] = m_key[6];

      m_state[14] = m_key[7];

      }

   m_state[6] = 0;

   m_state[7] = 0;

   m_state[8] = 0;

   m_state[9] = 0;

   m_position = 0;

   }

/*

* Salsa20 Key Schedule

*/

void Salsa20::key_schedule(const uint8_t key[], size_t length)

   {

   m_key.resize(length / 4);

   load_le<uint32_t>(m_key.data(), key, m_key.size());

   m_state.resize(16);

   m_buffer.resize(64);

   set_iv(nullptr, 0);

   }

/*

* Set the Salsa IV

*/

void Salsa20::set_iv(const uint8_t iv[], size_t length)

   {

   verify_key_set(m_state.empty() == false);

   if(!valid_iv_length(length))

      throw Invalid_IV_Length(name(), length);

   initialize_state();

   if(length == 0)

      {

      // Salsa20 null IV

      m_state[6] = 0;

      m_state[7] = 0;

      }

   else if(length == 8)

      {

      // Salsa20

      m_state[6] = load_le<uint32_t>(iv, 0);

      m_state[7] = load_le<uint32_t>(iv, 1);

      }

   else

      {

      // XSalsa20

      m_state[6] = load_le<uint32_t>(iv, 0);

      m_state[7] = load_le<uint32_t>(iv, 1);

      m_state[8] = load_le<uint32_t>(iv, 2);

      m_state[9] = load_le<uint32_t>(iv, 3);

      secure_vector<uint32_t> hsalsa(8);

      hsalsa20(hsalsa.data(), m_state.data());

      m_state[ 1] = hsalsa[0];

      m_state[ 2] = hsalsa[1];

      m_state[ 3] = hsalsa[2];

      m_state[ 4] = hsalsa[3];

      m_state[ 6] = load_le<uint32_t>(iv, 4);

      m_state[ 7] = load_le<uint32_t>(iv, 5);

      m_state[11] = hsalsa[4];

      m_state[12] = hsalsa[5];

      m_state[13] = hsalsa[6];

      m_state[14] = hsalsa[7];

      }

   m_state[8] = 0;

   m_state[9] = 0;

   salsa_core(m_buffer.data(), m_state.data(), 20);

   ++m_state[8];

   m_state[9] += (m_state[8] == 0);

   m_position = 0;

   }

bool Salsa20::valid_iv_length(size_t iv_len) const

   {

   return (iv_len == 0 || iv_len == 8 || iv_len == 24);

   }

size_t Salsa20::default_iv_length() const

   {

   return 24;

   }

Key_Length_Specification Salsa20::key_spec() const

   {

   return Key_Length_Specification(16, 32, 16);

   }

StreamCipher* Salsa20::clone() const

   {

   return new Salsa20;

   }

std::string Salsa20::name() const

   {

   return "Salsa20";

   }

/*

* Clear memory of sensitive data

*/

void Salsa20::clear()

   {

   zap(m_key);

   zap(m_state);

   zap(m_buffer);

   m_position = 0;

   }

void Salsa20::seek(uint64_t offset)

   {

   verify_key_set(m_state.empty() == false);

   // Find the block offset

   const uint64_t counter = offset / 64;

   uint8_t counter8[8];

   store_le(counter, counter8);

   m_state[8]  = load_le<uint32_t>(counter8, 0);

   m_state[9] += load_le<uint32_t>(counter8, 1);

   salsa_core(m_buffer.data(), m_state.data(), 20);

   ++m_state[8];

   m_state[9] += (m_state[8] == 0);

   m_position = offset % 64;

   }

}