chacha.cpp

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/*
* ChaCha
* (C) 2014,2018,2023 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
 
#include <botan/internal/chacha.h>
 
#include <botan/exceptn.h>
#include <botan/internal/fmt.h>
#include <botan/internal/loadstor.h>
#include <botan/internal/rotate.h>
 
#if defined(BOTAN_HAS_CPUID)
   #include <botan/internal/cpuid.h>
#endif
 
namespace Botan {
 
namespace {
 
/*
* RFC 8439 defines ChaCha with 96-bit nonces by stealing one of the
* words used for the block counter. With 64-bit nonces, the block
* counter is also 64 bits and practically not exhaustible.
*/
constexpr uint64_t chacha_96bit_nonce_cap = uint64_t{1} << 38;
 
inline void chacha_quarter_round(uint32_t& a, uint32_t& b, uint32_t& c, uint32_t& d) {
   a += b;
   d ^= a;
   d = rotl<16>(d);
   c += d;
   b ^= c;
   b = rotl<12>(b);
   a += b;
   d ^= a;
   d = rotl<8>(d);
   c += d;
   b ^= c;
   b = rotl<7>(b);
}
 
/*
* Generate HChaCha cipher stream (for XChaCha IV setup)
*/
void hchacha(uint32_t output[8], const uint32_t input[16], size_t rounds) {
   BOTAN_ASSERT(rounds % 2 == 0, "Valid rounds");
 
   uint32_t x00 = input[0];
   uint32_t x01 = input[1];
   uint32_t x02 = input[2];
   uint32_t x03 = input[3];
   uint32_t x04 = input[4];
   uint32_t x05 = input[5];
   uint32_t x06 = input[6];
   uint32_t x07 = input[7];
   uint32_t x08 = input[8];
   uint32_t x09 = input[9];
   uint32_t x10 = input[10];
   uint32_t x11 = input[11];
   uint32_t x12 = input[12];
   uint32_t x13 = input[13];
   uint32_t x14 = input[14];
   uint32_t x15 = input[15];
 
   for(size_t i = 0; i != rounds / 2; ++i) {
      chacha_quarter_round(x00, x04, x08, x12);
      chacha_quarter_round(x01, x05, x09, x13);
      chacha_quarter_round(x02, x06, x10, x14);
      chacha_quarter_round(x03, x07, x11, x15);
 
      chacha_quarter_round(x00, x05, x10, x15);
      chacha_quarter_round(x01, x06, x11, x12);
      chacha_quarter_round(x02, x07, x08, x13);
      chacha_quarter_round(x03, x04, x09, x14);
   }
 
   output[0] = x00;
   output[1] = x01;
   output[2] = x02;
   output[3] = x03;
   output[4] = x12;
   output[5] = x13;
   output[6] = x14;
   output[7] = x15;
}
 
}  // namespace
 
ChaCha::ChaCha(size_t rounds) : m_rounds(rounds) {
   BOTAN_ARG_CHECK(m_rounds == 8 || m_rounds == 12 || m_rounds == 20, "ChaCha only supports 8, 12 or 20 rounds");
}
 
size_t ChaCha::parallelism() {
#if defined(BOTAN_HAS_CHACHA_AVX512)
   if(CPUID::has(CPUID::Feature::AVX512)) {
      return 16;
   }
#endif
 
#if defined(BOTAN_HAS_CHACHA_AVX2)
   if(CPUID::has(CPUID::Feature::AVX2)) {
      return 8;
   }
#endif
 
   return 4;
}
 
std::string ChaCha::provider() const {
#if defined(BOTAN_HAS_CHACHA_AVX512)
   if(auto feat = CPUID::check(CPUID::Feature::AVX512)) {
      return *feat;
   }
#endif
 
#if defined(BOTAN_HAS_CHACHA_AVX2)
   if(auto feat = CPUID::check(CPUID::Feature::AVX2)) {
      return *feat;
   }
#endif
 
#if defined(BOTAN_HAS_CHACHA_SIMD32)
   if(auto feat = CPUID::check(CPUID::Feature::SIMD_4X32)) {
      return *feat;
   }
#endif
 
   return "base";
}
 
void ChaCha::chacha(uint8_t output[], size_t output_blocks, uint32_t state[16], size_t rounds) {
   BOTAN_ASSERT(rounds % 2 == 0, "Valid rounds");
 
#if defined(BOTAN_HAS_CHACHA_AVX512)
   if(CPUID::has(CPUID::Feature::AVX512)) {
      while(output_blocks >= 16) {
         ChaCha::chacha_avx512_x16(output, state, rounds);
         output += 16 * 64;
         output_blocks -= 16;
      }
   }
#endif
 
#if defined(BOTAN_HAS_CHACHA_AVX2)
   if(CPUID::has(CPUID::Feature::AVX2)) {
      while(output_blocks >= 8) {
         ChaCha::chacha_avx2_x8(output, state, rounds);
         output += 8 * 64;
         output_blocks -= 8;
      }
   }
#endif
 
#if defined(BOTAN_HAS_CHACHA_SIMD32)
   if(CPUID::has(CPUID::Feature::SIMD_4X32)) {
      while(output_blocks >= 4) {
         ChaCha::chacha_simd32_x4(output, state, rounds);
         output += 4 * 64;
         output_blocks -= 4;
      }
   }
#endif
 
   // TODO interleave rounds
   for(size_t i = 0; i != output_blocks; ++i) {
      uint32_t x00 = state[0];
      uint32_t x01 = state[1];
      uint32_t x02 = state[2];
      uint32_t x03 = state[3];
      uint32_t x04 = state[4];
      uint32_t x05 = state[5];
      uint32_t x06 = state[6];
      uint32_t x07 = state[7];
      uint32_t x08 = state[8];
      uint32_t x09 = state[9];
      uint32_t x10 = state[10];
      uint32_t x11 = state[11];
      uint32_t x12 = state[12];
      uint32_t x13 = state[13];
      uint32_t x14 = state[14];
      uint32_t x15 = state[15];
 
      for(size_t r = 0; r != rounds / 2; ++r) {
         chacha_quarter_round(x00, x04, x08, x12);
         chacha_quarter_round(x01, x05, x09, x13);
         chacha_quarter_round(x02, x06, x10, x14);
         chacha_quarter_round(x03, x07, x11, x15);
 
         chacha_quarter_round(x00, x05, x10, x15);
         chacha_quarter_round(x01, x06, x11, x12);
         chacha_quarter_round(x02, x07, x08, x13);
         chacha_quarter_round(x03, x04, x09, x14);
      }
 
      x00 += state[0];
      x01 += state[1];
      x02 += state[2];
      x03 += state[3];
      x04 += state[4];
      x05 += state[5];
      x06 += state[6];
      x07 += state[7];
      x08 += state[8];
      x09 += state[9];
      x10 += state[10];
      x11 += state[11];
      x12 += state[12];
      x13 += state[13];
      x14 += state[14];
      x15 += state[15];
 
      store_le(x00, output + 64 * i + 4 * 0);
      store_le(x01, output + 64 * i + 4 * 1);
      store_le(x02, output + 64 * i + 4 * 2);
      store_le(x03, output + 64 * i + 4 * 3);
      store_le(x04, output + 64 * i + 4 * 4);
      store_le(x05, output + 64 * i + 4 * 5);
      store_le(x06, output + 64 * i + 4 * 6);
      store_le(x07, output + 64 * i + 4 * 7);
      store_le(x08, output + 64 * i + 4 * 8);
      store_le(x09, output + 64 * i + 4 * 9);
      store_le(x10, output + 64 * i + 4 * 10);
      store_le(x11, output + 64 * i + 4 * 11);
      store_le(x12, output + 64 * i + 4 * 12);
      store_le(x13, output + 64 * i + 4 * 13);
      store_le(x14, output + 64 * i + 4 * 14);
      store_le(x15, output + 64 * i + 4 * 15);
 
      state[12]++;
      if(state[12] == 0) {
         state[13] += 1;
      }
   }
}
 
/*
* Combine cipher stream with message
*/
void ChaCha::cipher_bytes(const uint8_t in[], uint8_t out[], size_t length) {
   assert_key_material_set();
 
   if(m_iv_length == 12) {
      if(length > m_bytes_remaining) {
         throw Invalid_State("ChaCha 96-bit nonce keystream exhausted");
      }
      m_bytes_remaining -= length;
   }
 
   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);
      chacha(m_buffer.data(), m_buffer.size() / 64, m_state.data(), m_rounds);
 
      length -= available;
      in += available;
      out += available;
      m_position = 0;
   }
 
   xor_buf(out, in, &m_buffer[m_position], length);
 
   m_position += length;
}
 
void ChaCha::generate_keystream(uint8_t out[], size_t length) {
   assert_key_material_set();
 
   if(m_iv_length == 12) {
      if(length > m_bytes_remaining) {
         throw Invalid_State("ChaCha 96-bit nonce keystream exhausted");
      }
      m_bytes_remaining -= length;
   }
 
   while(length >= m_buffer.size() - m_position) {
      const size_t available = m_buffer.size() - m_position;
 
      // TODO: this could write directly to the output buffer
      // instead of bouncing it through m_buffer first
      copy_mem(out, &m_buffer[m_position], available);
      chacha(m_buffer.data(), m_buffer.size() / 64, m_state.data(), m_rounds);
 
      length -= available;
      out += available;
      m_position = 0;
   }
 
   copy_mem(out, &m_buffer[m_position], length);
 
   m_position += length;
}
 
void ChaCha::initialize_state() {
   static const uint32_t TAU[] = {0x61707865, 0x3120646e, 0x79622d36, 0x6b206574};
 
   static const uint32_t SIGMA[] = {0x61707865, 0x3320646e, 0x79622d32, 0x6b206574};
 
   m_state[4] = m_key[0];
   m_state[5] = m_key[1];
   m_state[6] = m_key[2];
   m_state[7] = m_key[3];
 
   if(m_key.size() == 4) {
      m_state[0] = TAU[0];
      m_state[1] = TAU[1];
      m_state[2] = TAU[2];
      m_state[3] = TAU[3];
 
      m_state[8] = m_key[0];
      m_state[9] = m_key[1];
      m_state[10] = m_key[2];
      m_state[11] = m_key[3];
   } else {
      m_state[0] = SIGMA[0];
      m_state[1] = SIGMA[1];
      m_state[2] = SIGMA[2];
      m_state[3] = SIGMA[3];
 
      m_state[8] = m_key[4];
      m_state[9] = m_key[5];
      m_state[10] = m_key[6];
      m_state[11] = m_key[7];
   }
 
   m_state[12] = 0;
   m_state[13] = 0;
   m_state[14] = 0;
   m_state[15] = 0;
 
   m_position = 0;
}
 
bool ChaCha::has_keying_material() const {
   return !m_state.empty();
}
 
size_t ChaCha::buffer_size() const {
   return 64;
}
 
/*
* ChaCha Key Schedule
*/
void ChaCha::key_schedule(std::span<const uint8_t> key) {
   m_key.resize(key.size() / 4);
   load_le<uint32_t>(m_key.data(), key.data(), m_key.size());
 
   m_state.resize(16);
 
   const size_t chacha_block = 64;
   m_buffer.resize(parallelism() * chacha_block);
 
   set_iv(nullptr, 0);
}
 
size_t ChaCha::default_iv_length() const {
   return 24;
}
 
Key_Length_Specification ChaCha::key_spec() const {
   return Key_Length_Specification(16, 32, 16);
}
 
std::unique_ptr<StreamCipher> ChaCha::new_object() const {
   return std::make_unique<ChaCha>(m_rounds);
}
 
bool ChaCha::valid_iv_length(size_t iv_len) const {
   return (iv_len == 0 || iv_len == 8 || iv_len == 12 || iv_len == 24);
}
 
void ChaCha::set_iv_bytes(const uint8_t iv[], size_t length) {
   assert_key_material_set();
 
   if(!valid_iv_length(length)) {
      throw Invalid_IV_Length(name(), length);
   }
 
   initialize_state();
 
   if(length == 0) {
      // Treat zero length IV same as an all-zero IV
      m_state[14] = 0;
      m_state[15] = 0;
   } else if(length == 8) {
      m_state[14] = load_le<uint32_t>(iv, 0);
      m_state[15] = load_le<uint32_t>(iv, 1);
   } else if(length == 12) {
      m_state[13] = load_le<uint32_t>(iv, 0);
      m_state[14] = load_le<uint32_t>(iv, 1);
      m_state[15] = load_le<uint32_t>(iv, 2);
   } else if(length == 24) {
      m_state[12] = load_le<uint32_t>(iv, 0);
      m_state[13] = load_le<uint32_t>(iv, 1);
      m_state[14] = load_le<uint32_t>(iv, 2);
      m_state[15] = load_le<uint32_t>(iv, 3);
 
      secure_vector<uint32_t> hc(8);
      hchacha(hc.data(), m_state.data(), m_rounds);
 
      m_state[4] = hc[0];
      m_state[5] = hc[1];
      m_state[6] = hc[2];
      m_state[7] = hc[3];
      m_state[8] = hc[4];
      m_state[9] = hc[5];
      m_state[10] = hc[6];
      m_state[11] = hc[7];
      m_state[12] = 0;
      m_state[13] = 0;
      m_state[14] = load_le<uint32_t>(iv, 4);
      m_state[15] = load_le<uint32_t>(iv, 5);
   }
 
   m_iv_length = length;
   m_state13_post_iv = m_state[13];
   if(length == 12) {
      m_bytes_remaining = chacha_96bit_nonce_cap;
   }
 
   chacha(m_buffer.data(), m_buffer.size() / 64, m_state.data(), m_rounds);
   m_position = 0;
}
 
void ChaCha::clear() {
   zap(m_key);
   zap(m_state);
   zap(m_buffer);
   m_position = 0;
   m_iv_length = 0;
   m_state13_post_iv = 0;
   m_bytes_remaining = 0;
}
 
std::optional<uint64_t> ChaCha::remaining_keystream_bytes() const {
   if(!has_keying_material() || m_iv_length != 12) {
      return std::nullopt;
   }
   return m_bytes_remaining;
}
 
std::string ChaCha::name() const {
   return fmt("ChaCha({})", m_rounds);
}
 
void ChaCha::seek(uint64_t offset) {
   assert_key_material_set();
 
   const uint64_t block = offset / 64;
 
   if(m_iv_length == 12) {
      // 96 bit nonce implies a 32-bit counter; prevent seeking beyond that
      if((block >> 32) != 0) {
         throw Invalid_Argument("ChaCha::seek with 96-bit nonce limited to 2^32 blocks (256 GiB)");
      }
      m_state[12] = static_cast<uint32_t>(block);
      m_state[13] = m_state13_post_iv;
      m_bytes_remaining = chacha_96bit_nonce_cap - offset;
   } else {
      // 64-bit block counter spanning state words 12 and 13.
      m_state[12] = static_cast<uint32_t>(block);
      m_state[13] = m_state13_post_iv + static_cast<uint32_t>(block >> 32);
   }
 
   chacha(m_buffer.data(), m_buffer.size() / 64, m_state.data(), m_rounds);
   m_position = offset % 64;
}
}  // namespace Botan