main.c

/*
MIT License
Copyright (c) 2020 Chiro Hiro <chiro8x@gmail.com>
*/

#include <stdio.h>
#include <string.h>
#include <immintrin.h>

// Global seed value
__m256i seed;

// Use SSE2 perform pesudo random for given seed
__m128i xor_shift_plus_pro()
{
  // t = 0
  __m128i t = _mm_setzero_si128();
  // s = 0
  __m128i s = _mm_setzero_si128();
  // t = seed >> 128
  // s = seed & 0xffffffffffffffff
  _mm256_storeu2_m128i(&t, &s, seed);
  // t ^= t << 23;
  t = _mm_xor_si128(t, _mm_bslli_si128(t, 23));
  // t ^= t >> 17;
  t = _mm_xor_si128(t, _mm_bsrli_si128(t, 17));
  // t ^= s ^ (t >> 26)
  t = _mm_xor_si128(t, _mm_xor_si128(s, _mm_bsrli_si128(t, 26)));
  // seed = (s << 128) | t
  seed = _mm256_set_m128i(s, t);
  return _mm_add_epi32(s, t);
}

// Xor plaintext by 128 bits 
char *xor_shit(char *plaintext)
{
  char *ciphertext = malloc(65);
  __m128i message;
  __m128i key;
  __m128i cipher;
  // Xor 128 bits
  for (int c = 0; c < 64; c += 16)
  {
    key = xor_shift_plus_pro();
    message = _mm_loadu_si128((const __m128i *)(plaintext + c));
    // Xor each 128 bits
    cipher = _mm_xor_si128(key, message);
    // Store cipher text
    _mm_storeu_si128((__m128i *)(ciphertext + c), cipher);
  }
  // String terminate NULL
  ciphertext[64] = 0;
  return ciphertext;
}

// Print hex string to console
void printHex(char *str)
{
  size_t l = strlen(str);
  for (int i = 0; i < l; i++)
  {
    printf("%x", (unsigned char)(str[i] & 0xff));
  }
  printf("\n");
}

// Build: clang main.c -mavx -o main && ./main
int main()
{
  // Seed with example key
  seed = _mm256_set_epi32(0xee4877a9,
                          0x5010c9c1,
                          0xaa807d3c,
                          0x354f178a,
                          0x980a7ce2,
                          0xbd66205a,
                          0xdcb4218a,
                          0x28ba8b49);
  // 64 bytes of plaintext
  char *plaintext = "Lorem ipsum dolor sit amet, consectetur adipiscing elit gravida.";
  char *ciphertext = xor_shit(plaintext);
  printf("plaintext:\t%s\n", plaintext);
  
  // Print ciphertext
  printf("ciphertext:\t");
  printHex(ciphertext);

  // Reset seed with the same key
  seed = _mm256_set_epi32(0xee4877a9,
                          0x5010c9c1,
                          0xaa807d3c,
                          0x354f178a,
                          0x980a7ce2,
                          0xbd66205a,
                          0xdcb4218a,
                          0x28ba8b49);
  char *deciphertext = xor_shit(ciphertext);
  printf("Deciphertext:\t%s\n", deciphertext);

  // Free result
  free(deciphertext);
  free(ciphertext);
}