Experimental SHA256 implementation for exploring behavior of compression function

snapsha2.c

#include <stdlib.h>
#include <stdio.h>

#include <string.h>

static const size_t kBlocksizeSHA256 = 64;

// Round constants
static const unsigned int K[] = {
  0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
  0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
  0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
  0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
  0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
  0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
  0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
  0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
};

unsigned int
  H0 = 0x6a09e667,
  H1 = 0xbb67ae85,
  H2 = 0x3c6ef372,
  H3 = 0xa54ff53a,
  H4 = 0x510e527f,
  H5 = 0x9b05688c,
  H6 = 0x1f83d9ab,
  H7 = 0x5be0cd19;

unsigned int RotateRight(unsigned int V, unsigned int shift) {
  return (V >> shift) | (V << (32 - shift));
}

unsigned int ByteSwap(unsigned int V) {
  return ((V & 0xFF000000) >> 24 ) |
    ((V & 0x00FF0000) >> 8 ) |
    ((V & 0x0000FF00) << 8 ) |
    ((V & 0x000000FF) << 24);
}

void SHA256RoundFunction(const unsigned char *message) {
  unsigned int W[64];

  memcpy(W, message, kBlocksizeSHA256);

  for (int i = 0; i < 16; ++i)
    W[i] = ByteSwap(W[i]);

  for (unsigned int i = 16; i < 64; ++i) {
    unsigned int S0 = RotateRight(W[i - 15], 7) ^
                      RotateRight(W[i - 15], 18) ^
                      (W[i - 15] >> 3);
    unsigned int S1 = RotateRight(W[i - 2], 17) ^
                      RotateRight(W[i - 2], 19) ^
                      (W[i - 2] >> 10);

    W[i] = W[i - 16] + W[i - 7] + S0 + S1;
  }

  for (int i = 0; i < 64; ++i)
    printf("%2d: %08x\n", i, W[i]);

  unsigned int
    A = H0,
    B = H1,
    C = H2,
    D = H3,
    E = H4,
    F = H5,
    G = H6,
    H = H7;

  printf("Initial: %08x %08x %08x %08x %08x %08x %08x %08x\n",
	 A, B, C, D, E, F, G, H);



  for (int i = 0; i < 64; ++i) {

    unsigned int S1 = RotateRight(E, 6) ^ RotateRight(E, 11) ^ RotateRight(E, 25);

    unsigned int ch = (E & F) ^ ((~E) & G);

    unsigned int temp1 = H + S1 + ch + K[i] + W[i];

    unsigned int S0 = RotateRight(A, 2) ^ RotateRight(A, 13) ^ RotateRight(A, 22);

    unsigned int majority = (A & B) ^ (A & C) ^ (B & C);

    unsigned int temp2 = S0 + majority;

    H = G;
    G = F;
    F = E;
    E = D + temp1;
    D = C;
    C = B;
    B = A;
    A = temp1 + temp2;

    printf("R%02d: %08X %08X %08X %08X %08X %08X %08X %08X\n",
	   i, A, B, C, D, E, F, G, H);
  }

  A += H0;
  B += H1;
  C += H2;
  D += H3;
  E += H4;
  F += H5;
  G += H6;
  H += H7;

  printf("Final: %08x %08x %08x %08x %08x %08x %08x %08x\n",
	 A, B, C, D, E, F, G, H);

}

void TestRotation() {
  unsigned int test = 0x12345678;
  for (int i = 0; i < 32; ++i)
    printf("%i: %08x\n", i, RotateRight(test, i));
}

int main(int argc, char **argv) {

  union {
    unsigned char bytes[kBlocksizeSHA256];
    unsigned int words[kBlocksizeSHA256 / sizeof(unsigned int)];
  } block = {};

  if (argc == 2) {
    const char *filename = argv[1];

    FILE *fp = fopen(filename, "rb");

    if (fp == NULL)
      return +1;

    int available = fread(block.bytes, 1, kBlocksizeSHA256, fp);
    printf("Read %d bytes.\n", available);
    fclose(fp);

  } else {
    unsigned int word_index = atoi(argv[1]);
    unsigned int word_value = atoi(argv[2]);

    block.words[word_index % kBlocksizeSHA256] = word_value;
  }

  SHA256RoundFunction(block.bytes);

  return 0;
}