sha256.c

#define uchar unsigned char		// 8-bit byte
#define uint unsigned int		// 32-bit word

// DBL_INT_ADD treats two unsigned ints a and b as one 64-bit integer and adds c to it
#define DBL_INT_ADD(a,b,c) if (a > 0xffffffff - (c)) ++b; a += c;
#define ROTLEFT(a,b) (((a) << (b)) | ((a) >> (32-(b))))
#define ROTRIGHT(a,b) (((a) >> (b)) | ((a) << (32-(b))))

#define CH(x,y,z) (((x) & (y)) ^ (~(x) & (z)))
#define MAJ(x,y,z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
#define EP0(x) (ROTRIGHT(x,2) ^ ROTRIGHT(x,13) ^ ROTRIGHT(x,22))
#define EP1(x) (ROTRIGHT(x,6) ^ ROTRIGHT(x,11) ^ ROTRIGHT(x,25))
#define SIG0(x) (ROTRIGHT(x,7) ^ ROTRIGHT(x,18) ^ ((x) >> 3))
#define SIG1(x) (ROTRIGHT(x,17) ^ ROTRIGHT(x,19) ^ ((x) >> 10))

typedef struct
{
	uchar data[64];
	uint datalen;
	uint bitlen[2];
	uint state[8];
} SHA256_CTX;

uint k[64] = {
	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
};


void sha256_transform(SHA256_CTX * ctx, uchar data[])
{

	uint a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];

	for (i = 0, j = 0; i < 16; ++i, j += 4)
		m[i] =
			(data[j] << 24) | (data[j + 1] << 16) | (data[j + 2] << 8) |
			(data[j + 3]);
	for (; i < 64; ++i)
		m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];

	a = ctx->state[0];
	b = ctx->state[1];
	c = ctx->state[2];
	d = ctx->state[3];
	e = ctx->state[4];
	f = ctx->state[5];
	g = ctx->state[6];
	h = ctx->state[7];

	for (i = 0; i < 64; ++i)
	{
		t1 = h + EP1(e) + CH(e, f, g) + k[i] + m[i];
		t2 = EP0(a) + MAJ(a, b, c);
		h = g;
		g = f;
		f = e;
		e = d + t1;
		d = c;
		c = b;
		b = a;
		a = t1 + t2;
	}

	ctx->state[0] += a;
	ctx->state[1] += b;
	ctx->state[2] += c;
	ctx->state[3] += d;
	ctx->state[4] += e;
	ctx->state[5] += f;
	ctx->state[6] += g;
	ctx->state[7] += h;
}

void sha256_init(SHA256_CTX * ctx)
{
	ctx->datalen = 0;
	ctx->bitlen[0] = 0;
	ctx->bitlen[1] = 0;
	ctx->state[0] = 0x6a09e667;
	ctx->state[1] = 0xbb67ae85;
	ctx->state[2] = 0x3c6ef372;
	ctx->state[3] = 0xa54ff53a;
	ctx->state[4] = 0x510e527f;
	ctx->state[5] = 0x9b05688c;
	ctx->state[6] = 0x1f83d9ab;
	ctx->state[7] = 0x5be0cd19;
}

void sha256_update(SHA256_CTX * ctx, uchar data[], uint len)
{
	uint t, i;
	for (i = 0; i < len; ++i)
	{
		ctx->data[ctx->datalen] = data[i];
		ctx->datalen++;
		if (ctx->datalen == 64)
		{
			sha256_transform(ctx, ctx->data);
			DBL_INT_ADD(ctx->bitlen[0], ctx->bitlen[1], 512);
			ctx->datalen = 0;
		}
	}
}

void sha256_final(SHA256_CTX * ctx, uchar hash[], int *result, int size, int P)
{
	uint i;

	i = ctx->datalen;

	// Pad whatever data is left in the buffer. 
	if (ctx->datalen < 56)
	{
		ctx->data[i++] = 0x80;
		while (i < 56)
			ctx->data[i++] = 0x00;
	}
	else
	{
		ctx->data[i++] = 0x80;
		while (i < 64)
			ctx->data[i++] = 0x00;
		sha256_transform(ctx, ctx->data);
		memset(ctx->data, 0, 56);
	}

	// Append to the padding the total message's length in bits and transform. 
	DBL_INT_ADD(ctx->bitlen[0], ctx->bitlen[1], ctx->datalen * 8);
	ctx->data[63] = ctx->bitlen[0];
	ctx->data[62] = ctx->bitlen[0] >> 8;
	ctx->data[61] = ctx->bitlen[0] >> 16;
	ctx->data[60] = ctx->bitlen[0] >> 24;
	ctx->data[59] = ctx->bitlen[1];
	ctx->data[58] = ctx->bitlen[1] >> 8;
	ctx->data[57] = ctx->bitlen[1] >> 16;
	ctx->data[56] = ctx->bitlen[1] >> 24;
	sha256_transform(ctx, ctx->data);

	// Since this implementation uses little endian byte ordering and SHA uses big endian,
	// reverse all the bytes when copying the final state to the output hash. 
	for (i = 0; i < 4; ++i)
	{
		hash[i] = (ctx->state[0] >> (24 - i * 8)) & 0x000000ff;
		hash[i + 4] = (ctx->state[1] >> (24 - i * 8)) & 0x000000ff;
		hash[i + 8] = (ctx->state[2] >> (24 - i * 8)) & 0x000000ff;
		hash[i + 12] = (ctx->state[3] >> (24 - i * 8)) & 0x000000ff;
		hash[i + 16] = (ctx->state[4] >> (24 - i * 8)) & 0x000000ff;
		hash[i + 20] = (ctx->state[5] >> (24 - i * 8)) & 0x000000ff;
		hash[i + 24] = (ctx->state[6] >> (24 - i * 8)) & 0x000000ff;
		hash[i + 28] = (ctx->state[7] >> (24 - i * 8)) & 0x000000ff;
	}
	//~ Hash to integer q
	char *buf = malloc(size + 3);
	printf(" - sha256(m):\t");
	for (i = 0; i < size; ++i)
	{
		printf("%02x ", hash[i]);

		//~ Convert hash to integer
		char tmp[size];
		snprintf(tmp, size, "%02x", hash[i]);
		strcpy(buf, "0x");
		strcat(buf, tmp);
		unsigned long un = strtoul(tmp, NULL, 16);
		*result += (un % P);
	}
}