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/*********************************************************************

* Filename:   sha256.c

* Author:     Brad Conte (brad AT bradconte.com)

* Copyright:

* Disclaimer: This code is presented "as is" without any guarantees.

* Details:    Implementation of the SHA-256 hashing algorithm.

			  SHA-256 is one of the three algorithms in the SHA2

			  specification. The others, SHA-384 and SHA-512, are not

			  offered in this implementation.

			  Algorithm specification can be found here:

			   * http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf

			  This implementation uses little endian byte order.

*********************************************************************/

/*************************** HEADER FILES ***************************/

#include <stdlib.h>

#include <memory.h>

#include "SHA256.h"

/****************************** MACROS ******************************/

#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))

/**************************** VARIABLES *****************************/

static const uint32_t 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

};

/*********************** FUNCTION DEFINITIONS ***********************/

void sha256_transform(SHA256_CONTEXT* ctx, const uint8_t data[])

{

	uint32_t 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 SHA256Init(SHA256_CONTEXT* ctx)

{

	ctx->datalen = 0;

	ctx->bitlen = 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 SHA256Update(SHA256_CONTEXT* ctx, const uint8_t data[], size_t len)

{

	uint32_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);

			ctx->bitlen += 512;

			ctx->datalen = 0;

		}

	}

}

void SHA256Final(SHA256_CONTEXT* ctx, uint8_t hash[])

{

	uint32_t 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.

	ctx->bitlen += ctx->datalen * 8;

	ctx->data[63] = ctx->bitlen;

	ctx->data[62] = ctx->bitlen >> 8;

	ctx->data[61] = ctx->bitlen >> 16;

	ctx->data[60] = ctx->bitlen >> 24;

	ctx->data[59] = ctx->bitlen >> 32;

	ctx->data[58] = ctx->bitlen >> 40;

	ctx->data[57] = ctx->bitlen >> 48;

	ctx->data[56] = ctx->bitlen >> 56;

	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;

	}

}