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/*********************************************************************
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* Filename:   sha256.c
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* Author:     Brad Conte (brad AT bradconte.com)
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* Copyright:
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* Disclaimer: This code is presented "as is" without any guarantees.
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* Details:    Implementation of the SHA-256 hashing algorithm.
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              SHA-256 is one of the three algorithms in the SHA2
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              specification. The others, SHA-384 and SHA-512, are not
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              offered in this implementation.
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              Algorithm specification can be found here:
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               * http://csrc.nist.gov/publications/fips/fips180-2/fips180-2withchangenotice.pdf
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              This implementation uses little endian byte order.
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*********************************************************************/
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/*************************** HEADER FILES ***************************/
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#include <stdlib.h>
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#include <memory.h>
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#include "sha256.h"
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/****************************** MACROS ******************************/
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#define ROTLEFT(a,b) (((a) << (b)) | ((a) >> (32-(b))))
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#define ROTRIGHT(a,b) (((a) >> (b)) | ((a) << (32-(b))))
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#define CH(x,y,z) (((x) & (y)) ^ (~(x) & (z)))
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#define MAJ(x,y,z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
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#define EP0(x) (ROTRIGHT(x,2) ^ ROTRIGHT(x,13) ^ ROTRIGHT(x,22))
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#define EP1(x) (ROTRIGHT(x,6) ^ ROTRIGHT(x,11) ^ ROTRIGHT(x,25))
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#define SIG0(x) (ROTRIGHT(x,7) ^ ROTRIGHT(x,18) ^ ((x) >> 3))
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#define SIG1(x) (ROTRIGHT(x,17) ^ ROTRIGHT(x,19) ^ ((x) >> 10))
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/**************************** VARIABLES *****************************/
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static const WORD k[64] = {
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	0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
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	0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
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	0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
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	0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
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	0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
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	0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
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	0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
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	0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
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};
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/*********************** FUNCTION DEFINITIONS ***********************/
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void sha256_transform(SHA256_CTX *ctx, const BYTE data[])
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{
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	WORD a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];
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	for (i = 0, j = 0; i < 16; ++i, j += 4)
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		m[i] = (data[j] << 24) | (data[j + 1] << 16) | (data[j + 2] << 8) | (data[j + 3]);
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	for ( ; i < 64; ++i)
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		m[i] = SIG1(m[i - 2]) + m[i - 7] + SIG0(m[i - 15]) + m[i - 16];
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	a = ctx->state[0];
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	b = ctx->state[1];
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	c = ctx->state[2];
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	d = ctx->state[3];
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	e = ctx->state[4];
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	f = ctx->state[5];
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	g = ctx->state[6];
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	h = ctx->state[7];
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	for (i = 0; i < 64; ++i) {
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		t1 = h + EP1(e) + CH(e,f,g) + k[i] + m[i];
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		t2 = EP0(a) + MAJ(a,b,c);
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		h = g;
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		g = f;
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		f = e;
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		e = d + t1;
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		d = c;
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		c = b;
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		b = a;
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		a = t1 + t2;
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	}
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	ctx->state[0] += a;
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	ctx->state[1] += b;
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	ctx->state[2] += c;
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	ctx->state[3] += d;
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	ctx->state[4] += e;
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	ctx->state[5] += f;
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	ctx->state[6] += g;
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	ctx->state[7] += h;
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}
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void sha256_init(SHA256_CTX *ctx)
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{
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	ctx->datalen = 0;
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	ctx->bitlen = 0;
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	ctx->state[0] = 0x6a09e667;
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	ctx->state[1] = 0xbb67ae85;
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	ctx->state[2] = 0x3c6ef372;
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	ctx->state[3] = 0xa54ff53a;
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	ctx->state[4] = 0x510e527f;
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	ctx->state[5] = 0x9b05688c;
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	ctx->state[6] = 0x1f83d9ab;
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	ctx->state[7] = 0x5be0cd19;
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}
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void sha256_update(SHA256_CTX *ctx, const BYTE data[], size_t len)
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{
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	WORD i;
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	for (i = 0; i < len; ++i) {
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		ctx->data[ctx->datalen] = data[i];
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		ctx->datalen++;
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		if (ctx->datalen == 64) {
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			sha256_transform(ctx, ctx->data);
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			ctx->bitlen += 512;
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			ctx->datalen = 0;
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		}
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	}
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}
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void sha256_final(SHA256_CTX *ctx, BYTE hash[])
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{
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	WORD i;
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	i = ctx->datalen;
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	// Pad whatever data is left in the buffer.
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	if (ctx->datalen < 56) {
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		ctx->data[i++] = 0x80;
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		while (i < 56)
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			ctx->data[i++] = 0x00;
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	}
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	else {
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		ctx->data[i++] = 0x80;
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		while (i < 64)
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			ctx->data[i++] = 0x00;
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		sha256_transform(ctx, ctx->data);
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		memset(ctx->data, 0, 56);
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	}
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	// Append to the padding the total message's length in bits and transform.
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	ctx->bitlen += ctx->datalen * 8;
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	ctx->data[63] = ctx->bitlen;
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	ctx->data[62] = ctx->bitlen >> 8;
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	ctx->data[61] = ctx->bitlen >> 16;
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	ctx->data[60] = ctx->bitlen >> 24;
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	ctx->data[59] = ctx->bitlen >> 32;
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	ctx->data[58] = ctx->bitlen >> 40;
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	ctx->data[57] = ctx->bitlen >> 48;
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	ctx->data[56] = ctx->bitlen >> 56;
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	sha256_transform(ctx, ctx->data);
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	// Since this implementation uses little endian byte ordering and SHA uses big endian,
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	// reverse all the bytes when copying the final state to the output hash.
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	for (i = 0; i < 4; ++i) {
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		hash[i]      = (ctx->state[0] >> (24 - i * 8)) & 0x000000ff;
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		hash[i + 4]  = (ctx->state[1] >> (24 - i * 8)) & 0x000000ff;
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		hash[i + 8]  = (ctx->state[2] >> (24 - i * 8)) & 0x000000ff;
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		hash[i + 12] = (ctx->state[3] >> (24 - i * 8)) & 0x000000ff;
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		hash[i + 16] = (ctx->state[4] >> (24 - i * 8)) & 0x000000ff;
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		hash[i + 20] = (ctx->state[5] >> (24 - i * 8)) & 0x000000ff;
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		hash[i + 24] = (ctx->state[6] >> (24 - i * 8)) & 0x000000ff;
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		hash[i + 28] = (ctx->state[7] >> (24 - i * 8)) & 0x000000ff;
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	}
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}
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