text: /*********************************************************************
  * Filename:   sha1.c
  * Author:     Brad Conte (brad AT bradconte.com)
  * Copyright:
  * Disclaimer: This code is presented "as is" without any guarantees.
  * Details:    Implementation of the SHA1 hashing algorithm.
                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 "sha1.h"
  
  /****************************** MACROS ******************************/
  #define ROTLEFT(a, b) ((a << b) | (a >> (32 - b)))
  
  /*********************** FUNCTION DEFINITIONS ***********************/
  void sha1_transform(SHA1_CTX *ctx, const BYTE data[]) {
  	WORD a, b, c, d, e, i, j, t, m[80];
  
  	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 < 80; ++i) {
  		m[i] = (m[i - 3] ^ m[i - 8] ^ m[i - 14] ^ m[i - 16]);
  		m[i] = (m[i] << 1) | (m[i] >> 31);
  	}
  
  	a = ctx->state[0];
  	b = ctx->state[1];
  	c = ctx->state[2];
  	d = ctx->state[3];
  	e = ctx->state[4];
  
  	for (i = 0; i < 20; ++i) {
  		t = ROTLEFT(a, 5) + ((b & c) ^ (~b & d)) + e + ctx->k[0] + m[i];
  		e = d;
  		d = c;
  		c = ROTLEFT(b, 30);
  		b = a;
  		a = t;
  	}
  	for (; i < 40; ++i) {
  		t = ROTLEFT(a, 5) + (b ^ c ^ d) + e + ctx->k[1] + m[i];
  		e = d;
  		d = c;
  		c = ROTLEFT(b, 30);
  		b = a;
  		a = t;
  	}
  	for (; i < 60; ++i) {
  		t = ROTLEFT(a, 5) + ((b & c) ^ (b & d) ^ (c & d)) + e + ctx->k[2] + m[i];
  		e = d;
  		d = c;
  		c = ROTLEFT(b, 30);
  		b = a;
  		a = t;
  	}
  	for (; i < 80; ++i) {
  		t = ROTLEFT(a, 5) + (b ^ c ^ d) + e + ctx->k[3] + m[i];
  		e = d;
  		d = c;
  		c = ROTLEFT(b, 30);
  		b = a;
  		a = t;
  	}
  
  	ctx->state[0] += a;
  	ctx->state[1] += b;
  	ctx->state[2] += c;
  	ctx->state[3] += d;
  	ctx->state[4] += e;
  }
  
  void sha1_init(SHA1_CTX *ctx) {
  	ctx->datalen = 0;
  	ctx->bitlen = 0;
  	ctx->state[0] = 0x67452301;
  	ctx->state[1] = 0xEFCDAB89;
  	ctx->state[2] = 0x98BADCFE;
  	ctx->state[3] = 0x10325476;
  	ctx->state[4] = 0xc3d2e1f0;
  	ctx->k[0] = 0x5a827999;
  	ctx->k[1] = 0x6ed9eba1;
  	ctx->k[2] = 0x8f1bbcdc;
  	ctx->k[3] = 0xca62c1d6;
  }
  
  void sha1_update(SHA1_CTX *ctx, const BYTE data[], size_t len) {
  	size_t i;
  
  	for (i = 0; i < len; ++i) {
  		ctx->data[ctx->datalen] = data[i];
  		ctx->datalen++;
  		if (ctx->datalen == 64) {
  			sha1_transform(ctx, ctx->data);
  			ctx->bitlen += 512;
  			ctx->datalen = 0;
  		}
  	}
  }
  
  void sha1_final(SHA1_CTX *ctx, BYTE hash[]) {
  	WORD 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;
  		sha1_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;
  	sha1_transform(ctx, ctx->data);
  
  	// Since this implementation uses little endian byte ordering and MD 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;
  	}
  }
  