text: /*********************************************************************
  * Filename:   md5.c
  * Author:     Brad Conte (brad AT bradconte.com)
  * Copyright:
  * Disclaimer: This code is presented "as is" without any guarantees.
  * Details:    Implementation of the MD5 hashing algorithm.
  				  Algorithm specification can be found here:
  				   * http://tools.ietf.org/html/rfc1321
  				  This implementation uses little endian byte order.
  *********************************************************************/
  
  /*************************** HEADER FILES ***************************/
  #include <stdlib.h>
  #include <memory.h>
  #include "md5.h"
  
  /****************************** MACROS ******************************/
  #define ROTLEFT(a,b) ((a << b) | (a >> (32-b)))
  
  #define F(x,y,z) ((x & y) | (~x & z))
  #define G(x,y,z) ((x & z) | (y & ~z))
  #define H(x,y,z) (x ^ y ^ z)
  #define I(x,y,z) (y ^ (x | ~z))
  
  #define FF(a,b,c,d,m,s,t) { a += F(b,c,d) + m + t; \
                              a = b + ROTLEFT(a,s); }
  #define GG(a,b,c,d,m,s,t) { a += G(b,c,d) + m + t; \
                              a = b + ROTLEFT(a,s); }
  #define HH(a,b,c,d,m,s,t) { a += H(b,c,d) + m + t; \
                              a = b + ROTLEFT(a,s); }
  #define II(a,b,c,d,m,s,t) { a += I(b,c,d) + m + t; \
                              a = b + ROTLEFT(a,s); }
  
  /*********************** FUNCTION DEFINITIONS ***********************/
  void md5_transform(MD5_CTX *ctx, const BYTE data[])
  {
  	WORD a, b, c, d, m[16], i, j;
  
  	// MD5 specifies big endian byte order, but this implementation assumes a little
  	// endian byte order CPU. Reverse all the bytes upon input, and re-reverse them
  	// on output (in md5_final()).
  	for (i = 0, j = 0; i < 16; ++i, j += 4)
  		m[i] = (data[j]) + (data[j + 1] << 8) + (data[j + 2] << 16) + (data[j + 3] << 24);
  
  	a = ctx->state[0];
  	b = ctx->state[1];
  	c = ctx->state[2];
  	d = ctx->state[3];
  
  	FF(a,b,c,d,m[0],  7,0xd76aa478);
  	FF(d,a,b,c,m[1], 12,0xe8c7b756);
  	FF(c,d,a,b,m[2], 17,0x242070db);
  	FF(b,c,d,a,m[3], 22,0xc1bdceee);
  	FF(a,b,c,d,m[4],  7,0xf57c0faf);
  	FF(d,a,b,c,m[5], 12,0x4787c62a);
  	FF(c,d,a,b,m[6], 17,0xa8304613);
  	FF(b,c,d,a,m[7], 22,0xfd469501);
  	FF(a,b,c,d,m[8],  7,0x698098d8);
  	FF(d,a,b,c,m[9], 12,0x8b44f7af);
  	FF(c,d,a,b,m[10],17,0xffff5bb1);
  	FF(b,c,d,a,m[11],22,0x895cd7be);
  	FF(a,b,c,d,m[12], 7,0x6b901122);
  	FF(d,a,b,c,m[13],12,0xfd987193);
  	FF(c,d,a,b,m[14],17,0xa679438e);
  	FF(b,c,d,a,m[15],22,0x49b40821);
  
  	GG(a,b,c,d,m[1],  5,0xf61e2562);
  	GG(d,a,b,c,m[6],  9,0xc040b340);
  	GG(c,d,a,b,m[11],14,0x265e5a51);
  	GG(b,c,d,a,m[0], 20,0xe9b6c7aa);
  	GG(a,b,c,d,m[5],  5,0xd62f105d);
  	GG(d,a,b,c,m[10], 9,0x02441453);
  	GG(c,d,a,b,m[15],14,0xd8a1e681);
  	GG(b,c,d,a,m[4], 20,0xe7d3fbc8);
  	GG(a,b,c,d,m[9],  5,0x21e1cde6);
  	GG(d,a,b,c,m[14], 9,0xc33707d6);
  	GG(c,d,a,b,m[3], 14,0xf4d50d87);
  	GG(b,c,d,a,m[8], 20,0x455a14ed);
  	GG(a,b,c,d,m[13], 5,0xa9e3e905);
  	GG(d,a,b,c,m[2],  9,0xfcefa3f8);
  	GG(c,d,a,b,m[7], 14,0x676f02d9);
  	GG(b,c,d,a,m[12],20,0x8d2a4c8a);
  
  	HH(a,b,c,d,m[5],  4,0xfffa3942);
  	HH(d,a,b,c,m[8], 11,0x8771f681);
  	HH(c,d,a,b,m[11],16,0x6d9d6122);
  	HH(b,c,d,a,m[14],23,0xfde5380c);
  	HH(a,b,c,d,m[1],  4,0xa4beea44);
  	HH(d,a,b,c,m[4], 11,0x4bdecfa9);
  	HH(c,d,a,b,m[7], 16,0xf6bb4b60);
  	HH(b,c,d,a,m[10],23,0xbebfbc70);
  	HH(a,b,c,d,m[13], 4,0x289b7ec6);
  	HH(d,a,b,c,m[0], 11,0xeaa127fa);
  	HH(c,d,a,b,m[3], 16,0xd4ef3085);
  	HH(b,c,d,a,m[6], 23,0x04881d05);
  	HH(a,b,c,d,m[9],  4,0xd9d4d039);
  	HH(d,a,b,c,m[12],11,0xe6db99e5);
  	HH(c,d,a,b,m[15],16,0x1fa27cf8);
  	HH(b,c,d,a,m[2], 23,0xc4ac5665);
  
  	II(a,b,c,d,m[0],  6,0xf4292244);
  	II(d,a,b,c,m[7], 10,0x432aff97);
  	II(c,d,a,b,m[14],15,0xab9423a7);
  	II(b,c,d,a,m[5], 21,0xfc93a039);
  	II(a,b,c,d,m[12], 6,0x655b59c3);
  	II(d,a,b,c,m[3], 10,0x8f0ccc92);
  	II(c,d,a,b,m[10],15,0xffeff47d);
  	II(b,c,d,a,m[1], 21,0x85845dd1);
  	II(a,b,c,d,m[8],  6,0x6fa87e4f);
  	II(d,a,b,c,m[15],10,0xfe2ce6e0);
  	II(c,d,a,b,m[6], 15,0xa3014314);
  	II(b,c,d,a,m[13],21,0x4e0811a1);
  	II(a,b,c,d,m[4],  6,0xf7537e82);
  	II(d,a,b,c,m[11],10,0xbd3af235);
  	II(c,d,a,b,m[2], 15,0x2ad7d2bb);
  	II(b,c,d,a,m[9], 21,0xeb86d391);
  
  	ctx->state[0] += a;
  	ctx->state[1] += b;
  	ctx->state[2] += c;
  	ctx->state[3] += d;
  }
  
  void md5_init(MD5_CTX *ctx)
  {
  	ctx->datalen = 0;
  	ctx->bitlen = 0;
  	ctx->state[0] = 0x67452301;
  	ctx->state[1] = 0xEFCDAB89;
  	ctx->state[2] = 0x98BADCFE;
  	ctx->state[3] = 0x10325476;
  }
  
  void md5_update(MD5_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) {
  			md5_transform(ctx, ctx->data);
  			ctx->bitlen += 512;
  			ctx->datalen = 0;
  		}
  	}
  }
  
  void md5_final(MD5_CTX *ctx, BYTE hash[])
  {
  	size_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 if (ctx->datalen >= 56) {
  		ctx->data[i++] = 0x80;
  		while (i < 64)
  			ctx->data[i++] = 0x00;
  		md5_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[56] = ctx->bitlen;
  	ctx->data[57] = ctx->bitlen >> 8;
  	ctx->data[58] = ctx->bitlen >> 16;
  	ctx->data[59] = ctx->bitlen >> 24;
  	ctx->data[60] = ctx->bitlen >> 32;
  	ctx->data[61] = ctx->bitlen >> 40;
  	ctx->data[62] = ctx->bitlen >> 48;
  	ctx->data[63] = ctx->bitlen >> 56;
  	md5_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] >> (i * 8)) & 0x000000ff;
  		hash[i + 4]  = (ctx->state[1] >> (i * 8)) & 0x000000ff;
  		hash[i + 8]  = (ctx->state[2] >> (i * 8)) & 0x000000ff;
  		hash[i + 12] = (ctx->state[3] >> (i * 8)) & 0x000000ff;
  	}
  }
  