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// Code by: B-Con (http://b-con.us)
// Released under the GNU GPL
// MD5 Hash Digest implementation (little endian byte order)


// Bah, signed variables are for wimps
#define uchar unsigned char
#define uint unsigned int

// 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 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); }


typedef struct {
   uchar data[64];
   uint datalen;
   uint bitlen[2];
   uint state[4];
} MD5_CTX;


void md5_transform(MD5_CTX *ctx, uchar data[])
{
   uint 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] = 0;
   ctx->bitlen[1] = 0;
   ctx->state[0] = 0x67452301;
   ctx->state[1] = 0xEFCDAB89;
   ctx->state[2] = 0x98BADCFE;
   ctx->state[3] = 0x10325476;
}

void md5_update(MD5_CTX *ctx, uchar data[], uint len)
{
   uint i;

   for (i=0; i < len; ++i) {
      ctx->data[ctx->datalen] = data[i];
      ctx->datalen++;
      if (ctx->datalen == 64) {
         md5_transform(ctx,ctx->data);
         DBL_INT_ADD(ctx->bitlen[0],ctx->bitlen[1],512);
         ctx->datalen = 0;
      }
   }
}

void md5_final(MD5_CTX *ctx, uchar hash[])
{
   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 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.
   DBL_INT_ADD(ctx->bitlen[0],ctx->bitlen[1],8 * ctx->datalen);
   ctx->data[56] = ctx->bitlen[0];
   ctx->data[57] = ctx->bitlen[0] >> 8;
   ctx->data[58] = ctx->bitlen[0] >> 16;
   ctx->data[59] = ctx->bitlen[0] >> 24;
   ctx->data[60] = ctx->bitlen[1];
   ctx->data[61] = ctx->bitlen[1] >> 8;
   ctx->data[62] = ctx->bitlen[1] >> 16;
   ctx->data[63] = ctx->bitlen[1] >> 24;
   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;
   }
}