//	5. Differences Between MD4 and MD5
//
//		 The following are the differences between MD4 and MD5:
//
//		   1.   A fourth round has been added.
//
//		   2.   Each step now has a unique additive constant.
//
//		   3.   The function g in round 2 was changed from (XY v XZ v YZ) to
//		   (XZ v Y not(Z)) to make g less symmetric.
//
//		   4.   Each step now adds in the result of the previous step.  This
//		   promotes a faster "avalanche effect".
//
//		   5.   The order in which input words are accessed in rounds 2 and
//		   3 is changed, to make these patterns less like each other.
//
//		   6.   The shift amounts in each round have been approximately
//		   optimized, to yield a faster "avalanche effect." The shifts in
//		   different rounds are distinct.
//
//	Rivest                                                          [Page 6]
//	
//	RFC 1321              MD5 Message-Digest Algorithm            April 1992
//
//
//	References
//
//	   [1] Rivest, R., "The MD4 Message Digest Algorithm", RFC 1320, MIT and
//		   RSA Data Security, Inc., April 1992.
//
//	   [2] Rivest, R., "The MD4 message digest algorithm", in A.J.  Menezes
//		   and S.A. Vanstone, editors, Advances in Cryptology - CRYPTO '90
//		   Proceedings, pages 303-311, Springer-Verlag, 1991.
//
//	   [3] CCITT Recommendation X.509 (1988), "The Directory -
//		   Authentication Framework."
//
//	APPENDIX A - Reference Implementation
//
//	   This appendix contains the following files taken from RSAREF: A
//	   Cryptographic Toolkit for Privacy-Enhanced Mail:
//
//		 global.h -- global header file
//
//		 md5.h -- header file for MD5
//
//		 md5c.c -- source code for MD5
//
//	   For more information on RSAREF, send email to <rsaref@rsa.com>.
//
//	   The appendix also includes the following file:
//
//		 mddriver.c -- test driver for MD2, MD4 and MD5
//
//	   The driver compiles for MD5 by default but can compile for MD2 or MD4
//	   if the symbol MD is defined on the C compiler command line as 2 or 4.
//
//	   The implementation is portable and should work on many different
//	   plaforms. However, it is not difficult to optimize the implementation
//	   on particular platforms, an exercise left to the reader. For example,
//	   on "little-endian" platforms where the lowest-addressed byte in a 32-
//	   bit word is the least significant and there are no alignment
//	   restrictions, the call to Decode in MD5Transform can be replaced with
//	   a typecast.
//
//	A.1 global.h
//
//	/* GLOBAL.H - RSAREF types and constants
//	 */
//
//	/* PROTOTYPES should be set to one if and only if the compiler supports
//	  function argument prototyping.
//	The following makes PROTOTYPES default to 0 if it has not already
//
//	Rivest                                                          [Page 7]
//	
//	RFC 1321              MD5 Message-Digest Algorithm            April 1992
//
//
//	  been defined with C compiler flags.
//	 */
//	#ifndef PROTOTYPES
//	#define PROTOTYPES 0
//	#endif
//
//	/* POINTER defines a generic pointer type */
//	typedef unsigned char *POINTER;
//
//	/* UINT2 defines a two byte word */
//	typedef unsigned short int UINT2;
//
//	/* UINT4 defines a four byte word */
//	typedef unsigned long int UINT4;
//
//	/* PROTO_LIST is defined depending on how PROTOTYPES is defined above.
//	If using PROTOTYPES, then PROTO_LIST returns the list, otherwise it
//	  returns an empty list.
//	 */
//	#if PROTOTYPES
//	#define PROTO_LIST(list) list
//	#else
//	#define PROTO_LIST(list) ()
//	#endif
//
//	A.2 md5.h
//
//	/* MD5.H - header file for MD5C.C
//	 */
//
//	/* Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All
//	rights reserved.
//
//	License to copy and use this software is granted provided that it
//	is identified as the "RSA Data Security, Inc. MD5 Message-Digest
//	Algorithm" in all material mentioning or referencing this software
//	or this function.
//
//	License is also granted to make and use derivative works provided
//	that such works are identified as "derived from the RSA Data
//	Security, Inc. MD5 Message-Digest Algorithm" in all material
//	mentioning or referencing the derived work.
//
//	RSA Data Security, Inc. makes no representations concerning either
//	the merchantability of this software or the suitability of this
//	software for any particular purpose. It is provided "as is"
//	without express or implied warranty of any kind.
//
//	Rivest                                                          [Page 8]
//	
//	RFC 1321              MD5 Message-Digest Algorithm            April 1992
//
//
//	These notices must be retained in any copies of any part of this
//	documentation and/or software.
//	 */
//
//	/* MD5 context. */
//	typedef struct {
//	  UINT4 state[4];                                   /* state (ABCD) */
//	  UINT4 count[2];        /* number of bits, modulo 2^64 (lsb first) */
//	  unsigned char buffer[64];                         /* input buffer */
//	} MD5_CTX;
//
//	void MD5Init PROTO_LIST ((MD5_CTX *));
//	void MD5Update PROTO_LIST
//	  ((MD5_CTX *, unsigned char *, unsigned int));
//	void MD5Final PROTO_LIST ((unsigned char [16], MD5_CTX *));
//
//	A.3 md5c.c
//
//	/* MD5C.C - RSA Data Security, Inc., MD5 message-digest algorithm
//	 */
//
//	/* Copyright (C) 1991-2, RSA Data Security, Inc. Created 1991. All
//	rights reserved.
//
//	License to copy and use this software is granted provided that it
//	is identified as the "RSA Data Security, Inc. MD5 Message-Digest
//	Algorithm" in all material mentioning or referencing this software
//	or this function.
//
//	License is also granted to make and use derivative works provided
//	that such works are identified as "derived from the RSA Data
//	Security, Inc. MD5 Message-Digest Algorithm" in all material
//	mentioning or referencing the derived work.
//
//	RSA Data Security, Inc. makes no representations concerning either
//	the merchantability of this software or the suitability of this
//	software for any particular purpose. It is provided "as is"
//	without express or implied warranty of any kind.
//
//	These notices must be retained in any copies of any part of this
//	documentation and/or software.
//	 */
//
//	#include "global.h"
//	#include "md5.h"
//
//	/* Constants for MD5Transform routine.
//	 */
//
//	Rivest                                                          [Page 9]
//	
//	RFC 1321              MD5 Message-Digest Algorithm            April 1992
//
//
//	#define S11 7
//	#define S12 12
//	#define S13 17
//	#define S14 22
//	#define S21 5
//	#define S22 9
//	#define S23 14
//	#define S24 20
//	#define S31 4
//	#define S32 11
//	#define S33 16
//	#define S34 23
//	#define S41 6
//	#define S42 10
//	#define S43 15
//	#define S44 21
//
//	static void MD5Transform PROTO_LIST ((UINT4 [4], unsigned char [64]));
//	static void Encode PROTO_LIST
//	  ((unsigned char *, UINT4 *, unsigned int));
//	static void Decode PROTO_LIST
//	  ((UINT4 *, unsigned char *, unsigned int));
//	static void MD5_memcpy PROTO_LIST ((POINTER, POINTER, unsigned int));
//	static void MD5_memset PROTO_LIST ((POINTER, int, unsigned int));
//
//	static unsigned char PADDING[64] = {
//	  0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
//	  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
//	  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
//	};
//
//	/* F, G, H and I are basic MD5 functions.
//	 */
//	#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)))
//
//	/* ROTATE_LEFT rotates x left n bits.
//	 */
//	#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))
//
//	/* FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4.
//	Rotation is separate from addition to prevent recomputation.
//	 */
//	#define FF(a, b, c, d, x, s, ac) { \
//	 (a) += F ((b), (c), (d)) + (x) + (UINT4)(ac); \
//	 (a) = ROTATE_LEFT ((a), (s)); \
//
//
//	Rivest                                                         [Page 10]
//	
//	RFC 1321              MD5 Message-Digest Algorithm            April 1992
//
//
//	 (a) += (b); \
//	  }
//	#define GG(a, b, c, d, x, s, ac) { \
//	 (a) += G ((b), (c), (d)) + (x) + (UINT4)(ac); \
//	 (a) = ROTATE_LEFT ((a), (s)); \
//	 (a) += (b); \
//	  }
//	#define HH(a, b, c, d, x, s, ac) { \
//	 (a) += H ((b), (c), (d)) + (x) + (UINT4)(ac); \
//	 (a) = ROTATE_LEFT ((a), (s)); \
//	 (a) += (b); \
//	  }
//	#define II(a, b, c, d, x, s, ac) { \
//	 (a) += I ((b), (c), (d)) + (x) + (UINT4)(ac); \
//	 (a) = ROTATE_LEFT ((a), (s)); \
//	 (a) += (b); \
//	  }
//
//	/* MD5 initialization. Begins an MD5 operation, writing a new context.
//	 */
//	void MD5Init (context)
//	MD5_CTX *context;                                        /* context */
//	{
//	  context->count[0] = context->count[1] = 0;
//	  /* Load magic initialization constants.
//	*/
//	  context->state[0] = 0x67452301;
//	  context->state[1] = 0xefcdab89;
//	  context->state[2] = 0x98badcfe;
//	  context->state[3] = 0x10325476;
//	}
//
//	/* MD5 block update operation. Continues an MD5 message-digest
//	  operation, processing another message block, and updating the
//	  context.
//	 */
//	void MD5Update (context, input, inputLen)
//	MD5_CTX *context;                                        /* context */
//	unsigned char *input;                                /* input block */
//	unsigned int inputLen;                     /* length of input block */
//	{
//	  unsigned int i, index, partLen;
//
//	  /* Compute number of bytes mod 64 */
//	  index = (unsigned int)((context->count[0] >> 3) & 0x3F);
//
//	  /* Update number of bits */
//	  if ((context->count[0] += ((UINT4)inputLen << 3))
//
//
//
//	Rivest                                                         [Page 11]
//	
//	RFC 1321              MD5 Message-Digest Algorithm            April 1992
//
//
//	   < ((UINT4)inputLen << 3))
//	 context->count[1]++;
//	  context->count[1] += ((UINT4)inputLen >> 29);
//
//	  partLen = 64 - index;
//
//	  /* Transform as many times as possible.
//	*/
//	  if (inputLen >= partLen) {
//	 MD5_memcpy
//	   ((POINTER)&context->buffer[index], (POINTER)input, partLen);
//	 MD5Transform (context->state, context->buffer);
//
//	 for (i = partLen; i + 63 < inputLen; i += 64)
//	   MD5Transform (context->state, &input[i]);
//
//	 index = 0;
//	  }
//	  else
//	 i = 0;
//
//	  /* Buffer remaining input */
//	  MD5_memcpy
//	 ((POINTER)&context->buffer[index], (POINTER)&input[i],
//	  inputLen-i);
//	}
//
//	/* MD5 finalization. Ends an MD5 message-digest operation, writing the
//	  the message digest and zeroizing the context.
//	 */
//	void MD5Final (digest, context)
//	unsigned char digest[16];                         /* message digest */
//	MD5_CTX *context;                                       /* context */
//	{
//	  unsigned char bits[8];
//	  unsigned int index, padLen;
//
//	  /* Save number of bits */
//	  Encode (bits, context->count, 8);
//
//	  /* Pad out to 56 mod 64.
//	*/
//	  index = (unsigned int)((context->count[0] >> 3) & 0x3f);
//	  padLen = (index < 56) ? (56 - index) : (120 - index);
//	  MD5Update (context, PADDING, padLen);
//
//	  /* Append length (before padding) */
//	  MD5Update (context, bits, 8);
//
//	Rivest                                                         [Page 12]
//	
//	RFC 1321              MD5 Message-Digest Algorithm            April 1992
//
//
//	  /* Store state in digest */
//	  Encode (digest, context->state, 16);
//
//	  /* Zeroize sensitive information.
//	*/
//	  MD5_memset ((POINTER)context, 0, sizeof (*context));
//	}
//
//	/* MD5 basic transformation. Transforms state based on block.
//	 */
//	static void MD5Transform (state, block)
//	UINT4 state[4];
//	unsigned char block[64];
//	{
//	  UINT4 a = state[0], b = state[1], c = state[2], d = state[3], x[16];
//
//	  Decode (x, block, 64);
//
//	  /* Round 1 */
//	  FF (a, b, c, d, x[ 0], S11, 0xd76aa478); /* 1 */
//	  FF (d, a, b, c, x[ 1], S12, 0xe8c7b756); /* 2 */
//	  FF (c, d, a, b, x[ 2], S13, 0x242070db); /* 3 */
//	  FF (b, c, d, a, x[ 3], S14, 0xc1bdceee); /* 4 */
//	  FF (a, b, c, d, x[ 4], S11, 0xf57c0faf); /* 5 */
//	  FF (d, a, b, c, x[ 5], S12, 0x4787c62a); /* 6 */
//	  FF (c, d, a, b, x[ 6], S13, 0xa8304613); /* 7 */
//	  FF (b, c, d, a, x[ 7], S14, 0xfd469501); /* 8 */
//	  FF (a, b, c, d, x[ 8], S11, 0x698098d8); /* 9 */
//	  FF (d, a, b, c, x[ 9], S12, 0x8b44f7af); /* 10 */
//	  FF (c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
//	  FF (b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
//	  FF (a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
//	  FF (d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
//	  FF (c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
//	  FF (b, c, d, a, x[15], S14, 0x49b40821); /* 16 */
//
//	 /* Round 2 */
//	  GG (a, b, c, d, x[ 1], S21, 0xf61e2562); /* 17 */
//	  GG (d, a, b, c, x[ 6], S22, 0xc040b340); /* 18 */
//	  GG (c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
//	  GG (b, c, d, a, x[ 0], S24, 0xe9b6c7aa); /* 20 */
//	  GG (a, b, c, d, x[ 5], S21, 0xd62f105d); /* 21 */
//	  GG (d, a, b, c, x[10], S22,  0x2441453); /* 22 */
//	  GG (c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
//	  GG (b, c, d, a, x[ 4], S24, 0xe7d3fbc8); /* 24 */
//	  GG (a, b, c, d, x[ 9], S21, 0x21e1cde6); /* 25 */
//	  GG (d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
//	  GG (c, d, a, b, x[ 3], S23, 0xf4d50d87); /* 27 */
//
//	Rivest                                                         [Page 13]
//	
//	RFC 1321              MD5 Message-Digest Algorithm            April 1992
//
//
//	  GG (b, c, d, a, x[ 8], S24, 0x455a14ed); /* 28 */
//	  GG (a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
//	  GG (d, a, b, c, x[ 2], S22, 0xfcefa3f8); /* 30 */
//	  GG (c, d, a, b, x[ 7], S23, 0x676f02d9); /* 31 */
//	  GG (b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */
//