MD5 C++ implementation

Here’s an implementation of the MD5 algorithm in C++.

Simply copy and paste into a file “md5.h”. Only dependencies are on <string.h> and <stdio.h>.

Originally adapted from the C reference implementation on this page

Tested in Visual Studio 2010.
Sample use:

Main.cpp

#include "md5.h"

int main()
{
  MD5 md5 ;
  puts( md5.digestString( "HELLO THERE I AM MD5!" ) ) ;

  // print the digest for a binary file on disk.
  puts( md5.digestFile( "C:\\WINDOWS\\notepad.exe" ) ) ;

  return 0;
}

md5.h

(No .cpp file)

#ifndef MD5_H
#define MD5_H

// 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.



// The original md5 implementation avoids external libraries.
// This version has dependency on stdio.h for file input and
// string.h for memcpy.
#include <stdio.h>
#include <string.h>

#pragma region MD5 defines
// Constants for MD5Transform routine.
#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 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)); \
  (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); \
  }
#pragma endregion

typedef unsigned char BYTE ;

// 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;


// convenient object that wraps
// the C-functions for use in C++ only
class MD5
{
private:
  struct __context_t {
    UINT4 state[4];                                   /* state (ABCD) */
    UINT4 count[2];        /* number of bits, modulo 2^64 (lsb first) */
    unsigned char buffer[64];                         /* input buffer */
  } context ;

  #pragma region static helper functions
  // The core of the MD5 algorithm is here.
  // MD5 basic transformation. Transforms state based on block.
  static void MD5Transform( 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 */
    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 */

    /* Round 3 */
    HH (a, b, c, d, x[ 5], S31, 0xfffa3942); /* 33 */
    HH (d, a, b, c, x[ 8], S32, 0x8771f681); /* 34 */
    HH (c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
    HH (b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
    HH (a, b, c, d, x[ 1], S31, 0xa4beea44); /* 37 */
    HH (d, a, b, c, x[ 4], S32, 0x4bdecfa9); /* 38 */
    HH (c, d, a, b, x[ 7], S33, 0xf6bb4b60); /* 39 */
    HH (b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
    HH (a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
    HH (d, a, b, c, x[ 0], S32, 0xeaa127fa); /* 42 */
    HH (c, d, a, b, x[ 3], S33, 0xd4ef3085); /* 43 */
    HH (b, c, d, a, x[ 6], S34,  0x4881d05); /* 44 */
    HH (a, b, c, d, x[ 9], S31, 0xd9d4d039); /* 45 */
    HH (d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
    HH (c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
    HH (b, c, d, a, x[ 2], S34, 0xc4ac5665); /* 48 */

    /* Round 4 */
    II (a, b, c, d, x[ 0], S41, 0xf4292244); /* 49 */
    II (d, a, b, c, x[ 7], S42, 0x432aff97); /* 50 */
    II (c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
    II (b, c, d, a, x[ 5], S44, 0xfc93a039); /* 52 */
    II (a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
    II (d, a, b, c, x[ 3], S42, 0x8f0ccc92); /* 54 */
    II (c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
    II (b, c, d, a, x[ 1], S44, 0x85845dd1); /* 56 */
    II (a, b, c, d, x[ 8], S41, 0x6fa87e4f); /* 57 */
    II (d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
    II (c, d, a, b, x[ 6], S43, 0xa3014314); /* 59 */
    II (b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
    II (a, b, c, d, x[ 4], S41, 0xf7537e82); /* 61 */
    II (d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
    II (c, d, a, b, x[ 2], S43, 0x2ad7d2bb); /* 63 */
    II (b, c, d, a, x[ 9], S44, 0xeb86d391); /* 64 */

    state[0] += a;
    state[1] += b;
    state[2] += c;
    state[3] += d;

    // Zeroize sensitive information.
    memset((POINTER)x, 0, sizeof (x));
  }

  // Encodes input (UINT4) into output (unsigned char). Assumes len is
  // a multiple of 4.
  static void Encode( unsigned char *output, UINT4 *input, unsigned int len )
  {
    unsigned int i, j;

    for (i = 0, j = 0; j < len; i++, j += 4) {
      output[j] = (unsigned char)(input[i] & 0xff);
      output[j+1] = (unsigned char)((input[i] >> 8) & 0xff);
      output[j+2] = (unsigned char)((input[i] >> 16) & 0xff);
      output[j+3] = (unsigned char)((input[i] >> 24) & 0xff);
    }
  }

  // Decodes input (unsigned char) into output (UINT4). Assumes len is
  // a multiple of 4.
  static void Decode( UINT4 *output, unsigned char *input, unsigned int len )
  {
    unsigned int i, j;

    for (i = 0, j = 0; j < len; i++, j += 4)
      output[i] = ((UINT4)input[j]) | (((UINT4)input[j+1]) << 8) |
      (((UINT4)input[j+2]) << 16) | (((UINT4)input[j+3]) << 24);
  }
  #pragma endregion


public:
  // MAIN FUNCTIONS
  MD5()
  {
    Init() ;
  }

  // MD5 initialization. Begins an MD5 operation, writing a new context.
  void Init()
  {
    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 Update(
    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))
      < ((UINT4)inputLen << 3))
      context.count[1]++;
    context.count[1] += ((UINT4)inputLen >> 29);

    partLen = 64 - index;

    // Transform as many times as possible.
    if (inputLen >= partLen) {
      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 */
    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.
  // Writes to digestRaw
  void Final()
  {
    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);
    Update( PADDING, padLen );

    // Append length (before padding)
    Update( bits, 8 );

    // Store state in digest
    Encode( digestRaw, context.state, 16);

    // Zeroize sensitive information.
    memset((POINTER)&context, 0, sizeof (context));

    writeToString() ;
  }

  /// Buffer must be 32+1 (nul) = 33 chars long at least 
  void writeToString()
  {
    int pos ;

    for( pos = 0 ; pos < 16 ; pos++ )
      sprintf( digestChars+(pos*2), "%02x", digestRaw[pos] ) ;
  }


public:
  // an MD5 digest is a 16-byte number (32 hex digits)
  BYTE digestRaw[ 16 ] ;

  // This version of the digest is actually
  // a "printf'd" version of the digest.
  char digestChars[ 33 ] ;

  /// Load a file from disk and digest it
  // Digests a file and returns the result.
  char* digestFile( char *filename )
  {
    Init() ;

    FILE *file;
    
    int len;
    unsigned char buffer[1024] ;

    if( (file = fopen (filename, "rb")) == NULL )
      printf( "%s can't be opened\n", filename ) ;
    else
    {
      while( len = fread( buffer, 1, 1024, file ) )
        Update( buffer, len ) ;
      Final();

      fclose( file );
    }

    return digestChars ;
  }

  /// Digests a byte-array already in memory
  char* digestMemory( BYTE *memchunk, int len )
  {
    Init() ;
    Update( memchunk, len ) ;
    Final() ;
    
    return digestChars ;
  }

  // Digests a string and prints the result.
  char* digestString( char *string )
  {
    Init() ;
    Update( (unsigned char*)string, strlen(string) ) ;
    Final() ;

    return digestChars ;
  }
} ;

#endif

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