C++:符合RFC1321规范的MD5计算C++实现

MD5使用比较广泛，并不只局限于数据加密，它的概念这里就不介绍了，这里只谈谈MD5的代码实现。
MD5计算的算法是统一的，但实现如果实现时参数不一样，同样一段数据，不同的算法计算出的结果就不一样。为了保证MD5算法实现在不同的平台，不同的语言实现时计算结果一致，人们制定了RFC1321规范。比如java中MD5的算法实现就是遵循RFC1321规范的。我们知道C/C++并没有内置MD5计算的函数，所以在C++/C环境下要实现与java平台一样的MD5计算，就要自己实现。
RFC1321的官方网站提供了MD5的C语言实现。这是很权威的了。
但如果想要C++的版本，就要仔细挑选了。我们当然希望自己的MD5实现计算出来的结果与别的系统计算的结果一样，所以遵循RFC1321是必须的。网上也可以找到很多C++版本的实现。但哪一个遵循RFC1321规范的呢？
最近我就遇到了这个问题，经过实际测试，可以确认下面这个版本是没问题的，遵循RFC1321，与java平台下计算的结果一致。
http://www.zedwood.com/article/cpp-md5-function

为防止链接失效，下面贴出源码，代码已经在VS2015,CLang下编译通过，并在win64、android/arm平台上测试验证通过，另外我在使用过程对下面的原始代码中一些不合理的地方做了一些修改，修改后的代码参见码云仓库地址：https://gitee.com/l0km/common_source_cpp/tree/master/md5
调用示例参见: https://gitee.com/l0km/feature_se/blob/master/jni/BeanUtilits.cpp

md5.h

/* MD5 converted to C++ class by Frank Thilo ([email protected]) for bzflag (http://www.bzflag.org) based on: md5.h and md5.c reference implementation of RFC 1321 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. */
 
#ifndef BZF_MD5_H
#define BZF_MD5_H
 
#include 
#include 
 
 
// a small class for calculating MD5 hashes of strings or byte arrays
// it is not meant to be fast or secure
//
// usage: 1) feed it blocks of uchars with update()
// 2) finalize()
// 3) get hexdigest() string
// or
// MD5(std::string).hexdigest()
//
// assumes that char is 8 bit and int is 32 bit
class MD5
{
public:
  typedef unsigned int size_type; // must be 32bit
 
  MD5();
  MD5(const std::string& text);
  void update(const unsigned char *buf, size_type length);
  void update(const char *buf, size_type length);
  MD5& finalize();
  std::string hexdigest() const;
  friend std::ostream& operator<<(std::ostream&, MD5 md5);
 
private:
  void init();
  typedef unsigned char uint1; // 8bit
  typedef unsigned int uint4;  // 32bit
  enum {blocksize = 64}; // VC6 won't eat a const static int here
 
  void transform(const uint1 block[blocksize]);
  static void decode(uint4 output[], const uint1 input[], size_type len);
  static void encode(uint1 output[], const uint4 input[], size_type len);
 
  bool finalized;
  uint1 buffer[blocksize]; // bytes that didn't fit in last 64 byte chunk
  uint4 count[2];   // 64bit counter for number of bits (lo, hi)
  uint4 state[4];   // digest so far
  uint1 digest[16]; // the result
 
  // low level logic operations
  static inline uint4 F(uint4 x, uint4 y, uint4 z);
  static inline uint4 G(uint4 x, uint4 y, uint4 z);
  static inline uint4 H(uint4 x, uint4 y, uint4 z);
  static inline uint4 I(uint4 x, uint4 y, uint4 z);
  static inline uint4 rotate_left(uint4 x, int n);
  static inline void FF(uint4 &a, uint4 b, uint4 c, uint4 d, uint4 x, uint4 s, uint4 ac);
  static inline void GG(uint4 &a, uint4 b, uint4 c, uint4 d, uint4 x, uint4 s, uint4 ac);
  static inline void HH(uint4 &a, uint4 b, uint4 c, uint4 d, uint4 x, uint4 s, uint4 ac);
  static inline void II(uint4 &a, uint4 b, uint4 c, uint4 d, uint4 x, uint4 s, uint4 ac);
};
 
std::string md5(const std::string str);
 
#endif

md5.cpp

/* MD5 converted to C++ class by Frank Thilo ([email protected]) for bzflag (http://www.bzflag.org) based on: md5.h and md5.c reference implemantion of RFC 1321 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. */
 
/* interface header */
#include "md5.h"
 
/* system implementation headers */
#include 
 
 
// 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
 
///////////////////////////////////////////////
 
// F, G, H and I are basic MD5 functions.
inline MD5::uint4 MD5::F(uint4 x, uint4 y, uint4 z) {
  return x&y | ~x&z;
}
 
inline MD5::uint4 MD5::G(uint4 x, uint4 y, uint4 z) {
  return x&z | y&~z;
}
 
inline MD5::uint4 MD5::H(uint4 x, uint4 y, uint4 z) {
  return x^y^z;
}
 
inline MD5::uint4 MD5::I(uint4 x, uint4 y, uint4 z) {
  return y ^ (x | ~z);
}
 
// rotate_left rotates x left n bits.
inline MD5::uint4 MD5::rotate_left(uint4 x, int n) {
  return (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.
inline void MD5::FF(uint4 &a, uint4 b, uint4 c, uint4 d, uint4 x, uint4 s, uint4 ac) {
  a = rotate_left(a+ F(b,c,d) + x + ac, s) + b;
}
 
inline void MD5::GG(uint4 &a, uint4 b, uint4 c, uint4 d, uint4 x, uint4 s, uint4 ac) {
  a = rotate_left(a + G(b,c,d) + x + ac, s) + b;
}
 
inline void MD5::HH(uint4 &a, uint4 b, uint4 c, uint4 d, uint4 x, uint4 s, uint4 ac) {
  a = rotate_left(a + H(b,c,d) + x + ac, s) + b;
}
 
inline void MD5::II(uint4 &a, uint4 b, uint4 c, uint4 d, uint4 x, uint4 s, uint4 ac) {
  a = rotate_left(a + I(b,c,d) + x + ac, s) + b;
}
 
//////////////////////////////////////////////
 
// default ctor, just initailize
MD5::MD5()
{
  init();
}
 
//////////////////////////////////////////////
 
// nifty shortcut ctor, compute MD5 for string and finalize it right away
MD5::MD5(const std::string &text)
{
  init();
  update(text.c_str(), text.length());
  finalize();
}
 
//////////////////////////////
 
void MD5::init()
{
  finalized=false;
 
  count[0] = 0;
  count[1] = 0;
 
  // load magic initialization constants.
  state[0] = 0x67452301;
  state[1] = 0xefcdab89;
  state[2] = 0x98badcfe;
  state[3] = 0x10325476;
}
 
//////////////////////////////
 
// decodes input (unsigned char) into output (uint4). Assumes len is a multiple of 4.
void MD5::decode(uint4 output[], const uint1 input[], size_type len)
{
  for (unsigned int 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);
}
 
//////////////////////////////
 
// encodes input (uint4) into output (unsigned char). Assumes len is
// a multiple of 4.
void MD5::encode(uint1 output[], const uint4 input[], size_type len)
{
  for (size_type i = 0, j = 0; j < len; i++, j += 4) {
    output[j] = input[i] & 0xff;
    output[j+1] = (input[i] >> 8) & 0xff;
    output[j+2] = (input[i] >> 16) & 0xff;
    output[j+3] = (input[i] >> 24) & 0xff;
  }
}
 
//////////////////////////////
 
// apply MD5 algo on a block
void MD5::transform(const uint1 block[blocksize])
{
  uint4 a = state[0], b = state[1], c = state[2], d = state[3], x[16];
  decode (x, block, blocksize);
 
  /* 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(x, 0, sizeof x);
}
 
//////////////////////////////
 
// MD5 block update operation. Continues an MD5 message-digest
// operation, processing another message block
void MD5::update(const unsigned char input[], size_type length)
{
  // compute number of bytes mod 64
  size_type index = count[0] / 8 % blocksize;
 
  // Update number of bits
  if ((count[0] += (length << 3)) < (length << 3))
    count[1]++;
  count[1] += (length >> 29);
 
  // number of bytes we need to fill in buffer
  size_type firstpart = 64 - index;
 
  size_type i;
 
  // transform as many times as possible.
  if (length >= firstpart)
  {
    // fill buffer first, transform
    memcpy(&buffer[index], input, firstpart);
    transform(buffer);
 
    // transform chunks of blocksize (64 bytes)
    for (i = firstpart; i + blocksize <= length; i += blocksize)
      transform(&input[i]);
 
    index = 0;
  }
  else
    i = 0;
 
  // buffer remaining input
  memcpy(&buffer[index], &input[i], length-i);
}
 
//////////////////////////////
 
// for convenience provide a verson with signed char
void MD5::update(const char input[], size_type length)
{
  update((const unsigned char*)input, length);
}
 
//////////////////////////////
 
// MD5 finalization. Ends an MD5 message-digest operation, writing the
// the message digest and zeroizing the context.
MD5& MD5::finalize()
{
  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
  };
 
  if (!finalized) {
    // Save number of bits
    unsigned char bits[8];
    encode(bits, count, 8);
 
    // pad out to 56 mod 64.
    size_type index = count[0] / 8 % 64;
    size_type padLen = (index < 56) ? (56 - index) : (120 - index);
    update(padding, padLen);
 
    // Append length (before padding)
    update(bits, 8);
 
    // Store state in digest
    encode(digest, state, 16);
 
    // Zeroize sensitive information.
    memset(buffer, 0, sizeof buffer);
    memset(count, 0, sizeof count);
 
    finalized=true;
  }
 
  return *this;
}
 
//////////////////////////////
 
// return hex representation of digest as string
std::string MD5::hexdigest() const
{
  if (!finalized)
    return "";
 
  char buf[33];
  for (int i=0; i<16; i++)
    sprintf(buf+i*2, "%02x", digest[i]);
  buf[32]=0;
 
  return std::string(buf);
}
 
//////////////////////////////
 
std::ostream& operator<<(std::ostream& out, MD5 md5)
{
  return out << md5.hexdigest();
}
 
//////////////////////////////
 
std::string md5(const std::string str)
{
    MD5 md5 = MD5(str);
 
    return md5.hexdigest();
}

测试代码
main.cpp

#include 
#include "md5.h"
 
using std::cout; using std::endl;
 
int main(int argc, char *argv[])
{
    cout << "md5 of 'grape': " << md5("grape") << endl;
    return 0;
}