MD5介绍以及应用(c++、Qt)

什么是MD5？
MD5的全称是Message-Digest Algorithm 5，在90年代初由MIT的计算机科学实验室和RSA Data Security Inc 发明，由 MD2/MD3/MD4 发展而来的。MD5的实际应用是对一段Message(字节串)产生fingerprint(指纹)，可以防止被“篡改”。

缺点？
MD5 is no longer considered cryptographically safe for digital signatures, however, because the md5 hash function is still useful for other purposes, code is provided below.

如果不是研究加密算法，我们没必要实现自己的md5，已经有很多大神写好了：
md5.h

/* MD5converted to C++ class by Frank Thilo ([e-mail])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. Allrights reserved.License to copy and use this software is granted provided that itis identified as the "RSA Data Security, Inc. MD5 Message-DigestAlgorithm" in all material mentioning or referencing this softwareor this function.License is also granted to make and use derivative works providedthat such works are identified as "derived from the RSA DataSecurity, Inc. MD5 Message-Digest Algorithm" in all materialmentioning or referencing the derived work.RSA Data Security, Inc. makes no representations concerning eitherthe merchantability of this software or the suitability of thissoftware 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 thisdocumentation and/or software.*/#ifndef BZF_MD5_H#define BZF_MD5_H#include <cstring>#include <iostream>// 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 bitclass 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

/* MD5converted to C++ class by Frank Thilo ([e-mail])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. Allrights reserved.License to copy and use this software is granted provided that itis identified as the "RSA Data Security, Inc. MD5 Message-DigestAlgorithm" in all material mentioning or referencing this softwareor this function.License is also granted to make and use derivative works providedthat such works are identified as "derived from the RSA DataSecurity, Inc. MD5 Message-Digest Algorithm" in all materialmentioning or referencing the derived work.RSA Data Security, Inc. makes no representations concerning eitherthe merchantability of this software or the suitability of thissoftware 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 thisdocumentation and/or software.*//* interface header */#include "md5.h"/* system implementation headers */#include <cstdio>// 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 initailizeMD5::MD5(){  init();}//////////////////////////////////////////////// nifty shortcut ctor, compute MD5 for string and finalize it right awayMD5::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 blockvoid 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 blockvoid 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 charvoid 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 stringstd::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();}

使用上面的代码：

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

Qt中的MD5
qt中内置了md5算法，直接调用就可以了：
http://doc.qt.io/qt-5/qcryptographichash.html

#include <QCryptographicHash>#include <QTextCodec>QString function::encrypt(QString qstr){QByteArray str = qstr.toAscii();QCryptographicHash *hash = new QCryptographicHash(QCryptographicHash::Md5);hash->addData(str);QByteArray str1 = hash->result();delete hash;QTextCodec *codec = QTextCodec::codecForName("KOI8-R");QString str_result = codec->toUnicode(str1);return str_result;}