linux c/c++ 后台开发常用算法之：md5算法c++版实现

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原创最新推荐文章于 2026-06-30 11:38:25 发布 3k 阅读 AI 写同款· GEO 优化 ›

MD5即Message-Digest Algorithm 5（消息摘要算法第五版）的简称，是当前计算机领域用于确保信息传输完整一致而广泛使用的散列算法之一（又译哈希算法、摘要算法等），主流编程语言普遍已有MD5的实现。将数据（如一段文字）运算变为另一固定长度值，是散列算法的基础，下面是c++版的MD5算法实现。

#ifndef MD5_H
#define MD5_H

#include <string.h>
#include <string>
#include <fstream>

/* Type define */
typedef unsigned char byte;
typedef unsigned long ulong;

using std::string;
using std::ifstream;

/* MD5 declaration. */
class MD5 {
public:
	MD5();
	MD5(const void *input, size_t length);
	MD5(const string &str);
	MD5(ifstream &in);
	void update(const void *input, size_t length);
	void update(const string &str);
	void update(ifstream &in);
	const byte* digest();
	string toString();
	void reset();
private:
	void update(const byte *input, size_t length);
	void final();
	void transform(const byte block[64]);
	void encode(const ulong *input, byte *output, size_t length);
	void decode(const byte *input, ulong *output, size_t length);
	string bytesToHexString(const byte *input, size_t length);

	/* class uncopyable */
	MD5(const MD5&);
	MD5& operator=(const MD5&);
private:
	ulong _state[4];	/* state (ABCD) */
	ulong _count[2];	/* number of bits, modulo 2^64 (low-order word first) */
	byte _buffer[64];	/* input buffer */
	byte _digest[16];	/* message digest */
	bool _finished;		/* calculate finished ? */

	static const byte PADDING[64];	/* padding for calculate */
	static const char HEX[16];
	static const size_t BUFFER_SIZE = 1024;
};

#endif/*MD5_H*/

#include "md5.h"

using namespace std;

/* 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.
*/
#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) + ac; \
	(a) = ROTATE_LEFT ((a), (s)); \
	(a) += (b); \
}
#define GG(a, b, c, d, x, s, ac) { \
	(a) += G ((b), (c), (d)) + (x) + ac; \
	(a) = ROTATE_LEFT ((a), (s)); \
	(a) += (b); \
}
#define HH(a, b, c, d, x, s, ac) { \
	(a) += H ((b), (c), (d)) + (x) + ac; \
	(a) = ROTATE_LEFT ((a), (s)); \
	(a) += (b); \
}
#define II(a, b, c, d, x, s, ac) { \
	(a) += I ((b), (c), (d)) + (x) + ac; \
	(a) = ROTATE_LEFT ((a), (s)); \
	(a) += (b); \
}


const byte MD5::PADDING[64] = { 0x80 };
const char MD5::HEX[16] = {
	'0', '1', '2', '3',
	'4', '5', '6', '7',
	'8', '9', 'a', 'b',
	'c', 'd', 'e', 'f'
};

/* Default construct. */
MD5::MD5() {
	reset();
}

/* Construct a MD5 object with a input buffer. */
MD5::MD5(const void *input, size_t length) {
	reset();
	update(input, length);
}

/* Construct a MD5 object with a string. */
MD5::MD5(const string &str) {
	reset();
	update(str);
}

/* Construct a MD5 object with a file. */
MD5::MD5(ifstream &in) {
	reset();
	update(in);
}

/* Return the message-digest */
const byte* MD5::digest() {
	if (!_finished) {
		_finished = true;
		final();
	}
	return _digest;
}

/* Reset the calculate state */
void MD5::reset() {

	_finished = false;
	/* reset number of bits. */
	_count[0] = _count[1] = 0;
	/* Load magic initialization constants. */
	_state[0] = 0x67452301;
	_state[1] = 0xefcdab89;
	_state[2] = 0x98badcfe;
	_state[3] = 0x10325476;
}

/* Updating the context with a input buffer. */
void MD5::update(const void *input, size_t length) {
	update((const byte*)input, length);
}

/* Updating the context with a string. */
void MD5::update(const string &str) {
	update((const byte*)str.c_str(), str.length());
}

/* Updating the context with a file. */
void MD5::update(ifstream &in) {

	if (!in)
		return;

	std::streamsize length;
	char buffer[BUFFER_SIZE];
	while (!in.eof()) {
		in.read(buffer, BUFFER_SIZE);
		length = in.gcount();
		if (length > 0)
			update(buffer, length);
	}
	in.close();
}

/* MD5 block update operation. Continues an MD5 message-digest
operation, processing another message block, and updating the
context.
*/
void MD5::update(const byte *input, size_t length) {

	ulong i, index, partLen;

	_finished = false;

	/* Compute number of bytes mod 64 */
	index = (ulong)((_count[0] >> 3) & 0x3f);

	/* update number of bits */
	if((_count[0] += ((ulong)length << 3)) < ((ulong)length << 3))
		_count[1]++;
	_count[1] += ((ulong)length >> 29);

	partLen = 64 - index;

	/* transform as many times as possible. */
	if(length >= partLen) {

		memcpy(&_buffer[index], input, partLen);
		transform(_buffer);

		for (i = partLen; i + 63 < length; i += 64)
			transform(&input[i]);
		index = 0;

	} else {
		i = 0;
	}

	/* Buffer remaining input */
	memcpy(&_buffer[index], &input[i], length-i);
}

/* MD5 finalization. Ends an MD5 message-_digest operation, writing the
the message _digest and zeroizing the context.
*/
void MD5::final() {

	byte bits[8];
	ulong oldState[4];
	ulong oldCount[2];
	ulong index, padLen;

	/* Save current state and count. */
	memcpy(oldState, _state, 16);
	memcpy(oldCount, _count, 8);

	/* Save number of bits */
	encode(_count, bits, 8);

	/* Pad out to 56 mod 64. */
	index = (ulong)((_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(_state, _digest, 16);

	/* Restore current state and count. */
	memcpy(_state, oldState, 16);
	memcpy(_count, oldCount, 8);
}

/* MD5 basic transformation. Transforms _state based on block. */
void MD5::transform(const byte block[64]) {

	ulong a = _state[0], b = _state[1], c = _state[2], d = _state[3], x[16];

	decode(block, x, 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;
}

/* Encodes input (ulong) into output (byte). Assumes length is
a multiple of 4.
*/
void MD5::encode(const ulong *input, byte *output, size_t length) {

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

/* Decodes input (byte) into output (ulong). Assumes length is
a multiple of 4.
*/
void MD5::decode(const byte *input, ulong *output, size_t length) {

	for(size_t i=0, j=0; j<length; i++, j+=4) {	
		output[i] = ((ulong)input[j]) | (((ulong)input[j+1]) << 8) |
			(((ulong)input[j+2]) << 16) | (((ulong)input[j+3]) << 24);
	}
}

/* Convert byte array to hex string. */
string MD5::bytesToHexString(const byte *input, size_t length) {
	string str;
	str.reserve(length << 1);
	for(size_t i = 0; i < length; i++) {
		int t = input[i];
		int a = t / 16;
		int b = t % 16;
		str.append(1, HEX[a]);
		str.append(1, HEX[b]);
	}
	return str;
}

/* Convert digest to string value */
string MD5::toString() {
	return bytesToHexString(digest(), 16);
}

#include "md5.h"
#include <iostream>

using namespace std;

void PrintMD5(const string &str, MD5 &md5) {
	cout << "MD5(\"" << str << "\") = " << md5.toString() << endl;
}

int main() {

	cout << MD5("abc").toString() << endl;

	MD5 md5;
	md5.update("");
	PrintMD5("", md5);

	md5.update("a");
	PrintMD5("a", md5);

	md5.update("bc");
	PrintMD5("abc", md5);

	md5.update("defghijklmnopqrstuvwxyz");
	PrintMD5("abcdefghijklmnopqrstuvwxyz", md5);

	md5.reset();
	md5.update("message digest");
	PrintMD5("message digest", md5);

	return 0;
}