MD5在百度百科里面的的解释是：MD5即Message-Digest Algorithm 5（信息-摘要算法5），用于确保信息传输完整一致。存在广泛的用途。     一般在文件或是程序的完整性校验方面用的比较广泛，本文主要讲讲MD5在C语言中的实现。 /* -- include the following line if the md5.h header file is separate -- */ /* #include "md5.h" */ /* forward declaration */ static void Transform (); static unsigned char PADDING[64] = { 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }; /* F, G and H are basic MD5 functions: selection, majority, parity */ #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); }
MD5初始化函数 void MD5Init (mdContext) MD5_CTX *mdContext; { mdContext->i[0] = mdContext->i[1] = (UINT4)0; /* Load magic initialization constants. */ mdContext->buf[0] = (UINT4)0x67452301; mdContext->buf[1] = (UINT4)0xefcdab89; mdContext->buf[2] = (UINT4)0x98badcfe; mdContext->buf[3] = (UINT4)0x10325476; }
void MD5Update (mdContext, inBuf, inLen) MD5_CTX *mdContext; unsigned char *inBuf; unsigned int inLen; { UINT4 in[16]; int mdi; unsigned int i, ii; /* compute number of bytes mod 64 */ mdi = (int)((mdContext->i[0] >> 3) & 0x3F); /* update number of bits */ if ((mdContext->i[0] + ((UINT4)inLen << 3)) < mdContext->i[0]) mdContext->i[1]++; mdContext->i[0] += ((UINT4)inLen << 3); mdContext->i[1] += ((UINT4)inLen >> 29); while (inLen--) { /* add new character to buffer, increment mdi */ mdContext->in[mdi++] = *inBuf++; /* transform if necessary */ if (mdi == 0x40) { for (i = 0, ii = 0; i < 16; i++, ii += 4) in[i] = (((UINT4)mdContext->in[ii+3]) << 24) | (((UINT4)mdContext->in[ii+2]) << 16) | (((UINT4)mdContext->in[ii+1]) << 8) | ((UINT4)mdContext->in[ii]); Transform (mdContext->buf, in); mdi = 0; } } }
void MD5Final (mdContext) MD5_CTX *mdContext; { UINT4 in[16]; int mdi; unsigned int i, ii; unsigned int padLen; /* save number of bits */ in[14] = mdContext->i[0]; in[15] = mdContext->i[1]; /* compute number of bytes mod 64 */ mdi = (int)((mdContext->i[0] >> 3) & 0x3F); /* pad out to 56 mod 64 */ padLen = (mdi < 56) ? (56 - mdi) : (120 - mdi); MD5Update (mdContext, PADDING, padLen); /* append length in bits and transform */ for (i = 0, ii = 0; i < 14; i++, ii += 4) in[i] = (((UINT4)mdContext->in[ii+3]) << 24) | (((UINT4)mdContext->in[ii+2]) << 16) | (((UINT4)mdContext->in[ii+1]) << 8) | ((UINT4)mdContext->in[ii]); Transform (mdContext->buf, in); /* store buffer in digest */ for (i = 0, ii = 0; i < 4; i++, ii += 4) { mdContext->digest[ii] = (unsigned char)(mdContext->buf[i] & 0xFF); mdContext->digest[ii+1] = (unsigned char)((mdContext->buf[i] >> 8) & 0xFF); mdContext->digest[ii+2] = (unsigned char)((mdContext->buf[i] >> 16) & 0xFF); mdContext->digest[ii+3] = (unsigned char)((mdContext->buf[i] >> 24) & 0xFF); } }
/* Basic MD5 step. Transform buf based on in. */ static void Transform (buf, in) UINT4 *buf; UINT4 *in; { UINT4 a = buf[0], b = buf[1], c = buf[2], d = buf[3]; /* Round 1 */ #define S11 7 #define S12 12 #define S13 17 #define S14 22 FF ( a, b, c, d, in[ 0], S11, 0xD76AA478); /* 1 */ FF ( d, a, b, c, in[ 1], S12, 0xE8C7B756); /* 2 */ FF ( c, d, a, b, in[ 2], S13, 0x242070DB); /* 3 */ FF ( b, c, d, a, in[ 3], S14, 0xC1BDCEEE); /* 4 */ FF ( a, b, c, d, in[ 4], S11, 0xF57C0FAF); /* 5 */ FF ( d, a, b, c, in[ 5], S12, 0x4787C62A); /* 6 */ FF ( c, d, a, b, in[ 6], S13, 0xA8304613); /* 7 */ FF ( b, c, d, a, in[ 7], S14, 0xFD469501); /* 8 */ FF ( a, b, c, d, in[ 8], S11, 0x698098D8); /* 9 */ FF ( d, a, b, c, in[ 9], S12, 0x8B44F7AF); /* 10 */ FF ( c, d, a, b, in[10], S13, 0xFFFF5BB1); /* 11 */ FF ( b, c, d, a, in[11], S14, 0x895CD7BE); /* 12 */ FF ( a, b, c, d, in[12], S11, 0x6B901122); /* 13 */ FF ( d, a, b, c, in[13], S12, 0xFD987193); /* 14 */ FF ( c, d, a, b, in[14], S13, 0xA679438E); /* 15 */ FF ( b, c, d, a, in[15], S14, 0x49B40821); /* 16 */ /* Round 2 */ #define S21 5 #define S22 9 #define S23 14 #define S24 20 GG ( a, b, c, d, in[ 1], S21, 0xF61E2562); /* 17 */ GG ( d, a, b, c, in[ 6], S22, 0xC040B340); /* 18 */ GG ( c, d, a, b, in[11], S23, 0x265E5A51); /* 19 */ GG ( b, c, d, a, in[ 0], S24, 0xE9B6C7AA); /* 20 */ GG ( a, b, c, d, in[ 5], S21, 0xD62F105D); /* 21 */ GG ( d, a, b, c, in[10], S22, 0x2441453); /* 22 */ GG ( c, d, a, b, in[15], S23, 0xD8A1E681); /* 23 */ GG ( b, c, d, a, in[ 4], S24, 0xE7D3FBC8); /* 24 */ GG ( a, b, c, d, in[ 9], S21, 0x21E1CDE6); /* 25 */ GG ( d, a, b, c, in[14], S22, 0xC33707D6); /* 26 */ GG ( c, d, a, b, in[ 3], S23, 0xF4D50D87); /* 27 */ GG ( b, c, d, a, in[ 8], S24, 0x455A14ED); /* 28 */ GG ( a, b, c, d, in[13], S21, 0xA9E3E905); /* 29 */ GG ( d, a, b, c, in[ 2], S22, 0xFCEFA3F8); /* 30 */ GG ( c, d, a, b, in[ 7], S23, 0x676F02D9); /* 31 */ GG ( b, c, d, a, in[12], S24, 0x8D2A4C8A); /* 32 */ /* Round 3 */ #define S31 4 #define S32 11 #define S33 16 #define S34 23 HH ( a, b, c, d, in[ 5], S31, 0xFFFA3942); /* 33 */ HH ( d, a, b, c, in[ 8], S32, 0x8771F681); /* 34 */ HH ( c, d, a, b, in[11], S33, 0x6D9D6122); /* 35 */ HH ( b, c, d, a, in[14], S34, 0xFDE5380C); /* 36 */ HH ( a, b, c, d, in[ 1], S31, 0xA4BEEA44); /* 37 */ HH ( d, a, b, c, in[ 4], S32, 0x4BDECFA9); /* 38 */ HH ( c, d, a, b, in[ 7], S33, 0xF6BB4B60); /* 39 */ HH ( b, c, d, a, in[10], S34, 0xBEBFBC70); /* 40 */ HH ( a, b, c, d, in[13], S31, 0x289B7EC6); /* 41 */ HH ( d, a, b, c, in[ 0], S32, 0xEAA127FA); /* 42 */ HH ( c, d, a, b, in[ 3], S33, 0xD4EF3085); /* 43 */ HH ( b, c, d, a, in[ 6], S34, 0x4881D05); /* 44 */ HH ( a, b, c, d, in[ 9], S31, 0xD9D4D039); /* 45 */ HH ( d, a, b, c, in[12], S32, 0xE6DB99E5); /* 46 */ HH ( c, d, a, b, in[15], S33, 0x1FA27CF8); /* 47 */ HH ( b, c, d, a, in[ 2], S34, 0xC4AC5665); /* 48 */ /* Round 4 */ #define S41 6 #define S42 10 #define S43 15 #define S44 21 II ( a, b, c, d, in[ 0], S41, 0xF4292244); /* 49 */ II ( d, a, b, c, in[ 7], S42, 0x432AFF97); /* 50 */ II ( c, d, a, b, in[14], S43, 0xAB9423A7); /* 51 */ II ( b, c, d, a, in[ 5], S44, 0xFC93A039); /* 52 */ II ( a, b, c, d, in[12], S41, 0x655B59C3); /* 53 */ II ( d, a, b, c, in[ 3], S42, 0x8F0CCC92); /* 54 */ II ( c, d, a, b, in[10], S43, 0xFFEFF47D); /* 55 */ II ( b, c, d, a, in[ 1], S44, 0x85845DD1); /* 56 */ II ( a, b, c, d, in[ 8], S41, 0x6FA87E4F); /* 57 */ II ( d, a, b, c, in[15], S42, 0xFE2CE6E0); /* 58 */ II ( c, d, a, b, in[ 6], S43, 0xA3014314); /* 59 */ II ( b, c, d, a, in[13], S44, 0x4E0811A1); /* 60 */ II ( a, b, c, d, in[ 4], S41, 0xF7537E82); /* 61 */ II ( d, a, b, c, in[11], S42, 0xBD3AF235); /* 62 */ II ( c, d, a, b, in[ 2], S43, 0x2AD7D2BB); /* 63 */ II ( b, c, d, a, in[ 9], S44, 0xEB86D391); /* 64 */ buf[0] += a; buf[1] += b; buf[2] += c; buf[3] += d; }
以上函数一般网上都能搜索得到，都是开源的。 下面的函数就是得到一个文件的MD5值： void MDFile (char *filename,unsigned char *md5sum) { FILE *inFile = fopen (filename, "rb"); MD5_CTX mdContext; int bytes; unsigned char data[1024]; if (inFile == NULL) { printf ("%s can't be opened. ", filename); return; } MD5Init (&mdContext); while ((bytes = fread (data, 1, 1024, inFile)) != 0) MD5Update (&mdContext, data, bytes); MD5Final (&mdContext); memcpy(md5sum,mdContext.digest,16); printf (" %s ", filename); fclose (inFile); }
输入文件名，就OK了。