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我们在开发中经常遇到安全问题，比如密码的加密传输、数字签名、安全访问认证、一致性验证等，这时需要我们进行加密传输，开发中常用的加密算法有MD5、RSA加密（更安全）。
MD5消息摘要算法（MD5 Message-Digest Algorithm），一种被广泛使用的密码散列函数，可以产生出一个128位（16字节）的散列值（hash value），用于确保信息传输完整一致。
MD5算法经常用以进行文件、应用到软件下载站、论坛数据库、系统文件安全校验等。MD5的典型应用是对一段信息（Message）产生信息摘要（Message-Digest），以防止被篡改。大致结构如下：
MD5 (“内容”) = 38b8c2c1093dd0fec383a9d9ac940515（32位）
Java已经为我们提供了md5算法，使用如下：
import java.math.BigInteger;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException;public class MD5Utils { public static String md5(String plainText) { byte[] secretBytes = null; try { secretBytes = MessageDigest.getInstance("md5").digest(plainText.getBytes()); } catch (NoSuchAlgorithmException e) { throw new RuntimeException("找不到md5算法"); } String md5code = new BigInteger(1, secretBytes).toString(16); for (int i = 0; i < 32 - md5code.length(); i++) { md5code = "0" + md5code; } return md5code; } //使用 public static void main(String[] args) { System.out.println(md5("123")); }} 原生的java使用还是比较麻烦的，如果我们项目中使用的第三方包可能也提供了md5算法，这种使用比较简单。只要导入相关的包基本一行代码完事。比如下面使用apache.common提供的md5算法：
import org.apache.commons.codec.digest.DigestUtils;public class MD5Utils { //使用 public static void main(String[] args) { System.out.println(DigestUtils.md5Hex("123")); }} public class MD5{ //四个链接变量 private final int A=0x67452301; private final int B=0xefcdab89; private final int C=0x98badcfe; private final int D=0x10325476; //ABCD的临时变量 private int Atemp,Btemp,Ctemp,Dtemp; //常量ti 公式:floor(abs(sin(i+1))×(2pow32) private final int K[]={ 0xd76aa478,0xe8c7b756,0x242070db,0xc1bdceee, 0xf57c0faf,0x4787c62a,0xa8304613,0xfd469501,0x698098d8, 0x8b44f7af,0xffff5bb1,0x895cd7be,0x6b901122,0xfd987193, 0xa679438e,0x49b40821,0xf61e2562,0xc040b340,0x265e5a51, 0xe9b6c7aa,0xd62f105d,0x02441453,0xd8a1e681,0xe7d3fbc8, 0x21e1cde6,0xc33707d6,0xf4d50d87,0x455a14ed,0xa9e3e905, 0xfcefa3f8,0x676f02d9,0x8d2a4c8a,0xfffa3942,0x8771f681, 0x6d9d6122,0xfde5380c,0xa4beea44,0x4bdecfa9,0xf6bb4b60, 0xbebfbc70,0x289b7ec6,0xeaa127fa,0xd4ef3085,0x04881d05, 0xd9d4d039,0xe6db99e5,0x1fa27cf8,0xc4ac5665,0xf4292244, 0x432aff97,0xab9423a7,0xfc93a039,0x655b59c3,0x8f0ccc92, 0xffeff47d,0x85845dd1,0x6fa87e4f,0xfe2ce6e0,0xa3014314, 0x4e0811a1,0xf7537e82,0xbd3af235,0x2ad7d2bb,0xeb86d391}; //向左位移数,计算方法未知 private final int s[]={ 7,12,17,22,7,12,17,22,7,12,17,22,7, 12,17,22,5,9,14,20,5,9,14,20,5,9,14,20,5,9,14,20, 4,11,16,23,4,11,16,23,4,11,16,23,4,11,16,23,6,10, 15,21,6,10,15,21,6,10,15,21,6,10,15,21}; //初始化函数 private void init(){ Atemp=A; Btemp=B; Ctemp=C; Dtemp=D; } //移动一定位数 private int shift(int a,int s){ return(a< >>(32-s));//右移的时候，高位一定要补零，而不是补充符号位 } //主循环 private void MainLoop(int M[]){ int F,g; int a=Atemp; int b=Btemp; int c=Ctemp; int d=Dtemp; for(int i = 0; i < 64; i ++){ if(i<16){ F=(b&c)|((~b)&d); g=i; }else if(i<32){ F=(d&b)|((~d)&c); g=(5*i+1)%16; }else if(i<48){ F=b^c^d; g=(3*i+5)%16; }else{ F=c^(b|(~d)); g=(7*i)%16; } int tmp=d; d=c; c=b; b=b+shift(a+F+K[i]+M[g],s[i]); a=tmp; } Atemp=a+Atemp; Btemp=b+Btemp; Ctemp=c+Ctemp; Dtemp=d+Dtemp; } /* *填充函数 *处理后应满足bits≡448(mod512),字节就是bytes≡56（mode64) *填充方式为先加一个0,其它位补零 *最后加上64位的原来长度 */ private int[] add(String str){ int num=((str.length()+8)/64)+1;//以512位，64个字节为一组 int strByte[]=new int[num*16];//64/4=16，所以有16个整数 for(int i=0;i >2]|=str.charAt(i)<<((i%4)*8);//一个整数存储四个字节，小端序 } strByte[i>>2]|=0x80<<((i%4)*8);//尾部添加1 //添加原长度，长度指位的长度，所以要乘8，然后是小端序，所以放在倒数第二个,这里长度只用了32位 strByte[num*16-2]=str.length()*8; return strByte; } //调用函数 public String getMD5(String source){ init(); int strByte[]=add(source); for(int i=0;i >i*8)%(1<<8))&0xff)).replace(' ', '0'); } return str; } //单例 private static MD5 instance; public static MD5 getInstance(){ if(instance==null){ instance=new MD5(); } return instance; } private MD5(){ }; public static void main(String[] args){ String str=MD5.getInstance().getMD5("123"); System.out.println(str); }} function md5(string) { function md5_RotateLeft(lValue, iShiftBits) { return (lValue << iShiftBits) | (lValue >>> (32 - iShiftBits)); } function md5_AddUnsigned(lX, lY) { var lX4, lY4, lX8, lY8, lResult; lX8 = (lX & 0x80000000); lY8 = (lY & 0x80000000); lX4 = (lX & 0x40000000); lY4 = (lY & 0x40000000); lResult = (lX & 0x3FFFFFFF) + (lY & 0x3FFFFFFF); if (lX4 & lY4) { return (lResult ^ 0x80000000 ^ lX8 ^ lY8); } if (lX4 | lY4) { if (lResult & 0x40000000) { return (lResult ^ 0xC0000000 ^ lX8 ^ lY8); } else { return (lResult ^ 0x40000000 ^ lX8 ^ lY8); } } else { return (lResult ^ lX8 ^ lY8); } } function md5_F(x, y, z) { return (x & y) | ((~x) & z); } function md5_G(x, y, z) { return (x & z) | (y & (~z)); } function md5_H(x, y, z) { return (x ^ y ^ z); } function md5_I(x, y, z) { return (y ^ (x | (~z))); } function md5_FF(a, b, c, d, x, s, ac) { a = md5_AddUnsigned(a, md5_AddUnsigned(md5_AddUnsigned(md5_F(b, c, d), x), ac)); return md5_AddUnsigned(md5_RotateLeft(a, s), b); }; function md5_GG(a, b, c, d, x, s, ac) { a = md5_AddUnsigned(a, md5_AddUnsigned(md5_AddUnsigned(md5_G(b, c, d), x), ac)); return md5_AddUnsigned(md5_RotateLeft(a, s), b); }; function md5_HH(a, b, c, d, x, s, ac) { a = md5_AddUnsigned(a, md5_AddUnsigned(md5_AddUnsigned(md5_H(b, c, d), x), ac)); return md5_AddUnsigned(md5_RotateLeft(a, s), b); }; function md5_II(a, b, c, d, x, s, ac) { a = md5_AddUnsigned(a, md5_AddUnsigned(md5_AddUnsigned(md5_I(b, c, d), x), ac)); return md5_AddUnsigned(md5_RotateLeft(a, s), b); }; function md5_ConvertToWordArray(string) { var lWordCount; var lMessageLength = string.length; var lNumberOfWords_temp1 = lMessageLength + 8; var lNumberOfWords_temp2 = (lNumberOfWords_temp1 - (lNumberOfWords_temp1 % 64)) / 64; var lNumberOfWords = (lNumberOfWords_temp2 + 1) * 16; var lWordArray = Array(lNumberOfWords - 1); var lBytePosition = 0; var lByteCount = 0; while (lByteCount < lMessageLength) { lWordCount = (lByteCount - (lByteCount % 4)) / 4; lBytePosition = (lByteCount % 4) * 8; lWordArray[lWordCount] = (lWordArray[lWordCount] | (string.charCodeAt(lByteCount) << lBytePosition)); lByteCount++; } lWordCount = (lByteCount - (lByteCount % 4)) / 4; lBytePosition = (lByteCount % 4) * 8; lWordArray[lWordCount] = lWordArray[lWordCount] | (0x80 << lBytePosition); lWordArray[lNumberOfWords - 2] = lMessageLength << 3; lWordArray[lNumberOfWords - 1] = lMessageLength >>> 29; return lWordArray; }; function md5_WordToHex(lValue) { var WordToHexValue = "", WordToHexValue_temp = "", lByte, lCount; for (lCount = 0; lCount <= 3; lCount++) { lByte = (lValue >>> (lCount * 8)) & 255; WordToHexValue_temp = "0" + lByte.toString(16); WordToHexValue = WordToHexValue + WordToHexValue_temp.substr(WordToHexValue_temp.length - 2, 2); } return WordToHexValue; }; function md5_Utf8Encode(string) { string = string.replace(/\r\n/g, "\n"); var utftext = ""; for (var n = 0; n < string.length; n++) { var c = string.charCodeAt(n); if (c < 128) { utftext += String.fromCharCode(c); } else if ((c > 127) && (c < 2048)) { utftext += String.fromCharCode((c >> 6) | 192); utftext += String.fromCharCode((c & 63) | 128); } else { utftext += String.fromCharCode((c >> 12) | 224); utftext += String.fromCharCode(((c >> 6) & 63) | 128); utftext += String.fromCharCode((c & 63) | 128); } } return utftext; }; var x = Array(); var k, AA, BB, CC, DD, a, b, c, d; var S11 = 7, S12 = 12, S13 = 17, S14 = 22; var S21 = 5, S22 = 9, S23 = 14, S24 = 20; var S31 = 4, S32 = 11, S33 = 16, S34 = 23; var S41 = 6, S42 = 10, S43 = 15, S44 = 21; string = md5_Utf8Encode(string); x = md5_ConvertToWordArray(string); a = 0x67452301; b = 0xEFCDAB89; c = 0x98BADCFE; d = 0x10325476; for (k = 0; k < x.length; k += 16) { AA = a; BB = b; CC = c; DD = d; a = md5_FF(a, b, c, d, x[k + 0], S11, 0xD76AA478); d = md5_FF(d, a, b, c, x[k + 1], S12, 0xE8C7B756); c = md5_FF(c, d, a, b, x[k + 2], S13, 0x242070DB); b = md5_FF(b, c, d, a, x[k + 3], S14, 0xC1BDCEEE); a = md5_FF(a, b, c, d, x[k + 4], S11, 0xF57C0FAF); d = md5_FF(d, a, b, c, x[k + 5], S12, 0x4787C62A); c = md5_FF(c, d, a, b, x[k + 6], S13, 0xA8304613); b = md5_FF(b, c, d, a, x[k + 7], S14, 0xFD469501); a = md5_FF(a, b, c, d, x[k + 8], S11, 0x698098D8); d = md5_FF(d, a, b, c, x[k + 9], S12, 0x8B44F7AF); c = md5_FF(c, d, a, b, x[k + 10], S13, 0xFFFF5BB1); b = md5_FF(b, c, d, a, x[k + 11], S14, 0x895CD7BE); a = md5_FF(a, b, c, d, x[k + 12], S11, 0x6B901122); d = md5_FF(d, a, b, c, x[k + 13], S12, 0xFD987193); c = md5_FF(c, d, a, b, x[k + 14], S13, 0xA679438E); b = md5_FF(b, c, d, a, x[k + 15], S14, 0x49B40821); a = md5_GG(a, b, c, d, x[k + 1], S21, 0xF61E2562); d = md5_GG(d, a, b, c, x[k + 6], S22, 0xC040B340); c = md5_GG(c, d, a, b, x[k + 11], S23, 0x265E5A51); b = md5_GG(b, c, d, a, x[k + 0], S24, 0xE9B6C7AA); a = md5_GG(a, b, c, d, x[k + 5], S21, 0xD62F105D); d = md5_GG(d, a, b, c, x[k + 10], S22, 0x2441453); c = md5_GG(c, d, a, b, x[k + 15], S23, 0xD8A1E681); b = md5_GG(b, c, d, a, x[k + 4], S24, 0xE7D3FBC8); a = md5_GG(a, b, c, d, x[k + 9], S21, 0x21E1CDE6); d = md5_GG(d, a, b, c, x[k + 14], S22, 0xC33707D6); c = md5_GG(c, d, a, b, x[k + 3], S23, 0xF4D50D87); b = md5_GG(b, c, d, a, x[k + 8], S24, 0x455A14ED); a = md5_GG(a, b, c, d, x[k + 13], S21, 0xA9E3E905); d = md5_GG(d, a, b, c, x[k + 2], S22, 0xFCEFA3F8); c = md5_GG(c, d, a, b, x[k + 7], S23, 0x676F02D9); b = md5_GG(b, c, d, a, x[k + 12], S24, 0x8D2A4C8A); a = md5_HH(a, b, c, d, x[k + 5], S31, 0xFFFA3942); d = md5_HH(d, a, b, c, x[k + 8], S32, 0x8771F681); c = md5_HH(c, d, a, b, x[k + 11], S33, 0x6D9D6122); b = md5_HH(b, c, d, a, x[k + 14], S34, 0xFDE5380C); a = md5_HH(a, b, c, d, x[k + 1], S31, 0xA4BEEA44); d = md5_HH(d, a, b, c, x[k + 4], S32, 0x4BDECFA9); c = md5_HH(c, d, a, b, x[k + 7], S33, 0xF6BB4B60); b = md5_HH(b, c, d, a, x[k + 10], S34, 0xBEBFBC70); a = md5_HH(a, b, c, d, x[k + 13], S31, 0x289B7EC6); d = md5_HH(d, a, b, c, x[k + 0], S32, 0xEAA127FA); c = md5_HH(c, d, a, b, x[k + 3], S33, 0xD4EF3085); b = md5_HH(b, c, d, a, x[k + 6], S34, 0x4881D05); a = md5_HH(a, b, c, d, x[k + 9], S31, 0xD9D4D039); d = md5_HH(d, a, b, c, x[k + 12], S32, 0xE6DB99E5); c = md5_HH(c, d, a, b, x[k + 15], S33, 0x1FA27CF8); b = md5_HH(b, c, d, a, x[k + 2], S34, 0xC4AC5665); a = md5_II(a, b, c, d, x[k + 0], S41, 0xF4292244); d = md5_II(d, a, b, c, x[k + 7], S42, 0x432AFF97); c = md5_II(c, d, a, b, x[k + 14], S43, 0xAB9423A7); b = md5_II(b, c, d, a, x[k + 5], S44, 0xFC93A039); a = md5_II(a, b, c, d, x[k + 12], S41, 0x655B59C3); d = md5_II(d, a, b, c, x[k + 3], S42, 0x8F0CCC92); c = md5_II(c, d, a, b, x[k + 10], S43, 0xFFEFF47D); b = md5_II(b, c, d, a, x[k + 1], S44, 0x85845DD1); a = md5_II(a, b, c, d, x[k + 8], S41, 0x6FA87E4F); d = md5_II(d, a, b, c, x[k + 15], S42, 0xFE2CE6E0); c = md5_II(c, d, a, b, x[k + 6], S43, 0xA3014314); b = md5_II(b, c, d, a, x[k + 13], S44, 0x4E0811A1); a = md5_II(a, b, c, d, x[k + 4], S41, 0xF7537E82); d = md5_II(d, a, b, c, x[k + 11], S42, 0xBD3AF235); c = md5_II(c, d, a, b, x[k + 2], S43, 0x2AD7D2BB); b = md5_II(b, c, d, a, x[k + 9], S44, 0xEB86D391); a = md5_AddUnsigned(a, AA); b = md5_AddUnsigned(b, BB); c = md5_AddUnsigned(c, CC); d = md5_AddUnsigned(d, DD); } return (md5_WordToHex(a) + md5_WordToHex(b) + md5_WordToHex(c) + md5_WordToHex(d)).toLowerCase();} 转载地址：http://jlrai.baihongyu.com/