这不是加密算法，而是摘要（哈希）算法，国内经常把二者搞混。
区别就在于，加密算法可逆，即通过一定的计算，明文、密文可以互推；摘要算法不可逆，即原文计算后可以得到摘要，但根据摘要不可计算得原文（彩虹表并非“计算”所得）。
MD5不是加密算法，它是Hash算法，所以它不可逆，也没法还原成原文。
你可以用base64、异或或者aes des等加密算法去实现。
1、base64加密
在页面中引入base64.js文件，调用方法为：
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123456789101112131415161718<!DOCTYPE HTML><html><head><meta charset="utf-8"><title>base64加密</title><script type="text/javascript" src="base64.js"></script><script type="text/javascript"> var b = new Base64() var str = b.encode("admin:admin") alert("base64 encode:" + str)//解密 str = b.decode(str) alert("base64 decode:" + str)</script></head><body></body></html>2、md5加密
在页面中引用md5.js文件，调用方法为
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1234567891011121314<!DOCTYPE HTML><html><head><meta charset="utf-8"><title>md5加密</title><script type="text/ecmascript" src="md5.js"></script><script type="text/javascript"> var hash = hex_md5("123dafd") alert(hash)</script></head><body></body></html>3、sha1加密
据说这是最安全的加密
页面中引入sha1.js，调用方法为
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1234567891011121314<!DOCTYPE HTML><html><head><meta charset="utf-8"><title>sha1加密</title><script type="text/ecmascript" src="sha1.js"></script><script type="text/javascript"> var sha = hex_sha1('mima123465') alert(sha)</script></head><body></body></html>一下为js们的源代码
base64.js：
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106/**** Base64 encode / decode** @author haitao.tu* @date 2010-04-26* @email tuhaitao@foxmail.com**/function Base64() { // private property _keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=" // public method for encoding this.encode = function (input) { var output = "" var chr1, chr2, chr3, enc1, enc2, enc3, enc4 var i = 0 input = _utf8_encode(input) while (i <input.length) { chr1 = input.charCodeAt(i++) chr2 = input.charCodeAt(i++) chr3 = input.charCodeAt(i++) enc1 = chr1 >>2 enc2 = ((chr1 &3) <<4) | (chr2 >>4) enc3 = ((chr2 &15) <<2) | (chr3 >>6) enc4 = chr3 &63 if (isNaN(chr2)) { enc3 = enc4 = 64 } else if (isNaN(chr3)) { enc4 = 64 } output = output + _keyStr.charAt(enc1) + _keyStr.charAt(enc2) + _keyStr.charAt(enc3) + _keyStr.charAt(enc4) } return output } // public method for decoding this.decode = function (input) { var output = "" var chr1, chr2, chr3 var enc1, enc2, enc3, enc4 var i = 0 input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "") while (i <input.length) { enc1 = _keyStr.indexOf(input.charAt(i++)) enc2 = _keyStr.indexOf(input.charAt(i++)) enc3 = _keyStr.indexOf(input.charAt(i++)) enc4 = _keyStr.indexOf(input.charAt(i++)) chr1 = (enc1 <<2) | (enc2 >>4) chr2 = ((enc2 &15) <<4) | (enc3 >>2) chr3 = ((enc3 &3) <<6) | enc4 output = output + String.fromCharCode(chr1) if (enc3 != 64) { output = output + String.fromCharCode(chr2) } if (enc4 != 64) { output = output + String.fromCharCode(chr3) } } output = _utf8_decode(output) return output } // private method for UTF-8 encoding _utf8_encode = function (string) { string = string.replace(/\r\n/g,"\n") var utftext = "" for (var n = 0n <string.lengthn++) { 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 } // private method for UTF-8 decoding _utf8_decode = function (utftext) { var string = "" var i = 0 var c = c1 = c2 = 0 while ( i <utftext.length ) { c = utftext.charCodeAt(i) if (c <128) { string += String.fromCharCode(c) i++ } else if((c >191) &&(c <224)) { c2 = utftext.charCodeAt(i+1) string += String.fromCharCode(((c &31) <<6) | (c2 &63)) i += 2 } else { c2 = utftext.charCodeAt(i+1) c3 = utftext.charCodeAt(i+2) string += String.fromCharCode(((c &15) <<12) | ((c2 &63) <<6) | (c3 &63)) i += 3 } } return string }}
