为了防止用户登陆过程中信息被拦截导致信息泄露，我们应该在客户端就对用户密码进行加密。浏览器提交给服务器的是加密后的信息，即使被恶意拦截，被拦截信息也已做了加密处理，现在比较安全的一种加密算法是MD5加密算法，尽管MD5是一种单向的加密算法，但网上也有破解网站，所以为了进一步提高安全性，可以进行两次md5加密，或者结合其他的加密方法如3des等进行二次加密。
代码如下：
js版：
var hexcase = 0;
function hex_md5(a) {
if (a == "")
return a;
return rstr2hex(rstr_md5(str2rstr_utf8(a)))
}
function hex_hmac_md5(a, b) {
return rstr2hex(rstr_hmac_md5(str2rstr_utf8(a), str2rstr_utf8(b)))
}
function md5_vm_test() {
return hex_md5("abc").toLowerCase() == "900150983cd24fb0d6963f7d28e17f72"
}
function rstr_md5(a) {
return binl2rstr(binl_md5(rstr2binl(a), a.length * 8))
}
function rstr_hmac_md5(c, f) {
var e = rstr2binl(c);
if (e.length > 16) {
e = binl_md5(e, c.length * 8)
}
var a = Array(16), d = Array(16);
for ( var b = 0; b < 16; b++) {
a[b] = e[b] ^ 909522486;
d[b] = e[b] ^ 1549556828
}
var g = binl_md5(a.concat(rstr2binl(f)), 512 + f.length * 8);
return binl2rstr(binl_md5(d.concat(g), 512 + 128))
}
function rstr2hex(c) {
try {
hexcase
} catch (g) {
hexcase = 0
}
var f = hexcase ? "0123456789ABCDEF" : "0123456789abcdef";
var b = "";
var a;
for ( var d = 0; d < c.length; d++) {
a = c.charCodeAt(d);
b += f.charAt((a >>> 4) & 15) + f.charAt(a & 15)
}
return b
}
function str2rstr_utf8(c) {
var b = "";
var d = -1;
var a, e;
while (++d < c.length) {
a = c.charCodeAt(d);
e = d + 1 < c.length ? c.charCodeAt(d + 1) : 0;
if (55296 <= a && a <= 56319 && 56320 <= e && e <= 57343) {
a = 65536 + ((a & 1023) << 10) + (e & 1023);
d++
}
if (a <= 127) {
b += String.fromCharCode(a)
} else {
if (a <= 2047) {
b += String
.fromCharCode(192 | ((a >>> 6) & 31), 128 | (a & 63))
} else {
if (a <= 65535) {
b += String.fromCharCode(224 | ((a >>> 12) & 15),
128 | ((a >>> 6) & 63), 128 | (a & 63))
} else {
if (a <= 2097151) {
b += String.fromCharCode(240 | ((a >>> 18) & 7),
128 | ((a >>> 12) & 63),
128 | ((a >>> 6) & 63), 128 | (a & 63))
}
}
}
}
}
return b
}
function rstr2binl(b) {
var a = Array(b.length >> 2);
for ( var c = 0; c < a.length; c++) {
a[c] = 0
}
for ( var c = 0; c < b.length * 8; c += 8) {
a[c >> 5] |= (b.charCodeAt(c / 8) & 255) << (c % 32)
}
return a
}
function binl2rstr(b) {
var a = "";
for ( var c = 0; c < b.length * 32; c += 8) {
a += String.fromCharCode((b[c >> 5] >>> (c % 32)) & 255)
}
return a
}
function binl_md5(p, k) {
p[k >> 5] |= 128 << ((k) % 32);
p[(((k + 64) >>> 9) << 4) + 14] = k;
var o = 1732584193;
var n = -271733879;
var m = -1732584194;
var l = 271733878;
for ( var g = 0; g < p.length; g += 16) {
var j = o;
var h = n;
var f = m;
var e = l;
o = md5_ff(o, n, m, l, p[g + 0], 7, -680876936);
l = md5_ff(l, o, n, m, p[g + 1], 12, -389564586);
m = md5_ff(m, l, o, n, p[g + 2], 17, 606105819);
n = md5_ff(n, m, l, o, p[g + 3], 22, -1044525330);
o = md5_ff(o, n, m, l, p[g + 4], 7, -176418897);
l = md5_ff(l, o, n, m, p[g + 5], 12, 1200080426);
m = md5_ff(m, l, o, n, p[g + 6], 17, -1473231341);
n = md5_ff(n, m, l, o, p[g + 7], 22, -45705983);
o = md5_ff(o, n, m, l, p[g + 8], 7, 1770035416);
l = md5_ff(l, o, n, m, p[g + 9], 12, -1958414417);
m = md5_ff(m, l, o, n, p[g + 10], 17, -42063);
n = md5_ff(n, m, l, o, p[g + 11], 22, -1990404162);
o = md5_ff(o, n, m, l, p[g + 12], 7, 1804603682);
l = md5_ff(l, o, n, m, p[g + 13], 12, -40341101);
m = md5_ff(m, l, o, n, p[g + 14], 17, -1502002290);
n = md5_ff(n, m, l, o, p[g + 15], 22, 1236535329);
o = md5_gg(o, n, m, l, p[g + 1], 5, -165796510);
l = md5_gg(l, o, n, m, p[g + 6], 9, -1069501632);
m = md5_gg(m, l, o, n, p[g + 11], 14, 643717713);
n = md5_gg(n, m, l, o, p[g + 0], 20, -373897302);
o = md5_gg(o, n, m, l, p[g + 5], 5, -701558691);
l = md5_gg(l, o, n, m, p[g + 10], 9, 38016083);
m = md5_gg(m, l, o, n, p[g + 15], 14, -660478335);
n = md5_gg(n, m, l, o, p[g + 4], 20, -405537848);
o = md5_gg(o, n, m, l, p[g + 9], 5, 568446438);
l = md5_gg(l, o, n, m, p[g + 14], 9, -1019803690);
m = md5_gg(m, l, o, n, p[g + 3], 14, -187363961);
n = md5_gg(n, m, l, o, p[g + 8], 20, 1163531501);
o = md5_gg(o, n, m, l, p[g + 13], 5, -1444681467);
l = md5_gg(l, o, n, m, p[g + 2], 9, -51403784);
m = md5_gg(m, l, o, n, p[g + 7], 14, 1735328473);
n = md5_gg(n, m, l, o, p[g + 12], 20, -1926607734);
o = md5_hh(o, n, m, l, p[g + 5], 4, -378558);
l = md5_hh(l, o, n, m, p[g + 8], 11, -2022574463);
m = md5_hh(m, l, o, n, p[g + 11], 16, 1839030562);
n = md5_hh(n, m, l, o, p[g + 14], 23, -35309556);
o = md5_hh(o, n, m, l, p[g + 1], 4, -1530992060);
l = md5_hh(l, o, n, m, p[g + 4], 11, 1272893353);
m = md5_hh(m, l, o, n, p[g + 7], 16, -155497632);
n = md5_hh(n, m, l, o, p[g + 10], 23, -1094730640);
o = md5_hh(o, n, m, l, p[g + 13], 4, 681279174);
l = md5_hh(l, o, n, m, p[g + 0], 11, -358537222);
m = md5_hh(m, l, o, n, p[g + 3], 16, -722521979);
n = md5_hh(n, m, l, o, p[g + 6], 23, 76029189);
o = md5_hh(o, n, m, l, p[g + 9], 4, -640364487);
l = md5_hh(l, o, n, m, p[g + 12], 11, -421815835);
m = md5_hh(m, l, o, n, p[g + 15], 16, 530742520);
n = md5_hh(n, m, l, o, p[g + 2], 23, -995338651);
o = md5_ii(o, n, m, l, p[g + 0], 6, -198630844);
l = md5_ii(l, o, n, m, p[g + 7], 10, 1126891415);
m = md5_ii(m, l, o, n, p[g + 14], 15, -1416354905);
n = md5_ii(n, m, l, o, p[g + 5], 21, -57434055);
o = md5_ii(o, n, m, l, p[g + 12], 6, 1700485571);
l = md5_ii(l, o, n, m, p[g + 3], 10, -1894986606);
m = md5_ii(m, l, o, n, p[g + 10], 15, -1051523);
n = md5_ii(n, m, l, o, p[g + 1], 21, -2054922799);
o = md5_ii(o, n, m, l, p[g + 8], 6, 1873313359);
l = md5_ii(l, o, n, m, p[g + 15], 10, -30611744);
m = md5_ii(m, l, o, n, p[g + 6], 15, -1560198380);
n = md5_ii(n, m, l, o, p[g + 13], 21, 1309151649);
o = md5_ii(o, n, m, l, p[g + 4], 6, -145523070);
l = md5_ii(l, o, n, m, p[g + 11], 10, -1120210379);
m = md5_ii(m, l, o, n, p[g + 2], 15, 718787259);
n = md5_ii(n, m, l, o, p[g + 9], 21, -343485551);
o = safe_add(o, j);
n = safe_add(n, h);
m = safe_add(m, f);
l = safe_add(l, e)
}
return Array(o, n, m, l)
}
function md5_cmn(h, e, d, c, g, f) {
return safe_add(bit_rol(safe_add(safe_add(e, h), safe_add(c, f)), g), d)
}
function md5_ff(g, f, k, j, e, i, h) {
return md5_cmn((f & k) | ((~f) & j), g, f, e, i, h)
}
function md5_gg(g, f, k, j, e, i, h) {
return md5_cmn((f & j) | (k & (~j)), g, f, e, i, h)
}
function md5_hh(g, f, k, j, e, i, h) {
return md5_cmn(f ^ k ^ j, g, f, e, i, h)
}
function md5_ii(g, f, k, j, e, i, h) {
return md5_cmn(k ^ (f | (~j)), g, f, e, i, h)
}
function safe_add(a, d) {
var c = (a & 65535) + (d & 65535);
var b = (a >> 16) + (d >> 16) + (c >> 16);
return (b << 16) | (c & 65535)
}
function bit_rol(a, b) {
return (a << b) | (a >>> (32 - b))
};
java版(代码来源：http://www.cnblogs.com/computer-lzy/archive/2011/04/28/2031649.html)：
package md5; import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
/*
* MD5 加密算法
*/
public class MD5 { // 全局数组
private final static String[] strDigits = { "0", "1", "2", "3", "4", "5",
"6", "7", "8", "9", "a", "b", "c", "d", "e", "f" }; public MD5() {
} // 返回形式为数字跟字符串
private static String byteToArrayString(byte bByte) {
int iRet = bByte;
// System.out.println("iRet="+iRet);
if (iRet < 0) {
iRet += 256;
}
int iD1 = iRet / 16;
int iD2 = iRet % 16;
return strDigits[iD1] + strDigits[iD2];
} // 返回形式只为数字
private static String byteToNum(byte bByte) {
int iRet = bByte;
System.out.println("iRet1=" + iRet);
if (iRet < 0) {
iRet += 256;
}
return String.valueOf(iRet);
} // 转换字节数组为16进制字串
private static String byteToString(byte[] bByte) {
StringBuffer sBuffer = new StringBuffer();
for (int i = 0; i < bByte.length; i++) {
sBuffer.append(byteToArrayString(bByte[i]));
}
return sBuffer.toString();
} public static String GetMD5Code(String strObj) {
String resultString = null;
try {
resultString = new String(strObj);
MessageDigest md = MessageDigest.getInstance("MD5");
// md.digest() 该函数返回值为存放哈希值结果的byte数组
resultString = byteToString(md.digest(strObj.getBytes()));
} catch (NoSuchAlgorithmException ex) {
ex.printStackTrace();
}
return resultString;
} public static void main(String[] args) {
MD5 getMD5 = new MD5();
System.out.println(getMD5.GetMD5Code(getMD5.GetMD5Code("aaaaaa")));
}
}
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