MD5的全称是Message-Digest Algorithm 5（信息-摘要算法）。
MD5算法加密~16位、32位、64位。
1991年，由Ronald L. Rivest开发出来，经MD2、MD3和MD4发展而来。MD5是非常安全的。
消息摘要（Message Digest）又称为数字摘要(Digital Digest)。它是一个唯一对应一个消息或文本的固定长度的值，它由一个单向Hash加密函数对消息进行作用而产生。如果消息在途中改变了，则接收者通过对收到消息的新产生的摘要与原摘要比较，就可知道消息是否被改变了。因此消息摘要保证了消息的完整性。 消息摘要采用单向Hash 函数将需加密的明文"摘要"成一串128bit的密文，这一串密文亦称为数字指纹(Finger Print)，它有固定的长度，且不同的明文摘要成密文，其结果总是不同的，而同样的明文其摘要必定一致。这样这串摘要便可成为验证明文是否是"真身"的"指纹"了。
因为MD5是基于消息摘要原理的，消息摘要的基本特征就是很难根据摘要推算出消息报文。
java实现代码：
package com.ts.u;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import sun.misc.BASE64Encoder;
/**
* MD5 encrypt algorithm.
* Encryption irreversible.
* @author Tony_tian
* @version 0.0.1
2015-10-15 12:57:12
* */
public final class MD5 {
/**Determine encrypt algorithm MD5*/
private static final String ALGORITHM_MD5 = "MD5";
/**UTF-8 Encoding*/
private static final String UTF_8 = "UTF-8";
/**
* MD5 16bit Encrypt Methods.
* @param readyEncryptStr ready encrypt string
* @return String encrypt result string
* @throws NoSuchAlgorithmException
* */
public static final String MD5_16bit(String readyEncryptStr) throws NoSuchAlgorithmException{
if(readyEncryptStr != null){
return MD5.MD5_32bit(readyEncryptStr).substring(8, 24);
}else{
return null;
}
}
/**
* MD5 32bit Encrypt Methods.
* @param readyEncryptStr ready encrypt string
* @return String encrypt result string
* @throws NoSuchAlgorithmException
* */
public static final String MD5_32bit(String readyEncryptStr) throws NoSuchAlgorithmException{
if(readyEncryptStr != null){
//Get MD5 digest algorithm's MessageDigest's instance.
MessageDigest md = MessageDigest.getInstance(ALGORITHM_MD5);
//Use specified byte update digest.
md.update(readyEncryptStr.getBytes());
//Get cipher text
byte [] b = md.digest();
//The cipher text converted to hexadecimal string
StringBuilder su = new StringBuilder();
//byte array switch hexadecimal number.
for(int offset = 0,bLen = b.length; offset < bLen; offset++){
String haxHex = Integer.toHexString(b[offset] & 0xFF);
if(haxHex.length() < 2){
su.append("0");
}
su.append(haxHex);
}
return su.toString();
}else{
return null;
}
}
/**
* MD5 32bit Encrypt Methods.
* @param readyEncryptStr ready encrypt string
* @return String encrypt result string
* @throws NoSuchAlgorithmException
* */
public static final String MD5_32bit1(String readyEncryptStr) throws NoSuchAlgorithmException{
if(readyEncryptStr != null){
//The cipher text converted to hexadecimal string
StringBuilder su = new StringBuilder();
//Get MD5 digest algorithm's MessageDigest's instance.
MessageDigest md = MessageDigest.getInstance(ALGORITHM_MD5);
byte [] b = md.digest(readyEncryptStr.getBytes());
int temp = 0;
//byte array switch hexadecimal number.
for(int offset = 0,bLen = b.length; offset < bLen; offset++){
temp = b[offset];
if(temp < 0){
temp += 256;
}
int d1 = temp / 16;
int d2 = temp % 16;
su.append(Integer.toHexString(d1) + Integer.toHexString(d2)) ;
}
return su.toString();
}else{
return null;
}
}
/**
* MD5 32bit Encrypt Methods.
* @param readyEncryptStr ready encrypt string
* @return String encrypt result string
* @throws NoSuchAlgorithmException
* */
public static final String MD5_32bit2(String readyEncryptStr) throws NoSuchAlgorithmException{
if(readyEncryptStr != null){
//The cipher text converted to hexadecimal string
StringBuilder su = new StringBuilder();
//Get MD5 digest algorithm's MessageDigest's instance.
MessageDigest md = MessageDigest.getInstance(ALGORITHM_MD5);
//Use specified byte update digest.
md.update(readyEncryptStr.getBytes());
byte [] b = md.digest();
int temp = 0;
//byte array switch hexadecimal number.
for(int offset = 0,bLen = b.length; offset < bLen; offset++){
temp = b[offset];
if(temp < 0){
temp += 256;
}
if(temp < 16){
su.append("0");
}
su.append(Integer.toHexString(temp));
}
return su.toString();
}else{
return null;
}
}
/**
* MD5 64bit Encrypt Methods.
* @param readyEncryptStr ready encrypt string
* @return String encrypt result string
* @throws NoSuchAlgorithmException
* @throws UnsupportedEncodingException
* */
public static final String MD5_64bit(String readyEncryptStr) throws NoSuchAlgorithmException, UnsupportedEncodingException{
MessageDigest md = MessageDigest.getInstance(ALGORITHM_MD5);
BASE64Encoder base64Encoder = new BASE64Encoder();
return base64Encoder.encode(md.digest(readyEncryptStr.getBytes(UTF_8)));
}
public static void main(String[] args) {
try {
String md516 = MD5.MD5_16bit("kaka123");
System.out.println("16bit-md5:\n" + md516); //
String md532 = MD5.MD5_32bit("kaka123");
String md5321 = MD5.MD5_32bit1("kaka123");
String md5322 = MD5.MD5_32bit2("kaka123");
System.out.println("32bit-md5:"); //5d052f1e32af4e4ac2544a5fc2a9b992
System.out.println("1: " + md532);
System.out.println("2: " + md5321);
System.out.println("3: " + md5322);
String md564 = MD5.MD5_64bit("kaka123");
System.out.println("64bit-md5:\n" + md564); //
} catch (Exception e) {
e.printStackTrace();
}
}
}
运行结果：
16bit-md5:
32af4e4ac2544a5f
32bit-md5:
1: 5d052f1e32af4e4ac2544a5fc2a9b992
2: 5d052f1e32af4e4ac2544a5fc2a9b992
3: 5d052f1e32af4e4ac2544a5fc2a9b992
64bit-md5:
XQUvHjKvTkrCVEpfwqm5kg==
转载自：https://blog.csdn.net/typa01_kk/article/details/49152173