Java中常用的加密算法应用MD5，SHA,RSA

http://www.west263.com/info/html/chengxusheji/Javajishu/20080225/35765.html

1. MD5加密，常用于加密用户名密码，当用户验证时。

protected byte[] encrypt(byte[] obj) ...{
try ...{
MessageDigest md5 = MessageDigest.getInstance("MD5");
md5.update(obj);
return md5.digest();
} catch (NoSuchAlgorithmException e) ...{
e.printStackTrace();
}
}

2. SHA加密，与MD5相似的用法，只是两者的算法不同。

protected byte[] encrypt(byte[] obj) ...{
try ...{
MessageDigest sha = MessageDigest.getInstance("SHA");
sha.update(obj);
return sha.digest();
} catch (NoSuchAlgorithmException e) ...{
e.printStackTrace();
}
}

3. RSA加密，RAS加密允许解密。常用于文本内容的加密。

import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import javax.crypto.Cipher;
/** *//**
* <b>RSAEncrypt</b>
* <p>
* @author maqujun
* @see
*/
public class RSAEncrypt ...{
/** *//**
* Main method for RSAEncrypt.
* @param args
*/
public static void main(String[] args) ...{
try ...{
RSAEncrypt encrypt = new RSAEncrypt();

String encryptText = "encryptText";
KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA");
keyPairGen.initialize(1024);
KeyPair keyPair = keyPairGen.generateKeyPair();
// Generate keys
RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
byte[] e = encrypt.encrypt(publicKey, encryptText.getBytes());
byte[] de = encrypt.decrypt(privateKey,e);
System.out.println(encrypt.bytesToString(e));
System.out.println(encrypt.bytesToString(de));
} catch (Exception e) ...{
e.printStackTrace();
}
}
/** *//**
* Change byte array to String.
* @return byte[]
*/
protected String bytesToString(byte[] encrytpByte) ...{
String result = "";
for (Byte bytes : encrytpByte) ...{
result = (char) bytes.intValue();
}
return result;
}
/** *//**
* Encrypt String.
* @return byte[]
*/
protected byte[] encrypt(RSAPublicKey publicKey, byte[] obj) ...{
if (publicKey != null) ...{
try ...{
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.ENCRYPT_MODE, publicKey);
return cipher.doFinal(obj);
} catch (Exception e) ...{
e.printStackTrace();
}
}
return null;
}
/** *//**
* Basic decrypt method
* @return byte[]
*/
protected byte[] decrypt(RSAPrivateKey privateKey, byte[] obj) ...{
if (privateKey != null) ...{
try ...{
Cipher cipher = Cipher.getInstance("RSA");
cipher.init(Cipher.DECRYPT_MODE, privateKey);
return cipher.doFinal(obj);
} catch (Exception e) ...{
e.printStackTrace();
}
}

return null;
}
}