The application of MD5,SHA,RSA encryption algorithm in Java

1. MD5 encryption, often used to encrypt user name passwords, when the user is authenticated.





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





2. Sha encryption, similar to the use of MD5, but the two algorithms are different.





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





3. RSA encryption, RAS encryption allows decryption. Often used for encryption of text content.



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; 


  } 


}