[Javasecurity]-AES encryption

1. AES algorithm

• The Advanced Encryption Standard (AES), also as known as Rijndael (its original name), was a specification for encryption O F Electronic data established by the U.S. National Institute, and Technology (NIST) in 2001.
• It uses a fixed long key to encrypt and decrypt data, available key size, $ A, 192, and bits.
• Use case:a want to send a message to friend B, and A does not want anyone else to see it. So a is a key to encrypt his message and share this key with B, tell B He need decrypt the message with this key later.

2. Encryption

1. Generate a key
2. Share This key with the B
3. Encrypt data with this key
4. transmit encrypted Data to B

Import Java.io.bufferedinputstream;import Java.io.bufferedoutputstream;import Java.io.fileinputstream;import Java.io.fileoutputstream;import Java.io.ioexception;import Java.security.invalidkeyexception;import Java.security.nosuchalgorithmexception;import Java.security.securerandom;import javax.crypto.BadPaddingException ; Import Javax.crypto.cipher;import Javax.crypto.illegalblocksizeexception;import Javax.crypto.keygenerator;import Javax.crypto.nosuchpaddingexception;import Javax.crypto.secretkey;import javax.crypto.shortbufferexception;/** * *            /public class Aesencrypt {public static void main (string[] args) throws NoSuchAlgorithmException, IOException, Nosuchpaddingexception, InvalidKeyException, Shortbufferexception, Illegalblocksizeexception, BADPADDINGEXC eption {//Generate key and store into file securerandom random = new SecureRandom ();//See below K        Eygenerator KeyGen = keygenerator.getinstance ("AES");    Keygen.init (random);    Secretkey Secretkey = Keygen.generatekey ();        FileOutputStream secretkeyout = new FileOutputStream (Util.path_secretkey);        Secretkeyout.write (secretkey.getencoded ());        Secretkeyout.close ();        Cipher Cipher aescipher = cipher.getinstance ("AES");        Aescipher.init (Cipher.encrypt_mode, Secretkey);        Encrypt Bufferedinputstream datain = new Bufferedinputstream (new FileInputStream (Util.path_data));        Bufferedoutputstream encrypteddataout = new Bufferedoutputstream (new FileOutputStream (util.path_data_encrypted));        byte[] inbytes = new byte[aescipher.getblocksize ()];        Byte[] Outbyte;        int Len;            while (len = Datain.read (inbytes)) >= 0) {outbyte = aescipher.update (inbytes, 0, Len);        Encrypteddataout.write (Outbyte);        } Outbyte = Aescipher.dofinal ();        Encrypteddataout.write (Outbyte);        Datain.close ();    Encrypteddataout.close (); }}

3. Decryption

1. Get and restore the key
2. Decrypt Data with key

Import Java.io.bufferedinputstream;import Java.io.bufferedoutputstream;import Java.io.fileinputstream;import Java.io.fileoutputstream;import Java.io.ioexception;import Java.security.invalidkeyexception;import Java.security.nosuchalgorithmexception;import Javax.crypto.badpaddingexception;import Javax.crypto.Cipher;import Javax.crypto.illegalblocksizeexception;import Javax.crypto.nosuchpaddingexception;import Javax.crypto.SecretKey; Import javax.crypto.spec.secretkeyspec;/** * Class documentation to being filled TODO */public class Aesdecrypt {public S tatic void Main (string[] args) throws IOException, ClassNotFoundException, NoSuchAlgorithmException, Nosuchpadd Ingexception, InvalidKeyException, illegalblocksizeexception, badpaddingexception {//Get key Fi        Leinputstream Secretkeyin = new FileInputStream (Util.path_secretkey);        byte[] secretkeybytes = new byte[secretkeyin.available ()];        Secretkeyin.read (secretkeybytes); Secretkeyin.closE ();        Secretkey Secretkey = new Secretkeyspec (secretkeybytes, "AES");        Cipher Cipher aescipher = cipher.getinstance ("AES");        Aescipher.init (Cipher.decrypt_mode, Secretkey); Decrypt Bufferedinputstream encrypteddatain = new Bufferedinputstream (New FileInputStream (Util.path_data_encrypt        ED));        Bufferedoutputstream decrypteddataout = new Bufferedoutputstream (new FileOutputStream (util.path_data_decrypted));        byte[] inbytes = new byte[aescipher.getblocksize ()];        Byte[] outbytes;        int Len;            while (len = Encrypteddatain.read (inbytes)) >= 0) {outbytes = aescipher.update (inbytes, 0, Len);        Decrypteddataout.write (outbytes);        } outbytes = Aescipher.dofinal ();        Decrypteddataout.write (outbytes);        Encrypteddatain.close ();    Decrypteddataout.close (); }}

Defectif key is intercepted puzzle the encrypted data are very easy.

[Javasecurity]-AES encryption