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1import java.util.Base64;    
2import javax.crypto.Cipher;  
3import javax.crypto.KeyGenerator;   
4import javax.crypto.SecretKey;
5
6public class EncryptionDecryptionAES {  
7    static Cipher cipher;  
8
9    public static void main(String[] args) throws Exception {
10        /* 
11         create key 
12         If we need to generate a new key use a KeyGenerator
13         If we have existing plaintext key use a SecretKeyFactory
14        */ 
15        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
16        keyGenerator.init(128); // block size is 128bits
17        SecretKey secretKey = keyGenerator.generateKey();
18
19        /*
20          Cipher Info
21          Algorithm : for the encryption of electronic data
22          mode of operation : to avoid repeated blocks encrypt to the same values.
23          padding: ensuring messages are the proper length necessary for certain ciphers 
24          mode/padding are not used with stream cyphers.  
25         */
26        cipher = Cipher.getInstance("AES"); //SunJCE provider AES algorithm, mode(optional) and padding schema(optional)  
27
28        String plainText = "AES Symmetric Encryption Decryption";
29        System.out.println("Plain Text Before Encryption: " + plainText);
30
31        String encryptedText = encrypt(plainText, secretKey);
32        System.out.println("Encrypted Text After Encryption: " + encryptedText);
33
34        String decryptedText = decrypt(encryptedText, secretKey);
35        System.out.println("Decrypted Text After Decryption: " + decryptedText);
36    }
37
38    public static String encrypt(String plainText, SecretKey secretKey)
39            throws Exception {
40        byte[] plainTextByte = plainText.getBytes();
41        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
42        byte[] encryptedByte = cipher.doFinal(plainTextByte);
43        Base64.Encoder encoder = Base64.getEncoder();
44        String encryptedText = encoder.encodeToString(encryptedByte);
45        return encryptedText;
46    }
47
48    public static String decrypt(String encryptedText, SecretKey secretKey)
49            throws Exception {
50        Base64.Decoder decoder = Base64.getDecoder();
51        byte[] encryptedTextByte = decoder.decode(encryptedText);
52        cipher.init(Cipher.DECRYPT_MODE, secretKey);
53        byte[] decryptedByte = cipher.doFinal(encryptedTextByte);
54        String decryptedText = new String(decryptedByte);
55        return decryptedText;
56    }
57}