java_encryption_PGP.java

//Generate Symmetric Key (AES with 128 bits)

KeyGenerator generator = KeyGenerator.getInstance("AES");
generator.init(128); // The AES key size in number of bits
SecretKey secKey = generator.generateKey();

//Encrypt plain text using AES
String plainText = "Please encrypt me urgently..."
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.ENCRYPT_MODE, secKey);
byte[] byteCipherText = aesCipher.doFinal(plainText.getBytes());

//Encrypt the key using RSA public key
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(2048);
KeyPair keyPair = kpg.generateKeyPair();

PublicKey puKey = keyPair.getPublic();
PrivateKey prKey = keyPair.getPrivate();

Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.PUBLIC_KEY, puKey);
byte[] encryptedKey = cipher.doFinal(secKey.getEncoded()/*Seceret Key From Step 1*/);

//Send encrypted data (byteCipherText) + encrypted AES Key (encryptedKey)
//On the client side, decrypt symmetric key using RSA private key

cipher.init(Cipher.PRIVATE_KEY, prKey);
byte[] decryptedKey = cipher.doFinal(encryptedKey);
//Decrypt the cipher text using decrypted symmetric key

//Convert bytes to AES SecertKey
SecretKey originalKey = new SecretKeySpec(decryptedKey , 0, decryptedKey .length, "AES");
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.DECRYPT_MODE, originalKey);
byte[] bytePlainText = aesCipher.doFinal(byteCipherText);
String plainText = new String(bytePlainText);`