To use CFB mode in Java JCE, you will need to follow these steps:

1. Import the necessary classes:

   import javax.crypto.Cipher;
   import javax.crypto.spec.IvParameterSpec;
   import javax.crypto.spec.SecretKeySpec;
   

2. Provide the key and initialization vector (IV) for your encryption/decryption process:

   String key = "0123456789abcdef"; // 16-byte key
   String iv = "1234567890abcdef"; // 16-byte initialization vector
   

3. Create instances of SecretKeySpec and IvParameterSpec using the provided key and IV:

   SecretKeySpec secretKeySpec = new SecretKeySpec(key.getBytes(), "AES");
   IvParameterSpec ivSpec = new IvParameterSpec(iv.getBytes());
   

4. Initialize the Cipher instance with the desired algorithm and mode:

   Cipher cipher = Cipher.getInstance("AES/CFB/NoPadding");
   

5. Initialize the Cipher instance in encryption or decryption mode with the specified key and IV:

   cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, ivSpec); // For encryption
   

   OR

   cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivSpec); // For decryption
   

6. Use the doFinal method to perform the encryption/decryption:

   byte[] input = "Hello, CFB!".getBytes();
   byte[] cipherText = cipher.doFinal(input);
   

Here’s a complete example of using CFB mode in Java JCE for encryption and decryption:

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class CFBExample {
    public static void main(String[] args) throws Exception {
        String key = "0123456789abcdef";
        String iv = "1234567890abcdef";

        SecretKeySpec secretKeySpec = new SecretKeySpec(key.getBytes(), "AES");
        IvParameterSpec ivSpec = new IvParameterSpec(iv.getBytes());

        Cipher cipher = Cipher.getInstance("AES/CFB/NoPadding");
        cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, ivSpec);

        byte[] input = "Hello, CFB!".getBytes();
        byte[] cipherText = cipher.doFinal(input);

        System.out.println("Encrypted text: " + new String(cipherText));

        cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, ivSpec);
        byte[] decryptedText = cipher.doFinal(cipherText);

        System.out.println("Decrypted text: " + new String(decryptedText));
    }
}

Remember to handle appropriate exceptions and provide error handling where necessary.

#Java #JCE