ECB (Electronic Codebook) mode is one of the simplest and most basic encryption modes in the Java Cryptography Extension (JCE). It is part of the Java Security API and allows for block encryption and decryption using a symmetric encryption algorithm with a fixed key.

ECB mode works by dividing the plaintext message into fixed-size blocks and encrypting each block independently using the same encryption key. This mode does not provide any additional security measures, as identical plaintext blocks will always produce identical ciphertext blocks. Therefore, it is not suitable for encrypting large messages or when confidentiality and security are paramount.

Here’s an example of how to use ECB mode in Java JCE to encrypt and decrypt a message using the AES (Advanced Encryption Standard) algorithm:

import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.util.Base64;

public class ECBModeExample {
    private static final String ENCRYPTION_ALGORITHM = "AES";
    private static final String ENCRYPTION_MODE = "ECB";
    private static final String PADDING_MODE = "NoPadding";

    public static void main(String[] args) throws Exception {
        String plaintext = "This is a secret message";
        String encryptionKey = "ThisIsASecretKey";

        // Create a secret key from the encryption key
        SecretKey secretKey = new SecretKeySpec(encryptionKey.getBytes(StandardCharsets.UTF_8), ENCRYPTION_ALGORITHM);

        // Initialize the cipher with the encryption algorithm, mode, and padding
        Cipher cipher = Cipher.getInstance(ENCRYPTION_ALGORITHM + "/" + ENCRYPTION_MODE + "/" + PADDING_MODE);
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);

        // Encrypt the plaintext message
        byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes(StandardCharsets.UTF_8));

        // Convert the encrypted bytes to a Base64-encoded string
        String encryptedText = Base64.getEncoder().encodeToString(encryptedBytes);

        System.out.println("Encrypted message: " + encryptedText);

        // Decrypt the encrypted message
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        byte[] decryptedBytes = cipher.doFinal(Base64.getDecoder().decode(encryptedText));

        // Convert the decrypted bytes to a string
        String decryptedText = new String(decryptedBytes, StandardCharsets.UTF_8);

        System.out.println("Decrypted message: " + decryptedText);
    }
}

In the above example, we first define the encryption algorithm (AES), encryption mode (ECB), and padding mode (NoPadding). Then, we generate a secret key from the encryption key using the SecretKeySpec class.

Next, we initialize the cipher with the encryption algorithm, mode, and padding using the Cipher.getInstance() method. We then encrypt the plaintext message using the doFinal() method and encode the encrypted bytes to a Base64-encoded string.

To decrypt the encrypted message, we initialize the cipher in decryption mode and decrypt the bytes using the same key and doFinal() method. Finally, we convert the decrypted bytes to a string and print it.

Remember, ECB mode is considered insecure for most practical applications, and it is recommended to use more secure modes like CBC (Cipher Block Chaining) or GCM (Galois/Counter Mode) along with a secure padding scheme.

#Java #JCE