One time pad, encryption and decryption

Question

I am trying to pick up cryptography and had been trying this exercise

Write a program (preferably Java) to generate a one-time pad, which is a relatively large file

Answer 1

Here you have a full working example:

    // convert secret text to byte array
    final byte[] secret = "secret".getBytes()

    final byte[] encoded = new byte[secret.length];
    final byte[] decoded = new byte[secret.length];

    // Generate random key (has to be exchanged)
    final byte[] key = new byte[secret.length];
    new SecureRandom().nextBytes(key);

    // Encrypt
    for (int i = 0; i < secret.length; i++) {
        encoded[i] = (byte) (secret[i] ^ key[i]);
    }

    // Decrypt
    for (int i = 0; i < encoded.length; i++) {
        decoded[i] = (byte) (encoded[i] ^ key[i]);
    }

    assertTrue(Arrays.equals(secret, decoded));