How to solve javax.crypto.IllegalBlockSizeException: data not block size aligned

Question

I am doing an assignment about use blowfish to do encryption & decryption in java.

I had added a provider, and get instance "Blowfish/ECB/NoPadding", but I still get this error when I do the encryption.

Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

e.g.:

public static byte[] encrypt(byte to_encrypt[], byte strkey[]) {
    try {           
        SecretKeySpec key = new SecretKeySpec(strkey, "Blowfish");
        Cipher cipher = Cipher.getInstance("Blowfish/ECB/NoPadding");
        cipher.init(Cipher.ENCRYPT_MODE, key);  
        return cipher.doFinal(to_encrypt); // <=========== error
    } catch (Exception e) { 
        e.printStackTrace();
        return null; 
    }
}

leads to

javax.crypto.IllegalBlockSizeException: data not block size aligned
    at org.bouncycastle2.jce.provider.JCEBlockCipher.engineDoFinal(JCEBlockCipher.java:686)
    at javax.crypto.Cipher.doFinal(Cipher.java:1171)

Thank you.

Answer 1

You've explicitly asked for a provider that doesn't do padding (notice the NoPadding in the instance name). Consequently, your input will not be padded.

Furthermore, this is a block cipher, so the input must be a multiple of the block length. With the crypto provider not doing padding, you need to ensure yourself that your input is a multiple of the block size, else encryption/decryption will not be possible and you'll get this error.

Thus you have two options in order to solve this:

1. Pad the input yourself to a multiple of the block size.
2. Choose a provider that does padding (e.g. PKCS5Padding), if you don't want to do it manually. Given the nature of your question, this is likely to be the best option.

Answer 2

You are using NoPadding and the size of your input data must not match the block size of the cipher, so an IllegalBlockSizeException is being thrown. If you use NoPadding you need to make sure that your input is a multiple of 8 bytes.

Try specifying a padding scheme. Change to Blowfish/CBC/PKCS5Padding and it should work.