XML String encryption giving me Data must not be longer than 245 bytes when using RSA

Question

I have created following to method

public static PublicKey readPublicKey(String filename) throws IOException, NoSuchAlgorithmException, InvalidKeySpecException {

    PublicKey key = null;
    CertificateFactory fact;

    try {

        // MBFS certificate to be used
        FileInputStream is = new FileInputStream(filename);
        fact = CertificateFactory.getInstance("X.509");
        System.out.println(is.toString());
        X509Certificate cer = (X509Certificate) fact.generateCertificate(is);
        key = cer.getPublicKey();
        System.out.println(key.getAlgorithm());

    } catch (CertificateException e) {

        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return key;
}

for encryption

public static byte[] encrypt(PublicKey key, byte[] plaintext) throws NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException {

    Cipher cipher = Cipher.getInstance("RSA");
    cipher.init(Cipher.ENCRYPT_MODE, key);
    return cipher.doFinal(plaintext);
}

I have long xml string and using these both method as following

byte[] message = xmlMessage.getBytes();

byte[] secret = encrypt(publicKey, message);

But it is giving me Data must not be longer than 256 bytes when using rsa

Certificate is shard by client it is saying Signature algorithm sha256RS.

Henry Henry · Accepted Answer · 2017-09-23T10:50:38

Typically, you would use a symmetric cipher to encrypt the document (with a random secret key) and then just encrypt the key with RSA. This does not only overcome the length problem but is also much faster.

XML String encryption giving me Data must not be longer than 245 bytes when using RSA

1 Answers