ECC Encryption and Decryption in Java

Question

Can we encrypt large files with ECC or it is like RSA works for small only? can anyone please recommend a good website for ECC Java implementation.

Thanks

Answer 1

In general you are required to perform hybrid encryption with ECC. ECIES for instance is basically a key agreement followed by symmetric encryption. So you cannot directly encrypt anything with ECIES, which is the most common ECC method for encryption. Basically you should couple it to a symmetric cipher. This is actually the best scheme for RSA encryption as well, most of the time.

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As you can see you can use this directly as a Cipher using CBC mode & PKCS#7 padding, but beware of the large header (117 bytes for a 384 curve, no less). This is required to perform the key derivation. Make sure that the public key is properly validated (I'm not sure about the Bouncy Castle code in this regards, haven't taken a look at it).

public static void main(String[] args) throws Exception {
    Security.addProvider(new BouncyCastleProvider());

    KeyPairGenerator ecKeyGen = KeyPairGenerator.getInstance("EC", BouncyCastleProvider.PROVIDER_NAME);
    ecKeyGen.initialize(new ECGenParameterSpec("brainpoolP384r1"));

    // doesn't work, which means we are dancing on the leading edge :)
    // KeyPairGenerator ecKeyGen = KeyPairGenerator.getInstance("EC");
    // ecKeyGen.initialize(new ECGenParameterSpec("secp384r1"));

    KeyPair ecKeyPair = ecKeyGen.generateKeyPair();
    System.out.println("What is slow?");

    Cipher iesCipher = Cipher.getInstance("ECIESwithAES");
    iesCipher.init(Cipher.ENCRYPT_MODE, ecKeyPair.getPublic());

    byte[] ciphertext = iesCipher.doFinal(com.google.common.base.Strings.repeat("owlstead", 1000).getBytes());

    iesCipher.init(Cipher.DECRYPT_MODE, ecKeyPair.getPrivate());
    byte[] plaintext = iesCipher.doFinal(ciphertext);

    System.out.println(Hex.toHexString(ciphertext));
    System.out.println(new String(plaintext));
}