Encryption & Decryption of username using KeyStore in Android M & older version?

Question

i\'m trying to encrypt and decrypt username in app using KeyStore,

Using KeyPairGeneratorSpec to create the key in older version like 18 to 22,

KeyPairGe

Answer 1

the cypher transformation depends on what parameters you give to KeyGenParameterSpec or KeyPairGeneratorSpec. If you want to use "RSA/ECB/PKCS1Padding" in both cases (Android M and below) change

spec.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_OAEP)

to

spec.setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1)

You can check which algorithms are available with the following piece of code:

    Provider[] providers = Security.getProviders();
    for (Provider p : providers) {
        Log.d(TAG, "provider: " + p.getName());
        Set<Provider.Service> services = p.getServices();
        for (Provider.Service s : services) {
            Log.d(TAG, "--> algorithm: " + s.getAlgorithm());
        }
    }

I avoided writing a lot of if-else by declaring an interface IKeyStoreHandler which provides all the necessary methods (add / remove keys, list all keys by their aliases, get private / public key, decrypt / encrypt text) and implementing it for both cases.