Crash casting AndroidKeyStoreRSAPrivateKey to RSAPrivateKey

I managed to get this working by removing the Provider from Cipher.getInstance and not casting to a RSAprivateKey.

KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry) entry;Cipher output = Cipher.getInstance("RSA/ECB/PKCS1Padding");output.init(Cipher.DECRYPT_MODE, privateKeyEntry.getPrivateKey());

I'm not 100% but I think the reason for this I believe is the change in marshmallow from OpenSSL to BoringSSL. https://developer.android.com/preview/behavior-changes.html#behavior-apache-http-client

Anyway, the above worked for M and below.

Issue

1. We are trying to parse "java.security.PrivateKey to java.security.interfaces.RSAPrivateKey" & "java.security.PublicKey to java.security.interfaces.RSAPublicKey". That's why we are getting ClassCastException.

Solution

1. We don't need to parse the key, we can directly use the "java.security.PrivateKey" & "java.security.PublicKey" for Encryption & Decryption.

Encryption

KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry)entry; PublicKey publicKey = privateKeyEntry.getCertificate().getPublicKey(); // Don't TypeCast to RSAPublicKey

Decryption

KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry)entry;PrivateKey privateKey = privateKeyEntry.getPrivateKey(); // Don't TypeCast to RSAPrivateKey

I resolved this issue by also following this(apart from @James answer above):On Android 6.0 you should not use "AndroidOpenSSL" for cipher creation, it would fail with "Need RSA private or public key" at cipher init for decryption. Simply use Cipher.getInstance("RSA/ECB/PKCS1Padding") and it will work.