Android - Encode & Decode Rsa With Private Key?

I am trying to encode and decode Strings on Android using a Private Key generated and stored using the Android Key Store Provider that was introduced in Android 4.3 I can successfu

Solution 1:

You are not using the public key for encryption.

When you are using asymmetric encryption algorithms, you need to use the public key to encrypt your data, and the private key only to decrypt it again.

Besides encryption, you can also use the private key for signing, but that's not what you want here, so let's forget about that for the moment.

If you take the public key from the generated pair, when you encrypt your string, and the private key when decrypting, you should get the desired result. The public key you can extract by accessing the certificate from the keystore-object that holds your private key.

Alternatively you could also use a symmetric algorithm like AES and by that make your work a lot easier. Plus, symmetric algorithms are usually much faster, which is why asymmetric algorithms are never used purely, but in conjunction with symmetric algorithms, building so-called hybrid algorithms.

Solution 2:

Signature generation is not the same thing as encryption. You need to encrypt with the public key and decrypt with the private key if you want encryption. If you want signature generation, you need to sign with the private key and verify with the public key. This order cannot be reversed nor can it be mixed (securely).