RSA Encryption: Difference between Java and Android

Question

I am using RSA to encrypt username and password on Android and decrypt them on server (tomcat 6, java 1.6). Android Encryption:

    PublicKey pubKey = readPublicKeyFromFile(mod, ex);
    Cipher cipher = Cipher.getInstance("RSA");
    cipher.init(Cipher.ENCRYPT_MODE, pubKey);
    byte[] cipherData = cipher.doFinal(data);
    return cipherData;

Java Tomcat Decryption:

    PrivateKey pubKey = readPrivateKeyFromFile(mod, ex);
    Cipher cipher = Cipher.getInstance("RSA");
    cipher.init(Cipher.DECRYPT_MODE, pubKey);
    byte[] cipherData = cipher.doFinal(data);
    return cipherData;

If I use the android part OUTSIDE android (Just in a main method) it works fine. But not inside my android (Emulator). On de server side I get the following error:

javax.crypto.BadPaddingException: Blocktype mismatch: 0
    at sun.security.rsa.RSAPadding.unpadV15(RSAPadding.java:311)
    at sun.security.rsa.RSAPadding.unpad(RSAPadding.java:255)
    at com.sun.crypto.provider.RSACipher.a(DashoA13*..)
    at com.sun.crypto.provider.RSACipher.engineDoFinal(DashoA13*..)
    at javax.crypto.Cipher.doFinal(DashoA13*..)

I keep the mod and ex as BigIntegers constants so I don't write them in to a file. I know that there are difference between java1.6 and java 1.5 encryption, so both are compiled with java 1.6.

Some debug info:

During debug in android I can see that pubKey contains modulus and exponent in hexadecimal. And if I debug in a main method (again the same code) I can see that pubKey contains modulus and exponent in decimal.

What am I doing wrong?

Thanks

Answer 1

Im doing RSA Encrypt in Android 2.2+ and decrypt on a tomcat 6 java 1.6 server.

I was getting this exact problem, reading all over the place and in part thanks to @Femi 's answer I came across what I needed.

The solution was to use the folowing algorithm specification for the Cipher:

Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");

This works doing encryption from both Android and BlackBerry smartphones. I know its been four months since the question was asked, but just in case someone else goes through this problem.

Answer 2

I suggest you use specific cipher initialization: as an example,

Cipher cipher = Cipher.getInstance("RSA/ECB/NoPadding");

will work on both. The exception you are getting ( BadPaddingException ) is occuring because the default cipher initialization padding appears to be different between the desktop JVM and the Android JVM.

Answer 3

Firstly, it looks like you're initializing both ciphers with the public key. Encryption uses public key, decryption used private key. I hope that's just a typo though.

I had a lot of trouble with RSA encryption as well, much was trial and error. I suggest you try another provider. I managed to implement RSA using BouncyCastle.

Cipher wrapper = Cipher.getInstance("RSA", "BC");
wrapper.init(Cipher.ENCRYPT_MODE, publicKey);
encryptedData= wrapper.doFinal(unencryptedData);

Although, I generated my own keypair since this was a session encryption.

kpg = KeyPairGenerator.getInstance("RSA");
        kpg.initialize(1024);
        KeyPair kp = kpg.genKeyPair();
        publicKey = kp.getPublic();
        privateKey = kp.getPrivate();