javax.crypto.BadPaddingException : Decryption error

Question

I am trying to implement an RSA based encryption communication between my client and server. For this I generated RSA public and private keys using openssl in the following way :

openssl genrsa -out private.pem 2048 
openssl rsa -in private.pem -outform PEM -pubout -out public.pem
--generate modulus and exponent
openssl rsa -pubin -in public_key.pem -modulus -noout 
openssl rsa -pubin -in public_key.pem -text -noout

Using the above files, encryption is done on the Android side as follows :

   public static byte[] encrypt(BigInteger modulus, BigInteger exp, byte[] data) {
        try {
            KeyFactory kf = KeyFactory.getInstance("RSA");
            RSAPublicKeySpec keySpec = new RSAPublicKeySpec(modulus, exp);
            PublicKey publicKey = kf.generatePublic(keySpec);
            final Cipher cipher = Cipher.getInstance("RSA");
            cipher.init(Cipher.ENCRYPT_MODE, publicKey);
            return cipher.doFinal(data);
        } catch (Exception e) {
            FileLog.e("module" , e);
        }
        return null;
    }

This works fine and does encrypt the data. Now on the server side, I used the following code to decrypt. The private key is stored as a pkcs8 format key and that is read by java.

public static byte[] decrypt(byte[] data) throws IOException, NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException{
    String fileName = "location/of/private_key/file";
    File f = new File(fileName);
    FileInputStream fis = new FileInputStream(f);
    DataInputStream dis = new DataInputStream(fis);
    byte[] keyBytes = new byte[(int)f.length()];
    dis.readFully(keyBytes);
    dis.close();
    PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(keyBytes);
    KeyFactory kf = KeyFactory.getInstance("RSA");
    PrivateKey rsaPrivate = kf.generatePrivate(spec);
    Cipher cipher = Cipher.getInstance("RSA");
    cipher.init(Cipher.DECRYPT_MODE, rsaPrivate);
    return cipher.doFinal(data);
    }

On running this using eclipse on the server, I get the BadPaddingException: Decryption error problem. The length of the data is exactly 256 bytes and hence the length should not be an issue.

Any help would be truly helpful.

Thanks

Answer 1

Android using different padding algorithm. You need to use other algorithm like below:

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

There are quit number of posts out there.

You can refer

RSA BadPaddingException in Java - encrypt in Android decrypt in JRE

RSA Encryption: Difference between Java and Android