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

Solution

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