javax.crypto.BadPaddingException: Decryption error : while doing only Decrypt to an already encypted string from DB

Question

This error is already discussed in several links.

I got the similar kind of errors, But my scenario is little different than others. I need

only Decryption . not Encryption.

In my case, an encrypted message is already stored in the DB. I got that as String and now need to only decrypt it to get the original String.

Any suggestions will be very helpful.

My piece of code is as follows:

String encodedStr = "c2J7RiP1CY++gfdE7Ke/xD1fSOOdO7DvprdZZUDws9Yl8DmYJV64zGV9vvK/TMEfALqSPH8KcZik8XvmLowpjJWzYY2Of1aytHaya0ULwmopklRWlkaS5sjL80jjyhaRN2O+zQNarbAQy8g3VtXX643T2AhDTsT+NKFsCcpH4xbqmViwD1GXQQLsLwuKZx1POAtyC0UaMjQ2SrzR+eVEiSgKPDABDKIRbOyBEXRcJMK/t/P7uIk9tJ/p1X2JqQOO7GMO/1x7rvF6Pb1Fik2tmQv5qL1W6/kV97/VT5Hpi9uh6zdCFO7sstYvgkxxbs3gTyJ5raWlATVU6a/0B/Q50w==";
KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");
keyGen.initialize(2048);
KeyPair pair = keyGen.generateKeyPair();
PrivateKey privateKey = pair.getPrivate();
PublicKey publicKey = pair.getPublic();

Cipher cipher = Cipher.getInstance("RSA");
// Encryption is not required.
//cipher.init(Cipher.ENCRYPT_MODE, privateKey);
//String ss =Base64.encodeBase64String(cipher.doFinal(encodedStr.getBytes("UTF-8")));
//System.out.println(ss);

// Only decryption is required.
cipher.init(Cipher.DECRYPT_MODE, publicKey);
String sss = new String(cipher.doFinal(Base64.decodeBase64(encodedStr)), "UTF-8");
System.out.println(sss);

And I'm getting below exception everytime at the line cipher.doFinal(Base64.decodeBase64(encodedStr) :

Exception in thread "main" javax.crypto.BadPaddingException: Decryption error
    at sun.security.rsa.RSAPadding.unpadV15(RSAPadding.java:383)
    at sun.security.rsa.RSAPadding.unpad(RSAPadding.java:294)
    at com.sun.crypto.provider.RSACipher.doFinal(RSACipher.java:356)
    at com.sun.crypto.provider.RSACipher.engineDoFinal(RSACipher.java:389)
    at javax.crypto.Cipher.doFinal(Cipher.java:2164)
    at com.sprint.neo.bc4j.util.TestMain.main(TestMain.java:20)

Though I don't require encryption, the Cipher.ENCRYPT_MODE is working fine. But incase of Cipher.DECRYPT_MODE , it's throwing exception. Please suggest me, how can I only decrypt an already existing encrypted String from DB, to get the original String value.

Answer 1

Here is the piece of code which works:

public static void main(String[] args) {

    byte[] txt = "message".getBytes();
    byte[] encText;
    try{

        // Load the keystore
        KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
        char[] password = "keystorePassword".toCharArray();

        Key rsakey = ks.getKey("mykeyalias", password);
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");

        // Encrypt
        Certificate cert = ks.getCertificate("mykeyalias");
        try
        {
            cipher.init(Cipher.ENCRYPT_MODE, cert.getPublicKey());
            encText = cipher.doFinal(txt);
            System.out.println(encText.toString());
        }
        catch (Throwable e)
        {
            e.printStackTrace();
            return;
        }

        // Decrypt
        cipher.init(Cipher.DECRYPT_MODE, rsakey);
        String decrypted = new String(cipher.doFinal(encText));
        System.out.println(decrypted);


    } catch (Exception e) {
        System.out.println("error" + e);
    }

}

Answer 2

Your publicKey generated will be different each time and hence the encrypted String will be different. The string generated will no longer be valid for decryption. Try to read key secret from a file and use same encrypted string to decrypt.