private static byte [] encrypt(String plaintext) throws Exception {

        KeyStore keyStore = getKeyStore();
        Certificate[] certs = keyStore.getCertificateChain("alias");
        Cipher cipher = Cipher.getInstance("RSA","BC");
        cipher.init(Cipher.ENCRYPT_MODE, certs[0].getPublicKey());
        return cipher.doFinal(plaintext.getBytes());
    }

KeyStore keyStore = getKeyStore();
    PrivateKey privateKey = (PrivateKey) keyStore.getKey("alias",
            "password".toCharArray());
    Cipher cipher = Cipher.getInstance("RSA","BC");
    cipher.init(Cipher.DECRYPT_MODE, privateKey);
    byte[] cipherbyte=cipher.doFinal(ciphertext);
    return new String(cipherbyte);
}

Caused by: javax.crypto.BadPaddingException: Given final block not properly padded
    at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:966)
    at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:824)
    at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:436)
    at javax.crypto.Cipher.doFinal(Cipher.java:2165)
    at