Android Encryption RSA InvalidKeyException

Question

Dears,

I need help to understand why decryptString doesn't work and throw "java.security.InvalidKeyException: Need RSA private or public key". When call encrypt method, i use public key by the private key/certificate.

Thanks for any help!

public class KeysHandler {

    /***
     * Generate and store in AndroidKeyStore a security KeyPair keys.
     * @param alias - Alias to create the key.
     * @return KeyPair object with: private and public key.
     */
    public static KeyPair generateKeyPair(String alias) {
        KeyPair kp = null;
        if (alias != null) {
            try {

                KeyPairGenerator kpg = KeyPairGenerator.getInstance(KeyProperties.KEY_ALGORITHM_RSA, "AndroidKeyStore");
                kpg.initialize(new KeyGenParameterSpec.Builder(alias,
                        KeyProperties.PURPOSE_SIGN |
                        KeyProperties.PURPOSE_VERIFY |
                        KeyProperties.PURPOSE_ENCRYPT |
                        KeyProperties.PURPOSE_DECRYPT)
                        .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_RSA_PKCS1)
                        .build());

                kp = kpg.generateKeyPair();

            } catch (NoSuchProviderException | NoSuchAlgorithmException | InvalidAlgorithmParameterException ex) {
                kp = null;
            }
        }
        return kp;
    }

    public static String encryptString(String alias, String textToEncrypt) {
        String cipheredText = null;

        try {
            KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
            keyStore.load(null);

            KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry)keyStore.getEntry(alias, null);

            // Encrypt the text
            if(textToEncrypt != null && textToEncrypt.length() > 0) {

                Cipher input = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
                input.init(Cipher.ENCRYPT_MODE, privateKeyEntry.getCertificate().getPublicKey());

                ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
                CipherOutputStream cipherOutputStream = new CipherOutputStream(
                        outputStream, input);
                cipherOutputStream.write(textToEncrypt.getBytes("UTF-8"));
                cipherOutputStream.close();

                byte[] vals = outputStream.toByteArray();
                cipheredText = Base64.encodeToString(vals, Base64.DEFAULT);
            }
        } catch (Exception e) {
            cipheredText = null;
        }

        return cipheredText;
    }


    public static String decryptString(String alias, String cipheredText) {

        String clearText = null;
        try {
            KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
            keyStore.load(null);

            KeyStore.PrivateKeyEntry privateKeyEntry = (KeyStore.PrivateKeyEntry)keyStore.getEntry(alias, null);

            Cipher output = Cipher.getInstance("RSA/ECB/PKCS1Padding", "AndroidOpenSSL");
            output.init(Cipher.DECRYPT_MODE, privateKeyEntry.getPrivateKey());

            CipherInputStream cipherInputStream = new CipherInputStream(
                    new ByteArrayInputStream(Base64.decode(cipheredText, Base64.DEFAULT)), output);
            ArrayList<Byte> values = new ArrayList<>();
            int nextByte;
            while ((nextByte = cipherInputStream.read()) != -1) {
                values.add((byte)nextByte);
            }

            byte[] bytes = new byte[values.size()];
            for(int i = 0; i < bytes.length; i++) {
                bytes[i] = values.get(i).byteValue();
            }

            clearText = new String(bytes, 0, bytes.length, "UTF-8");

        } catch (Exception e) {
            clearText = null;
        }

        return clearText;
    }
}

FrederikVH · Accepted Answer · 2017-02-15 13:11:18Z

5

Try omitting the cipher provider:

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

Secondly, you can instantiate the provider first to make sure that works, then pass it along as the second argument to Cipher.getInstance(). The second argument can be either a String (provider name) or a Provider (object). Using the second might make debugging easier.

answered Feb 15, 2017 at 13:11

FrederikVH

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3 Comments

Mateus Over a year ago

@FrederikHV really thanks, it worked like a charm when omitting "AndroidOpenSSL". Have a good week for you!

sandeepmaaram Over a year ago

Where you omitted? In encryption and decryption both places omitted? Thanks.

FrederikVH Over a year ago

@sandeepmaaram Wherever you call Cipher.getInstance

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