RSA OAEP, Golang Encrypt, Java Decrypt -BadPaddingException: Decryption error

Question

I'm trying to decrypt a string which is encrypted in Golang using RSA-OAEP. but getting BadPaddingException: Decryption error. Having hard time to figure out what am I missing..

Here is the Golang encrypt method

func encryptString() {
rootPEM := io_related.ReadFile("../../resources/pubkey.pem")
    //fmt.Printf("Cert String %q \n", rootPEM)

    block, _ := pem.Decode([]byte(rootPEM))
    var cert *x509.Certificate
    cert, _ = x509.ParseCertificate(block.Bytes)
    rsaPublicKey := cert.PublicKey.(*rsa.PublicKey)

    secretMessage := []byte("password")
    label := []byte("")

    // crypto/rand.Reader is a good source of entropy for randomizing the
    // encryption function.
    rng := rand.Reader

    ciphertext, err := rsa.EncryptOAEP(sha256.New(), rng, rsaPublicKey, secretMessage, label)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error from encryption: %s\n", err)
        return
    }

    // Since encryption is a randomized function, ciphertext will be
    // different each time.

    base64EncodedString := base64.StdEncoding.EncodeToString(ciphertext)
    fmt.Println(base64EncodedString)
}

and my java decrypt method as

public void decryptString(String base64String) throws NoSuchAlgorithmException, CertificateException, IOException, KeyStoreException, UnrecoverableKeyException, NoSuchPaddingException, InvalidKeyException, IllegalBlockSizeException, BadPaddingException{
        FileInputStream is = new FileInputStream("priv.p12");
        KeyStore keystore = KeyStore.getInstance("PKCS12");
        keystore.load(is, "".toCharArray());
        System.out.println("Successfully loaded");


        String keyAlias = "1";


        PrivateKey key = (PrivateKey)keystore.getKey(keyAlias, "".toCharArray());

        System.out.println("key "+Base64.encodeBase64String(key.getEncoded()));
        Cipher rsaDecryptCipher;
        rsaDecryptCipher = Cipher.getInstance("RSA/ECB/OAEPWITHSHA-256ANDMGF1PADDING");
        rsaDecryptCipher.init(Cipher.DECRYPT_MODE, key);
        final byte[] plainText = rsaDecryptCipher.doFinal(Base64.decodeBase64(base64String));

        System.out.println("Plain   : " + new String(plainText));

    }

1. I made sure I'm using the same key pair and not a different private key
2. Made sure hash algorithm used same in both encrypt and decrypt "SHA256"

I might be missing something, Please let me know if anyone need more details. Appreciate the help!!. Thanks

Answer 1

OAEP uses two hash algorithms: one on the label (fka parameters) and one within the Mask Generation Function (MGF1); these can be different. See 7.1.1 and B.2.1 in rfc8017.

I don't know whether that Go code sets one (and which) or both, but what Java does with that getInstance varies depending on which provider you are using, which in turn depends at least partly on what implementation of Java you are using. The SunJCE provider configured by default in Sun/Oracle and OpenJDK implementations changes only the label hash, keeping MGF1 at SHA1; the BouncyCastle provider changes both. I don't know what IBM and Android do here.

Once you determine (or guess) what Go is doing you can match it by adding to your .init call an appropriate OAEPParameterSpec and related MGF1ParameterSpec.

Mostly dupe OAEPwithMD5andMGF1Padding in node-rsa
and Breaking down RSA/ECB/OAEPWithSHA-256AndMGF1Padding
(copied at https://security.stackexchange.com/questions/97548/breaking-down-rsa-ecb-oaepwithsha-256andmgf1padding )