Java RSA/ECB/PKCS1Padding encryption with .NET

Question

I need to encrypt a password on a web site using a public key. The public key is delivered through a Java web service with the information: The key is a RSA key to be used with RSA/ECB/PKCS1Padding algorithm. The public key is delivered as JSON in the form:

{
    "kid":"PWD",
    "kty":"RSA",
    "use":"enc",
    "n":"MTA0OTgzNjg0OTMxMzE2NjkwNTU4Mjg3NDIwMDg1NTY0ODEyMjg1MDk2NTcwNzU5NDIzNzM0O
    DA3OTA2MzA0MDczNTU0NDQ2Njg3ODY2ODk2NTk0NjYzNTAxMzg0NzE1OTExMjA0MjU1MzMzOTIzMjA
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
    zcwMjA3MzQxOTcwNzc4NDAwNzM3MTY2NDMyNzIwNjMwMDQwOTMwOTQ0MTA2OTE1NDEzMDAwNTMyMTE
    5ODM0MTA2MjAzMDIyODEwMjYyMDM3MDQ0NzkxNzIzNTU1MjQyNjYxMzE2ODc4OTc5NzY1OTgzMjg4M
    zQ0NDc3OTYwNTg3MzE2NTUwMDgx",
    "e":"NjU1Mzc"
 }

I tried to encrypt the password using the public key but the key generated is not correct. Here is my code:

encryptedPassword = EncrypIt("Password01", "MTA1MzQxNzIwODA3NjUwNzg5ND
Y4ODU2Mjc0NDA3ODIwMjQ1ODQ5NDE1MDk1MDIzMTM3MjM0NzAwNzYzNjc2MTgwNjg3ODMxMjA3
NTY0NTcxMjg2MzM4NjQ1NzEwMDcyMjY2MTQyNDIzMTczMjkwMDk0MTc0MTA5MTc5MzI0NjYwMjQ4NzI3NzM0MTQ5NDY0MjUwODkwO
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
c2OTAzNjc3NzQzODM3NzM0MjE2ODM0NjY4MjM4MTQ0OTA3MDQ3MTk1Njc1NzU3OTE2NjEyNzkzMzM2MzI3MDUyNjg0NDI5NDExNjI
2MzA0MzM5", "NjU1Mzc");

    public static string EncrypIt(string password, string publicKey, string exponent)
    {
        UnicodeEncoding ByteConverter = new UnicodeEncoding();
        byte[] publicKeyByte = ByteConverter.GetBytes(publicKey);
        byte[] passwordByte = ByteConverter.GetBytes(password);

        RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
        RSAParameters RSAKeyInfo = new RSAParameters();
        RSAKeyInfo = RSA.ExportParameters(false); //Export only public key
        //Set RSAKeyInfo to the public key values. 
        RSAKeyInfo.Modulus = publicKeyByte;
        //RSAKeyInfo.Exponent = exponentBytes; //I tried to set exponent but I have an error
        RSA.ImportParameters(RSAKeyInfo);
        byte[] encryptedPassword = RSA.Encrypt(passwordByte, false);
        return Convert.ToBase64String(encryptedPassword);
    }

(The public key is different between the JSON and my code but don't pay attention to it, I just copied information from different sources)

• The encrypted password I obtained is far too long: The encrypted password should be 172 characters (I know because I have a small Java program that allows me to encrypt passwords correctly) but I get 1100 characters.
• I do not use the exponent: Should I ?
• Could I not use the JSON to directly configure the RSACryptoServiceProvider correctly ?

The answer from owlstead helped me to get an encrypted password with the right string size but the service using the encrypted string reject it with the message: javax.crypto.IllegalBlockSizeException: Data must not be longer than 128 bytes

I otained the code of the java program wich is doing the correct encryption (see below). I need to achieve the same encryption using .NET.

public class EncryptionServiceImpl
{

    private static final Charset UTF8 = Charset.forName("UTF-8");

    @Resource(name = "briqueAuthentificationClient")
    private BriqueAuthentificationClientImpl briqueAuthentificationClient;

    protected static final String ALGORITHM_RSA = "RSA";

    protected static final String TRANSFORMATION_RSA_ECB_PKCS1PADDING = "RSA/ECB/PKCS1Padding";

    private static final Logger LOG = LoggerFactory.getLogger(EncryptionServiceImpl.class);

    public EncryptionServiceImpl() {
        LOG.info("constructeur EncryptionServiceImpl");
    }

    /**
     * @param briqueAuthentificationClient the briqueAuthentificationClient to set
     */
    public void setBriqueAuthentificationClient(final BriqueAuthentificationClientImpl briqueAuthentificationClient) {
        this.briqueAuthentificationClient = briqueAuthentificationClient;
    }

    public String encrypt(final String input) throws GeneralSecurityException {

        if (StringUtils.isNotBlank(input)) {
            final CertificateDto certificate = this.briqueAuthentificationClient.getCurrentCertificate();

            if (certificate != null) {
                return new String(this.encryptAndEncode(input.getBytes(), certificate), EncryptionServiceImpl.UTF8);
            } else {
                throw new RuntimeException("Certificate is null");
            }
        }
        return null;
    }

    protected byte[] encryptAndEncode(final byte[] input, final CertificateDto currentCertificate)
            throws GeneralSecurityException {

        // Création de la clé publique
        final PublicKey publicKey = this.buildPublicKey(currentCertificate);

        // Chiffre
        final byte[] inputEncrypted = this.encrypte(input, publicKey);

        // Encode
        return this.encodeBase64Url(inputEncrypted);
    }

    protected PublicKey buildPublicKey(final CertificateDto currentCertificate) throws GeneralSecurityException {

        if ("RSA".equals(currentCertificate.getKeyType())) {
            return this.buildRSAPublicKey(currentCertificate);
        }
        LOG.error(String.format("Tentative de création d'une clé publique avec un algorithme non connu [%s]",
                currentCertificate.getKeyType()));
        return null;
    }

    protected PublicKey buildRSAPublicKey(final CertificateDto currentCertificate) throws GeneralSecurityException {

        final BigInteger modulus = new BigInteger(new String(Base64.decodeBase64(currentCertificate.getModulus()),
                EncryptionServiceImpl.UTF8));
        final BigInteger publicExponent = new BigInteger(new String(Base64.decodeBase64(currentCertificate
                .getPublicExponent()), EncryptionServiceImpl.UTF8));

        try {
            return KeyFactory.getInstance(ALGORITHM_RSA).generatePublic(new RSAPublicKeySpec(modulus, publicExponent));
        } catch (InvalidKeySpecException e) {
            throw e;
        } catch (NoSuchAlgorithmException e) {
            throw e;
        }
    }

    protected byte[] encrypte(final byte[] input, final RSAPublicKeySpec rsaPublicKeySpec)
            throws GeneralSecurityException {

        PublicKey publicKey;
        try {
            publicKey = KeyFactory.getInstance(ALGORITHM_RSA).generatePublic(
                    new RSAPublicKeySpec(rsaPublicKeySpec.getModulus(), rsaPublicKeySpec.getPublicExponent()));
        } catch (InvalidKeySpecException e) {
            throw e;
        } catch (NoSuchAlgorithmException e) {
            throw e;
        }
        return this.encrypte(input, publicKey);
    }

    protected byte[] encrypte(final byte[] input, final PublicKey publicKey) throws GeneralSecurityException {

        try {
            final Cipher cipher = Cipher.getInstance(TRANSFORMATION_RSA_ECB_PKCS1PADDING);
            cipher.init(Cipher.ENCRYPT_MODE, publicKey);
            return cipher.doFinal(input);
        } catch (NoSuchAlgorithmException e) {
            throw e;
        } catch (NoSuchPaddingException e) {
            throw e;
        } catch (IllegalBlockSizeException e) {
            throw e;
        } catch (BadPaddingException e) {
            throw e;
        }

    }

    protected byte[] decrypte(final byte[] input, final RSAPrivateKeySpec rsaPrivateKeySpec)
            throws GeneralSecurityException {

        final BigInteger modulus = rsaPrivateKeySpec.getModulus();
        final BigInteger privateExponent = rsaPrivateKeySpec.getPrivateExponent();

        try {
            final PrivateKey privateKey = KeyFactory.getInstance(ALGORITHM_RSA).generatePrivate(
                    new RSAPrivateKeySpec(modulus, privateExponent));

            final Cipher cipher = Cipher.getInstance(TRANSFORMATION_RSA_ECB_PKCS1PADDING);
            cipher.init(Cipher.DECRYPT_MODE, privateKey);
            return cipher.doFinal(input);

        } catch (NoSuchAlgorithmException e) {
            throw e;
        } catch (NoSuchPaddingException e) {
            throw e;
        } catch (IllegalBlockSizeException e) {
            throw e;
        } catch (BadPaddingException e) {
            throw e;
        } catch (InvalidKeySpecException e) {
            throw e;
        } catch (InvalidKeyException e) {
            throw e;
        }

    }

    protected byte[] encodeBase64Url(final byte[] input) {
        return Base64.encodeBase64(input, false);
    }

    protected byte[] decodeBase64Url(final byte[] input) {
        return Base64.decodeBase64(input);
    }

    /**
     * Method to connect to an url
     * 
     * @param httpclient the http connection
     * @return the response GetMethod
     * @throws OAuthException in cas of connection error
     */
    private GetMethod connect(final HttpClient httpclient, final String url) {

        final GetMethod httpget = new GetMethod(url);
        try {

            httpclient.executeMethod(httpget);

        } catch (final UnknownHostException e) {
            throw new RuntimeException("Connection ERROR - Host could not be determined.", e);
        } catch (final IOException e) {
            throw new RuntimeException("Connection ERROR - Input/Output error.", e);
        }
        return httpget;
    }

}

The steps I accomplished with the help of owlstead are in the answer below. When I use this Java program to encode the string Password01 I obtain a string like:

sy5/XElHvuYA4Rbq8OBydLymT82R+z77jy6MU2sNal7VenzPEbARgy7p3zWgYgG13Cypk+zbnnB5L37fVUhgOgCqCyLtikzxJBNmPyzUK9+beiHJKyONZwifDzQ44hXTeXcZ0bmF9b5dLFy9QS/N5m28vIyBSGY8K2B7EB2FF38=  

This encrypted password can be decrypted on Java side

When I use the .NET code the string is like:

ACZXYj/KudyxKBB510SxSouKaVwssmEUM6Jpreh8jTtrIH9eGb18GIdkBU7rXzMuLYbAhyREbFLbR87zW/2DNa4tN97FOlqr6k1JppJ/SSS/9fGdMvSOAQbWjsxksDH7fRu9dCvK0m0exFtGfXG7Yua9bB1m0dTNiwCZUZM0LnEM  

This encrypted password failed to be decrypted on Java side. Failed with the error message:

javax.crypto.IllegalBlockSizeException: Data must not be longer than 128 bytes

Answer 1

You first need to perform base 64 decoding using Convert.FromBase64String of n and e , convert the result from ASCII encoding to a string and then parse the result using BigInteger.parse . Then you can convert using toByteArray to bytes, but beware that BigInteger is little endian, and RSAParameters expects big endian , so you have to reverse the bytes.

Your .NET RSA ciphertext (which you probably shouldn't reverse) is preceded by a 00h valued byte, which makes it an invalid ciphertext. RSA ciphertext must be of the exact length in bytes of the key.

Answer 2

Thank you sirs for the answers and comments, it help me to finally solve my issue:

For exponent, I got an error message: Invalid length for a Base-64 char array or string This is because a base 64 value should be a multiple of 4. If this is not the case we should append equal sign (=) to reach a multiple of 4. Thus after changing the exponent string from "NjU1Mzc" to "NjU1Mzc=" the value can be decoded.

Then I applied the solution provided by owlstead. Here is the final code which works fine:

//Decode from base 64
byte[] publicKeyByte = Convert.FromBase64String(rsaPublicKey.modulo);
byte[] exponentByte = Convert.FromBase64String(rsaPublicKey.exponent);

//Convert to ASCII string
UTF8Encoding ByteConverter = new UTF8Encoding();
string publicKeyString = System.Text.Encoding.Default.GetString(publicKeyByte);
string exponentString = System.Text.Encoding.Default.GetString(exponentByte);

//Convert to BigInteger
BigInteger publicKeyBI = BigInteger.Parse(publicKeyString);
BigInteger exponentBI = BigInteger.Parse(exponentString);

//Convert back to byte array
byte[] publicKeyByte2 = publicKeyBI.ToByteArray();
byte[] exponentByte2 = exponentBI.ToByteArray();

//We must remove the 129th sign byte which is added when converting to BigInteger
if (publicKeyByte2.Length == 129) Array.Resize(ref publicKeyByte2, 128);

//Create crypto service
RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
RSAParameters RSAKeyInfo = new RSAParameters();

//Assign RSA key modulus/exponent reversing from little endian to big endian
RSAKeyInfo.Modulus = publicKeyByte2.Reverse().ToArray();
RSAKeyInfo.Exponent = exponentByte2.Reverse().ToArray();
RSA.ImportParameters(RSAKeyInfo);

//Convert password string to byte array
byte[] passwordByte = ByteConverter.GetBytes(clearPassword);

//Encrypt the password and encode 64
encryptedPassword = Convert.ToBase64String(RSA.Encrypt(passwordByte, false));

The missing point from owlstead is that: the method returns a byte array with an extra element whose value is zero to disambiguate positive values See Microsoft documentation for more information on this point: BigInteger.ToByteArray Method

This code encrypts the password as a 172 characters string which ends with a = sign which is what I expected and it is correctly decrypted on Java side with the private key.

Answer 3

I tried this and it encrypts correctly

    var input = "String to Encode.";
    var mod = "MTA1MzQxNzIwODA3NjUwNzg5NDY4ODU2Mjc0NDA3ODIwMjQ1ODQ5NDE1MDk1MDIzMTM3MjM0NzAwNzYzNjc2MTgwNjg3ODMxMjA3NTY0NTcxMjg2MzM4NjQ1NzEwMDcyMjY2MTQyNDIzMTczMjkwMDk0MTc0MTA5MTc5MzI0NjYwMjQ4NzI3NzM0MTQ5NDY0MjUwODkwOXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXc2OTAzNjc3NzQzODM3NzM0MjE2ODM0NjY4MjM4MTQ0OTA3MDQ3MTk1Njc1NzU3OTE2NjEyNzkzMzM2MzI3MDUyNjg0NDI5NDExNjI2MzA0MzM5==";
    var exp = "NjU1Mzc=";
    var intValue = int.Parse(Encoding.UTF8.GetString(Convert.FromBase64String(exp)));

    var rsaParam = new RSAParameters();
    rsaParam.Modulus = Convert.FromBase64String(mod);
    rsaParam.Exponent = BitConverter.GetBytes(intValue);
    using (var rsa = new RSACryptoServiceProvider())
    {
        rsa.ImportParameters(rsaParam);
        Console.WriteLine(Convert.ToBase64String(rsa.Encrypt(Encoding.UTF8.GetBytes(input), false)));
    }
    Console.ReadLine();

I think the issue is the exponent is strange. Exp = 65537;