Java Encryption C# Decryption

Question

I got a module which RSA encrypts the data and passes on to the C#. C# needs to decrypt it based on the public key (64 bit encoded) and the passed token.

I have token , 64 bit encoded public key, can some help me get with the sample to get started. All I know from Java end is, it is using. I have got the result from Java end and need to write a parser in C# to decrypt this. I get both public key and token as a string value.

    Cipher cipher = Cipher.getInstance(ALGORITHM); //Algorithm = "RSA"
    cipher.init(Cipher.DECRYPT_MODE, key);

Thanks

Please look at the update to my answer. – erickson Oct 20 '09 at 19:18 — erickson, Oct 20 '09 at 19:18

erickson · Accepted Answer · 2009-10-20T19:17:39.473

To get started, you'll need the private key to decrypt the message. By "public key (64 bit encoded)", I'm guessing what you really have is a Base-64–encoded certificate, with a header line that says "----- BEGIN CERTIFICATE-----" and a footer that says "-----END CERTIFICATE-----".

If that's correct, you'll need to find the private key. This is sometimes stored in a PKCS #12 format file, with a ".p12" or ".pfx" extension. You'll need a password to access the private key if it is stored in such a file.

Alternatively, OpenSSL and other utilities use private key files that can be Base-64–encoded or binary. These have a variety of extensions, and may or may not be password-protected. If the file that you have has a header line of "-----BEGIN RSA PRIVATE KEY-----" or "-----BEGIN PRIVATE KEY-----", that is actually the private key.

Finally, Windows can store private keys in its internal key store.

When you clarify the location of the private key, please update your question.

If the private key is used on the Java side, it may be an attempt to perform a digital signature. While all of several Java providers I've tested produce correct results when (ab)used this way, if you are doing a signature, the Signature class should be used. The C# code should use a signature object to "verify" the signature as well.

Encryption is performed with the private key. Since the public key is public, anyone can decrypt the message; i.e., the message is not confidential. Public keys are used by recipients to verify signed messages.

The encoding is done using the private key in Java side. I assume public key can be used in C# end to decrypt this? — bkhanal, Oct 20 '09 at 17:53
Thanks. So, given I have public key (not the certificate) - I think I can get it,but the code is passing me the key from certificate instead, where do I start? :)... — bkhanal, Oct 20 '09 at 19:41

score 1 · Answer 2 · answered Oct 20 '09 at 17:52

Check this code out.

public static string Decrypt(string inputText)
      {
        RijndaelManaged rijndaelCipher = new RijndaelManaged();
        byte[] encryptedData = Convert.FromBase64String(inputText.Replace(" ","+"));
        PasswordDeriveBytes secretKey = new PasswordDeriveBytes(ENCRYPTION_KEY, SALT);

        using (ICryptoTransform decryptor = rijndaelCipher.CreateDecryptor(secretKey.GetBytes(32), secretKey.GetBytes(16)))
        {
          using (MemoryStream memoryStream = new MemoryStream(encryptedData))
          {
            using (CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read))
            {
              byte[] plainText = new byte[encryptedData.Length];
              int decryptedCount = cryptoStream.Read(plainText, 0, plainText.Length);
              return Encoding.Unicode.GetString(plainText, 0, decryptedCount);
            }
          }
        }

RijndaelManaged : looks like a different algorithm to me? – bkhanal Oct 20 '09 at 19:42 — bkhanal, Oct 20 '09 at 19:42

Java Encryption C# Decryption

2 Answers2