Does RSA in C # not produce the same encrypted string for certain keys?

Question

I have a requirement when I need to encrypt the connection string in one application and decrypt it in another. With this in mind, I save the public key and private keys in the App.Config application, respectively.

Now shouldn't RSA give me the same encrypted string with the same keys that I use?

I get different encrypted strings all the time using the same keys. !! Please help me resolve the confusion. I don’t understand how I can solve this problem, I get a BAD Data strong> exception if I use a saved encrypted string, since every time the encryption gives me different encrypted strings.

Here is my code:

private string connecString; private RSACryptoServiceProvider rsaEncryptDecrypt; public EncryptAndDecrypt(string connecString) { this.connecString = connecString; this.rsaEncryptDecrypt = new RSACryptoServiceProvider(4096); } public string EncryptTheConnecString(string publicKeyValue) { byte[] encryptedData; rsaEncryptDecrypt.FromXmlString(publicKeyValue); byte[] message = Encoding.UTF8.GetBytes(connecString); encryptedData = rsaEncryptDecrypt.Encrypt(message, false); return Convert.ToBase64String(encryptedData); } public string DecryptTheConnecString(string privateKeyValue, string encrystr) { byte[] decryptedData; rsaEncryptDecrypt.FromXmlString(privateKeyValue); byte[] message = Convert.FromBase64String(encrystr); decryptedData = rsaEncryptDecrypt.Decrypt(message, false); return Encoding.UTF8.GetString((decryptedData)); } 

Thanks in advance.

Update 1: I used

 UnicodeEncoding ByteConverter = new UnicodeEncoding(); ByteConverter.GetBytes("data to encrypt"); //Which is not Connection string but a small test str 

However, I see that the encrypted data changes every time. But the error Bad information is no longer displayed. However, I cannot use UTF16 (UnicodeEncoding) Encoding.UTF8 , because it cannot encrypt a huge string, such as a connection string, and throws an exception:

  CryptographicException: Key not valid for use in specified state. 

Update 2:

I could solve the problem with bad data using UTF8Encoding ByteConverter = new UTF8Encoding(); and then doing ByteConverter .GetString("HUGE STRING");

Answer 1

This may be due to random padding .

Answer 2

In general, the answer to your question is yes, it should always give the same result if the same parameters are specified.

The best way to solve these problems is to get as close as possible to the best practical code, currently you are using a cryptographic provider slightly different from the proposed framework document, see the following:

 static public byte[] RSAEncrypt(byte[] DataToEncrypt, RSAParameters RSAKeyInfo, bool DoOAEPPadding) { byte[] encryptedData; //Create a new instance of RSACryptoServiceProvider. using (RSACryptoServiceProvider RSA = new RSACryptoServiceProvider()) { //Import the RSA Key information. This only needs //toinclude the public key information. RSA.ImportParameters(RSAKeyInfo); //Encrypt the passed byte array and specify OAEP padding. //OAEP padding is only available on Microsoft Windows XP or //later. encryptedData = RSA.Encrypt(DataToEncrypt, DoOAEPPadding); } return encryptedData; } 

This is an excerpt from an official MSDN document:
http://msdn.microsoft.com/en-us/library/system.security.cryptography.rsacryptoserviceprovider.aspx

Try and adopt the best practice first, and then see if this problem has occurred.