.NET Framework RsaCng exception

Question

I am learning about Cryptography in .NET and I wrote the following function as a test:

byte[] foo(byte[] input, string keyContainerName)
{
   CngKey key = CngKey.Open(keyContainerName);
   RSACng rsa = new RSACng(key);
   rsa.KeySize = 2048;
   byte[] v = rsa.Encrypt(input, RSAEncryptionPadding.OaepSHA512);

   CngKey keyb = CngKey.Open(keyContainerName);
   RSACng rsab = new RSACng(keyb);
   rsab.KeySize = 2048;
   return rsab.Decrypt(v, RSAEncryptionPadding.OaepSHA512);
}

When I try executing it, rsab.Decrypt() throws a Cryptographic exception with the message: "The parameter is incorrect.".

Why is this happening? Where did I go wrong?

P.S. I previously created a key pair in the KSP with CngKey.Create(). foo is called with keyContainerName beeing the keyName passed to CngKey.Create().

Are you experimenting with RSA cryptographic functions by writing your own or you want to use RSA in some sort of application. In the second case a better approach would be to use an encryption library like 'ExpressSecurity' — Sangeeth Nandakumar, May 06 '21 at 13:21
I am creating a cryptographic app that will provide the user the ability to encrypt/decrypt text messages (or files) using symmetric and asymmetric algorithms (in background, only a symmetric key would be encrypted). The asymmetric methods wrote by me wouldn't work so I started testing. '''foo''' is a synthesis of what is not working for me. //edit: I searched for 'ExpressSecurity'. My app is an offline .NET Framework Windows Forms project. It is used to encrypt/decrypt things locally (sent using other means). — XpoizonEximus, May 06 '21 at 13:31
The encrypt key and decrypt key has to be the same. Every time you call new RSACng a new key is generated so you decrypt key is different from the encrypt key. — jdweng, May 06 '21 at 14:26
If that's the case, which is the role of the Key Storage Provider? — XpoizonEximus, May 06 '21 at 19:54
If your pre-created key is 2048 bits, assigning the KeySize property at best does nothing. If it wasn’t, assigning the property detached from your key and made a new random one. — bartonjs, Jan 12 '22 at 12:56

Sangeeth Nandakumar · Answer 1 · 2021-05-06T13:57:17.267

If you want to create an app that does symmetric and asymmetric encryption and decryption, You can try integrating ExpressSecurity library via NuGet

More info: https://github.com/sangeethnandakumar/Express-Security-Library

AES - Symetric Encryption (For files)

var password = "sangeeth123";
var inputPath = "C:\sample.txt";
var outputPath = "C:\sample.txt.aes";

//AES Encription
AESEncription.AES_Encrypt(inputPath, password);
//AES Description
AESEncription.AES_Decrypt(outputPath, password);

RSA - Asymmetric Encryption (For strings and text)

//Generate Keys
var publicKeyPath = "C:\public_key.rsa";
var privateKeyPath = "C:\private_key.rsa";
RSAEncription.MakeKey(publicKeyPath, privateKeyPath);

var input = "sangeeth"

//RSA Encription
var ciphertext = RSAEncription.EncryptString(input, publicKeyPath);
//RSA Description
input = RSAEncription.DecryptString(ciphertext, privateKeyPath);

.NET Framework RsaCng exception

1 Answers1