How to do signature using SHA256withRSA algorithm in C#

Question

I tried search solution to my query, I couldn't able find match I am looking for, this is very basic, but to my better understanding I am posting below query.

I want to encode and do signature for my string using "SHA256withRSA" algorithm. I could able to see lot of sample code in java using "SHA256withRSA" but in C# I could see first we are hashed data using SHA256 then we are sign hash using RSACryptoServiceProvider.

My questions are:

1. In C# we have separate algorithm of "SHA256withRSA", If yes, help with sample code.

2. If no then what would be better approach to achieve it in C#?

Answer 1

Do not use RSACryptoServiceProvider unless you are doing interop with CAPI, like opening a named key.

To do RSA signing with SHA-(2-)256:

byte[] signature = rsa.SignData(data, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);

You can get the RSA object from a cert:

using (RSA rsa = cert.GetRSAPrivateKey())
{
    ...
}

Or you can make one up from existing RSA parameters:

using (RSA rsa = RSA.Create(rsaParameters))
{
   ...
}

Or you can make up a new key from nothing:

using (RSA rsa = RSA.Create(2048))
{
    // you’ll need to save the parameters somewhere to have a stable key
    rsaParameters = rsa.ExportParameters(true));
    ...
}