Signing data with private key in c#

Question

I need to sign some data with one private key using Algorithm SHA1RSA ,Rsa Key length 2048 with 64 base encoding.My code is like this

       string sPayload          


        

Answer 1

You have computed the SHA-1 hash of sPayload, not the RSA-SHA1 signature.

If you have an X509Certificate2:

using (RSA rsa = cert.GetRSAPrivateKey())
{
    return rsa.SignData(sPayload, HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);
}

If you already have a raw RSA key then just leave off the using statement.

If you have to compute the hash of sPayload for some other reason you can do it like

byte[] hash;
byte[] signature;

using (HashAlgorithm hasher = SHA1.Create())
using (RSA rsa = cert.GetRSAPrivateKey())
{
    hash = hasher.ComputeHash(sPayload);
    signature = rsa.SignHash(hash, HashAlgorithmName.SHA1, RSASignaturePadding.Pkcs1);
}

SignHash still requires the HashAlgorithmName value because the algorithm identifier is embedded within the signature.