在C＃中使用sha256获取私钥文件

Question

Currently I perform this operation through openssl, and I have had no problem with the generated file

openssl dgst -sha256 -sign privateKey.key -out file.txt.signature file.txt

Now, we want to automate the generation of the file using C #, but I have not been able to get the same result.

public class Program
{

    static void Main(string[] args)
    {
        Console.WriteLine(CreateToken("key...", "text"));
        Console.ReadLine();
    }

    public static string CreateToken(string key, string message)
    {
        System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
        byte[] keyByte = encoding.GetBytes(key);

        HMACSHA256 hmacsha256 = new HMACSHA256(keyByte);

        byte[] messageBytes = encoding.GetBytes(message);
        byte[] hashmessage = hmacsha256.ComputeHash(messageBytes);

        return System.Text.Encoding.UTF8.GetString(hashmessage);
    }

}

I'm new to working with this, what would be the right way?

Am I not retrieving the information properly ?, Should I get the content directly from the file?

Thank you very much.

Answer 1

Signature generation is not the same thing as HMAC message authentication and it uses a different key. As HMAC can use a key of any size, it will probably take the private key, but that's not how it is supposed to work. RSA is an asymmetric algorithm that uses private and public keys, MAC uses symmetric, secret keys. The dgst -sign instead uses RSA PKCS#1 v1.5 padding to sign the file.

From the OpenSSL Wiki on dgst :

When signing a file, dgst will automatically determine the algorithm (RSA, ECC, etc) to use for signing based on the private key's ASN.1 info. When verifying signatures, it only handles the RSA, DSA, or ECDSA signature itself, not the related data to identify the signer and algorithm used in formats such as x.509, CMS, and S/MIME.

HMAC is not the same thing as SHA-256 either. RSA signature generation uses a hash, not a HMAC. You should use the SHA256 class to create a hash. HMAC is a message authentication code build using the SHA-256 hash. However, the SHA class is not needed as signature generation usually includes the hash generation (you sign a message, not a hash value).

So to create a signature, take a look at the RSAPKCS1SignatureFormatter class, it includes an example at the bottom. Try again using this example.

Make sure your message only contains ASCII (both in the text file as in your string) or your result may fail as well.