Authenticate the KEY file in certificate using C#

Quote:

C#

string base64cert = Convert.ToBase64String(File.ReadAllBytes(pemFilePath));
var cert = new X509Certificate2(Convert.FromBase64String(base64cert), certAuthCode);

First obvious problem: converting the byte array read from the file to a Base64 string, only to convert that string back to a byte array on the following line, is a waste of resources. Simply pass the byte array directly to the constructor, without the intermediate conversion.

However, your variable name suggests that you are reading a PEM file[^]. This is a text file which contains the Base64-encoded certificate data within specific delimited sections. Passing the raw bytes of the file to the X509Certificate2 constructor won't work.

In .NET 5 or later, the RSA class offers the ImportFromPem method[^], which might work. Otherwise, you'll need to use a library to parse the file - for example, bouncycastle[^] or pem-utils[^]. For specific details, see this SO thread[^].