Permitski

A simple .NET library for generating crypgraphically signed documents.

First you generate a key

var key = DocumentSigner.GenerateKey();

which you might want to hold on to, because it's your secret.

If you lose the key, you lose the ability to sign documents and validate signatures of signed documents, so you can probably imagine that it's pretty important.

With the key in hand, you can create a signer like this:

using(var signer = new DocumentSigner(key))
{
	// sign & validate stuff in here
}

Since it's relying on unmanaged resources some place deep within the bowels of the .NET framework, you want to make sure that you dispose the signer properly.

Now, let's pretend we have some important data we want to pass around with a signature, so we can validate its authenticity later on. Here's the class that represents our important data:

class ImportantData
{
    public string Data { get; }

    public ImportantData(string data)
    {
        Data = data;
    }
}

Let's sign it, so we can give it to someone:

var importantData = new ImportantData("hemmelig");

var signed = signer.Sign(importantData);

Console.WriteLine(signed);

which in this case yielded the following output:

{
  "Document": {
    "Data": "hemmelig"
  },
  "Signature": "YHZxo95/CfP4P/ndfh+49m5kmjb2Zj8xkGrkvKVFbcw="
}

Let's see if it's valid - if we store the JSON shown above in a string called json, we can check its validity like this:

Console.WriteLine($"The document is valid: {signer.IsValid(json)}");

which on my machine yielded:

The document is valid: True

Neat!