/// <summary>
/// Verify the json web signature of an attachment
/// </summary>
/// <param name="content">The attachment content to be verified.</param>
/// <returns>True - signature is valid; False - signature is missing or invalid.</returns>
public static async Task <bool> VerifyJsonWebSignature(this AttachmentContent content)
{
try
{
var did = content.JsonWebSignature.Header.Kid;
var verkey = DidUtils.ConvertDidKeyToVerkey(did);
var message = $"{content.JsonWebSignature.Protected}.{content.Base64}";
return(await Crypto.VerifyAsync(verkey, Encoding.ASCII.GetBytes(message),
content.JsonWebSignature.Signature.GetBytesFromBase64()));
}
catch (Exception)
{
return(false);
}
}
/// <summary>
/// Sign attachment content using json web signature
/// </summary>
/// <param name="content">The attachment content to be signed.</param>
/// <param name="wallet">The wallet.</param>
/// <param name="verkey">The verkey to be used for the signing.</param>
/// <exception cref="NullReferenceException">Throws if payload is null.</exception>
public static async Task SignWithJsonWebSignature(this AttachmentContent content, Wallet wallet, string verkey)
{
var payload = content.Base64;
if (payload == null)
{
throw new NullReferenceException("No data to sign");
}
var did = DidUtils.ConvertVerkeyToDidKey(verkey);
var protectedHeader = new
{
alg = "EdDSA",
kid = did,
jwk = new
{
kty = "OKP",
crv = "Ed25519",
x = Multibase.Base58.Decode(verkey).ToBase64UrlString(),
kid = did
}
}.ToJson().ToBase64Url();
var message = $"{protectedHeader}.{payload}";
var signature = (await Crypto.SignAsync(wallet, verkey, Encoding.ASCII.GetBytes(message))).ToBase64UrlString();
content.JsonWebSignature = new JsonWebSignature
{
Header = new JsonWebSignatureHeader {
Kid = did
},
Protected = protectedHeader,
Signature = signature
};
}