static void Main(string[] args) { var appId = "https://snappy.local/app-id.json"; var challenge = Encoding.UTF8.GetBytes("{\"challenge\":\"zImw3II_G5JKACzFB4I1FLFTmo2lmEs4Jg2gOP2dYNk\",\"origin\":\"https://snappy.local\",\"typ\":\"navigator.id.getAssertion\"}"); var keyHandle = Convert.FromBase64String("mizejqv8eHXSToeUEbxLzT65XIvIKY5YJdzSKGhvtP7SHDo/o4IXuEuGdajO172g1pXE2DZ+veI5/mmVCiZp4Q=="); var signature = U2f.Sign(appId, challenge, keyHandle); Console.WriteLine(Convert.ToBase64String(signature)); }