ECDsa for Xamarin.Forms

Question

I develop Xamarin.Forms application and need to use ECDsa digital signature. I've tried to use System.Security.Cryptography methods for ECDsa ( in Xamarin.Forms CngKey.Create shows "operation not implemented" error ), but because Mono.Android doesn't support it ( Are ECDSA and ECDH available for mono? ), I have no idea how to do it. So could you, please, give me advice on how to use ECDsa digital signature in my Android application?
Also, I kinda don't fully understand the principles of Mono, .Net and PCL libraries, so maybe the solution is in changing the way I develop app in Xamarin.
Moreover, my Android is ver.4.4.0, so then solution should support old devices.

Answer 1

Have a look at https://github.com/onovotny/bc-csharp/tree/netstandard . It is a portable version (.NET 4, .NET Standard 1.0-2.0, WP, Silverlight, MonoAndroid, Xamarin.iOS, .NET Core) of popular cryptographic algorithms.

According to their documentation at https://www.bouncycastle.org/csharp/ it supports ECDSA.

It is available on NuGet https://www.nuget.org/packages/Portable.BouncyCastle/