This library implements transaction signing algorithm secp256k1 which is used in several blockchains like Bitcoin, EOS and Graphene-based Steem, Golos, BitShares. The library is based on https://github.com/warner/python-ecdsa and https://github.com/bitcoin-core/secp256k1) No other curves are included. C#, MIT license.
//Sign message
var seckey = Hex.HexToBytes("80f3a375e00cc5147f30bee97bb5d54b31a12eee148a1ac31ac9edc4ecd13bc1f80cc8148e");
var data = Sha256Manager.GetHash(msg);
var sig = Secp256K1Manager.SignCompressedCompact(data, seckey);
Install-Package Cryptography.ECDSA.Secp256k1