Only namespace is CSChaCha20
Either copy the CSChaCha20.cs to your project or use LibChaCha20 nuget package
Then do code like
using CSChaCha20;
byte[] mySimpleTextAsBytes = Encoding.ASCII.GetBytes("Plain text I want to encrypt");
// Do not use these key and nonce values in your own code!
byte[] key = new byte[32] { 142, 26, 14, 68, 43, 188, 234, 12, 73, 246, 252, 111, 8, 227, 57, 22, 168, 140, 41, 18, 91, 76, 181, 239, 95, 182, 248, 44, 165, 98, 34, 12 };
byte[] nonce = new byte[12] { 139, 164, 65, 213, 125, 108, 159, 118, 252, 180, 33, 88 };
uint counter = 1;
// Encrypt
ChaCha20 forEncrypting = new ChaCha20(key, nonce, counter);
byte[] encryptedContent = new byte[mySimpleTextAsBytes.Length];
forEncrypting.EncryptBytes(encryptedContent, mySimpleTextAsBytes);
// Decrypt
ChaCha20 forDecrypting = new ChaCha20(key, nonce, counter);
byte[] decryptedContent = new byte[encryptedContent.Length];
forDecrypting.DecryptBytes(decryptedContent, encryptedContent);You can try out the code in .NET Fiddle
All the code is licensed under ISC License