using System;

using System.Security.Cryptography;

using System.Text;

​

public class Program

{

    public static void Main()

    {

        var videoId = "12345";

        var signingKey = "ABCDEF1234567890";

        var expiryTimestamp = DateTime.Now.AddHours(1).ToUniversalTime().ToString("YYYYMMDDHHmmss");

        var stringToHash = $"video:{videoId}:{signingKey}:{expiryTimestamp}";

        MD5 md5 = MD5.Create();

        byte[] inputBytes = System.Text.Encoding.ASCII.GetBytes(stringToHash);

        byte[] hash = md5.ComputeHash(inputBytes);

        // step 2, convert byte array to hex string

        StringBuilder sb = new StringBuilder();

        for (int i = 0; i < hash.Length; i++)

        {

            sb.Append(hash[i].ToString("X2"));

        }

        Console.WriteLine($"input String: {stringToHash}");

        Console.WriteLine($"output string: {sb.ToString()}");

    }   

}

​