Extensions to convert Unix time to DateTime

UnixTimeExtensions.cs

namespace System
{
    public static class UnixTimeExtensions
    {
        public static long ToUnixTime(this DateTime datetime)
        {
            return (long)(datetime.ToUniversalTime() - new DateTime(1970, 1, 1, 0, 0, 0)).TotalSeconds;
        }

        public static DateTime FromUnixTime(long time)
        {
            return (new DateTime(1970, 1, 1, 0, 0, 0)).AddSeconds(time);
        }
    }
}