public enum AppSettings
{
    MySetting
}

public class Extentions
{
    public static string Value(this AppSettings source)
    {
        return WebConfigurationManager.AppSettings[source.ToString()];
    }

    public static string ToHexString(this IEnumerable<byte> source)
    {
        var stringBuilder = source.Aggregate(new StringBuilder(), (builder, aByte) => builder.AppendFormat("{0:x2}", aByte));
        return stringBuilder.ToString();
    }
}