static method that behaves just like PHP, etc.

sha1.cs

    /// <summary>
    /// plain string -> sha1 string implementation, behaves identically to php's sha1() function.
    /// </summary>
    /// <param name="input">
    /// A <see cref="System.String"/>
    /// </param>
    /// <returns>
    /// A <see cref="System.String"/>
    /// </returns>
    public static string sha1(string input) {
        byte[] bytes = Encoding.ASCII.GetBytes(input);
        var hashData = new SHA1Managed().ComputeHash(bytes);

        string hash = String.Empty;
        foreach ( byte b in hashData) {
            hash += String.Format("{0:x2}", b);
        }
        return hash;
    }