String ToHex -> Hex ToString

public string ConvertStringToHex(string asciiString)
{
    string hex = "";
    foreach (char c in asciiString)
    {
        int tmp = c;
        hex += String.Format("{0:x2}", (uint)System.Convert.ToUInt32(tmp.ToString()));
    }
    return hex;
}

public string ConvertHexToString(string HexValue)
{
    string StrValue = "";
    while (HexValue.Length > 0)
    {
        StrValue += System.Convert.ToChar(System.Convert.ToUInt32(HexValue.Substring(0, 2), 16)).ToString();
        HexValue = HexValue.Substring(2, HexValue.Length - 2);
    }
    return StrValue;
}