local password save

using System.Security.Cryptography;
//[...]
private byte[] GetEntropy(string EntropyString)
{

    MD5 md5 = MD5.Create();
    return md5.ComputeHash(Encoding.UTF8.GetBytes(EntropyString));
}

private bool EncryptPassword()
{
    if (string.IsNullOrEmpty(ProxyPassword)) return true;
    if (string.IsNullOrEmpty(ProxyAddress) || string.IsNullOrEmpty(ProxyUser))
        return false;

    byte[] entropy = GetEntropy(ProxyAddress + ProxyUser);
    byte[] pass = Encoding.UTF8.GetBytes(ProxyPassword);
    byte[] crypted=ProtectedData.Protect(pass,
        entropy, DataProtectionScope.LocalMachine);
    ProxyPassword = Convert.ToBase64String(crypted);

    return true;
}

private bool DecryptPassword()
{
    if (string.IsNullOrEmpty(ProxyPassword)) return true;
    if (string.IsNullOrEmpty(ProxyAddress) || string.IsNullOrEmpty(ProxyUser))
        return false;

    byte[] pass = null;
    try
    {
        pass = Convert.FromBase64String(ProxyPassword);
    }
    catch (Exception ex)
    {
        ConfigError = ex.Message;
        return false;
    }
    byte[] entropy = GetEntropy(ProxyAddress + ProxyUser);

    try
    {
        pass = ProtectedData.Unprotect(pass, entropy, DataProtectionScope.LocalMachine);
    }
    catch (Exception ex)
    {
        ConfigError = ex.Message;
        return false;
    }
    ProxyPassword = Encoding.UTF8.GetString(pass);

    return true;
}