How to convert a string to securestring explicitly

Question

I want the text entered in the textbox to be converted to securestring in c#.

Answer 1

The simplest approach is to iterate over the source string and append one character at a time to the secure string, like so:

var secure = new SecureString();
foreach (char c in textbox1.Text)
{
    secure.AppendChar(c);
}

Answer 2

Invent once and reuse lots. Create a simple extension method to extend the string base class and store it some static utilities class somewhere

using System.Security;

/// <summary>
/// Returns a Secure string from the source string
/// </summary>
/// <param name="Source"></param>
/// <returns></returns>
public static SecureString ToSecureString(this string source)
{
    if (string.IsNullOrWhiteSpace(source))
        return null;
    else
    {
        SecureString result = new SecureString();
        foreach (char c in source.ToCharArray())
            result.AppendChar(c);
        return result;
    }
}

and then call as follows:

textbox1.Text.ToSecureString();

Answer 3

You should make the SecureString readonly. So the code should look like this:

static class SecureStringExtensions
{
    public static string ToUnsecureString(this SecureString secureString)
    {
        if (secureString == null) throw new ArgumentNullException("secureString");

        var unmanagedString = IntPtr.Zero;
        try
        {
            unmanagedString = Marshal.SecureStringToGlobalAllocUnicode(secureString);
            return Marshal.PtrToStringUni(unmanagedString);
        }
        finally
        {
            Marshal.ZeroFreeGlobalAllocUnicode(unmanagedString);
        }
    }

    public static SecureString ToSecureString(this string unsecureString)
    {
        if (unsecureString == null) throw new ArgumentNullException("unsecureString");

        return unsecureString.Aggregate(new SecureString(), AppendChar, MakeReadOnly);
    }

    private static SecureString MakeReadOnly(SecureString ss)
    {
        ss.MakeReadOnly();
        return ss;
    }

    private static SecureString AppendChar(SecureString ss, char c)
    {
        ss.AppendChar(c);
        return ss;
    }
}