设置密码框的文本

Question

I am creating an application that requires user login (username + password). As this is a secure application, I'm using WPF's PasswordBox.SecurePassword to securely create a hash of the password (using SHA512CryptoServiceProvider, hashing from a custom Stream) to use as a password for Rfc2898DeriveBytes. Let's say I have an AES-256-CBC implementation which securely retrieves and stores key+IV so that is not an issue.
I am currently implementing a way for users to be able to store their password so they don't have to put them every time they log in. So far I am able to store the password securely using the AES custom implementation and I can read the password securely (that is, without ever putting it completely in Memory in plain text).
What I am having problem is when I try to replace the text in the PasswordBox. PasswordBox.SecurePassword is read-only and I have tried to use PasswordBox.SecurePassword.AppendChar(someChar) but the field/value remains empty. I imagine that PasswordBox.SecurePassword only returns a copy (SecureString.Copy()) and not the original variable ( looking at .NET source code confirms this ).
Is there any way I can achieve what I want or do I need to create a custom WPF control?

Answer 1

To set the text of the PasswordBox in WPF use the following code:

PasswordBox1.Password = "yourpassword";

You don't need to use the SecurePassword function as long as you are able to get the password in plain text then you will be able to set it using the Password function. As you mentioned the SecurePassword function is read only this is because this retrieves the password in a secure form, it does not allow you to set the text in the PasswordBox. MSDN Documentation

If you want to be able to put the secure password in the PasswordBox you can also use this method, but you cannot put it in plain text, because you'd effectively be asking to break the encryption, but if you have the key and you can decrypt it then do that first and then set the text in the PasswordBox.

To view the password entered in the PasswordBox in plain text use the following code:

PasswordBox1.Password;

Answer 2

This can be considered to be solved.
We decided to use an animation to show the user that they don't need to put the password again.
It's a shame you cannot programmatically add characters to the SecurePassword property like you can do with a normal SecureString.