Re: UserNameToken with SendNone on Password

From: William Stacey [MVP] (staceywREMOVE_at_mvps.org)
Date: 02/15/05 

Date: Mon, 14 Feb 2005 21:38:30 -0500

> I have created a full working sample using the method you described in
your
> blog.

Great.

> To keep everyone happy, it's partially in C# and partially in VB.NET ;o)

I would rather have all in one or the other myself. Or complete projects in
each if you wanted to show both.

> Nothing too fancy anyway, just hashing, Rijndael, and RSA helper classes.

So why not just include them in your Utils class as static methods? That is
what I did, then I don't need another class for those simple methods.

> * I use the machine key store to store the RSA key pair. A program is
> included that will allow you to create an RSA key pair and store it in the
> machine key store.

You can use the machine store, or *.snk file, or embedded string. The
client only needs the public key. If you are using SN assems, then the
public key in the Assembly is convient as you have the public key you know
the server has a private key for. You can also embed the public key string
in the client so a simple sn -R will not work to do a MITM attack. On the
server side, you could use key store or load from .snk.

> * I have split the SCTMessage class in 2: a request class and a response
> class.

I had thought about that originally, but any null values, by default, don't
serialize so the effect is the same if using one doc class and you can drop
another class. No value type fields, so we can pull this off kinda neat.
If I had more fields and/or value type fields, I would probably go with
another class as well.

> * I include the length of the salt string in the request message.

I wanted to include only that which was required or added security. I don't
see the salt length as adding security. The RSA recommendation is that it
be random and >= 64 bits. So 8 or more bytes should do fine. Then just
remove that many and you can drop another field from the protocol. The salt
is there to make it harder to do dictionary attacks on the username or
password encrypted fields. To pull that off, you would need to guess or
brute force the correct key, IV, salt, and password at the *same time. I
just added it to the username field as it is cheap and pretty simple. And
if you think about it. The username can be just as important to keep secret
as its plain text can be valuable information to an attacker.

> * In order to keep the code clean, I do not actually verify the
> username/password against the windows database or any other credential
> store. There is plenty of info available about those things, I don't see
the
> need to add another example.

I might go ahead and include that logic for others as it is important to the
protocol. You should only return a SCT if you authenticate with correct
username/password combo. So that integration is at heart of the solution.
Your web methods should also require all soap bodies signed with a SCT.
That is how you force a prior authentication and the other side has an
*authenticated SCT. For example, your IsCustomerValid() web method should
have the logic to require an authenticated SCT signed the soap body. As it
is, any client could call that method without including any token (unless I
missed something.) Cheers. 

-- 
William Stacey, MVP
http://mvp.support.microsoft.com

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