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Posted by Ben C on 01/10/08 22:07
On 2008-01-10, Alexander Mueller <noemail@example.org> wrote:
> Ben C wrote:
[...]
>> How does munging alter that situation? If he can replay the first access
>> (by getting hold of the hash used) then won't he just get his very own
>> replaysalt in just the same way?
>>
>> Can you describe an example, step-by-step, of a session in which the
>> replaysalt provides some benefit that one-time session numbers don't?
>
> 1.) The user requests a site.
> 2.) The server sends the login form, issues a random replay salt and
> stores it in a session.
> 3.) The user enters the necessary information.
> 4.) The browser hashes the entered password and hashes the result once
> more with the replay salt.
> 5.) The server hashes the stored hash with the previously issued replay
> salt and compares the result to the given value.
So why wouldn't this work just as well:
1. The user requests a site.
2. The server sends the login form, which also contains a hidden input
whose value is a number picked out of a hat, which we call x.
3. The user enters the necessary information and submits the form.
4. The browser receives in the formdata at least two items: the password
and a number. It checks the user's password (by hashing it and
looking for it in a list of stored hashes, for the sake of argument)
and also that the number is equal to x. If either check fails it
refuses to go any further. Either way it makes a note never to accept
x again.
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