> Consider the following attempt at el-cheapo (no hardware) > authentication: [...]
> It is possible to imagine an authentication scheme that wants to use > something like a certificate with signing, encrypting random nonces > etc., to verify that someone agrees to some transaction(s). If the > certificate is on a PC, though, it gets exposed to theft. There is no way to avoid this (as long as you stick to the no-hardware restriction). You can get clever with third parties and whatnot all you like, but anything the user's desktop can do with the data it has (possibly including data that is typed in by the user during operation as intended), an impostor who has the same data (lifted from disk, snooped on keystrokes, whatever) can do equally well. To defeat this, in principle, you need *something* the user's computer does not have access to. This can be as simple as the next entry on a list of nonces (sent to the user by some other means such as snailmail) all the way up to something as complex as the stuff underlying SecurID. Of course, that's not to say that simpler measures can't defeat any specific examples, such as current attacks. You can make it moderately difficult, in fact. But you can't make it impossible. /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML [EMAIL PROTECTED] / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B _______________________________________________ Secure Coding mailing list (SC-L) SC-L@securecoding.org List information, subscriptions, etc - http://krvw.com/mailman/listinfo/sc-l List charter available at - http://www.securecoding.org/list/charter.php
