From: Daniel (deepergmail.com)
Date: Sun Nov 27 2005 - 16:29:06 CST

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Word of warning, if you are doing this in the UK you will be arrested
and charged under the Computer Misuse Act

On 11/22/05, Javier Fernandez-Sanguino <jfernandezgerminus.com> wrote:
> Andrew van der Stock wrote:
>
> > Transaction signing for my point of view is not C/R two factor
> > authentication, which as I said, not that useful. If you pay for trx
> (...)
>
> > Phish threat model for trx signing / sms (A)
> (...)
>
> > Now, it may be possible that a user with a trx signing calculator may
> > answer the phone and give these details up, but I doubt it. A user who
> > gets a SMS transfer message when they're not using the system would
> > rightly either ignore it or ring the bank. Honestly, a phisher in
> > Brazil or the former eastern bloc country would have almost zero chance
> > to make an out of band connection with enough users to make this
> > worthwhile, particularly since it would require a lot of access to
> > telephones at the right time and knowledge of a lot of people's
> > numbers. Not impossible, but highly unlikely.
>
> Now, I don't think you've considered the scenario of a wide VoIP
> deployment in which VoIP terminals are able to interact with the
> cellphone network and can provide the same services (i.e. SMS sent
> through VoIP phones, just like you can do that through regular, not
> cell-, phones in some telephone networks).
>
> In that case, attackers have access to a lot of telephones at the
> right time. You don't have the phone number, but you can slightly
> change the MITM session so you ask for the user's number "for
> confirmation purposes".
>
> And consider the "what if?" scenario of cellphones with zillions of
> differnet functions (think Java phones) connected to a 3G network
> which is, for all pursoses, IP based. In this case attackers can
> consider compromising cellphones, yes, cellphones, to do the MITM
> session there too.
>
> Most cellphone networks are working towards UMTS/3G and that means
> that they will be eventually on the same "medium" that your average
> computer is meaning that they will get compromised/trojaned just like
> computers are. Oh, if cellphones would just nowadays just be the
> traditional "call-only, SMS-only" thingies they were years ago. Now
> you have a full computing platform, to which people download software
> into (think: games, sounds) and that can get compromised remotely
> (just look at how virus have spread through weak bluetooth
> implementations)
>
> >
> > MITM threat model for trx signing (B) / sms (C)
> >
>
> (..)
>
> > Scenario B) IB platform asks user for transaction signing for
> > transaction B (usually based upon $, transaction reference and
> > destination account)
>
> IB platform might be compromised as it might rely on the user's
> cellphone and that's already compromised (see above). If the phone is
> trojaned all bets are off.
>
> (...)
>
> > Scenario C is much stronger than no transaction signing, but it has one
> > weakness - that the user's mobile number might be obtainable somehow. I
> > really don't think this is practical on a widespread basis like
> > phishing attacks for non-2FA / non-TS internet banking. For retail IB,
> > SMS is acceptable right now until trx signing calculators are available
> > to all IB users.
>
> The problem here is that you assume that the phone network is
> completely separated from the Internet network so that, even if the
> Internet network is somehow compromised (trojan on the PC, MITM attack
> through pharming or phishing) then there is no way to get access to
> the phone network. That is true for your average cellphone network
> right now but it is not that much in the future of 3G networks in
> which cellphones are really just an end-node of a data communications
> network connected to the Internet which just happens to use radio
> circuits instead of your regular fiber or network cables.
>
> In this environment, attackers will focus on compromising computers
> used for Internet banking, get the cellphone through some devious
> means (think: MITM sessions that modify the pages and ask for your
> cellphone number, even if the bank already has it) and then go for the
> cellphones. You could even imagine an scenario in which attackers are
> compromising *both* computers and cellphones and just check when
> somebody's computer (A) uses Internet Banking X to generate a
> transacion and recevies the session confirmation in cellphone (B).
> They correlate these and determine that A and B are associated for X,
> and that's again where the fun begins.
>
> Maybe I'm being too pessimistic, but in a network where everything
> converges to a data IP-based network, all network nodes (from
> computers to cellphones) are feature full (and, consequentely,
> vulnerability-full) cellphones are as useful as an offline C/R
> mechanisms.
>
> Indeed, you are raising the bar in the mid-term (just like if you are
> if using offline C/R) so that *your* bank is more difficult to attack
> than a different bank not using those mechanisms. But, again, given
> sufficient economic incentive, attackers will develop the tools to be
> able to compromise your carefully crafted authentication mechanism.
>
> Just my 2c
>
> Javier
>

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