Is NFC host card-emulation safe for payments? (part I)


An earlier series of posts compared the security properties of NFC applications implemented using host card-emulation against the same scenario backed by a dedicated hardware secure element. It was not much of a contest; hardware SE easily wins on raw security considerations:

  1. Much stronger tamper-resistance against attacks involving physical access
  2. Greatly reduced attack surface, due to stripped down operating system and locked-down application ecosystem, unlike the anything-goes approach to third-party applications on the average phone
  3. Possible to protect against attacks originating from the host operating system itself
  4. Defense against remote relay attacks using interface detection on the NFC controller

It’s natural to ask: does this mean HCE is not suitable for payments? There have been vocal critics making precisely that claim. NFC Times quotes the Gemalto CEO pursuing this line of argument. Of course Gemalto has a significant business in providing UICC chips– a type of hardware secure element in SIM form factor– to wireless carriers, who are currently making a desperate push for land-grab in the payments space. Having cast its lot with carriers and already reeling from MasterCard/Visa support for HCE, it is not surprising the company does not look kindly on HCE displacing extra hardware. But Gemalto is not alone in trying to “rescue” the world from NFC payments without SE. Whether it is Trustzone or some other snake-oil solution, every vendor seems to have latched on the market failure of secure elements to gain traction as an opportunity to trumpet an alternative to “save” payments from the perils of HCE.

Risk-management versus risk-elimination

First observation is that keeping the fraud level in payments down is a problem of risk management. It is about keeping the frequency and total losses from fraud down to an “optimal level” and distributing the liability appropriately within the system.  More surprising is that optimal level need not be zero, and consumers may be just fine with that arrangement as long as the consequences are not reflected directly on the individual card holder. That second property is important because “optimal” risk can be very different for each participant in the system:

  • Issuing bank who underwrites the card, for example Citibank issuing a MasterCard.
  • Card network facilitating the transactions eg MasterCard.
  • Merchants that accept a particular brand of payment cards
  • Acquiring banks and payment processors helping that merchant accept card transactions
  • Individual card holders

Optimization problem

With the exception of the card-holder, all of these participants are effectively trying to maximize profit. (Strictly speaking, some  issuing banks can be non-profit institutions such as credit unions.) Minimizing fraud is only relevant to the extent that it furthers that objective. This is an important distinction. Earning $100 but losing $10 to fraud may be preferable to earning $50 while only suffering $1 in losses. Granted absolute amounts are not the only concern; increased fraud rates may have second-order effects such as discouraging consumers or merchants from using credit cards. But all of these effects can be quantified. All else being equal, increasing number and dollar-amount of transactions is in the interests of all participants except possibly the card-holder. Security measures designed to combat fraud can end up being counter-productive if they introduce friction, cause transactions to become less reliable or otherwise decrease the revenue stream for the participants. Conversely a technology that is less “safe” in the absolute sense may be preferable for these participants if it boosts overall activity in the ecosystem, provided the attendant fraud can be managed.

Consumer view

Card holders however face a different problem since they can not “average” away profit and loss across many cards. One incident of fraud maxing out a single credit card is a drop in the bucket for Citibank. That same amount can be very significant for the customer involved, enough to wipe out their savings. It doesn’t help that there is great information asymmetry: card networks know a lot about the incidence and impact of fraud while this information is generally not available to consumers, making it difficult to estimate risks. (Is it safe to pay with a credit card online? What about at a street fair?) Worse they have little negotiating power to set terms, other than a rudimentary version of “voting with the wallet” by choosing from offerings from different banks on take-it-leave-it terms.

Fortunately this is where regulation comes in. Consumer protection laws can compensate for the information asymmetry and lack of bargaining power by creating a baseline of  fraud protection that all issuers must adhere to. Such regulations can limit the downside, indemnifying users from losses. The prevailing arrangement in the US via Fair Credit Billing Act (FCBA)  leads to exactly this outcome. Consumers are not liable for fraudulent transactions, a fact that is repeatedly drilled in many an advertisement harping on “zero liability.” Of course what this means more precisely is that we are not directly responsible for reimbursing the issuing bank, merchant or whoever ended up absorbing the loss. Instead those losses are “diffused” across  the system and reflected back to consumers in the form of higher prices at stores (which reflect the expected incidence of charge-backs), higher interest rates on balances carried or greater cut taken by middlemen to offset expected losses.

With consumers effectively neutralized in this manner, card networks have great leverage to move risk around the system, squeezing either banks (unlikely) or more commonly merchants. Similarly they are free to set standards on the design and operation of payment technologies without having to face significant consumer backlash. The average card-holder has little at stake directly to care whether that PIN pad is really living up to its tamper-resistance promise or that point-of-sale terminal is not compromised by malware waiting to skim cards. If there is a security problem anywhere in this chain, it is someone else’s problem to make the consumer whole.

[continued]

CP

One thought on “Is NFC host card-emulation safe for payments? (part I)

  1. I particularly agree with what you say about information asymmetry; particularly in the US, there is very little data provided about how effective the various security systems actually are at preventing unauthorised card transactions, and there is no sharing of data outside of the affected organisation. I think the Merchants are the ones who really get squeezed though, when the risk for the online transaction is deflected back over to them; the rest of the chain is just incorporating a margin of insurance against the probability of fraud, and as you say, averaging away the profit levels

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