Usably Secure, Low-Cost Authentication for Mobile Banking* Saurabh Panjwani, Ed Cutrell Microsoft Research India * Many thanks to Anupam Varghese (EKO India Financial Services Ltd.). Thanks also to Aishwarya Ratan, Indrani Medhi, Prasad Naldurg, Raghav Bhaskar (Microsoft Research)

Mobile Banking Over 1 billion people in the world with mobile phones but no bank accounts Banks say, Lets use phones to serve these people! Several mobile banking services exist today – M-PESA (Kenya), Wizzit (S.A.), GCash (Philippines) – > 100 million dollars transacted per day

How does it work? A network of human agents mediate transactions – Run small businesses: mobile recharge, pharmacy etc – Commissioned by m-banking provider M-banking outlet in Delhi An m-banking agent sends an SMS to the bank for a deposit transaction Courtesy: CKS

How does it work? Agent Bank Hari deposits 100/- Credit Haris a/c with 100/- Haris a/c credited Hari

How does it work? Agent Bank Hari withdraws 100/- Credit agents a/c with 100/- Agents a/c credited Hari

Benefits Benefit to customers: – Low-cost, low-effort savings (often, theres interest) – A new remittance channel – Others that evolve contextually (m-payments) Benefit to agents: – A second source of income Note: different from mobile banking for the rich There, the goal is convenience ; here, it is access.

Security Issues Phones can be lost or stolen. Banks must authenticate users. Hari Bank Credit agents a/c with 100/- Is this really Hari?

Challenges How do we authenticate via a phone like this? No GPRS, Cant install software Typical m-banking users phone Courtesy: EKO … while also ensuring A simple interface (want low-literate users to use it) Low cost (want it to scale)

Current Practice Most banks use PINs to authenticate users For good security, PINs must be protected Cant rely on GSM security – Network-layer protection only + several known attacks Then how do banks protect PINs? – Some dont care! – Others protect them, but dont tell you how!

Our work Partnered with EKO, m-banking service in India – 1.5 years in operation, 70K customers, partners of SBI – Support from Gates Foundation EKO uses PINs + security tokens for authentication Endorsed by Verisign Inc. Our contribution: – Find a flaw in EKOs scheme – Propose a new solution – Test it with real users EKO locations

EKOs Authentication Solution Every user has a PIN & holds a unique codebook – Appends a signature to each transaction message – A fresh signature each time Example: If PIN = 6391, OTP = , then, Signature = Each entry is a 10-digit string with a 6-digit one-time password and 4 gaps, denoted Our Finding: Given 7 such signatures from a user, the PIN can be recovered.

Implications The PIN is redundant in EKOs scheme – Security rests on codebook and phone, not on PIN PIN loss could have other bad consequences – Users use same PIN across different accounts; loss of PIN could damage other accounts they hold

The New Scheme* Like EKOs scheme, uses one-time passwords, but each OTP is a 10-digit random number Variant of the well-known one-time pad scheme Caveat: Need PINs with distinct digits Example: PIN = 2340, signature is: * Developed in collaboration with EKO India Financial Services Ltd.

How do they compare? Method Secure against impersonation Secure against PIN recovery Secure against impersonation, given booklets Secure against man-in-the- middle forgeries Plain PIN NO EKO YESNO Ours YES (Ongoing work) New scheme is more secure than plain PIN entry and EKOs scheme

How do they compare? New scheme is more usable than EKOs scheme. (Based on a usability study with 34 current and potential m- banking customers in Delhi, Bihar*) 65% of participants found the new scheme easier to use than EKOs. (10% were neutral.) * Thanks to CKS India Pvt. Ltd. for helping us conduct the study.

What do users say? Users reported several advantages of new scheme: – new scheme is easy as it involves typing only 4 digits – only matching of numbers needs to be done, which is easy – everything is given in the booklet, just needs to be looked up Offered interesting cognitive explanations –.. need to lay less stress on my brain and more on my eyes, which is why it is easier to handle. Pro-actively spoke about security benefits – the PIN is mixed up here and not written in plain, which means it is more secure –new scheme is more easy to use: it is more secure, therefore it is more easy

Beyond Mobile Banking PIN-entry using our scheme provides better security than PIN-entry at ATMs – Secure against skimming attacks. (Skimming attacks caused a loss of > $1 billion in 2009.) – Reasonably secure against shoulder-surfing attacks Similar solution is used for online-banking by some European banks – Drawback: phishing attacks. Caveat: Decreased usability (users need to carry tokens)

Conclusion Cryptanalyzed EKOs authentication scheme Proposed a new authentication solution – More secure, more usable! – Easy to deploy (no software installation, no changing network protocol) – Potentially applicable beyond mobile banking Future work – Get rid of the codebook, can we?