EMV Operation and Attacks Tyler Moore CS7403, University of Tulsa Reading: Anderson Security Engineering, Ch (136—138), (328—343) Papers on Course Schedule 1

Agenda EMV Design EMV Attacks EMV’s Context in Overall Payment Fraud 2

Mag-strip Payment Cards are Vulnerable ATM, credit cards embed key information in magnetic strip – PAN (primary account number) – Version Number – Expiration date Mag-strip cards can be easily copied – Anyone reading the mag-strip can copy its contents – Can also recreate if the PAN, expiry is observed Industry response: CVV (cardholder verification value) – 3-digit MAC on mag-strip contents, written on back 3

EMV EMV: Europay, Mastercard, VISA – Suite of protocols for smartcard-based payments – Huge variation in requirements across banks (VISA protocol specification is 3600 pages long) EMV’s goals – Use smartcards to reduce “card-present” fraud by preventing card counterfeiting and theft from loss – Be interoperable internationally Deployment began in Europe, recently hit US 4

EMV Transaction Security 1.Card Authentication – Validate card either online or offline 2.Cardholder Verification – Methods: offline PIN, online PIN, signature, none 3.Transaction authorization – Online: same as for mag-stripe cards, communication with issuer – Offline also permitted 5

Card Authentication Figure courtesy Steven Murdoch 6

Card Authentication Options 1.Static Default Authentication (SDA) – Default, cheapest option 2.Dynamic Default Authentication (DDA) – More expensive, now more common 3.Combined Data Authentication (CDA) 7

Static Data Authorization (SDA) Under SDA, the card information is signed once and reused across transactions – Card not capable of public-key crypto operations – Card is preloaded with signature by issuer {PAN, expiration, CA Issuer, Cert Issuer } – Card sends terminal issuer’s digital certificate, PAN and other mag-strip data, plus signature of data using card issuer’s private key (see above) – Terminal verifies the signature using issuer’s public key 8

Dynamic Data Authorization (DDA) SDA cards vulnerable to replay attacks DDA uses more expensive cards capable of public-key cryptography 1.When card inserted to terminal, the terminal sends a dynamically generated nonce N 2.Card signs the nonce {N} and sends to terminal 3.Terminal sends transaction data plus PIN encrypted using card’s public key 9

Cardholder Verification (Offline PIN) Figure courtesy Steven Murdoch 10

Cardholder Verification Methods: offline PIN, online PIN, signature, none Offline PIN – If PIN auth used, customer inputs at terminal, then sent in clear to card if SDA used – PIN checked by card, if OK card generates a MAC (called application data cryptogram) on transaction info, using key shared between card and issuer 11

Transaction Authorization Figure courtesy Steven Murdoch 12

Transaction Authorization Key used to compute application data cryptogram is shared between issuer and card – Thus, the terminal cannot validate the cryptogram – Only the issuing bank can validate the cryptogram – Thus, the terminal optionally checks online with issuer that cryptogram is OK 13

What Goes Wrong with EMV Under SDA, vulnerable to replay attacks – Anyone who obtains issuer signature of card data and replays the information can impersonate card – Attacker can read the signature off the card, write it to a new card and then use it for offline card authentication – Countermeasure: only permit online card authentication Furthermore, communications between terminal and card are sent in the clear – Therefore, keeping the communications between terminal and card secure is very important – EMV achieves this by making terminals tamper-resistant 14

Figure courtesy Steven Murdoch 15

Figure courtesy Steven Murdoch 16

Figure courtesy Steven Murdoch 17

Figure courtesy Steven Murdoch 18

What Goes Wrong with EMV Criminal gets everything necessary to make a magnetic stripe card – Card #, expiration date, CVV, PIN – Compromising a single terminal in a shop can enable fraudulent cash withdrawals from ATMs Countermeasures – Banks have stopped storing mag-strip data – Mag-strip fallback transactions are being phased out 19

What Goes Wrong With EMV Cards using DDA are still vulnerable to attacks – No link between the act of proving freshness (exchanging the nonce) and accepting the PIN – In other words, the card authentication step and cardholder verification step are disconnected, which an attacker can exploit (e.g., saying PIN has been verified when it hasn’t) Countermeasure: Combined Data Authentication (CDA) – Cardholder verification decision included in the card’s signature – Even CDA remains vulnerable to no-PIN attack (see “Chip and PIN is Broken” paper) 20

What Really Goes Wrong with EMV There is evidence that criminals have carried out attacks exploiting weaknesses in SDA, DDA, and other protocol flaws But EMV has shifted the fraud landscape to two main approaches – Exploiting mag-strip fallback – Shifting fraud away from more secure “card- present” transactions to “card-not-present” ones 21

The UK Case for EMV 22

Shift from Card-Present to CNP Fraud (UK Fraud Losses) 23

Counterfeit Cards Cashed Out Overseas 24

Externalities of EMV Adoption 25

Conclusion EMV improves card authentication over magnetic stripe technology Supports PIN-based cardholder authentication Many configurations, many weaknesses Shift in payment card fraud to jurisdictions with weaker security: card-not-present transactions and countries not adopting EMV 26