EMV Contactless: VSDC vs. M/Chip Advance Contactless
Both Visa and Mastercard define their own contactless application specifications built on the ISO/IEC 14443 contactless communication standard and the EMVCo contactless framework:
- VSDC Contactless (Visa): Visa's contactless application, processed via Kernel 3 of the EMVCo Contactless Kernel Specifications. VSDC contactless transactions use a Cryptogram Version Number (CVN) and a dedicated ARQC generation algorithm. Online-capable VSDC contactless transactions carry a full TC/ARQC cryptogram; offline-only transactions at transit gates use a reduced data set with an offline-approved flag.
- M/Chip Advance Contactless (Mastercard): Mastercard's contactless application, processed via Kernel 2. M/Chip Advance supports both online and offline contactless modes, with the issuer's chip profile configuring the CVM List and contactless transaction limits. M/Chip Advance uses Application Cryptograms (ACs) for transaction authentication — the AC type (ARQC, TC, AAC) communicates the card's decision outcome to the issuer host.
Kernel differences matter for terminal certification and card personalisation: Kernel 3 and Kernel 2 have distinct Application Identifier (AID) structures, PPSE selection logic and Offline Data Authentication (ODA) requirements. Cards supporting both schemes carry both AIDs — terminal kernel selection at PPSE determines which contactless application is invoked.
PPSE — Proximity Payment System Environment
PPSE (2PAY.SYS.DDF01) is the EMV contactless application directory — the first SELECT command issued by a contactless terminal to enumerate available payment applications on a card or device. The PPSE response contains a list of ADF (Application Definition File) entries, each with an AID, application label and optional priority indicator. Application selection logic — governed by both the terminal's supported kernel list and the card's priority order — determines which payment application is selected when multiple AIDs are present. Incorrectly configured PPSE entries are a common cause of contactless interoperability failures during scheme certification.
CDCVM — Consumer Device CVM
CDCVM (Consumer Device Cardholder Verification Method) allows the consumer's device biometric or PIN — unlocking the OEM wallet — to serve as the CVM for a contactless payment, replacing the need for a separate PIN entry at the terminal. When CDCVM is performed successfully prior to the tap:
- The wallet sets the CDCVM bit in the transaction data sent to the terminal.
- The terminal's CVM list processing recognises CDCVM as a valid CVM outcome and does not prompt for terminal-side PIN.
- CDCVM enables higher contactless transaction limits — many issuers apply lower limits to no-CVM contactless transactions (e.g., £100) but allow higher limits (e.g., £500+) when CDCVM is confirmed.
CDCVM is critical to the premium contactless UX in OEM wallets — without it, high-value tap-and-go transactions would require a separate PIN entry that defeats the speed advantage of contactless.
Express Transit & Zero-Amount Tap
Transit use cases — metro, bus, barrier tap — impose stringent latency requirements (typically <500 ms transaction completion) that preclude online authorisation at the point of tap. Both Visa (XpressWay / Transit Express) and Mastercard (Transit Express) define programmes for offline or deferred-auth transit acceptance:
- Zero-amount pre-authorisation: The transit terminal sends a zero-amount tap to the issuer to validate card validity without an amount. The issuer responds with an ATQC (Authorisation Transit Quick Code) or equivalent approval flag. Subsequent boarding taps within a defined session window proceed without individual online authorisations, accumulating a deferred balance settled at end of journey or end of day.
- ATQC handling: The issuer must configure ATQC response generation and the card profile must be personalised with transit-specific CVM configuration (typically CVM=No CVM for transit) to enable no-PIN, no-signature transit taps below scheme-defined floor limits.
- Aggregated clearing: Transit acquirers submit aggregated clearing records covering multiple taps per journey — the clearing record carries the total journey fare, not individual boarding amounts. Issuers must handle the clearing amount differing from any individual zero-amount tap authorisation.