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EMV Contactless Kernels — Hierarchy & Dependencies

How EMVCo's contactless specification fans out into seven scheme kernels and the unified Kernel 8: the structural dependency tree, what happens during a tap, and how the scheme kernels converge into C-8.

Kernel-to-scheme mapping

Book B (Entry Point) reads the card's AID and activates exactly one Book C kernel. Each kernel below links to its full guide.

KernelBookSchemeProductStatus
Kernel 2C-2MastercardPayPass / M-ChipActiveGuide →
Kernel 3C-3VisapayWave / qVSDCActiveGuide →
Kernel 4C-4American ExpressExpressPayActiveGuide →
Kernel 5C-5JCBJ/SpeedyActiveGuide →
Kernel 6C-6DiscoverD-PASActiveGuide →
Kernel 7C-7UnionPayQuickPassActiveGuide →
Kernel 8C-8EMVCo (common)Unified kernel v1.1EmergingGuide →

Kernel 1 (C-1) is retired — removed in Book A v2.7; its Visa AIDs migrated to C-3 and JCB AIDs to C-5.

Structural dependency

Spec families → Books → kernels → schemes, mapped onto the L1/L2/L3 runtime stack. Solid lines are static composition; the orange path is the Entry Point's runtime, AID-driven dispatch.

EMVCoSpecification owner & certifierEMV ContactBooks 1–4 (ICC)EMV ContactlessBooks A–D(one bundle)Book AArchitecture & reader configBook BEntry Point — kernel dispatcherBook C-2…C-8the kernels (L2)Book DContactless comm protocol (L1)L3 · TERMINAL / ACQUIRER APPLICATIONPayment / acquirer appOutcome, online auth, receiptsBook B — Entry PointPPSE → AID match → activate 1 kernelL2 · BOOK C KERNELS (Entry Point activates exactly one)Kernel 2 · C-2MastercardPayPass / M-ChipCert: Mastercard test planKernel 3 · C-3VisapayWave / qVSDCCert: Visa · absorbed C-1 Visa AIDsKernel 4 · C-4American ExpressExpressPayCert: Amex test planKernel 5 · C-5JCBJ/SpeedyCert: JCB · absorbed C-1 JCB AIDsKernel 6 · C-6DiscoverD-PASCert: Discover test planKernel 7 · C-7UnionPayQuickPassCert: UnionPay test planKernel 1 · C-1RetiredRemoved in Book A v2.7AIDs → C-3 (Visa), C-5 (JCB)Kernel 8 · C-8EMVCo unifiedv1.1 (2022) · royalty-freeCert: EMVCo test plan & envC-2…C-7 converge → C-8activates 1 kerneloutcome → appL1 · RF TRANSPORT (Book D)Contactless protocol · ISO/IEC 14443 A/BAnalog RF, framing, anticollision — carries APDUs for every kernelCard / devicepresents AIDcard AIDComposition (static "part-of")Entry Point selection (AID-driven)Convergence → unified C-8

Runtime tap sequence

What happens during a tap: PPSE → candidate AID list → Entry Point match → kernel activation → outcome. Book B drives the dispatch; the activated Book C kernel then runs the exchange.

Card / devicepresents AIDReaderL1 · Book D RFEntry PointBook BKernel C-xL2 · Book CTerminal appL3 · acquirer1 · DISCOVERY (RF + PPSE)Start transaction (amount, currency)RF field on · ISO 14443 activation / anticollisionSELECT PPSE (2PAY.SYS.DDF01)FCI: directory of supported AIDs + kernel IDs + priorities2 · COMBINATION SELECTION (Book B Entry Point — the dispatch)Candidate AID list ↑Entry Point logic (Book B):• intersect card AIDs ∩ terminal-supported AIDs• order by priority → highest → resolve Kernel IDActivate exactly one kernel (Kernel ID → C-x)AID determines the kernel — Visa AID → C-3, Mastercard AID → C-23 · KERNEL PROCESSING (selected Book C kernel runs the tap)GET PROCESSING OPTIONS (PDOL: amount, country, TVR, unpredictable no.)AIP + AFLREAD RECORD(s) — per AFLPAN, track2, certs, CDOL, card risk dataGENERATE AC (+ offline data auth: fast / CDA path varies by kernel)Application Cryptogram (ARQC / TC / AAC) + CIDKernel-specific behaviour (why C-x matters):• CVM selection, offline limits, torn-txn recovery differ per kernel• C-2 (M-Chip) vs C-3 (qVSDC) flows diverge here• C-8 unifies these paths into one kernel→ the layer PayProbe's per-scheme test matrix targetsKernel outcome (Approve offline / Online request / Decline)4 · COMPLETIONIf ARQC → online authorization (issuer host)Issuer response / scripts(optional) 2nd GENERATE AC / issuer script — many contactless flows skipCommandCard responseEntry Point dispatch (AID-driven)

APDU detail is illustrative; exact tags and flow vary by kernel and Books A–D bundle version.

Convergence to Kernel 8

Six scheme kernels run in parallel under one Books A–D bundle, then fold into the unified EMVCo kernel. Verified anchors marked ◆: C-1's retirement and C-8's publication (v1.0 Oct 2022, v1.1 2022/23).

EMV Contactless Specifications — Books A–D (single versioned bundle, 2.x line)C-2 · MastercardPayPass → M-ChipC-3 · VisapayWave / qVSDCC-4 · American ExpressExpressPayC-5 · JCBJ/SpeedyC-6 · DiscoverD-PASC-7 · UnionPayQuickPassC-1 · legacy kernelBook A v2.7 — C-1 removedVisa AIDs → C-3 · JCB AIDs → C-5C-8 · Unified Kernelv1.0 — Oct 2022 ◆ · v1.1 2022/23Royalty-free, licensed from EMVCoFolds C-2…C-7 into one kernelEMVCo-managed test plan + envConvergence target — phased adoption~20072015201820222023→Scheme-kernel origin dates are approximate; ◆ marks verified anchors (C-1 retirement, C-8 publication).◆ Verified anchorConvergence into C-8AID migration (C-1 → C-3 / C-5)

PayProbe note: C-2…C-7 stay live during rollout — test both the scheme kernels and C-8 in parallel.

Kernel 8 adoption (October 2026): EMVCo has approved Book C-8 implementations from Ingenico (the first, October 2024, when type-approval testing opened), Castles Technology (July 2026) and ID TECH (August 2026). The specification is still v1.1, corrected by SB 325, and no card scheme has published a deadline for terminal support yet.

Bulletins to know (EMVCo Q2 2026): SB 317 removes the Mag-stripe Mode implementation option from Kernel 2, leaving "with/without Data Exchange" and "Data Storage"; SB 314 / SB 319 extend Kernel 2's Terminal Risk Management Data (tag 9F1D) with Deferred Authorisation and Transit Gate bits plus a payment-system byte; SB 325 corrects Book C-8 (Service Code removed, "decryption failed" signal, First Wire flag length); SB 326/327 correct Books A and B v2.11; DSB 331 adds RRP timing parameters for Kernel 2. TTA Bulletin 293 confirms every kernel with a Letter of Approval valid before January 2031 must keep processing after the 2038 date rollover.

Per-kernel guides & tools

Kernel 2 · Mastercard →Kernel 3 · Visa →Kernel 4 · Amex →Kernel 5 · JCB →Kernel 6 · Discover →Kernel 7 · UnionPay →Kernel 8 · EMVCo →Contactless features (RRP, DS, MSD) →

Live decoders: TTQ Decoder · CTQ Decoder · Kernel 8 Qualifier · EMV TLV Decoder

Put it into practice

Next steps

ToolTTQ DecoderDecode Terminal Transaction Qualifiers (tag 9F66) — what a contactless reader supports and requires.Open the tool ToolKernel 8 Qualifier DecoderDecode the EMVCo Kernel 8 Kernel Qualifier (tag 9F2B) — version, local-authentication flag, and secure-channel / certificate algorithm suite indicators.Open the tool ToolEMV TLV DecoderDecode TLV-encoded hex bytes (e.g. DE55 field) into a structured, annotated list of EMV tag/length/value records.Open the tool FlowA contactless tap, RF layer to cryptogramSee the animated message flow, step by step, between every party involved.Watch the flow
Keep reading

Related articles

CompliancePOS & SoftPOS Compliance: The Certification PathEMV L1/L2/L3, PCI PTS vs MPoC, brand and acquirer certification — generalised for terminals and SoftPOS apps side by sideRead article ContactlessContactless Features: RRP, DS & MSDRelay Resistance Protocol, Data Storage containers, legacy mag-stripe mode with CVC3Read article ContactlessUnionPay Kernel 7QuickPass contactless: TTQ/CTQ bit layouts, fDDA, the CTQ-driven CVM decisionRead article ContactlessNFC in PaymentsHow a contactless tap works end to end — from RF layer to cryptogramRead article

Common questions

What is the EMV contact kernel?

The EMV Level 2 software that runs a chip-insert transaction: application selection, reading records, offline data authentication, cardholder verification, terminal risk management and the GENERATE AC exchange defined in EMV Books 1–4. One contact kernel serves every scheme, unlike contactless.

What is the difference between contact and contactless kernels?

Contact uses a single EMV kernel for all schemes. Contactless historically had one kernel per scheme (C-2 Mastercard, C-3 Visa, C-4 Amex, C-5 JCB, C-6 Discover, C-7 UnionPay); EMVCo’s Kernel 8 is a common contactless kernel designed to replace them over time.