In today’s digital payment ecosystem, EMV (Europay, Mastercard, and Visa) compliance has become the gold standard for secure, chip-based card transactions. Among the multiple layers of EMV architecture, one of the most crucial yet complex integrations occurs between the EMV Level 2 Kernel and the Payment Application (Level 3)—a relationship that determines whether the entire terminal solution can be certified and deployed successfully in the market.
This integration is not just a technical linkage between EMV software components; it is a carefully orchestrated interaction between the terminal’s transaction manager, kernel, and host communication layer, ensuring that every card transaction whether contact, contactless, or hybrid follows the precise EMV flow from card insertion to final authorization.
Understanding the EMV Layered Architecture
The EMV architecture is divided into several functional levels, each addressing a specific layer of the transaction stack.
- Level 1: Defines physical and electrical characteristics for communication between the card and terminal interface (e.g., contact and contactless).
- Level 2: Represents the EMV Kernel that handles the application-level logic required for card authentication, data exchange, risk management, and cryptogram generation.
- Level 3: Involves the host or acquirer integration—responsible for message formatting, network communication, online authorization, reversals, and settlement.
While Level 1 and Level 2 focus on communication with the card, Level 3 connects the terminal to the external financial network. The payment application (or transaction manager) acts as the middleware, bridging the card-centric logic of the kernel and the host-centric logic of the acquiring system.
For an EMV terminal to achieve Level 3 certification, it must demonstrate perfect synchronization among these layers.
The Role of the EMV Level 2 Kernel
At the heart of every EMV-compliant terminal lies the Level 2 Kernel. This certified software module is responsible for executing the EMV transaction flow according to the EMVCo specifications. It interacts directly with the card, managing critical steps such as:
- Application Selection – Choosing the correct application identifier (AID) supported by both card and terminal.
- Card Authentication – Performing Static or Dynamic Data Authentication (SDA/DDA) and verifying the authenticity of the card.
- Risk Management – Applying floor limits, velocity checks, and random transaction selection to decide whether the transaction must go online.
- Cardholder Verification (CVM) – Determining how the cardholder will be verified (PIN, signature, or none).
- Cryptogram Generation – Creating ARQC (Authorization Request Cryptogram) for online authorization and TC (Transaction Certificate) for completion.
The kernel essentially acts as the intelligence layer that enforces EMV rules, ensuring that both the card and terminal comply with the transaction flow required by global payment schemes.
The Role of the Transaction Manager (Payment Application)
Above the kernel sits the transaction manager, which handles all business logic and user interactions within the terminal application. This layer acts as a controller that coordinates between the user interface, kernel, and host communication modules.
Its core functions include:
- Managing transaction states (Idle, Insert Card, Processing, Online, Approved, Declined).
- Collecting and validating input from the user (amount, merchant ID, transaction type).
- Invoking kernel commands in the correct sequence (Initialize Transaction → Application Selection → Read Records → Generate AC).
- Displaying prompts such as “Insert/Swipe/Tap Card,” “Enter PIN,” or “Remove Card.”
- Capturing the output data (TVR, TSI, Cryptograms, AIP, AFL) from the kernel and formatting them for host messages.
- Handling reversals, voids, and offline transactions.
The transaction manager translates the technical responses from the kernel into meaningful actions and messages for both the host and the end user.
The Role of the Host Logic (Acquirer Integration Layer)
The host logic, often known as the L3 layer, deals with the terminal’s communication with the acquirer or payment processor. It formats the EMV data into ISO 8583 messages or scheme-specific APIs and sends them to the acquiring bank for authorization.
It performs vital functions such as:
- Message Construction and Parsing – Mapping EMV data (Field 55) to ISO message formats required by different card schemes.
- Network Communication – Managing TCP/IP, SSL, or dial-up connections to the acquirer.
- Authorization Processing – Sending ARQC to the acquirer, waiting for ARPC (Authorization Response Cryptogram), and updating transaction results.
- Settlement and Reconciliation – Storing completed transactions and sending batch settlement files.
- Error Handling and Reversals – Managing network failures, timeouts, and duplicate transactions.
The L3 layer ensures the terminal’s transaction data is properly structured, transmitted, and validated by the payment host—critical for certification.
How the EMV Kernel Interacts with Host Logic and Transaction Manager
The integration between the EMV kernel, transaction manager, and host logic follows a step-by-step transaction flow, designed to ensure accuracy, compliance, and security.
- Transaction Initialization
When a transaction begins, the terminal application collects transaction details such as the amount, transaction type, and merchant data. The transaction manager initializes the kernel with this data and starts the EMV transaction.
- Application Selection
The kernel selects the appropriate application based on the AIDs supported by the card and terminal. The transaction manager updates the display and manages user input in case of multiple available applications.
- Card Data Reading and Authentication
The kernel reads the card records, retrieves essential tags, and performs card authentication. The transaction manager receives and logs these responses for host communication.
- Risk Management and CVM
The kernel evaluates transaction risk and executes the required CVM method. If a PIN is needed, the transaction manager interfaces with the PIN pad to collect and securely transmit the PIN block.
- Cryptogram Generation and Online Request
Once the kernel recommends an online authorization, it generates the ARQC and provides it to the transaction manager. The manager then packages this EMV data (Field 55) into an ISO 8583 message and sends it to the acquirer through the host logic layer.
- Host Authorization and ARPC Handling
The host verifies the ARQC and returns an ARPC with the authorization response. The transaction manager provides this ARPC to the kernel, which performs Generate AC to complete the EMV flow and generate a TC or AAC (Transaction Certificate or Application Authentication Cryptogram).
- Completion and Settlement
Once the transaction is approved, the transaction manager records the data, prints the receipt, and marks it for settlement. The host logic handles the final batch file communication with the acquirer.
Data Exchange Between the Layers
A successful EMV transaction involves multiple data exchanges between the kernel, transaction manager, and host:
Flow Direction | Data Type | Purpose |
Kernel → Transaction Manager | EMV Tags (TVR, TSI, AIP, AFL, ARQC) | For transaction decision and host message formatting |
Transaction Manager → Host Logic | ISO 8583 / API fields | For sending authorization requests |
Host Logic → Kernel (via Transaction Manager) | ARPC, Authorization Code | For completing the cryptographic verification |
Transaction Manager → Host Logic | Settlement & Reversal Data | For post-transaction reporting |
Every exchange must follow EMV and scheme-specific encoding, including TLV format, tag sequence, and cryptogram verification—failure in any of these leads to Level 3 certification issues.
Why Integration Matters for EMV Level 3 Certification
Level 3 certification is not just a regulatory checkbox it validates the complete interoperability of a terminal with both card and host. It ensures that the terminal’s EMV Kernel (L2) and Application (L3) work seamlessly together across all card brands, transaction types, and error scenarios.
Certification labs and schemes test parameters such as:
- Correct EMV data mapping in ISO 8583 Field 55.
- Valid ARQC and ARPC generation and response handling.
- Accurate CVM execution and PIN handling.
- Proper online/offline decision logic.
- Reversal and retry mechanisms.
- Correct terminal behavior during partial approvals, declines, or host timeouts.
Any mismatch or deviation between kernel and host handling can cause the L3 certification process to fail.
Common Integration Challenges
Despite careful development, many terminal projects face integration difficulties during EMV certification. The most common issues include:
- Incorrect Field 55 Formatting – EMV tags missing or out of order.
- Improper ARPC Handling – Kernel not correctly processing host cryptograms.
- PIN Block Misalignment – Mismatch between acquirer encryption format and terminal encryption.
- Inconsistent Transaction States – Terminal displays “Approved” while the host declines due to timeout.
- Offline Transaction Mismanagement – Card or kernel disallowing offline approvals, yet terminal attempts to process one.
Resolving these issues early through detailed system integration testing can drastically reduce certification cycles.
Best Practices for Smooth Kernel and Host Integration
- Understand Scheme Requirements Early – Each network (Visa, Mastercard, RuPay, etc.) has different data and message mapping rules for L3 certification.
- Use an Acquirer Simulator – Simulate ARQC/ARPC flows to validate EMV tag transmission before live host testing.
- Validate Field 55 Composition – Confirm tag structure, order, and values using trace tools.
- Ensure Consistent State Machines – Terminal states (Approved, Declined, Reversal) must align across kernel, app, and host.
- Comprehensive Error Testing – Test fallbacks, power loss recovery, and dual-message handling.
- Maintain Version Control and Logs – Store transaction traces for certification audit and debugging.
Following these best practices ensures that your EMV kernel and host logic integration pass certification with minimal rework.
The integration of the EMV Level 2 kernel with the payment application and host logic is the foundation of a secure, compliant, and certifiable EMV terminal. Every function—from card authentication and cryptogram generation to ISO message formatting—depends on the precise coordination between these layers.
As the industry continues shifting toward contactless, NFC, and SoftPOS ecosystems, understanding how these EMV components communicate remains a critical skill for developers, testers, and certification engineers. EMV Level 3 certification isn’t just about meeting compliance it’s about ensuring that every transaction, in every environment, follows the highest standards of reliability, interoperability, and security.
