Understanding EMV Card File Structure: Unraveling ADFs, SFIs and More

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EMV (Europay, Mastercard, Visa) cards are ubiquitous payment tools that employ advanced security features to protect sensitive financial data. At the core of these secure transactions lies a complex file structure that governs how card information is stored, accessed, and processed. In this article, we'll dive into the intricacies of EMV card architecture, focusing specifically on Application Data File (ADF) structures, Secure Card Frame (SCF), and their role in ensuring payment security.

### Introduction to ADF Files

Application Data Files (ADFs) are fundamental components within an EMV card's file structure. They serve as containers for various applications that provide specific functionality or services to the cardholder. Each application is identified by a unique Application Identifier (AID), which helps the card's Secure Element (SE) distinguish between different ADFs.

In our example, we have three ADF files:

1. `ADF1`: Hosting an unspecified application with Aid: `AID1`

2. `ADF2`: Housing another application with Aid: `AID2`

3. `ADF3`: Containing a third application identified by Aid: `AID3`

### Secure Card Frame (SCF) Structure

The Secure Card Frame is a critical element within the EMV card architecture, acting as an entry point for various applications and services. It serves multiple purposes:

1. Secure Data Storage: The SCF provides secure storage space for sensitive information.

2. Application Management: It acts as a management layer between different application components.

The Secure Card Frame is always referenced by the Tag `DF20`. This tag will consistently occupy 64 bytes in length across all implementations, ensuring compatibility and predictability within EMV card architectures.

Within the value part of Tag `DF20`, additional tags or SFI/Record references may be included. However, these are issuer-dependent and can vary significantly between different banks and payment providers.

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In conclusion, understanding the complex structure of an EMV card is essential for anyone involved in developing secure payments solutions. From Application Data Files (ADFs) to Secure Card Frames (SCF), each component plays a vital role in ensuring the security, integrity, and privacy of financial transactions. By grasping these fundamental concepts, we can better design and implement robust payment systems that protect cardholder data while facilitating fast, efficient, and secure transactions.

### References

1. EMV Specifications: Book 5 - IC Card Personalization

2. Contactless Cards with Dual Interface (Contact & Contactless): An Introduction

Emv card sfi strcutre