How ATR tools work

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ATR (Answer To Reset) tools are used to analyze and diagnose smart cards such as chip bank cards, SIM cards, electronic ID cards and other microprocessor-based devices. These tools help developers, testers and security specialists understand how the card works, what protocols it supports and what data it provides to the terminal during initialization.

Let's take a closer look at how ATR tools work, their functionality and practical application.

1. What do ATR tools do?​

ATR tools analyze the smart card's response to the RESET command, which contains technical information about the card. The main tasks of such tools are:

1. Reading ATR:
   • The tool sends a RESET command to the card via a reader (e.g. USB reader).
   • Receives the ATR as a sequence of bytes.
2. ATR Decoding:
   • Parses ATR into its component parts: start characters, interface characters, history bytes, and checksum.
   • Converts hexadecimal values into a readable format.
3. Defining the characteristics of the card:
   • Identifies the card manufacturer.
   • Specifies the supported communication protocols (T=0, T=1, etc.).
   • Shows the card operating parameters (frequency, voltage).
4. Diagnosing problems:
   • Checks the correctness of the ATR (e.g. checksum verification).
   • Detects discrepancies between the card and the terminal.

2. What tools are used to work with ATR?​

There are many software and hardware tools for working with ATR. Here are some of them:

2.1 Software tools​

These programs run on a computer in conjunction with a USB reader to read card data.

1. PCSC Tools:
   • A set of utilities for working with cards via PC/SC (Personal Computer/Smart Card) interface.
   • The pcsc_scan command allows you to get the ATR of a card.
2. Smart Card Explorer:
   • Graphical tool for reading and analyzing ATR.
   • Supports ATR decoding and card information display.
3. ATR Analysis Online:
   • Online services such as smartcard-atr.appspot.com allow you to enter the ATR manually or download it for analysis.
4. PySim:
   • Python library for working with SIM cards, which can also analyze ATR.
5. Cardpeek:
   • Program for analyzing the contents of smart cards, including ATR.

2.2. Hardware tools​

These devices are used to physically interact with smart cards.

1. USB readers:
   • Devices such as the OMNIKEY 3121 or ACR38 that connect to a computer and allow the card data to be read.
   • Work with software for ATR analysis.
2. Programmable readers:
   • Devices that support low-level interaction with cards (e.g. Proxmark, ChameleonMini).
   • Used for advanced analysis and card emulation.

3. How does the ATR analysis process work?​

The ATR analysis process can be divided into several stages:

Step 1: Reading ATR​

1. The card is inserted into the reader (or tapped if contactless mode is used).
2. The reader sends a RESET command.
3. The card transmits ATR as a hexadecimal string.

ATR example:

3B 68 00 00 00 73 C8 40 12 00 90 00

Step 2: Decoding ATR​

The tool breaks down ATR into its components:

• 3B: Initial Character (TS).
• 68: Format Character (T0).
• 00 00 00: Interface Characters (TA, TB, TC).
• 73 C8 40 12 00: Historical Bytes.
• 90 00: Checksum (TCK).

Step 3: Interpret the data​

The tool translates ATR into a readable format:

• Manufacturer: For example, "G&D" (Giesecke+Devrient).
• Protocol: For example, T=1 (asynchronous protocol).
• Parameters: Frequency, voltage, supported standards.

Step 4: Diagnostics​

The tool checks:

• Correctness of the checksum.
• ATR complies with ISO/IEC 7816 standards.
• Possible compatibility issues with the terminal.

4. Practical application of ATR tools​

4.1. Software development​

• Payment system and POS terminal developers use ATR to test device compatibility.
• The tools help to configure data exchange protocols.

4.2. Testing cards​

• Card manufacturers check that the card generates ATR correctly.
• Various scenarios for using the card are being tested.

4.3. Security​

• Security researchers analyze ATR to identify vulnerabilities.
• Carders can use ATR to create fake cards.

4.4. Debugging Problems​

• If the terminal cannot work with the card, ATR analysis helps to find the reason (for example, protocol mismatch).

5. Example of ATR analysis​

Let's take ATR as an example:

3B 68 00 00 00 73 C8 40 12 00 90 00

1. Initial Character (TS):
   • 3B: Indicates little endian bits.
2. Format Character (T0):
   • 68: Number of historical bytes = 8.
3. Interface Characters (TA, TB, TC):
   • 00 00 00: Indicates the card's operating parameters (for example, frequency 3.57 MHz).
4. Historical Bytes:
   • 73 C8 40 12 00: Contains information about the manufacturer (eg G&D) and the card type.
5. Checksum (TCK):
   • 90 00: Checksum is correct.

Result:

• Manufacturer: Giesecke+Devrient.
• Protocol: T=1.
• Parameters: Frequency 3.57 MHz, voltage 5 V.

6. Conclusion​

ATR tools play an important role in smart card analysis and diagnostics. They help:

• Understand how the card works.
• Set up interaction between the card and the terminal.
• Identify compatibility and security issues.

If you work with charts or develop systems to process them, knowing how ATR tools work will make your job much easier. For starters, it is recommended to use simple programs such as PCSC Tools or online services for ATR analysis.

Additional information on this topic: What is ATR and how does it work?

If you have specific questions about working with ATR or examples of use, ask them!