CyberChef Parse TLV Operation

What is TLV?

TLV stands for Type-Length-Value, a data encoding format widely used in telecommunications, smart cards, and network protocols. It's a simple yet powerful way to structure binary data by dividing information into three parts: a type identifier, a length indicator, and the actual value.

Why TLV Matters

TLV encoding is essential in many real-world applications including credit card chip transactions (EMV), network protocol messages, configuration files, and IoT device communication. Understanding TLV helps you analyze and debug these systems.

TLV Structure Explained

Type (Tag)

The Type field identifies what kind of data follows. It's typically 1-2 bytes and acts as an identifier. For example, in EMV payment cards, type 9F02 represents "Amount, Authorized".

Length

The Length field specifies how many bytes of data are in the Value field. This can be simple (1 byte for lengths up to 255) or use multi-byte encoding for larger values. Knowing the length allows parsers to jump directly to the next TLV element.

Value

The Value field contains the actual data. It can be any format: text, numbers, binary data, or even nested TLV structures. The Type field tells you how to interpret these bytes.

Using Parse TLV in CyberChef

The Parse TLV operation in CyberChef converts TLV-encoded data into a readable JSON format. This is extremely useful when analyzing network packets, smart card data, or any system using TLV encoding.

Steps to Parse TLV:

1. Open CyberChef and find the "Parse TLV" operation
2. Input your TLV data (usually in hexadecimal format)
3. Select the appropriate input format (Hex, Base64, etc.)
4. The operation outputs a structured JSON object showing all Type-Length-Value triplets

TLV Format Visualizer

Understanding how TLV data is structured helps you work with it more effectively. This interactive visualizer breaks down TLV encoding step by step:

Common TLV Tags Reference

Different systems use different tag sets. Here are some common examples from EMV payment systems:

Best Practices

When working with TLV data in CyberChef, follow these guidelines for best results:

• Verify input format: Ensure your data is properly encoded as hexadecimal before parsing
• Check for nested TLV: Some values contain nested TLV structures that require additional parsing
• Reference tag documentation: Keep tag reference documentation handy to interpret Type fields correctly
• Validate length fields: Ensure Length values match the actual data to detect corruption
• Handle unknown tags: Not all tags may be documented; focus on the ones you recognize

Common Use Cases

• Analyzing EMV chip card transaction data
• Debugging network protocol messages
• Inspecting smart card APDUs
• Parsing configuration files in TLV format
• Reverse engineering proprietary protocols

Common Issues & Solutions

Invalid Hex String

If parsing fails, ensure your input contains only valid hexadecimal characters (0-9, A-F). Remove spaces, colons, or other separators unless the parser explicitly supports them.

Incorrect Length Values

If the output looks wrong, the Length field might be corrupted or incorrectly encoded. This causes the parser to read the wrong number of bytes for the Value.

Empty or Incomplete Output

Incomplete TLV data will result in partial parsing. Ensure you have the complete message, including all bytes specified by each Length field.

Nested Structures Not Showing

Some TLV implementations use nested structures where a Value contains more TLV elements. You may need to parse these recursively or run Parse TLV again on specific value fields.

Summary

The Parse TLV operation in CyberChef is an essential tool for analyzing structured binary data. By converting TLV-encoded information into readable JSON format, it helps you understand complex data formats used in payment systems, network protocols, and smart cards. Remember to verify your input format, reference appropriate tag documentation, and validate the parsed output against expected values.