TLV Editor

What is TLV Editing?

TLV (Tag-Length-Value) editing involves creating, modifying, and building structured data in the TLV format. This is particularly important for EMV payment applications, where data is organized in TLV structures for card-terminal communications.

TLV Structure Components

• Tag: Identifies the type of data (1-3 bytes)
  • Class (bits 8-7): Universal, Application, Context-specific, or Private
  • Constructed/Primitive (bit 6): Indicates if the value contains nested TLV elements
  • Number (bits 5-1): The tag number
  • If bits 5-1 are all 1's (0x1F), it's a multi-byte tag, and subsequent bytes are part of the tag identifier
• Length: Indicates the length of the value field (1 or more bytes)
  • Short form (0-127): Single byte with the most significant bit set to 0
  • Long form (128+): First byte has the most significant bit set to 1, and the remaining bits indicate how many subsequent bytes encode the length
• Value: The actual data (can contain nested TLV structures for constructed tags)

Common Use Cases

• Building EMV Commands: Creating APDU commands with TLV data for card communications
• Modifying Transaction Data: Editing CDOL (Card Data Object List) or TDOL (Terminal Data Object List) data
• Testing EMV Applications: Creating test data for EMV certification or debugging
• Analyzing Card Responses: Modifying and rebuilding TLV data to understand card behavior

Best Practices

• Validate Tag Format: Ensure tags follow the BER-TLV format (correct class, P/C bit, etc.)
• Check Length Encoding: Use the appropriate length encoding based on the value size
• Maintain Nested Structure: For constructed tags, ensure the nested elements are properly structured
• Verify Mandatory Tags: Ensure all required tags for a specific EMV operation are included
• Test with Real Devices: Validate the edited TLV data with actual EMV cards and terminals when possible