Emv Tlv Tree

When you insert a chip card into a payment terminal, the card and the terminal do not exchange JSON or XML. They exchange highly compressed binary data formatted in a standard called EMV (Europay, Mastercard, and Visa).

EMV uses a TLV (Tag-Length-Value) encoding scheme. Every piece of data is serialized into three distinct, consecutive parts.

1. Tag: A 1 or 2 byte hexadecimal identifier (e.g., 9F02 represents the Amount Authorized).
2. Length: A byte indicating exactly how many bytes the Value payload occupies (e.g., 06 means the next 6 bytes belong to this tag).
3. Value: The actual data payload (e.g., 000000001500 representing $15.00).

Smart card microchips have kilobytes of memory and tiny processors powered solely by the electrical contact from the terminal.

A TLV parser reads a hex string left-to-right. When it sees a Tag, it reads the Length byte, and uses that integer to slice exactly that many bytes forward in memory to extract the Value. It then immediately expects the next byte to be the start of a new Tag. This forward-only, pointer-based parsing is incredibly fast and requires almost zero RAM overhead compared to parsing the brackets and quotes of a JSON string.