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"APDU"

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Diagram of the Command APDU structure fields: CLA, INS, P1, P2, Lc, Data Field, Le

Online & Authorization

What is an APDU (Application Protocol Data Unit) Command?

An APDU is an application-level protocol defined in ISO 7816-4 and used between a smart card and a POS, ATM, etc. There are two types of APDU: Command APDU and Response APDU. The structure of the APDU is given below.

Diagram illustrating the EMV Tag-Length-Value (TLV) data structure used in card transactions

Online & Authorization

What are EMV Tags?

In EMV, data is stored in Tag-Length-Value (TLV) format, and it is carried between the card, the POS terminal, and the authorization system in this same format. This post lists every EMV Tag, its type, and its description.

Diagram showing the PSE (Payment System Environment) directory used for application selection on an EMV chip card

Credit Card

What is PSE (Payment System Environment)?

PSE (Payment System Environment) is a directory on the card named 1PAY.SYS.DDF01 for a contact chip and 2PAY.SYS.DDF01 for a contactless chip. The Candidate List built via PSE is called indirect or implicit Application Selection.