AID Lookup

Structure of an AID

An Application Identifier is 5 to 16 bytes. The first 5 are the RID — the Registered Application Provider Identifier, assigned by ISO, which identifies the scheme. Anything after that is the PIX, the Proprietary Application Identifier Extension, chosen by the scheme to distinguish products.

So A0000000031010 splits into RID A000000003 (Visa) and PIX 1010 (credit or debit). A0000000041010 is the same PIX under Mastercard's RID. Once you can see the split, most AIDs become guessable.

Where AIDs appear

In EMV tag 4F (ADF Name) when the terminal builds its candidate list from the PSE, in tag 84 (DF Name) in the SELECT response, and in tag 9F06 as the terminal's own configured AID. They also appear as the GUID in EMVCo QR merchant account templates.

Partial selection and why lengths vary

Terminals may select an AID by partial name, matching only the leading bytes. That is how a terminal configured for A0000000031010 can still transact with a card carrying A000000003101001. It also means the AID a terminal is configured with and the AID the card returns in tag 84 are frequently different lengths — that is expected, not a fault.

American Express AIDs are notably short at 6 bytes, and German girocard runs to 10. Anything that assumes 7 bytes will break on both.

Application selection order

When a card offers several applications, the terminal orders candidates by the Application Priority Indicator (tag 87). Bits 1-4 are the priority; bit 8 set means the cardholder must confirm. This is why a dual-branded card can behave differently on two terminals that both support both brands — the AID priority on the card and the configured AID list on the terminal interact.