Android HCE: are there rules for AID?

Question

I\'m trying to use an ACR122 NFC reader to select an application emulated in one Nexus 5 using Android Host Card Emulation. However, small AIDs are not recognized.

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Answer 1

According to EMV standards, an AID is made up of a Registered Application Provider Identifier (RID) having a minimum of 5 bytes, and an optional Application Identifier Extension (PIX) or proprietary Application Identifier having a maximum length of 11 bytes, which together make up the Application ID (AID), thus, the application ID can never be less than 5 bytes in length. If there are several applications present in the card, the AIDs will have the optional app identifiers appended to the RID to differentiate between the applications present in the card. Please read up on EMV standards on their site: EMVCO, and especially their books, Book 1 to Book 4, to understand more in this.