contactless smartcard - emv tag 0x9F37 unpredictable numbers length -


i have noticed in of cases in emv transactions, tag 9f37(tag_unpredictable_number) length not 4 bytes, read tag cannot set it. please explain me must 4 bytes or can of length upto 4 bytes. , please guide me how number generated , can cause length.

as name denotes should not predictable means , can use random number generation algorithm create value whether developing card application or terminal app explained below.

  1. unpredictable number used during offline enciphered pin verification ensure pin block generated different @ times. generated chip , length 8 bytes(image 1). unpredictable number not see @ host , need tool fime smartspy or keolab nomadlab value.

  2. another unpredictable number generated terminal used in cryptogram generation ensuring different cryptogram generated every time when other cdol elements same. length 4 bytes(image 2)

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image 2

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