Developing for EMV, Part II - ID TECH
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In Part I of this post, we talked a bit about EMV transactions and how they’re structured. We saw that: Unlike MSR (magstripe) transactions, an EMV transaction occurs in multiple stages. Most of the back-and-forth talk between the chip card and the reader happens at the kernel level, outside the control of application logic. Transaction results are returned in TLVs (“tags”). A cryptogram (a unique 8-byte piece of data produced by the card, using a private key known only to the card) is produced before the Completion stage of the transaction; and a second cryptogram is produced after the call to complete the transaction. The cryptogram comes back from the card in tag 9F26 (an EMVCo-defined tag, not a proprietary ID TECH tag). Generally, you’ll package up the first cryptogram (and...