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You wrote, I think most of any delay is dependent on the merchant's payment system & their POS terminals age. ...

I think this maybe two-fold. First, some POS systems are probably still connecting via some kind of dial-up link. Second, I *think* the original scheme involved the reader cryptographically signing the entire transaction record, which requires the chip be inserted into the reader. I've not looked into it, but I suspect they've gone to signing some kind of preamble instead just to authenticate that they were in possession of the chip. I think the actual charge amount / transaction record is no longer being signed.

The second part is evident by the fact that you can remove your card these days before the merchant is done ringing up your transaction. Since the card is required to generate that signature, they couldn't be signing the entire transaction record ... or anything with the charge total. Anything that is not signed can in theory be modified without detection during the transmittal.

If I'm right that actually creates a small security vulnerability. While it proves the merchant was in possession of the card, it doesn't prevent someone in the middle from modifying the charge amount. This is a much harder attack to accomplish and it doesn't actually do the same kind of thing you usually think of as credit card fraud; but it might let a clever hacker steal from the bank and/or merchant without any obvious or at least immediate repercussions. Still, attacking the system in this way is probably a much smaller threat so they may have understood the issue and decided to make the change for the sake of convenience.

- Joel
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