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Capital One recently sent my plastic credit card by post mail and its activation code by a separate post mail. What security problem does this mitigate?

If a rogue element has access to my mail box or home, they will have both the plastic card as well as the activation code. The only thing I can think of is that they are preventing rogue elements on their side from having access to the two pieces at the same time? Or is it something else?

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    Out of curiosity, did they arrive at the same time? – msanford Oct 18 at 19:54
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    @msanfordNo. They did not. That would not really be a sucurity measure would it? There is no way to know if I am at home to intercept at least one of the mails on time. Or both mails could be waiting in my mailbox fro me or the salacious actor. – Lord Loh. Oct 18 at 19:55
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    Exactly: they hope to mitigate against intercepting one of them. Mailbox break-in and they nick a credit card, but it's useless without the code, chucked in the bin. – msanford Oct 18 at 20:18
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    @kelalaka they do that as well in the UK, often checking the number you phone from. – Ian Ringrose Oct 19 at 20:29
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    In addition to arguments centered on the receiver end (= you), this is pure speculation but: on the sender's end, maybe they send each of the two mails from different facilities, hence mitigating the damage of a malicious actor in the postal service close to one of the places from which they send. – a3nm Oct 20 at 22:41
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Many low level crimes are ones of opportunity, not planned out attacks. By separating the two needed pieces of mail in time, it forces the attacker to intercept the same person's mail more than once.

This prevents a mail thief from simply walking up to homes and looking for credit cards and activating them all in one step. Now suddenly the thief has to go back to the same house, or intercept the same person's mail at least twice, and possibly multiple days in a row. That takes time, effort, and additional exposure.

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    when factoring luck and other people into the equation, doing something twice is more than twice as hard as doing it once, yet the cost for the creditor is only twice, which makes for a security bargain. – dandavis Oct 18 at 20:18
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    In addition you can check for plastic cards in an envelope by bending it. You can't check for activation codes in the same way. So an attacker would have to open the verification, while he could find a probable credit card without opening anything. – vidarlo Oct 19 at 9:07
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    Don't forget that the guy with the easiest opportunity to steal a card is the postman! Putting the card and authorization in one package makes it too easy - the postman wouldn't even need to open the package to know what it was and sell it to a third party. – alephzero Oct 19 at 9:20
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    Not just the postman who delivers to your door; postal depot staff too. – Michael Harvey Oct 19 at 14:18
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    Also, sometimes mail ends up in the wrong mailbox. – Andrew Morton Oct 19 at 15:21
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A lot of people get a credit card and leave it in the envelope for a considerable amount of time.

Further, separating the data complicates life very greatly for a mail thief. To snatch one piece of mail is a crime of opportunity. But to snatch two on separate days requires veritable stalking. Having gotten one piece, the thief must now return to the scene of the crime often. That greatly increases exposure, both because of the lingering and the repeated visits.

Further, it's likely the correspondence is not obviously marked with a sender, so the thief does not know which piece of mail to steal, and must steal a lot of it. This greatly increases the chance of the owner noticing their mail is going missing, which would defeat the entire exercise as the owner would cancel the card.

And after all that, there's a fair chance that the piece the thief lifted was the second to arrive... In which case the other half of the puzzle will never show up. The thief could check for weeks and never get it. When to give up?

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Credit cards are stochastically secure (like all banking).

They aren't trying to make the system unbreakable, they are trying to make the fraud losses be a suitably low percentage of the margin.

(And optimise for cost and convenience - if you had to visit a branch and show three forms of ID, as well as their needing many expensive branch clerks, a lot of customers would never activate their card and hence never generate any revenue).

  • make that "like all security". Noone with a working brain invests in security if cost is greater damage times probability. – Haukinger Oct 21 at 14:20
  • @Haukinger Actually making such a bad investment is the foundation of insurances. Your mark relates only to mass market (here: the bank issuing many credit cards) where the law of big numbres evens out any risk aversion. From the perspective of a one-time "player" and with damage comparable to their capacity, things are different – Hagen von Eitzen Oct 21 at 16:05
  • @HagenvonEitzen but insurances only work, because people are dumb and do not realize that "self-insuring" is a better deal. If you have an information advantage, of course, things look different, and also if you don't have enough money to set aside for your "self-insurance" (indemnity insurance comes to mind, and, to a lesser degree, health insurance) – Haukinger Oct 21 at 20:20

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