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Comment by nostromo | Hacker News Reader

Cash may not always be so anonymous. It seems plausible that banks at some point may start tracking bank notes by serial, or some other method, which would be very useful for law enforcement and the IRS.

Example: Alice withdraws $100 from an ATM to buy illegal drugs from Bob, who then deposits it in his bank to pay rent. Bob is later found guilty of distributing drugs. Law enforcement could now request from his bank his deposit history, including bank note serial numbers. Repeated deposits of banknotes that were last seen from Alice could lead investigators to her door.

It's the kind of big data tracking scheme that 10 years ago would be impossibly hard to do, but with today's technology wouldn't be so hard.

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There were only 15,497,240,200 EURO banknotes in circulation in June 2013 [1]. There is a study which says most go straight from the ATM to the consumer to the merchant and back to the bank. Using a big data engine, it would be very easy to trace:

- Banknotes withdrawn by a person, which haven't been seen for 2 or 3 months,

- Banknotes caught in drug cartel offenses and the consumer who withdrew them,

- Banknotes regularly withdrawn in rich neighbourhoods and spent in poor neighbourhoods, minus direct employees of rich neighbourhoods. Banknotes deposited to a bank for the purchase of second hand cars.

- As a side note, pattern changes in someone's CC spendings. A gap may mean he's aggregating money to invest on the black market.

[1] https://en.m.wikipedia.org/wiki/Euro_banknotes#Circulation

I don't think people will accept this. For people with other means of payment, the main function of cash is anonymous transactions. There is no other way to anonymously transfer money. The article incorrectly lists bitcoin as being anonymous when it's quite the opposite (though with some finagling can approach the functionality of anonymity.)

Also, in your example above, who's to say that Alice didn't give the money to Joe who then gave it to Bob? Or that Alice didn't buy something legal from Bob? Simply having serial numbers and tracking the money is not enough if the money can be transferred without the transactions being recorded (like they are at a bank). That immediately makes it a lot less useful for law enforcement.

That's honestly trivial to thwart if you're aware that such tracking exists.

Alice can just withdraw a big note and break it up by buying a coffee, then use the change from that transaction to buy the drugs instead.

Granted, some extra creativity would be required for drug purchases involving large amounts of cash

That thwarting is honestly trivial to counterthwart without even trying. The register at the coffee shop knows which note Alice paid with and which ones they gave in change.

If I buy coffee at Starbucks with a $5 bill, and you come in later, pay with a $20 and get my $5 in change, in order for the government to follow the money like that Starbucks would have to scan every bill and correlate the scans with individual transactions. Even if people were okay with that (which I doubt), it would be a costly imposition on businesses and a huge time waster for everyone.

Until it becomes standard in all registers.

Doesn't matter. You'd still have to feed the bills, individually, into some kind of scanner.

Knows that a note Alice withdrew was received and what notes were exchanged. But not necessarily that it was Alice (though other data might corroborate that).

I don't think that would work so well, since you could never prove how many intermediary cash-only transactions the bill has gone through before it was seen by the bank again.

Agreed, for a single transaction it would not meet the "beyond a reasonable doubt" threshold. However it might be possible to build a stronger case around a pattern of transactions, e.g. bills withdrawn from the ATM by Alice routinely appear in bank deposits by Bob. At some point this would harder to explain as random chance.

"It seems plausible that banks at some point may start tracking bank notes by serial, or some other method"

I would be very surprised if this is not already happening.

It's now an option on ATMs.[1][2] Especially in China, where the People's Bank of China has required it for all ATMs.[3] "As at the end of June 2013, there are 197,800 ATMs in use on the mainland, of which 100,700 or 55.28% have been upgraded with the serial number enquiry function. According to schedule, by late 2015, the serial number of every Rmb100 note withdrawn from banks by members of the public can be traced."

Here's an overview of the available hardware.[4] Not only ATMs are recording serial numbers. So are cash counting and sorting machines.

[1] http://www.atmmarketplace.com/news/ci-tech-intros-retrofit-s... [2] http://www.diebold.com/~/media/diebold/diebold-asset-library... [3] http://economists-pick-research.hktdc.com/business-news/arti... [4] http://currencypath.blogspot.com/

Banks would start tracking notes if they had some reason to, but they don't. Getting big companies to coordinate to do something new is extremely hard.

Bank note serial numbers are used today, to estimate the average lifespan of a note (a 5 pound note has around a 6 month lifespan on average IIRC). And something like 95% of 20 pound notes have traces of cocaine on them.

What's the big deal in the article about tracking? I think the vast majority of people don't really give a damn about being "tracked".

They just take cash anonymity for granted.

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