| Photo from author |
Do you ever find yourself in Germany? And have you ever taken a close look at a receipt there? Well, I have. And what immediately caught my eye was the cryptographic information printed on it.
To be
clear: when I talk about crypto, I mean cryptography, not digital money like
bitcoin. Cryptography is the mathematical art of securing data, as someone at a
conference recently put it. But what exactly was on that receipt, and more
importantly: why?
There were
long strings of letters and numbers, as you can see in the photo. My attention
went straight to the ‘PublicKey’ line at the very bottom of the receipt. Behind
it: a blob of 132 characters. The receipt also contains a similar string
representing a digital signature. You don’t often see information about digital
signatures printed on an analogue medium (the paper slip).
The reason
lies in German law: the Kassensicherungsverordnung (Cash Register
Security Ordinance, or oddly abbreviated KassenSichV). It requires electronic
tills to be equipped with a Technische Sicherheitseinrichtung (TSE –
Technical Security Module). The TSE prevents tampering with the till: every
transaction is logged in order, assigned a sequential number, and digitally
signed. This allows the Finanzamt (tax administration) to check for
irregularities, such as missing receipts. A shopkeeper using a till without a
certified TSE can be fined up to € 25,000 (almost US$ 30,000).
All that
cryptographic work happens inside the register. But why print that information
on the receipt? Because the receipt itself must also be verifiable. You as a
customer won’t do anything with it – you may consider
the fact that I noticed it a case of professional deformation. But the tax administration
can run spot checks, for instance by sending in a mystery shopper who later has
their receipt verified. In the past, retailers could hand the customer a
perfectly decent-looking receipt while deleting or altering the transaction
inside the system. That’s no longer possible: the digital signature would
expose it immediately.
On more
modern receipts, the printed TSE information has been replaced by a QR code.
That makes the life of inspectors easier (even though it’s marketed as a
paper-saving measure). Even more eco-friendly is the digital receipt which,
very un‑German, is called a fiskaly receipt (they actually use the English word
receipt). The customer scans a QR code on the till. But it can be even simpler:
at the supermarket we visit from time to time to buy things they don’t have
here or that are much cheaper there, you can receive the receipt directly in
the store’s app.
That
digitalisation is great, but I do see one problem. When I buy something with a
warranty, I scan the receipt and store it under a meaningful filename on my
computer. I do this for two reasons: printed receipts fade, and my computer can
search for me. Digitally issued receipts, however, I never find back. Once you
realise that, you then need to remember which shop sold you the product, so you
can search the relevant app or website. To work around this, I now store a
small file in my records noting where the product was purchased. Another tip
for fellow administrative nerds: since clothing tends to break or fray, I store
a photo of the garment alongside the scanned receipt. Then you always know
which receipt belongs to which pair of trousers.
One more
thing that stood out on the receipt from Shawarma Al‑Zaiem: the line ‘Es
bediente Sie: LPADMIN’ (“You were served by”). The administrator was logged in
at the till. Now, Al‑Zaiem is a small place where only two people were working,
but still: using an admin account for routine operations is never a good idea.
Send me
photos of your bewildered travel companions the next time you find yourself
attentively studying your receipt in Germany (-;
And in the big bad world…
- the personal data of millions of Odido and Ben customers have been stolen.
- state actors are currently conducting spear‑phishing attacks on Signal accounts.
- the Nigerian prince now pretends to be an Emirati.
- ransomware continues to grow rapidly.
- a
hacker provides insight into Russian disinformation. [GERMAN]
- stalkerware is frequently hacked and leaked.
- Russia is blocking WhatsApp, and even Telegram.
- the
Dutch Tax Administration remains stuck with M365 for now. [DUTCH]
- Europe
cannot realistically free itself from American tech. [DUTCH]
- Belgian
bank customers are getting a guardian angel. [DUTCH]