Q-Day arrives tomorrow: what is the first thing in your life that breaks?

[Dylan98]

This forum is named after Q-Day, the hypothetical day when a quantum computer becomes powerful enough to break the public key encryption that protects most of the internet. We talk about it a lot in abstract terms, with NSA deadlines, migration plans and post-quantum algorithms. I thought it would be interesting to bring it down to a personal level. What would it mean for you in practice?

Let's imagine, purely as a thought experiment, that tomorrow morning someone announces a working machine that can break RSA and elliptic curve cryptography. Most systems have not migrated yet. What is the first thing in your daily life that would stop being safe or stop working?

Online banking and card payments are the obvious answer, though banks have been preparing. Messaging apps rely on encryption, as do software updates, which use digital signatures to prove they are authentic. Cryptocurrencies like Bitcoin rely on elliptic curve signatures, so wallets with exposed public keys could be at risk. Then there are less obvious things, like smart home devices and car keys

Harvest now, decrypt later means old data could be exposed too. Emails, medical records and private messages captured years ago could suddenly become readable. That is the part I find most unsettling. Old data does not expire just because we stopped thinking about it

So what breaks first in your life, and what would you do about it? Let's keep it light hearted rather than doom laden, as this is a what if rather than a prediction