If all encryption broke tomorrow a thought experiment on trust and society

[QQQ]

TL;DR

• This is a thought experiment, not a prediction: real world migration to post quantum cryptography is well under way, and symmetric encryption such as AES-256 would remain strong
• Imagining a sudden collapse of public key encryption reveals how much everyday trust quietly depends on mathematics most people never see
• Banking, online shopping, messaging, software updates, identity checks and even elections rely on the ability to prove who you are and keep secrets
• Societies would likely fall back on older forms of trust: physical presence, paper records, personal relationships and institutions
• The exercise helps explain why preparation matters and invites reflection on what trust really means in a digital world

Why imagine the worst

Philosophers and scientists have long used thought experiments to explore ideas that are impractical or impossible to test directly. Einstein imagined riding alongside a beam of light, and philosophers have imagined trolleys, veils of ignorance and brains in vats. These scenarios are not predictions. They are tools for noticing assumptions we normally take for granted

This thread proposes a thought experiment for the Q-Day community. Suppose that tomorrow morning, without warning, all the public key cryptography used on the internet stopped protecting anything. Anyone could read encrypted messages, impersonate websites and forge digital signatures. What would happen to daily life, and what would it teach us about trust

Before going further, a reassurance is important. This is not what experts expect. Real quantum computers capable of breaking today's encryption do not yet exist, migration to post quantum cryptography is already under way, and symmetric encryption such as AES-256 would remain robust. The scenario is deliberately extreme so that we can see the hidden structures more clearly

Estimates of what such a machine would need have fallen sharply, though. In March 2026, Google Quantum AI and the start-up Oratomic published separate papers suggesting far fewer qubits might be needed than once thought, and in October 2026 Alice and Bob estimated that RSA-2048 could be broken with about 22,600 cat qubits in around three days. These are theoretical designs, and today's largest machines remain far too small and error prone. They are a reminder of why migration is happening now rather than later

Hour one: the invisible locks vanish

Most people would notice nothing at first. Websites would still load and messages would still send. The difference would be that the locks protecting them had silently disappeared. Anyone with access to the network between you and a website could read everything, change pages and pretend to be the bank or shop you meant to visit

Technical teams would notice quickly. Security researchers would raise alarms, and governments would hold emergency meetings. The first big question would be whether to keep systems running or switch them off. Keeping them on risks fraud and theft, while switching them off stops commerce and communication

This dilemma reveals something important. Modern life depends not only on technology working but on people trusting that it works. Encryption is mostly invisible, yet it underpins the confidence that lets us type a card number or send a private message without thinking twice. Remove that confidence, and behaviour changes immediately

Different people would experience the crisis differently. Those who rely heavily on digital services, such as people living alone, remote workers or those with disabilities, could feel cut off quickly. Communities with strong local ties might cope better. The thought experiment highlights how unevenly digital dependence is distributed

Money and markets

Banking would be among the first areas to respond. Online banking and card payments rely on encrypted connections and digital signatures to prove that transactions are genuine. Without them, banks might freeze online services to prevent fraud, and card networks might pause transactions. Cash, cheques and in person banking would suddenly matter again

Financial markets might halt trading to prevent manipulation through forged orders or fake data. Payment systems between banks would need alternative ways to verify instructions, perhaps by phone calls between known staff or physical couriers. Some of these fallback procedures exist already for emergencies. Stretched across a whole economy, they would be slow and expensive

Cryptocurrencies would face a particularly sharp crisis. Their ownership depends entirely on digital signatures, so if those could be forged, coins with exposed public keys could be stolen by anyone with the capability. Unlike banks, most blockchains have no central authority to reverse transactions. The thought experiment shows why crypto communities debate quantum migration so intensely

Insurance, contracts and law would face their own puzzles. If digital signatures on contracts could be forged, courts might need to rely on witnesses, paper records and other evidence to decide what was agreed. Disputes could multiply. Legal systems would adapt, but slowly

Communication and privacy

Messaging apps, email and video calls would lose their privacy. People might switch to phone calls, letters or face to face meetings for anything sensitive. Journalists, lawyers, doctors and activists would face particular difficulties protecting sources and clients. Some might revert to methods used before the internet, such as couriers and coded language

A deeper problem would be authenticity. If digital signatures could be forged, you could not be sure an email from your employer, a message from a friend or an official announcement was real. This would be more disruptive than lost privacy. Societies function because people can generally trust who they are dealing with

Older trust mechanisms would gain importance. Recognising someone's voice, meeting in person, using shared secrets known only to family members, and relying on trusted intermediaries such as local bank branches or community leaders would all become more valuable. In a sense, society would rediscover the human foundations of trust that digital systems had replaced

Software, devices and infrastructure

Software updates rely on digital signatures to prove they come from the real developer. If signatures could be forged, attackers could push malicious updates to phones, computers, cars and industrial systems. Organisations might stop updating devices altogether, leaving known security holes unpatched. That would create a painful choice between two kinds of risk

Critical infrastructure such as power grids, water systems and hospitals uses encrypted and authenticated communications for remote monitoring and control. Operators might switch to manual control, staff sites in person and isolate networks from the internet. Many engineers already plan for such scenarios as part of resilience exercises. The thought experiment suggests why those plans matter

Healthcare deserves particular thought. Electronic health records, prescriptions and connected medical devices depend on secure communications. Hospitals might revert to paper records and in person handovers, as many already practise during outages. Patient safety would depend on staff training and calm leadership

Government, identity and democracy

Digital identity systems, from passport chips to online government services, depend on cryptography. Governments might suspend online services and revert to in person verification with physical documents. Border controls could slow as electronic passport checks became unreliable. Benefits, taxes and licences would revert to slower paper processes

Elections raise particularly sensitive questions. Many countries vote on paper, which would be largely unaffected, while others use electronic systems for registration, counting or transmitting results. Trust in results would depend on paper trails, observers and transparent processes. The thought experiment highlights why many election security experts value verifiable paper records

How long would recovery take

Recovery would involve rolling out replacement cryptography to billions of devices and systems at once. In reality, that replacement already exists in the form of NIST's post quantum standards published in August 2024, with a further signature standard, FN-DSA, still in draft. Many systems already use them, including Chrome, Signal, Apple's iMessage and OpenSSH, which made a post quantum key exchange its default in 2025. In our imaginary world, emergency deployment would still take months or years for the long tail of devices. Some older equipment would simply need replacing

Social recovery might take longer than technical recovery. Once people had experienced a world where any message could be faked, rebuilding confidence would take time. Institutions that communicated clearly and openly during the crisis would likely emerge with more trust. Those that hid problems or overpromised might lose credibility for years

What the thought experiment teaches

The first lesson is how much invisible trust we rely on. Most people never think about encryption, yet it underpins nearly every digital interaction. That invisibility is a mark of success. It also means the consequences of failure would be felt by everyone

The second lesson is the value of preparation. Because the world has standards, timelines and early deployments in place, the real Q-Day is very unlikely to resemble this sudden collapse. Migration is designed to replace the locks long before anyone can pick them. The thought experiment shows what that preparation protects us from

Governments have also set clear deadlines. The UK National Cyber Security Centre has asked organisations to finish migrating by 2035, with planning milestones in 2028 and 2031, and the United States has similar targets. Those dates exist precisely so that the scenario in this thread never happens

The third lesson is philosophical. Trust is not only a technical property but a social one. Technology can support trust, but people, relationships and institutions ultimately sustain it. In a crisis, societies fall back on human connections, which suggests those connections deserve care even in a digital age

Questions to discuss

• Which part of daily life do you think would be hit hardest in this scenario
• Would you trust banks and governments to manage such a crisis well
• What older forms of trust would you rely on first
• Should societies keep paper and in person alternatives available as a safety net
• Does this thought experiment make you more or less worried about the real Q-Day

Closing thoughts

Imagining a world where encryption suddenly fails is uncomfortable, but it helps us see the hidden structures that make modern life work. It also shows why the steady, unglamorous work of migrating to post quantum cryptography matters so much. Real Q-Day preparation is designed to make this thought experiment remain just that. Meanwhile, the exercise reminds us that trust ultimately rests on people as well as mathematics

Please share your own version of the scenario in the replies. What would you do on the first day, and what would you miss most? Creative and thoughtful answers are very welcome


Further reading

• NIST FIPS 203, 204 and 205, post quantum cryptography standards, August 2024
• UK NCSC, Timelines for migration to post quantum cryptography, March 2025
• Alice and Bob, Shor's algorithm compiled on cat qubits, IACR ePrint, October 2026
• Onora O'Neill, A Question of Trust, BBC Reith Lectures, 2002
• Stanford Encyclopedia of Philosophy, Thought Experiments