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Glossary

The section's words, explained.

Every cryptography term gets an everyday example before the definition. The technical names stay here too, for anyone who meets them in a tender, a contract or a standard.

Q-Day

formerly: Q-Day
In everyday life
The day someone shows up with a master key that opens the padlock model the whole city uses.
What it means here
The day the first quantum computer able to break today's cryptography switches on. Nobody knows the date: there are estimates from different sources, and they move.
Where it appears
HubThe deadline

Quantum computer that breaks today's cryptography

formerly: CRQC · cryptographically relevant quantum computer
In everyday life
Not a faster computer for everything; a very specific tool, like a master key that opens only one kind of lock.
What it means here
The CRQC: a quantum computer large and stable enough to run Shor's algorithm against public-key locks. It does not exist yet; estimates of when it will are the heart of this section.
Where it appears
The deadlineThe quantum stack

Cryptography that resists quantum computers

formerly: PQC · post-quantum cryptography
In everyday life
Swapping the door padlock for a model the new master key can't open, before that key reaches town.
What it means here
New algorithms that run on today's ordinary computers but rest on mathematical problems even a quantum computer can't solve quickly. NIST standardized the first ones in August 2024.
Where it appears
HubThe inventoryEncrypted telemetry

Today's locks

formerly: RSA · ECDH · ECDSA · secp256k1 · public-key cryptography
In everyday life
The padlock with two keys: one anyone can have to lock it, another, only yours, to open it.
What it means here
The public-key cryptography that protects almost everything: RSA and ECDH to agree on a conversation's password (the HTTPS padlock), ECDSA to sign (prove who sent it), secp256k1 for Bitcoin and Ethereum wallets. These are exactly the ones a quantum computer breaks.
Where it appears
The deadlineThe inventoryDevice identity

The shared-secret lock

formerly: symmetric cryptography · AES-256 · SHA-256
In everyday life
The safe whose combination both people already know: there is no public part to attack.
What it means here
AES-256 encrypts the content; SHA-256 takes the fingerprint. The best known quantum attack on them (Grover) only halves their strength: AES-256 keeps the equivalent of 128 bits, which is enough. This is not where you need to migrate.
Where it appears
HubEncrypted telemetry

The algorithm that opens today's locks

formerly: Shor's algorithm
In everyday life
A method that, with the right tool, works out the opening key just by looking at the padlock.
What it means here
The 1994 recipe that, on a large quantum computer, finds the private key from the public key in RSA and elliptic curves. It already exists on paper; the machine is what is missing.
Where it appears
The quantum stackThe deadline

The shortcut that only halves

formerly: Grover's algorithm
In everyday life
Hunting for one key in a ring of a thousand by trying each, but with a trick that cuts the tries to the square root.
What it means here
The quantum attack on the shared-secret lock. A real shortcut, but modest: doubling the key size undoes the gain. That is why AES-256 stays safe.
Where it appears
The quantum stack

Store now, open later

formerly: harvest now, decrypt later · HNDL
In everyday life
Photocopying sealed letters you can't read today and keeping them in a drawer until someone figures out how to open the seal.
What it means here
Whoever records traffic encrypted with public-key locks today can read it on Q-Day. So the deadline that matters is not Q-Day: it is Q-Day minus the time your data must stay secret.
Where it appears
HubThe deadlineDevice identity

The new key exchange

formerly: ML-KEM · FIPS 203 · Kyber
In everyday life
The new way for two people to agree on a password in public without an eavesdropper deducing it, even with the quantum master key.
What it means here
The NIST-standardized replacement (FIPS 203) for ECDH when agreeing on a conversation's password. It migrates first, because it is what protects against "store now, open later".
Where it appears
Encrypted telemetryThe quantum stackBACEN before 2028

The new digital signature

formerly: ML-DSA · FIPS 204 · Dilithium · SLH-DSA · FIPS 205
In everyday life
A notarized signature, in a style the forger holding the new master key can't imitate.
What it means here
The NIST-standardized replacements for ECDSA and RSA when signing: ML-DSA (FIPS 204) for everyday use and SLH-DSA (FIPS 205) as the more conservative alternative. Signatures get bigger, which weighs on certificates and small channels.
Where it appears
Device identityEncrypted telemetry

The hard problem behind the new locks

formerly: lattice · Module-LWE
In everyday life
Finding the nearest point on a grid with millions of dimensions, deliberately jumbled with a little noise.
What it means here
Most new locks (ML-KEM, ML-DSA) rest on this kind of problem, which nobody knows how to solve fast, not even with a quantum computer. Every so often a claimed break appears; the 2024 one fell apart in about eight days. That is why this section insists on swapping the lock without swapping the door.
Where it appears
The quantum stackThe FHE frontier

Padlock with two locks

formerly: hybrid TLS · X25519+ML-KEM
In everyday life
Putting the old padlock and the new one on the door at the same time: the thief has to open both.
What it means here
Agreeing on the conversation's password with today's lock and the new one together. If the new one has an unknown flaw, the old one holds; if the quantum computer arrives, the new one holds. It is how major browsers and servers are already migrating.
Where it appears
Encrypted telemetryThe deadline

Certificate infrastructure

formerly: PKI · X.509 certificate · CA
In everyday life
The registry office that issues each server's and device's ID card, and whoever checks that ID at the door.
What it means here
The set of authorities, certificates and checks that proves who each end of a connection is. It is the layer furthest behind in the migration: key exchange is moving, identity barely.
Where it appears
Device identityBACEN before 2028

Device root of trust

formerly: RoT · root of trust · HSM · TPM
In everyday life
The safe soldered onto the board that keeps the key and only uses it inside, never handing it out.
What it means here
A piece of hardware that stores the device's key and performs the signing math without exposing it. In fleets that stay 15 to 20 years in the field, it has to be born ready for the new locks.
Where it appears
Device identity

Swapping the lock without swapping the door

formerly: crypto-agility
In everyday life
A door built to take another padlock model without being ripped out of its frame.
What it means here
Systems designed to change algorithm through configuration, not rewrites. It matters twice: to migrate now and to migrate again if a new lock falls.
Where it appears
The inventoryDevice identity

The list of locks

formerly: cryptographic inventory · CBOM
In everyday life
Before changing a company's padlocks, walking the building and noting where each padlock is, what model and who holds the key.
What it means here
The survey of where cryptography is, of what kind and with what expiry: in code, dependencies, certificates and devices. It is the first step of any migration, and the one most often skipped.
Where it appears
The inventoryThe assessment

The message's authenticity seal

formerly: AEAD · GCM tag · AES-256-GCM
In everyday life
The envelope seal that, once broken, reveals someone opened it on the way.
What it means here
Encrypting and sealing at once: AES-256-GCM locks the content and attaches a 16-byte seal that exposes any tampering. In heavily compressed telemetry, that seal can weigh more than the data itself.
Where it appears
Encrypted telemetry

Physical qubit and useful qubit

formerly: physical qubit · logical qubit · error correction
In everyday life
A choir of a thousand off-key voices singing together to sound like one voice in tune.
What it means here
Physical qubits make many errors; grouping many of them with error correction yields a reliable "logical qubit". Q-Day estimates depend on how many logical qubits a break needs and on keeping the machine running non-stop for hours or days.
Where it appears
The deadlineThe quantum stack

Computing on encrypted data

formerly: FHE · homomorphic encryption · fully homomorphic encryption
In everyday life
Sending a locked safe to the accountant, who does the sum inside through gloved holes, never seeing what is being added.
What it means here
A family of techniques that computes on data that stays encrypted the whole time; only the key holder reads the result. It also rests on lattices. It works today for shallow batch computations; long computations are still expensive.
Where it appears
20 applicationsFHE maturityThe FHE frontierInteractive tutorial

The noise clean-up

formerly: bootstrapping · bootstrap (FHE)
In everyday life
Every sum done in the dark leaves a little dust; after a few, you must stop and sweep before continuing.
What it means here
In FHE, each multiplication piles noise onto the encrypted data. The clean-up clears that noise without opening the data, and it is the expensive part: on our bench, with real 128-bit parameters, 1 min 18 s per operation and 10.26 GB of keys.
Where it appears
The FHE frontierFHE maturity
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