Every term gets an everyday example before the definition. The technical names stay here, for whoever meets them in a paper, a proposal or a vendor meeting.
Specimen · the locked box with gloves
Illustration, not measurement: the glass box with gloves is the image we use across the section. Figures quoted in the terms come from the section's pages, measured on our bench.
A locked glass box with gloves built in: the jeweller makes the ring through the gloves without ever holding the key.
What it means here
A way of encrypting data that still lets a server compute on it. The server adds, multiplies and compares without opening it; only the key holder reads the result.
The gold inside the box: it is there, you can work on it through the gloves, but nobody outside can take it.
What it means here
Data after encryption. It is much larger than the original (one encrypted vote in our demo takes 131,406 bytes) and carries a little deliberate noise, which is what makes it secure.
also: evaluation key · relinearisation and rotation keys
In everyday terms
The box's gloves: they give the jeweller the power to work the gold, not the power to take it out.
What it means here
Extra keys, derived from the secret one, that the server receives to multiply and to move positions inside the locked data. They can be huge: for cleanup at real security, 10.26 GB sent before starting.
Every time the jeweller works through the gloves, the glass fogs a little. After too much work, you can no longer see the gold.
What it means here
Encrypted data carries deliberate noise. Every operation adds to it; multiplication adds a lot. Past the limit, the result is wrong, and silently so: on our bench, the eighth multiplication returned 28323 where the answer was 282, with no warning.
How many times you can work the gold before the glass fogs for good.
What it means here
The budget of multiplications in sequence, fixed before starting. At real security it is small: our bench found that the parameter where it counted 8 fits only 2 levels.
Stopping, cleaning the glass from inside without opening the box, and only then carrying on.
What it means here
The operation that removes accumulated noise and restores the operation budget. It exists and works, but it is expensive: 1 min 18 s per run and 10.26 GB of keys on our bench, at real security.
Three different workshops: one works with counted pieces, one with approximate measurements, one piece by piece, on or off.
What it means here
There is no single FHE. There are three families, and each application needs one: exact integers, approximate decimal numbers, and bit-by-bit logic gates. Mixing them is possible and expensive.
Counting votes in a ballot box: every unit counts, nothing extra, nothing missing.
What it means here
The dialect for whole-number arithmetic, without rounding. It is the one in our encrypted vote: each vote is a 1 in the candidate's position, and the sum comes out exact.
A kitchen scale: it gives the weight to a few decimals, and nobody expects lab precision.
What it means here
The dialect for real numbers, which accepts a small error at the end. Good for averages, scores and the last layer of AI models; not for deciding "which is largest" precisely.
A switchboard: each operation turns a lamp on or off depending on two others.
What it means here
The dialect that computes one bit at a time, with the cleanup built into every step. Good for logic and branches ("if this, then that"); slow for large arithmetic.
An ice tray: you fill every cavity at once and freeze them together.
What it means here
A single locked value carries thousands of numbers side by side (16,384 in our vote), and each operation applies to all of them at once. The costly part is not multiplying: it is moving numbers from one position to another inside the pack.
Finding an exact point in a gigantic grid, in hundreds of dimensions, when someone nudged every coordinate a little.
What it means here
The mathematical problem FHE relies on. It is the same kind of problem behind the new post-quantum locks, which is why FHE also resists a quantum computer.
A luggage padlock and a safe lock: both close, but one opens with a hairpin.
What it means here
The number that sets how large (and secure) the locked data is. The "toy" one (logN=13) is ~40 times faster than the real-security one (logN=16). When reading a vendor figure, ask which one they used.
A password that, tried at the fastest possible pace, would take longer than the age of the universe to guess.
What it means here
The level the standard requires before calling a lock serious. Several published measurements (including some of our older ones) used weaker parameters than the label; on our pages, every figure says which level it was measured at.
Asking a blindfolded person which of two boxes is heavier, without lifting either.
What it means here
Only two moves exist under encryption: add and multiply. Comparing two values becomes a long chain of operations that uses 40 levels of the budget; without cleanup it is impossible, with cleanup picking the largest of 4 took 23 min 31 s.
A salesman who, just from seeing you accept or refuse offers, works out how much is in your wallet.
What it means here
When the encrypting side hands back to the server anything that depends on the decrypted result ("accepted or refused"), the server can learn the secret without attacking the key. In our measurements, in about 47 queries.
The canary miners took into the mine: if it fell ill, there was gas.
What it means here
Positions with known values hidden in the pack. If they come back changed, someone tampered. They catch 100% of blind tampering and only 0.37% of someone who picks where to tamper: hygiene, not a guarantee.
also: confidentiality vs integrity · verifiable FHE
In everyday terms
A sealed envelope guarantees nobody read the letter; it does not guarantee the postman delivered the right letter.
What it means here
FHE hides the data but does not prove the server did the agreed computation. If the server may be malicious, you need a proof of the computation or an attested machine, with published overheads from ~2% to over 1000%.
Proving you know the safe's combination by opening it in front of someone, without saying the combination.
What it means here
A mathematical proof that something is true which does not reveal the secret. In the encrypted vote, each ballot carries a proof that it marks exactly one candidate, without saying which.
A notary stamping a paper inside a carbon-lined envelope: the stamp goes through, the contents stay hidden.
What it means here
A signature given without seeing what is signed. In the vote, the notary authorises the voter without knowing which credential will be used at the ballot box, so nobody can link the vote to the voter.
A bank vault with five managers, where three must turn their keys together to open it.
What it means here
The decryption key is split among five authorities; any three together can decrypt the result, none alone can. In our demo: electoral court, bar association, public prosecutor, university and civil society.
Shaking the ballot box before opening it, so nobody knows whose ballot was first.
What it means here
Even encrypted, the order of votes can reveal who voted ("vote 42 belongs to whoever came in at 14:03"). Three servers shuffle and re-lock them, each without knowing the others' order.
The ATM slip: you keep a number and later check on the public statement that the transaction is there.
What it means here
When you vote, you get the fingerprint of your locked ballot. On a public board, each entry chains to the previous one; changing a vote breaks the chain, and anyone can redo the sum and check the result.