For the GirlsJoin the group

How it works

How we prove every selection is random

Every week, one member is randomly selected. No one chooses who it is. Not the admins, not us, not anyone. And you don’t have to take our word for it. Here’s how it works and how you can check it yourself.

  1. We seal the list

    Before each selection, we take the list of every eligible member and put it in a fixed, repeatable order. (Computers sort letters by their code, so names starting with an accented letter, like Åsa, come after Z. That’s expected.) Then we create its fingerprint, a long code made from the list. Change a single letter of a single name and the fingerprint comes out completely different. The moment the list is sealed, we ask independent timestamp authorities — services that exist to prove a document existed at a given moment — to sign over that fingerprint and the round number we are about to use. They have no idea who we are and nothing to gain either way. The round number and the fingerprint also go on screen during the Live, before the random number exists. From that moment the list is sealed: if anyone changed it afterward, the fingerprint wouldn’t match.
    For the technically curious

    The fingerprint is a SHA-256 hash of the list (names normalized, sorted by UTF-16 code unit order (identical to Unicode code point order for virtually all names), one per line, UTF-8). SHA-256 is the same hash function used to secure banking and software downloads. There is no practical way to create a different list with the same fingerprint. The timestamps are RFC 3161 tokens over "fingerprint:round:chainHash". Each token is published with the selection, and the checker verifies its signature and that its attested time comes before the round published.

  2. We commit to a random number that doesn’t exist yet

    The random number doesn’t come from us. It comes from drand, a public service run by the League of Entropy, a group of independent universities and companies around the world. drand publishes a new random number every 3 seconds, numbered in order, and every one of them stays public forever. When we seal the list, we also pick a drand number a few minutes in the future, say number 32,500,000, and post which one it is in the group. At that moment, nobody on Earth knows what that number will be. Not us, not drand’s operators, not anyone. Think of it like writing down “whatever the dice roll at 7:05 decides” before the dice exist, and the dice are rolled by strangers on the other side of the world.
    For the technically curious

    drand uses threshold BLS signatures. Each round’s randomness is created jointly by many independent operators, and no single operator, or small group of them, can predict or bias it. Our system checks each number’s cryptographic signature against drand’s published key before using it, so a fake or altered number is rejected automatically.

  3. The math picks the member

    When the drand number publishes, it’s combined with the list’s fingerprint and run through a fixed formula that produces one member number. Same inputs, same answer, every time, on any computer. In plain terms, the formula turns the random number and the fingerprint into a giant number, then counts around the list until it lands on a spot. With 1,000 members, it lands on one of the 1,000 spots, each equally likely.
    For the technically curious

    member number = (SHA-256(randomness + ":" + fingerprint) mod N) + 1, where N is the number of members on the list. The result is a 256-bit number, so the bias from the modulo step is smaller than 1 in 10 to the 70th power, which is effectively zero.

  4. Anyone can check it

    Everything needed to repeat the math is public: the fingerprint, the drand number (public forever), and the signed timestamps proving when we committed. Anyone can run the formula and confirm the same member number comes out. The list of names itself stays inside the group, so members can check their own name against it without it being public. Our checker page does this for you in your browser. It fetches the drand number itself and never sends your data to us.
    For the technically curious

    The audit record for each selection contains the list, its fingerprint, the drand chain hash and round, the randomness, and the resulting member number — everything needed to recompute the result offline.

Check a selection yourself

Questions

Do I have to give every week, or at all?
No. Giving is always optional. Give when you can, skip when you can’t, no guilt and no tracking. Giving never affects your chances of being selected, and nobody keeps score.
Do I need an account on this website?
No. Everything here is public to read. The group itself lives on Facebook.
What is drand?
A public service that produces one new random number every 3 seconds, and has been doing it without a break since 2023. Anyone in the world can read any of them, and they never change. The part that matters is who makes the number: nobody. It is produced by a group of independent universities and companies in different countries, and no single one of them can make it alone — each holds one piece of a key, and enough of them have to combine their pieces to produce a number at all. That gives three things. Nobody can know a number before it is published, including drand’s own operators. Nobody can nudge it: each round has exactly one correct value, so there is no second attempt to be had. And anyone can check it afterward, because every number is signed and the signature can be verified against drand’s published key. We name which future number we will use, in public, 20 seconds before it exists. After that there is nothing left for us to steer.
How is my member number decided?
It is simply your position on that week’s sealed list, which is sorted by name. The random number tells us how far to count down the list, and wherever the counting stops is who is selected. So your number is not an ID and it is not permanent — it belongs to one week’s list, not to you. One new registration earlier in the alphabet moves everyone after her down by one. (The sorting is done by character code rather than the way a person would alphabetise, so a name beginning with an accented letter, like Åsa, sorts after Z. That is expected: it is what lets anyone, on any computer anywhere, rebuild exactly the same list and get the same answer.)
When do registrations close each week?
Two hours before the Live. Anything that arrives inside those two hours is not in that week’s drawing, and is in the next one. The gap is what lets the list be built, sealed and timestamped before anything else happens — a list that could still change would not be worth sealing.
Could the admins pick someone they like?
No. The list is sealed and independently timestamped before the random number exists, and the random number comes from outside the group. Once that timestamp is signed, the outcome is fixed by math nobody controls. The timestamp is a request to someone else’s service, so once in a while nobody answers in time. We do not hide those weeks: the public record shows how many signatures a selection got, and the Live recording stands as the witness instead.
What if they didn’t like the result and started over?
Every selection attempt is recorded publicly, including any that were restarted, and a restart requires a written reason that also becomes public. A quiet do-over would leave a visible trail.
How do I know the list was really sealed before the random number existed?
This is the most important check, and you can do it yourself. When we seal the list we ask independent timestamp authorities to sign over it. Their signature says, in effect, “this exact list and this exact round existed at this moment” — and it is their signature, not ours. Compare that time with when the drand number published (our public record lists it, and drand’s own site shows it too). The signature comes first, by 20 seconds. Our checker does both halves for you: it verifies the signature in your own browser and tells you plainly whether it came before the randomness. We cannot forge those signatures, and we cannot backdate them. The weekly Live is a second witness. The round number and the start of the fingerprint are on screen before the random number exists, in a recording we cannot alter after the fact. The full fingerprint is in the public record, and on screen too on the rare occasions no authority answered in time — then the recording is the only witness there is, and we say so.
Can’t you just change the database?
Our records are built so they can’t be edited or deleted during normal operation. We won’t claim that makes tampering impossible, though, because whoever runs a database can ultimately change it. That’s exactly why the proof doesn’t depend on our database. It depends on signatures from timestamp authorities and on drand, and we control neither.
Does “random” mean everyone always has the same chance?
Everyone on a given week’s list has exactly the same chance that week. Who’s on the list is decided by the group’s rules and the admins who run it. The randomness guarantees the selection from the list is fair. It doesn’t decide who’s on the list.
Why aren’t recipients’ names on this website?
To protect members’ privacy. Names are shared only inside the group. The public record shows everything needed to check the math, minus names.
Do I need to understand any of this?
Not at all. It’s here so that anyone who wants to check, can. That’s the whole point: fairness you can verify, not fairness you have to trust.
Selection info