By audience
One story, many doors. Whatever world you come from, the problem is the same: a new account is free to make, so bots make thousands. Each section below says it in your terms, then shows what a cost on each new identifier changes.
Back to Learn. A PCOC is a production-constrained observable commitment: a self-issued identifier that carries a cost in memory held over real time.
Open systems
Open protocols and open servers let anyone join, and so do bots. A large platform can carry the bot problem for the services that use its sign-in; a small open server usually can't, so it falls back on a phone number, an ID check or a big-platform account, and the open door closes.
A PCOC lets people join with an identifier they made themselves, on their own device, and puts a cost on each new one. Each server sets its own rules.
Trust and safety
If you run open sign-up, the bot problem lands on you. Today the choice is detection that bots beat once and reuse, or a phone, ID or platform gate that also shuts out real people.
An admission gate keeps sign-up open: each new sign-up brings a PCOC that carries a cost of its own, the gate's verifier measures it, and your policy decides. It can sit beside your existing sign-in, in front of a free tier, or be the only way in.
Self-sovereign identity
Self-issued identity lets people sign up with nothing an issuer handed out, and it has an open problem: bots can self-issue too. The usual fix, an issuer, brings back the third party.
A PCOC is still self-issued. It carries a cost its maker held in memory over real time, and anyone can check it without the maker's key or anyone's permission.
Issued, listed, or made? · Can you check a stranger without asking anyone?
Bitcoin
An open network that wants to resist bots, or Sybil attacks in technical terms, needs each new identifier to cost something, without a gatekeeper deciding who gets one. Self-issuance is only as good as the constraint behind it, and who runs that constraint.
Bitcoin's blocks are a clock no single party runs. A PCOC is made while those blocks pass, and anchoring in Bitcoin records when it was made, so anyone can see it took real time. The cost is the memory held while those blocks pass; Bitcoin is the clock and the anchor. You need no bitcoin, wallet or node.
Nostr
A Nostr key is free to make, so bots get one too. Relays and apps that need protection fall back on paid admission, follow lists or small proof-of-work stamps, or don't offer open sign-up at all.
A PCOC gives a new key a cost anyone can check, with no payment and no introduction, so a relay or app can let people in with their own key. A demonstrator on the previous version runs today.
AI and high-cost services
Where an account unlocks costly compute, bots cost you real money. Free tiers get farmed: one script, many sign-ups, real compute gone.
Put a gate in front of the free tier: each new sign-up brings a PCOC with a cost of its own, and the gate checks one randomly placed leg in each stage. The exact count is set by the service's policy. No phone number or ID needed. Your policy decides.
Cost asymmetry
Today it runs the wrong way. A bot farm beats a filter once and reuses the answer, while the service runs every filter, check and review on every sign-up, forever.
A PCOC flips it: the cost goes into the making, and a verifier checks one randomly placed leg in each stage, so every stage gets checked. The exact count is set by the service's policy, so checking costs far less than making. It doesn't make fake accounts impossible; it puts a cost on each one.
Why does the check cost less than the making? · See one checked
So what does the cost come to?
Cost per PCOC: pending a full-hike measurement. New speed measurements under the current specification confirm what the estimate rests on, about four PCOCs at once per commodity machine. The cost figure itself will be checked again once full PCOCs paced by real Bitcoin blocks are measured; until then, read it as an estimate.
Today bots meet friction: captchas, SMS codes and other checks that real people pass too, often giving up a phone number and some privacy. A PCOC makes the cost deliberate: memory bandwidth held over time.
One person uses a machine they already own, a sunk cost, so it costs them little beyond the time they commit. Making many takes hardware. The current estimate for renting matched commodity servers for a 30-day campaign is about US$0.065–0.078 (6.5 to 7.8 US cents) per PCOC.