The Sybil bound

The defining property of 6d trust is not that it scores people. Plenty of systems score people. The defining property is what an attacker cannot do: no matter how many fake identities they create, they cannot manufacture trust they were not given by a real edge.

Trust is a current, not a tally

Most reputation systems count. More followers, more upvotes, more endorsements — more standing. Counting is exactly what a Sybil attacker exploits: identities are cheap, so anything you can accumulate by creating identities is for sale.

6d trust does not count. It solves a max-flow problem. Trust flows out from your seed identities like a current through the vouch graph. Each node is given a capacity that shrinks with its distance from the seeds, and every node is split so that being accepted costs one unit of flow. A node is trusted only if the current actually reaches it.

The bottleneck is the honest edge

Here is the consequence, and it is the whole point. The number of bogus identities that can enter the trusted set is bounded by the capacity of the real edges leading into them — not by how many fakes exist.

An attacker spins up a million accounts and vouches for each other in a dense mesh. It buys them nothing. If only one trusted person vouches into that cluster, only a trickle of trust crosses that single edge, and the millions behind it starve. The attacker controls the size of their cluster but not the capacity of the one honest edge feeding it — and that edge is the bottleneck.

The attacker can grow the cluster without limit. They cannot grow the edge.

Why this is the right shape for a trust service

Because the bound depends only on honest structure, the service itself never has to judge. It holds no global opinion, maintains no blocklist, makes no call about who is real. It computes a flow relative to your chosen seeds and reports where the current reached. The attack resistance is a property of the math, not of a moderator — which is exactly why it can be a neutral calculator instead of an authority.

The metric is Raph Levien’s, designed for Advogato twenty-five years early. Our one change is minted roots — each with its own seed set. The Sybil bound is his.