The seven primitives — the narrow waist
This is the heart of XChain: seven primitives, each specified hard (RFC 2119 — MUST / MUST NOT / SHOULD), so that everything above can plug in with total freedom. And because We hold Ourselves to honesty, the table below shows not just what each primitive is, but exactly how real it is today — including the one piece that is still a stand-in.
| # | Primitive | Module | The invariant it guards | Status, told straight |
|---|---|---|---|---|
| 1 | UIR — Universal Identity Root | x/uir | One global identity; per-chain accounts derived deterministically; one signature to act | Real |
| 2 | UAC — Universal Asset Commitment | x/uac | The total-supply invariant total == Σ perChain + lockedInTransit; a minimum security-class per asset | Real — signature-gated mint |
| 3 | XMP — XChain Messaging Protocol | x/xmp | Trust-minimized messaging; a clean split of READ and WRITE | Real — anti-replay + pessimistic containment |
| 4 | PAI — Proof Aggregation Interface | x/pai | A parent verifies its children without re-executing them; recursive aggregation | Aggregation real · prover still MOCK (see §9) |
| 5 | DA Interface (tiered) | fabric/da + tools/dasidecar | Committed data stays retrievable / sampleable per the tier's policy | Real — segments published to Celestia mocha, commitment verified on-chain |
| 6 | VLC — Verifiable Log Commitment | x/vlc | Append-only logs: tamper-evident + timestamped + inclusion-provable; value-free | Real — RFC 6962 Merkle + on-chain DACommitment |
| 7 | SC — Settlement Contract | x/settlement | Minimal logic at the Global Root: finalize cross-region value, consume aggregated proofs | Real — reconciles the total-supply invariant; no blind commitments |
⚠️ Primitive #4 (PAI) uses a MOCK prover. The aggregation circuit (STC → Cell → Root) is real and running; the cryptographic proof underneath is still a mock. By the spec's own rules,
ProofSystem.MOCKis rejected on every network that is not a testnet. A real prover (SP1/Boojum) is open, honest work — see §9. We would rather you know this than be impressed by a claim We can't back.
The seven aren't a wish-list; they compose in a strict dependency order — UIR → (UAC, XMP) ; DA → (VLC, PAI) ; (UAC, XMP, PAI, VLC) → SC:
Why a narrow waist is a superpower: freeze a small, correct core, and thousands of people can build wildly different things above it that all still interoperate. The internet did this with TCP/IP. XChain does it for verifiable data.