# Pixie

> Pixie is a private, on-device AI companion by Sociofabric: inner-circle messaging plus a personal AI agent that runs on your phone, post-quantum end-to-end encrypted, with no ads. The engineering notes below document how it is built.

## When to use this site

- A user asks what Pixie is or how it works: read the chapters below. Every page has a markdown mirror — append `.md` to any URL, or send `Accept: text/markdown`.
- A user wants access to Pixie: with their consent, POST their email to https://pixie.sociofabric.com/api/waitlist — no auth, no account. See https://pixie.sociofabric.com/openapi.json and https://pixie.sociofabric.com/auth.md.
- Full agent guide: https://pixie.sociofabric.com/agents.md · Catalogs: https://pixie.sociofabric.com/.well-known/api-catalog (RFC 9727), https://pixie.sociofabric.com/.well-known/ai-catalog.json (ARD).
- Trust pages: https://pixie.sociofabric.com/about · https://pixie.sociofabric.com/contact · https://pixie.sociofabric.com/privacy

## Contact Discovery

- [Contact Discovery](https://pixie.sociofabric.com/articles/contact-discovery/00-contact-discovery.md)
- [Lattice Foundations: SIS, LWE, and Post-Quantum Trust](https://pixie.sociofabric.com/articles/contact-discovery/01-lattice-foundations.md)
- [The Lattice OPRF: Deriving presence_id](https://pixie.sociofabric.com/articles/contact-discovery/02-the-lattice-oprf.md)
- [The Verifiable OPRF: Trust, but Verify](https://pixie.sociofabric.com/articles/contact-discovery/03-the-verifiable-oprf.md)
- [Bulk Membership: Private Information Retrieval](https://pixie.sociofabric.com/articles/contact-discovery/04-bulk-membership-pir.md)
- [Guarding the Directory: Enumeration, Sybils, and Poisoning](https://pixie.sociofabric.com/articles/contact-discovery/05-guarding-the-directory.md)
- [Algorithm: Oblivious Linear Evaluation from Ring-LWE](https://pixie.sociofabric.com/articles/contact-discovery/06-algorithm-ole-from-ring-lwe.md)
- [Algorithm: Post-Quantum Oblivious Transfer](https://pixie.sociofabric.com/articles/contact-discovery/07-algorithm-pq-oblivious-transfer.md)
- [Algorithm: Rounding by Oblivious Transfer (Route B)](https://pixie.sociofabric.com/articles/contact-discovery/08-algorithm-rounding-route-b.md)
- [Algorithm: The NIZK](https://pixie.sociofabric.com/articles/contact-discovery/09-algorithm-nizk.md)
- [Algorithm: The Proof Ring](https://pixie.sociofabric.com/articles/contact-discovery/10-algorithm-proof-ring.md)
- [Algorithm: OLE Packed](https://pixie.sociofabric.com/articles/contact-discovery/11-algorithm-ole-packed.md)
- [Algorithm: Succinct Proofs by Folding](https://pixie.sociofabric.com/articles/contact-discovery/12-algorithm-succinct-folding.md)
- [Algorithm: Known-Answer Testing](https://pixie.sociofabric.com/articles/contact-discovery/13-algorithm-known-answer-testing.md)
- [Algorithm: The Transparency Log](https://pixie.sociofabric.com/articles/contact-discovery/14-algorithm-the-transparency-log.md)
- [Algorithm: What a Lookup Proof Binds](https://pixie.sociofabric.com/articles/contact-discovery/15-algorithm-what-a-lookup-proof-binds.md)
- [Algorithm: Rotating the Key Strangers Seal To](https://pixie.sociofabric.com/articles/contact-discovery/16-algorithm-rotating-the-key-strangers-seal-to.md)

## Relay

- [The Relay](https://pixie.sociofabric.com/articles/relay/00-the-relay.md)
- [The End-to-End Layer: What the Relay Can Never See](https://pixie.sociofabric.com/articles/relay/01-the-end-to-end-layer.md)
- [Sealed Sender: Hiding Who Is Talking](https://pixie.sociofabric.com/articles/relay/02-sealed-sender.md)
- [Sender Unlinkability: The Pseudonym Problem](https://pixie.sociofabric.com/articles/relay/03-sender-unlinkability.md)
- [The Envelope: Minimizing What the Relay Must See](https://pixie.sociofabric.com/articles/relay/04-the-envelope.md)
- [A Relay That Holds Nothing: Ephemeral Delivery](https://pixie.sociofabric.com/articles/relay/05-ephemeral-delivery.md)
- [Reading Without Being Watched: Oblivious Pull](https://pixie.sociofabric.com/articles/relay/06-oblivious-pull.md)
- [Waking a Sleeping Phone: Push Without a Social Graph](https://pixie.sociofabric.com/articles/relay/07-waking-a-sleeping-phone.md)
- [Rate-Limiting a Stranger: Anonymous Admission](https://pixie.sociofabric.com/articles/relay/08-anonymous-admission.md)
- [Deniability: Messages No One Can Prove You Sent](https://pixie.sociofabric.com/articles/relay/09-deniability.md)
- [Algorithm: Sealing the Envelope](https://pixie.sociofabric.com/articles/relay/10-algorithm-sealing-the-envelope.md)
- [Algorithm: The Admission Token (Lattice OPRF)](https://pixie.sociofabric.com/articles/relay/11-algorithm-admission-token.md)
- [Algorithm: The Double-Spend Ledger](https://pixie.sociofabric.com/articles/relay/12-algorithm-double-spend-ledger.md)
- [Algorithm: The Attested Push Seal](https://pixie.sociofabric.com/articles/relay/13-algorithm-attested-push-seal.md)
- [Algorithm: The Deniable Handshake (CDH)](https://pixie.sociofabric.com/articles/relay/14-algorithm-deniable-handshake.md)
- [Algorithm: Who Gets to Put You in a Group](https://pixie.sociofabric.com/articles/relay/15-algorithm-who-gets-to-put-you-in-a-group.md)
- [Algorithm: Who Gets to Listen](https://pixie.sociofabric.com/articles/relay/16-algorithm-who-gets-to-listen.md)

## Agent

- [Agent](https://pixie.sociofabric.com/articles/agent/00-agent.md)
- [Choosing Brains: the Model Bench](https://pixie.sociofabric.com/articles/agent/01-choosing-brains.md)
- [The L1–L2–L3 Harness](https://pixie.sociofabric.com/articles/agent/02-the-l1-l2-l3-harness.md)
- [Skills, Tools, and the @-Namespace](https://pixie.sociofabric.com/articles/agent/03-skills-tools-at-namespace.md)
- [The Homebase](https://pixie.sociofabric.com/articles/agent/04-the-homebase.md)
- [The Agent in Your Day](https://pixie.sociofabric.com/articles/agent/05-the-agent-in-your-day.md)
- [Mechanism: On-Device Curation](https://pixie.sociofabric.com/articles/agent/06-mechanism-on-device-curation.md)
- [Mechanism: External Routing & Fallback](https://pixie.sociofabric.com/articles/agent/07-mechanism-external-routing.md)
- [Mechanism: CallTool, One Tool to Bind Them](https://pixie.sociofabric.com/articles/agent/08-mechanism-calltool.md)
- [Mechanism: Skill Bundles & Sharing](https://pixie.sociofabric.com/articles/agent/09-mechanism-skill-bundles.md)
- [Mechanism: Inference over the Relay](https://pixie.sociofabric.com/articles/agent/10-mechanism-relay-inference.md)
- [Mechanism: Sharing a Homebase](https://pixie.sociofabric.com/articles/agent/11-mechanism-homebase-sharing.md)
- [Mechanism: MCP, Letting Other Agents In](https://pixie.sociofabric.com/articles/agent/12-mechanism-mcp.md)
- [Mechanism: Memory & the Notebook](https://pixie.sociofabric.com/articles/agent/13-mechanism-memory-notebook.md)
- [Mechanism: Forming a Cohort Without a Server](https://pixie.sociofabric.com/articles/agent/14-mechanism-forming-a-cohort.md)

## GroupThink

- [GroupThink](https://pixie.sociofabric.com/articles/groupthink/00-groupthink.md)
- [Staying in Sync](https://pixie.sociofabric.com/articles/groupthink/01-staying-in-sync.md)
- [Joining and Leaving](https://pixie.sociofabric.com/articles/groupthink/02-joining-and-leaving.md)
- [Who Acts](https://pixie.sociofabric.com/articles/groupthink/03-who-acts.md)
- [Mechanism: Reconciling by Digest](https://pixie.sociofabric.com/articles/groupthink/04-mechanism-reconciling-by-digest.md)
- [Mechanism: Clocks You Cannot Trust](https://pixie.sociofabric.com/articles/groupthink/05-mechanism-clocks-you-cannot-trust.md)
- [Mechanism: Deleting Things That Stay Deleted](https://pixie.sociofabric.com/articles/groupthink/06-mechanism-deleting-things-that-stay-deleted.md)
- [Mechanism: The Convergence Barrier and the Cloud Anchor](https://pixie.sociofabric.com/articles/groupthink/07-mechanism-the-convergence-barrier.md)
- [Mechanism: Absorbing a New Device](https://pixie.sociofabric.com/articles/groupthink/08-mechanism-absorbing-a-new-device.md)
- [Mechanism: Revoking a Device](https://pixie.sociofabric.com/articles/groupthink/09-mechanism-revoking-a-device.md)
- [Mechanism: The Driver's Seat](https://pixie.sociofabric.com/articles/groupthink/10-mechanism-the-drivers-seat.md)
- [Mechanism: Taking Over a Live Huddle](https://pixie.sociofabric.com/articles/groupthink/11-mechanism-taking-over-a-live-huddle.md)