PUBLIC BUYER BRIEF · VERSION 1.0 · 10 AUGUST 2026
Architecture and evidence brief
This concise brief routes reviewers to the current public evidence for City of Hats. It is first-party material, not a certification, warranty, independent audit, or substitute for a scoped security assessment.
Documented architecture boundary
Current first-party material describes authorized endpoints as the places where plaintext and message keys are available, while the delivery service handles ciphertext. It describes hybrid X25519 plus ML-KEM-768 key agreement, Double Ratchet-style key evolution, and AES-256-GCM for content protection. Buyers must distinguish a published design claim from independent implementation assurance.
Identity and metadata
A Hat can be created without a phone number or email address. This reduces coupling to an address-book identity; it does not eliminate routing, timing, device, abuse-prevention, recipient, network, or operational metadata.
Current public evidence status
| Public Security Evidence Center | Available | Claims, boundaries, architecture, limitations, and verification dates. |
|---|---|---|
| Responsible disclosure and security.txt | Available | A published reporting route for security researchers. |
| Public cryptographic architecture description | Available | Algorithm and data-boundary claims are documented as first-party technical material. |
| Independent cryptographic audit | Not published | Do not treat internal review or documentation as an independent audit. |
| Public penetration-test report | Not published | A buyer should request current private evidence if required for procurement. |
| Public customer case studies | Not published | No customer names, outcomes, or metrics are invented for this page. |
| Formal compliance certifications | Not claimed here | Certification and legal applicability require scoped, current evidence. |