Security — Fileexchange

Keys stay client-side

A transfer key is derived in the client and placed in the URL fragment. Browsers never send fragments to a server, so the key does not reach us even by accident.

Ciphertext at rest

Blocks are sealed with XChaCha20-Poly1305 before upload. We hold ciphertext, block hashes and sizes — enough to route and deduplicate, not to read.

Integrity end to end

Every block carries a SHA-256 declared in the manifest. A block that does not match is rejected at ingest, not silently stored.

What an attacker with our storage gets

Data	Visible to us	Note
File contents	no	Sealed client-side; the key never leaves the sender.
File names	no	Part of the encrypted manifest.
Block sizes and count	yes	Required for routing and dedupe. Padding is available per session.
Sender's key ID	yes	Needed for billing and the audit log.
Recipient address family and ASN	yes	Kept 14 days for abuse handling, then discarded.
Full recipient IP	no	Truncated at ingest before anything is written.

Traffic analysis is not solved. Block sizes and timing are observable to us and to a network observer. Per-session padding raises the cost of that analysis; it does not eliminate it. Anyone claiming otherwise is selling something.

Retention

Objects are erased within 24 hours of expiry or revocation, replicas included
Request lines — time, method, path, status, bytes, duration — kept 14 days
Request and response bodies are never written to disk, in any environment
Audit entries are append-only and retained for the plan's history window
Backups of metadata are encrypted and expire on the same 24-hour clock as the objects

Reporting a vulnerability

Send the details to security@fileexchange.site. We acknowledge within two business days and will tell you plainly whether we consider it in scope. Please do not run load or denial-of-service tests against production.

In scope: authentication and authorisation, key handling, tenant isolation, link policy enforcement. Out of scope: findings that require a compromised sender device, missing headers with no demonstrated impact, and reports produced solely by a scanner.