Layer 1
Content-addressed storage
Chunking, deduplication, deterministic manifests. Every file becomes a Merkle tree with a stable root hash that anchors the entire evidence chain.
System design
A layered architecture for verifiable file sharing
SafeDrop separates concerns into explicit layers so each subsystem can be built, tested, and extended independently. The architecture keeps frontier research out of the critical MVP path.
System layers
Architecture layers
From storage primitives at the bottom to user-facing explanation surfaces at the top.
Layer 2
Evidence & audit
Append-only audit log, signed segment receipts, delivery confirmations, and exportable evidence bundles. Useful before any ZK wrappers are added.
Layer 3
Share lifecycle
Link creation, capability tokens, expiry enforcement, resumable transfers, and revocation. Each state transition emits an audit event.
Layer 4
Reachability
UPnP/NAT-PMP port mapping, signed external probes, ICE hole-punching, dynamic DNS binding, and encrypted relay fallback.
Layer 5
Privacy & policy
Metadata aliases, size bucketing, timestamp coarsening, consent tracking, and regulatory-compliant export bundles.
Layer 6
Explanation surface
Human-readable evidence cards, admin dashboard, status explanations, and operator trust interface. Explain, never hide.
Diagrams
Visual system model
Architecture stack
Layered component view
Each component communicates through defined interfaces. No layer reaches through another.
Reachability flow
Path selection with evidence
The reachability subsystem tries direct binding first and falls back through progressively more assisted methods.
Security
Threat model highlights
The threat model covers network adversaries, storage compromise, relay trust, and metadata inference.
Network
Path integrity
Every reachability path is signed and bound to the session. Man-in-the-middle attacks are detected through certificate pinning and signed probes.
Storage
At-rest protection
Envelope encryption with per-object keys. Deletion uses crypto-shredding with attested key destruction events.
Relay
Zero-knowledge relay
The relay sees only encrypted ciphertext and blinded session identifiers. No file contents or metadata are exposed to the relay operator.