Map: Metadata Privacy

Why metadata is harder

End-to-end encryption protects content. Packet headers, timing, sizes, and routing decisions stay visible. A global passive adversary can correlate flows without breaking any cipher. Metadata privacy requires changing observable patterns, not just hiding payloads.

What leaks at each layer

Defenses by mechanism

Network-level mixing

Overview - Mix Networks covers Tor, Nym, Katzenpost, and I2P. Layered encryption combined with path multiplicity. Loopix-style mixnets add latency and cover traffic for stronger guarantees against global adversaries.

Sealed sender and metadata-light envelopes

• Signal sealed sender: the sender identity is encrypted to the recipient, so the server only sees the recipient.
• Nostr NIP-17 gift wrap: gift wraps conceal the original sender but expose the recipient’s public key and delivery timing.
• SimpleX queue model: pairwise queues addressed by random IDs, with no user accounts.

Private retrieval

Overview - Private Information Retrieval lets a client fetch records without revealing the index. Practical for DNS, certificate transparency, key servers, and LLM RAG.

Padding and cover traffic

• Cover traffic and padding: Loopix adds cover messages; Tor has padding mechanisms. WireGuard persistent keepalives preserve NAT mappings and are not constant-rate traffic-analysis protection.
• Length padding: message-length flooring so sizes do not leak.

Onion-routed authentication

• Tor v3 client authorization: only authorized keys can connect to a hidden service. The access log does not even see attempts.
• Hashcash and blind tokens: pay or prove human-ness without identifying yourself.

Timing decorrelation

• Asynchronous messaging: store-and-forward with random delivery delay.
• Batching: Mixmaster's classic "send when N arrived"; modern variants in Katzenpost.

Useful patterns

Sealed message over a mixnet

Signal Protocol envelope plus Nym SURBs (single-use reply blocks). The recipient can reply without learning the sender's network identity.

Confidential RAG

PIR over a public corpus, FHE-evaluated retrieval scoring, and a TEE-hosted LLM with no logging.

Ephemeral peer ID

did:peer or per-relationship keypairs so a persistent ID does not leak across contexts. Foundation of Overview - Identity & Pseudonymity.

Files most relevant

• Overview - Mix Networks
• Overview - Private Information Retrieval
• Overview - Encrypted Messaging
• Overview - Confidential Computing
• Confidential-AI-Inference
• Overview - Identity & Pseudonymity

Primary sources

• Tor: The Second-Generation Onion Router
• The Loopix Anonymity System
• Pung: Unobservable Communication over Fully Untrusted Infrastructure
• RFC 8446: TLS 1.3
• Nostr NIP-59: visible recipient tags
• WireGuard: persistent keepalives
• Signal: sealed sender
• Vuvuzela: Scalable Private Messaging Resistant to Traffic Analysis

Also in Secure Messaging