To build a working solution for offline message delivery in a P2P chat model like Keychat but without relying heavily on relays for anything but temporary message forwarding, we need to introduce an ephemeral message storage mechanism that:
Respects the decentralized, encrypted nature of the system.
Only stores messages meant for users who are currently offline.
Syncs them when the recipient comes back online.
Let’s break this down and offer a fully working architecture and protocol strategy.
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🧠 Problem Recap
In a pure P2P setup, when Alice sends a message to Bob and Bob is offline, Alice has nowhere to send it.
> Who holds the message until Bob is online?
That’s the crux of the issue.
We want:
Temporary storage (with no authority or trust).
End-to-end encryption (nobody can read the message).
No dependence on centralized relays (or at least, their role is purely dumb forwarding).
No requirement for Alice to stay online until Bob is back.
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✅ Solution: Use Opportunistic Store-and-Forward Nodes ("Dead Drops")
> Introduce a class of nodes called Dead Drop Nodes (DDNs) or Dropboxes.
These are volunteer or self-hosted nodes that temporarily store encrypted messages for offline peers. They’re dumb in that:
They don’t interpret, filter, or inspect the content.
They can’t read messages (everything is E2E encrypted).
They only hold ciphertext addressed to a public key.
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🔐 Core Principles
1. E2E Encryption: Alice encrypts her message with Bob’s public key before uploading it.
2. Dead Drop Storage: Encrypted message is sent to 1+ dropbox nodes (could be Bob’s own node, friend’s node, or a random volunteer).
3. Polling or Gossip Retrieval: When Bob comes online, he polls or gossips with known DDNs to fetch messages addressed to him.
4. Automatic Deletion: Once Bob confirms retrieval, message is deleted (or expires after N hours/days).
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🧱 System Components
1. 📱 Alice’s Client
When Alice wants to send a message:
Encrypt the message using Bob’s public key.
Create a message envelope:
{
"to": "npub1bob...",
"from": "npub1alice...",
"ciphertext": "
"timestamp": 1680000000,
"ttl": 86400 // optional: seconds to live
}
Push this to one or more DDNs.
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2. 🧩 Dead Drop Node (DDN)
Any node can run this. It:
Accepts incoming envelopes.
Stores them keyed by to.
Offers a REST/WebSocket/WebRTC or gossip interface for receivers to pull messages.
Deletes messages after TTL or on confirmation of receipt.
🛠 Simple Python Flask Server (DDN prototype)
from flask import Flask, request, jsonify
import time
app = Flask(__name__)
storage = {} # {pubkey: [messages]}
@app.route("/drop", methods=["POST"])
def drop_message():
data = request.json
recipient = data.get("to")
if recipient not in storage:
storage[recipient] = []
storage[recipient].append({
"msg": data,
"ts": time.time()
})
return jsonify({"status": "stored"}), 200
@app.route("/pickup/
def pickup(pubkey):
messages = storage.get(pubkey, [])
storage[pubkey] = [] # Wipe after retrieval
return jsonify([msg["msg"] for msg in messages])
app.run(port=3000)
---
3. 📥 Bob’s Client
When Bob comes online:
Connect to one or more DDNs.
Pull messages addressed to npub1bob....
Decrypt them locally.
Acknowledge (if protocol requires).
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🛡 Security + Redundancy Considerations
Redundancy: Store in 3+ DDNs to ensure availability.
Metadata privacy: You could encrypt metadata (like to field) to hide recipients from DDNs. But that requires more complexity (e.g., anonymous routing or using proxy keys).
Spam protection: Use proof-of-work (a small one) or ZK-based tokens to reduce spam.
Access Control: Optionally, DDNs can be permissioned to only store messages for certain pubkeys.
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🧠 Inspiration from Existing Systems
Briar: Uses direct sync when peers are online. For offline delivery, it uses trusted peer storage, essentially what we’re doing here.
Bitmessage: Everyone stores everything, and recipients pick their messages. Ours is more efficient and targeted.
Keet: Uses Hyperswarm + hole punching, but needs both peers online. Our DDN method supplements this.
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🌐 Integration with Nostr
To integrate this with Nostr, you could:
Use kind: 4 (encrypted DM) events sent to a relay that acts as DDN.
Or use a custom kind: 30000 event and tag it with recipient pubkey.
Or build a lightweight NIP for Dead Drop nodes (proposed).
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✅ TL;DR Working Protocol (Minimum Viable Spec)
1. Alice:
Encrypts message for Bob.
Sends JSON envelope to 3+ DDNs via HTTP POST.
2. DDN:
Stores message keyed by recipient.
Responds to Bob’s client with message list on GET.
3. Bob:
Fetches messages on startup.
Decrypts locally.
Notifies DDNs (or not) to delete after confirmation.
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📡 Decentralized Deployment
DDNs can be run by anyone (like Nostr relays).
Messages can be replicated across them.
There can be incentives (e.g., Lightning tips, Cashu tokens) for uptimeor message delivery guarantees.
Best regards ChatGpt 😁😁