Umbra

1. Executive Summary

Umbra is a cross-platform, end-to-end encrypted messaging platform built on a zero-trust architecture. Unlike conventional messaging applications that rely on centralized servers to process and store messages, Umbra ensures that all message content is encrypted on the user's device before transmission, making it cryptographically impossible for relay servers, network operators, or any third party to access message content.

Key Differentiators

• Self-Sovereign Identity — Users own their cryptographic identity via a 24-word recovery phrase. No phone numbers, emails, or accounts required.
• Peer-to-Peer Architecture — Direct connections between users when possible, with relay fallback for offline messaging.
• Open Protocol — Built on open standards (W3C DIDs, libp2p) enabling interoperability and auditability.
• Cross-Platform — Native applications for iOS, Android, macOS, Windows, Linux, and web browsers.

2. The Problem: Privacy in Modern Messaging

2.1 Centralized Trust Models

Traditional messaging platforms operate on a centralized trust model where users must trust the service provider with their communications. Even platforms claiming "end-to-end encryption" often retain significant metadata, require phone number registration, or implement server-side key escrow mechanisms.

2.2 Key Vulnerabilities in Existing Solutions

2.3 The Metadata Problem

Even with strong message encryption, metadata — who communicates with whom, when, and how often — reveals sensitive information. Research has demonstrated that metadata analysis can reveal personal relationships, political affiliations, medical conditions, and more. Traditional messaging platforms collect and retain this metadata indefinitely.

3. The Solution: Umbra Platform Overview

Umbra addresses these fundamental privacy challenges through a combination of cryptographic innovation and architectural design decisions that minimize trust requirements.

3.1 Trust Minimization

Umbra's architecture is designed to minimize the trust users must place in any single entity:

• No trusted servers — Relay servers see only ciphertext; compromising them reveals nothing.
• No trusted third parties — Key generation and management happens entirely on-device.
• Verifiable cryptography — All cryptographic operations use audited, open-source libraries.
• User-controlled identity — Recovery phrases enable identity portability without server involvement.

4. Technical Architecture

4.1 System Components

4.2 Technology Stack

4.3 Relay Server Architecture

Relay servers provide three core functions while maintaining zero knowledge of message content:

1. Signaling Relay — Forwards WebRTC SDP offers/answers and ICE candidates for peer connection establishment.
2. Offline Message Queue — Stores encrypted message blobs for offline recipients (7-day TTL, 1000 messages per user).
3. Session Relay — Enables QR code-based friend adding without requiring both parties to be online simultaneously.

5. Cryptographic Security Model

5.1 Cryptographic Primitives

Umbra employs a carefully selected set of cryptographic primitives, all implemented using audited, pure-Rust libraries from the dalek-cryptography and RustCrypto projects:

5.2 Key Hierarchy

5.3 Message Encryption Protocol

Each message is encrypted using the following protocol:

1. Shared Secret Computation — X25519 ECDH between sender's private key and recipient's public key produces a 32-byte shared secret.
2. Key Derivation — HKDF-SHA256 derives the encryption key using the shared secret, conversation ID as salt, and domain string "umbra-message-encryption-v1".
3. Encryption — AES-256-GCM encrypts the message with:
   • 256-bit derived key
   • 96-bit random nonce (unique per message)
   • Additional Authenticated Data (AAD): sender_did || recipient_did || timestamp
4. Signature — Ed25519 signature over the ciphertext and metadata ensures authenticity.

5.4 Decentralized Identifiers (DIDs)

Umbra uses the DID:key method for self-certifying identifiers:

did:key:z6MkhaXgBZDvotDUGRy7K9L7M2yvCpREH5eXtbA8vwFRNbfH

The DID encodes the user's Ed25519 public key directly, enabling:

• Self-certification — The identifier proves ownership without external verification
• Offline resolution — No registry lookup required to resolve the public key
• Interoperability — W3C standard compatible with other DID-based systems

6. Platform Features

6.1 Messaging

6.2 Voice & Video Calling

Umbra supports encrypted 1:1 voice and video calls using WebRTC:

• Direct P2P connections — Media flows directly between peers when possible
• TURN fallback — Self-hosted TURN servers for restrictive NAT environments
• DTLS-SRTP encryption — All media encrypted in transit
• Call quality — Adaptive bitrate up to 4K video

6.3 Communities

Large-scale community support with Discord-like features:

• Spaces & Channels — Organize discussions into categories and channels
• Roles & Permissions — Fine-grained access control with custom roles
• Moderation — Admin tools for managing members (mute, ban, warnings)
• Threads — Inline discussion threads within channels
• File Sharing — Encrypted file uploads within communities

6.4 Identity & Social

6.5 Unlimited File Sharing

Umbra's P2P architecture enables unrestricted file sharing that competitors cannot match:

Technical Implementation

• Chunked transfers — Files split into 256KB chunks (user-configurable) with SHA-256 content addressing
• P2P first, relay fallback — WebRTC DataChannels tried first (2s timeout), relay for NAT-blocked peers
• Resume support — Transfer state persisted to SQLite; interrupted transfers resume from last chunk
• Adaptive flow control — TCP-like congestion control with sliding window (2→8 based on ACK latency)
• Per-file encryption — HKDF derives unique AES-256-GCM key per file from conversation shared secret

6.6 Plugin & Extension Ecosystem

Umbra's plugin system enables community-driven growth while maintaining security through sandboxed execution:

Why This Matters for Users

6.7 How Plugins Fuel Platform Growth

Traditional platforms grow based on corporate roadmaps and investor demands. Umbra grows based on what users actually want:

Real Examples of Community-Driven Features

6.8 How Other Platforms Monetize Your Data

When a service is free, you are the product. Here's how major platforms and their partners profit from your private communications:

The Data Harvesting Pipeline

Documented Cases of Data Exploitation

Why This Is Impossible on Umbra

6.9 Security Breaches That Cannot Happen on Umbra

Centralized platforms are honeypots for attackers. Here are real breaches that are architecturally impossible on Umbra:

Major Messaging Platform Breaches

Classes of Attacks Eliminated by Architecture

6.10 Network Effects: More Users = Stronger Network

Unlike traditional platforms where more users means more server costs and infrastructure burden, Umbra's P2P architecture means every new user strengthens the entire network.

The P2P Scaling Advantage

How User Growth Reduces Infrastructure Dependency

What Happens as the Network Grows

6.11 Boost Nodes: Community-Powered Infrastructure

Boost nodes are community-operated servers that enhance network performance without compromising privacy. They're the bridge between full P2P and traditional infrastructure.

How Boost Nodes Work

Boost Node Capabilities

Who Runs Boost Nodes?

6.12 Communities: Encrypted Spaces for Groups

Umbra Communities bring the best of Discord and Slack to a privacy-first platform. Large groups can collaborate with channels, roles, and permissions — all end-to-end encrypted.

Community Architecture

Community Features

How Communities Stay Private

Communities vs Traditional Platforms

6.13 Honest Assessment: Potential Challenges

Transparency is a core value. While we believe Umbra offers significant advantages, we also acknowledge the challenges and tradeoffs of our approach:

Technical Challenges

Adoption Challenges

Known Limitations

7. Comparison with Existing Solutions

Privacy & Security

Architecture & Ownership

File Sharing Capabilities

Features & Extensibility

Business Model & Trust

✓ = Full support · ◐ = Partial/Limited · ✗ = Not supported · ∞ = Unlimited

7.1 Key Advantages

7.2 User-Facing Benefits Enabled by Architecture

Umbra's technical architecture directly translates to tangible user benefits:

Data Sovereignty

Future-Proof Platform

Real-World Scenarios

8. Conclusion

Umbra represents a fundamental rethinking of how private messaging platforms should be built. By combining:

• Industry-standard cryptography — Ed25519, X25519, AES-256-GCM, HKDF
• Self-sovereign identity — BIP-39 recovery phrases and DID:key
• Zero-trust architecture — Relay servers see only encrypted blobs
• Peer-to-peer connectivity — Direct connections minimize server involvement
• Unlimited P2P file sharing — No artificial size limits, direct transfers, per-file encryption
• Community-driven plugin ecosystem — Extensibility without vendor lock-in
• Cross-platform availability — Native apps for all major platforms

Umbra delivers a messaging platform that does not compromise between privacy and usability. Users enjoy the features they expect from modern messaging — group chats, communities, voice/video calls, unlimited file sharing — while maintaining cryptographic guarantees that their communications remain private.

Further Reading