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Find answers to common questions about Sphurja's zero-knowledge architecture, experimental Virtual HSM, and account recovery.
Frequently Asked Questions
Is Sphurja an experimental solo indie developer project?
Yes. Sphurja is an independent proprietary software project created and maintained by a solo indie developer—not a corporation, business entity, or open-source foundation.
While our pairwise messaging relies on standard, battle-tested Signal Protocol cryptography, our custom edge components—specifically the RFC 9807 OPAQUE Virtual HSM and the Blind Mailbox Storage Spool—are experimental, proprietary implementations that have not yet undergone formal, third-party cryptographic audits. It is intended for testing, personal exploration, and non-critical use.
How does Sphurja's End-to-End Encryption work?
Sphurja uses the Signal Protocol (Double Ratchet algorithm, Pre-Keys, and post-quantum Kyber protection) combined with a Blind Mailbox Storage model. Messages and media are encrypted on your device using ephemeral symmetric keys. Edge servers act as a blind store-and-forward spool: we route and queue sealed envelopes, but cannot read or decrypt your conversations.
How does Account Recovery & the Virtual HSM work?
Sphurja provides a zero-knowledge recovery mechanism powered by an RFC 9807 OPAQUE Virtual HSM running in isolated Cloudflare Durable Objects. You configure a 6-digit PIN and receive a 64-digit Master Recovery Key. When you set up a new device, your PIN authenticates through an Oblivious Pseudorandom Function (OPRF)—meaning our servers verify your PIN without ever seeing or storing it in plaintext.
What is the 10-Attempt Auto-Shred Invariant?
To defend against brute-force attacks by unauthorized parties, our Virtual HSM enforces a strict hardware-grade lockout: if ten (10) consecutive incorrect PIN attempts are made, the Virtual HSM permanently and irreversibly destroys your OPAQUE PIN vault.
If your PIN vault is shredded, you can still restore your account using your offline 64-digit Master Recovery Key. If you lose both your PIN and your 64-digit Master Recovery Key, your encrypted data cannot be recovered by anyone, including the developer.
How many devices can I link?
You can link up to five (5) companion devices (such as the Sphurja Web client or secondary tablets) to your primary phone. Companion devices are linked by scanning a QR code, which delegates trust via an Ed25519 cryptographic certificate without exposing your primary private key. You can view and remotely revoke linked devices at any time from Settings > Linked Devices.
How long are messages saved in the cloud?
Edge blind mailbox messages are ephemeral catch-up spools retained for a maximum of thirty (30) days. Once your devices download and decrypt your messages, the local WatermelonDB database on your device becomes the permanent source of truth.
What happens when I Unsend a message or Delete a Chat?
Sphurja executes a two-tier purge: within less than 5ms, sealed message rows are synchronously wiped from the edge Cloudflare D1 mailbox and a tombstone barrier is created to prevent delayed queue messages from resurrecting. Media blobs in Cloudflare R2 are subsequently scheduled for immediate archival destruction.
How do I permanently delete my account?
You can completely erase your identity from within the app: go to Settings > Account > Delete Account. This triggers an immediate, irreversible wipe of your phone registration, device links, pre-keys, Virtual HSM vaults, and pending mailbox messages.
Independent Project
Need direct assistance or want to report a bug? Reach out directly to the maintainer or start an in-app support chat.
Open In-App SupportDeveloper Channels:
- Developer: [email protected]
- Support: [email protected]
Legal Documents: