Security
What our servers cannotsee.
"Zero-knowledge" is not a slogan: it is a constraint the code imposes on itself. The key that opens your vaults is derived from your passphrase, on your workstation, and never reaches us. Everything we hold is unreadable without it — for us as for anyone who would steal from us.
What the server sees
- ✓An account identifier and a public key
- ✓Encrypted blocks, and their version number
- ✓Who is allowed to open which vault
- ✓The time of each request, and its signature
What it never sees
- ✕Your name, your vaults, your passwords
- ✕What is inside those blocks
- ✕The key that opens it
- ✕Your passphrase, never transmitted
The chain
Named algorithms, and their parameters.
Nothing here is a home-made choice. Every building block is a public standard, with the settings we actually use in the application.
t = 3, m = 256 MiB, p = 4
Argon2id
Your passphrase becomes a key on your workstation. A quarter of a gigabyte of memory per attempt: a brute-force attack costs more than it yields.
vaults
XChaCha20-Poly1305
Each vault is encrypted and authenticated before leaving the machine. A block altered in transit does not decrypt.
key sharing
X25519
A shared vault's key is sealed for each member with their public key. Removing a member means no longer sealing the next one for them.
every request
Ed25519
Every call to the server is signed by the device. A stolen token is not enough: you would also need the device key, which never leaves its keychain.
derivation
HKDF-SHA-256
Secondary keys derive from the master key without ever revealing it.
transport
TLS 1.3, pinned certificate
The application only accepts our certificate. A compromised authority cannot impersonate us.
On the workstation, on the server
What protects you day to day.
A new workstation must be approved
Attaching a machine requires the approval of an already enrolled workstation, with a fingerprint to compare out loud. An intercepted code is not enough.
Every request is signed
The device signs every call with a key that never leaves its keychain (DPAPI on Windows). A stolen session token opens nothing.
Second factor on sensitive actions
Opening a shared vault, inviting, revoking: a one-time code is required. Not for reading what you already opened this morning.
Automatic locking
After inactivity, when the Windows session locks, on sleep. The most common way of forgetting is covered.
A recovery key, shown once
It reopens the account if the passphrase is lost. We cannot replace it — that is the price of not being able to read you.
Audit log on the server
Who opened what, when, from which device. Kept one year, readable by the account's administrators.
Encrypted, off-site backups
A consistent snapshot every night, encrypted with AES-256-GCM, copied to a second machine in France, and re-read to check that it opens.
Pinned certificate, TLS 1.3
The application only accepts our certificate to talk to the server. A compromised authority cannot impersonate us.
Compliance
GDPR, ANSSI: what is done, and where to read it.
Data processing (GDPR, article 28)
For your vaults, STELIX DIGITAL SAS is a processor: we host data we cannot read. A data processing agreement compliant with article 28 is attached to every contract — subject matter, duration, instructions, security measures, breach notification, help with data subject rights, fate of the data at the end. It is summarised on the page GDPR data processing.
Hosting
Servers and backups in France, with SLBCLOUD (5 rue de la Planche, 22190 Plerin, France). No transfer outside the European Union, no further processor without informing you.
Cryptography (French LCEN, article 30)
Software that encrypts must be declared to ANSSI, the French cybersecurity agency, before being put on the market. STELIX VAULT's file — description of the means, algorithms, key lengths — is prepared; its filing with ANSSI is in progress. This is not a certification: it is a declarative obligation.
What we do not claim
No SecNumCloud certification, no third-party audit published to date. We are two people, the software is a month old, and we prefer to write what is true. The encryption code relies exclusively on public, audited libraries (@noble), never on a home-made implementation.