Security you can verify yourself.

How Authsidian protects your vault, with the exact parameters the apps use. Every claim here matches our privacy policy.

Your master password becomes two separate keys.

Key derivation runs on your device when you sign in. Only one of the two resulting keys ever reaches our server, and it cannot decrypt anything.

  1. Master password

    Typed on your device. Never sent anywhere.

  2. Argon2id

    Memory-hard, so brute-forcing it on GPUs or ASICs gets expensive.

    memory
    64 MBmemory
    iterations
    3iterations
    parallelism
    4parallelism
    random salt, unique to you
    16 Brandom salt, unique to you

  3. HKDF-SHA256

    Splits the result into two independent 32-byte keys.

  4. Stays on your device

    Encryption key

    Held in memory only while your vault is unlocked.

    Sent to our server

    Authentication key

    Proves you know your master password. It cannot decrypt your vault.

Every item is sealed on its own.

Each item is encrypted with AES-256-GCM, a fresh random IV and an authentication tag. If a single bit of the stored data changes, your device detects it and rejects it.

IV

12 bytes, random for every item

Ciphertext

Your item, unreadable without your key

Auth tag

16 bytes that detect tampering

What our servers store, and whether we can read it.

Our servers act as blind storage for your vault. This is the complete list of what we keep, and whether we can read it:

Vault contentsEncrypted
Names, usernames, passwords, notes, cards, 2FA secrets and attachments are stored only as ciphertext that we cannot read.
Email addressReadable by us
Identifies your account and lets us contact you about it.
Key-derivation settingsReadable by us
Your salt, iteration count and memory cost, so each of your devices derives the same keys. They do not reveal your master password.
Authentication valueReadable by us
Used to verify sign-ins. It is derived from your master password but is separate from your encryption key and cannot decrypt your vault.
Item type and website domainReadable by us
Stored in plain text next to each encrypted item (for example "login" and "github.com") to operate sync between your devices.
Timestamps and sizesReadable by us
When each item was created and updated, and the size of your encrypted vault.
Devices and sessionsReadable by us
Device name and type, last activity and session records. Refresh tokens are stored only as SHA-256 hashes.
Security eventsReadable by us
Sign-ins and device pairings, including the device name and IP address, shown to you in your security history.
SubscriptionReadable by us
Your plan, billing interval, status and renewal or end date, plus the customer and subscription identifiers Lemon Squeezy assigns. We never receive your card details.
Email aliasesReadable by us
Only if you use them: alias addresses, labels, on/off status and how many emails were forwarded.
Push notification tokensReadable by us
Only in the mobile app: the token, platform and device name used to deliver notifications.
FeedbackReadable by us
Only if you send it: the message, its type, your language and, if you choose to add it, your email address so we can reply.

Our API also uses IP addresses briefly to rate-limit requests. Those records expire automatically. We do not keep request logs of the content you sync.

Limits we chose on purpose.

No password recovery

We cannot recover your master password.

There is no "reset password" and no backdoor. If you forget your master password and have no other way to recover it, the data in your vault is permanently unrecoverable, by you or by us.

The mobile app lets you create an Emergency Kit, which splits your master password into three fragments; any two of them rebuild it. The fragments are generated on your device and kept by you, and we never receive them. Anyone who obtains two fragments can recover your master password, so store them in separate, safe places.

Zero-knowledge trash

Deleted items go to a 30-day trash. The trash marker lives inside the encrypted item, so our servers do not know which of your items are in the trash. After 30 days your apps permanently delete expired items and remove their encrypted copy from our servers.

Authsidian Send

Authsidian Send lets you share a file or secret through an end-to-end encrypted link.

  • The file is encrypted on your device. The decryption key travels only in the link fragment (the part after "#"), which browsers never send to our servers.
  • Each transfer is limited to 250 MB, measured after encryption.
  • You can protect a link with a password. We store only a hash of that password, never the password itself.
  • Transfers self-destruct: they are deleted when they reach their download limit, and expired transfers are removed automatically.
  • The file name, size and type are stored in plain text and are visible to anyone with the link. Avoid putting sensitive information in file names.

Telemetry and analytics

The Authsidian desktop, mobile and browser extension apps include no analytics, advertising or crash-reporting SDKs and send no usage telemetry. They contact our servers only to sign in, sync your encrypted vault and run the features you choose.

Our website, authsidian.com, respects your privacy and uses no personal tracking cookies or third-party analytics scripts. We rely strictly on privacy-preserving, server-level metrics to measure aggregate visits without profiling visitors. The website loads Lemon Squeezy’s checkout script only when you choose to purchase a plan.

Generate a strong secret right here.

It works just like in the app, using your browser’s cryptographic randomness. Nothing you generate leaves this page.

Very strong · 123 bits of entropy

Time to crack at a trillion guesses per second: over a trillion years

20

Found a vulnerability?

Write to the security team with the steps to reproduce it, and give us a chance to fix it before you disclose it.

security@authsidian.comRead the full privacy policy