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Encrypted address book
Browse contacts with online / recent / all filters. View full profiles (avatar, bio, status). Each contact’s profile data is encrypted to your key — only you can read it.
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Application · Contacts
Contacts.
Encrypted by default.
People and groups
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Capabilities
What you can do with Contacts.
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Named groups for chat and mail
Create named groups and address them as one in uChat and uMail. Group membership updates propagate encrypted across every member.
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One-time invite links
Generate invite links for new people. Each link is single-use and expires. Invites do not leak the inviter’s address book to the invitee.
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Protection
Security for Contacts.
Content in Contacts is inside the end-to-end encrypted envelope: it is encrypted in your browser before it is transmitted, and the server stores ciphertext it holds no key for.
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Post-quantum cryptography by default
All authentication and key exchange uses NIST-standardized ML-DSA-65 (FIPS 204) signatures and ML-KEM-768 (FIPS 203) key encapsulation. There is zero RSA, zero elliptic-curve, zero classical-only crypto in the authentication path. Defeats store-now-decrypt-later attacks.
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End-to-end encryption on your device
Every payload is encrypted in your browser using XChaCha20-Poly1305 (RFC 8439) with a 192-bit nonce and a Poly1305 authentication tag. The plaintext exists only in your tab's memory. When you close the tab, the plaintext is gone.
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The server holds ciphertext it cannot open
For Contacts content the server only ever stores ciphertext and public keys. It cannot decrypt your data — by architecture, not by promise: there is no backdoor, no master key and no key escrow, because no key that would open it ever reaches the server.
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Your keys stay on your device
Your private keys are derived in your browser from three secrets only you control, and are held in memory for the session only — never written to browser storage, never sent to the server. A new device derives the same keys locally from the same three secrets.
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Mechanics
How Contacts works.
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Open Contacts in your browser
UltimaOS runs in any modern browser — Chrome, Firefox, Safari, Edge. Nothing to install. Sign in by re-entering the three secrets your keys are derived from, and the same keys are rebuilt locally on whatever device you are using.
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Your data is encrypted before it leaves your device
Sending a message, uploading a file, writing a note — the content is encrypted with XChaCha20-Poly1305 and authenticated with an ML-DSA-65 signature before any byte crosses the network boundary.
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The server stores ciphertext and returns it on demand
The server keeps an opaque blob it has no key for. When you open Contacts, those blobs are streamed to your device, decrypted locally and rendered. Plaintext exists only in your tab.
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Changes follow you across devices
Any change you make is uploaded and picked up by every other device you are signed in on, so Contacts looks the same wherever you open it.
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Inside the suite
How Contacts fits in the suite.
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uChat
Start chats with one click from a contact's profile. Presence status syncs across both apps.
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uMail
Compose to a contact without typing the address. Mail benefits from Contacts' type-ahead everywhere.
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Calendar
Share free/busy, propose-meeting or full-manage scopes with specific contacts. Calendar respects the scope.
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Account
Contacts are encrypted to your private key. Only you can read them. Recovery via Account covers Contacts too.
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Get started
Get started with Contacts.
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Open Contacts in your browser
UltimaOS runs in Chrome, Firefox, Safari and Edge. Nothing to install. Sign in with your passphrase to derive your private key locally.
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Open the workspace and launch Contacts
The launcher shows every app. Contacts is right there with its capsule video preview. Click to open.
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Connect it with the rest of the suite
Contacts works alone, but it shines when combined with the rest of the UltimaOS apps. Same identity, same workspace, one place to work.
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Frequently asked
Questions about Contacts.
Is Contacts end-to-end encrypted?
Short answer
Yes. All content in Contacts is encrypted in your browser using XChaCha20-Poly1305 with a fresh key per item. The UltimaOS server only ever stores ciphertext and public keys — it cannot decrypt your data, no matter who asks.
What cryptography does Contacts use?
Short answer
Contacts uses the same post-quantum stack as every other UltimaOS app: ML-DSA-65 (FIPS 204) for authentication, ML-KEM-768 (FIPS 203) for key encapsulation, XChaCha20-Poly1305 (RFC 8439) for symmetric encryption, and HKDF-SHA256 for key derivation.
Can I use Contacts on multiple devices?
Short answer
Yes. Sign in on any device by re-entering your three secrets and the same keys are derived locally, so your Contacts content follows you. Changes sync live across all signed-in devices.
Is Contacts GDPR-compliant?
Short answer
Yes. UltimaOS is built and operated in the European Union by an EU company. The architecture is GDPR-compliant by design — encrypted data, EU-only infrastructure, no US CLOUD Act exposure, no advertising, no third-party trackers. See the GDPR page for the full breakdown.
How much does Contacts cost?
Short answer
UltimaOS is free for individuals and families — permanently, not as a trial. Organizations pay per seat once early access ends, and that is what funds the free accounts. There is no per-app add-on.
Can I export my Contacts data?
Short answer
Yes. UltimaOS supports encrypted export of all your content for backup and portability. The export is encrypted to a key you control; you can store it on your own infrastructure or in a personal encrypted backup.
Can I import my existing contacts?
Short answer
Yes. Contacts can be imported from a vCard file or from another address book. Each imported contact is encrypted before being added to your Personal Storage layer.