Encryption

Every message is encrypted. Every mail, every chat, every group.

Your message is encrypted on your device before it leaves. Only the recipients' devices can open it — not us, not our hosting provider, not anyone in between. Our server holds locked copies it cannot open.

How it works, in plain words

Two keys, one lock, and a server that only ever sees the locked box

You do not need to understand the mathematics. Four steps cover everything that happens to a message on Private.Ki.

Your device makes a pair of keys
When you sign up, your device creates two keys. The public key is like a padlock: anyone can use it to lock something for you. The private key is the only key that opens it. It never leaves your device and is protected by your passphrase.
You write, your device locks
When you write to someone, your device fetches their public key — their padlock — and locks the message with it. This happens before anything is sent.
The server passes on the locked box
Our server relays and stores only the locked message. It has no key that opens it, and it never had one. That is what "we cannot read it" means, literally.
The recipient's device unlocks it
Only the recipient's private key fits the padlock. Their device opens the message locally, and the app shows a padlock next to it: encrypted, and signed by you.

Groups work the same way — once per member

One message, locked once for every member of the group. Each member's device unlocks its own copy with its own private key. The server still sees only locked copies, however many people are in the group.

A group of three: the message is locked three times, one padlock per member. Adding a fourth member means a fourth locked copy of every new message — and nothing of what was said before, because those messages were never locked for them.

There is no such thing as an unencrypted chat or group on Private.Ki. There is no setting to turn encryption off, no "secret chat" mode that is safer than the ordinary one, and no group type that skips it. Every mail, every chat message, every group message, every attachment and every voice note goes through the four steps above.

What exactly is encrypted

The content, always. The addressing, never — because delivery needs it.

"End to end" means locked on your device and opened on theirs, with nobody in between able to read it. Here is the complete list of what is and is not inside the locked box.

What	Encrypted end to end?	Detail
Mail
Mail body, between Private.Ki users	Yes	Locked on your device with the recipient's public key.
Mail subject, between Private.Ki users	Yes	The subject travels inside the locked message.
Attachments — file name and contents	Yes	Up to 25 MB per file. The server sees only how many and how large.
Mail to or from other providers (Gmail, Outlook, a company server)	Yes, when they have a PGP key	We look up their public key, or you import it. Without a key, the mail is delivered normally and clearly flagged as not encrypted.
Chat and groups
Chat messages	Yes	Every message, in every chat.
Group messages	Yes	Locked once per member.
Reactions and emoji	Yes	They travel inside encrypted messages, including which message they belong to.
Voice messages	Yes	Recorded on your device, encrypted like any other attachment.
Unsend and destroy instructions	Yes	The server cannot tell which message an unsend refers to.
Self‑destruct timers on messages	Yes	Which messages and what delay stay inside the encrypted content. The server only sees that a conversation has a timer at all.
Not encrypted — the server needs it to deliver
Who wrote to whom, and when	No	Delivery metadata. Any service that delivers mail has this.
Message sizes, attachment counts, group membership	No	Needed to store and route the locked copies.
Headers of mail arriving from other providers	No	Sender, recipients, subject and dates arrive readable over ordinary SMTP. We encrypt the whole mail to your key the moment it lands, but we saw the headers first.
Your public key	No	Public by design — it is the padlock other people use to write to you.

The full, maintained list of both columns lives on one page: What our server can and cannot see →

Your keys

Made on your device. Protected by a passphrase we never see.

Your key pair is generated on your device during sign‑up. The public key is published so people can write to you. The private key is encrypted with a key derived from your passphrase and is stored only in that encrypted form — on your device, and as an encrypted blob on our server so your other devices can fetch it.

The passphrase itself is never sent to us. That is deliberate, and it has a consequence: we cannot reset it. If you lose your passphrase, there are zero ways to recover your key — not for us, not for anyone. The app makes you acknowledge this before the key is created.

A recovery address, if you set one, is for account notices. It cannot recover a passphrase.

Generated on your deviceLong and random, shown to you once during sign‑up. Write it down somewhere safe.

Export your public keyGive it to anyone, on any provider, who wants to write to you encrypted.

Import theirsPaste someone's public key and mail you send to that address is encrypted from then on.

For the technically minded

The same story, with the real names

Everything above uses standard, published cryptography. Nothing is proprietary, and nothing depends on trusting us.

Keys

Each account has an Ed25519 key pair generated on the device with OpenPGP.js. The private key is encrypted with a master key derived from the passphrase (HKDF‑SHA‑256) and stored only in encrypted form. The passphrase and the master key never leave the device.

Messages

Every message body — mail or chat — is encrypted with AES‑256‑GCM under a fresh session key. That session key is encrypted to each recipient's public key using standard OpenPGP packaging, once per recipient. Messages are signed with the sender's private key; the app shows a padlock for encryption and a shield for a valid signature on every message.

Attachments, voice, reactions

Attachments and voice messages are encrypted on the device before upload and stored as ciphertext (25 MB per file). Reactions, unsend and destroy instructions and per‑message timers are carried inside encrypted messages, so the server cannot see what they refer to.

Transport and server

All traffic runs over TLS, on top of the end‑to‑end layer. The server stores ciphertext, public keys and delivery metadata. Mail from other providers arrives over SMTP and is encrypted to your key on arrival; its headers are readable to us at that moment.

Sign‑in and sessions

Sign‑in uses OPAQUE, so your password is never transmitted. Sessions are bound to a key on your device with DPoP. These protect access to your account; they are not part of message encryption. Details on the Account security page.

Audit status

An independent security audit is on our roadmap and has not been published yet. We say so rather than imply otherwise.

One address. Everything on it encrypted.

Free, no phone number, no invitation. Your keys are made on your device the moment you sign up.

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