When a message is end-to-end encrypted (E2EE), only people with a matching private key can read its body and attachments. The server cannot. SipherMail encrypts automatically in one case and leaves the rest to you.
When a message is encrypted automatically#
A message is end-to-end encrypted automatically when both of these are true at the moment you send it:
- You are in Privacy mode, you have an encryption key, and Encrypt automatically to SipherMail users in Privacy Mode is on in Settings > Encryption. It is on by default.
- Every recipient, including Cc and Bcc, is a SipherMail address whose owner is in Privacy mode and has a key.
Otherwise the message is sent without end-to-end encryption. The composer shows which addresses stop it, and why, before you send.
What that means in practice:
- An account in AI mode does not send or receive automatically encrypted mail. Its mail stays readable so Sipher AI can work on it. Switching to Privacy mode changes this for new mail.
- People at other providers are never encrypted to automatically. You can choose to encrypt to them with PGP when they have an OpenPGP key, or send an expiring or password-protected message.
- Shared inboxes are not covered.
- The body, attachments and inline images are encrypted. The subject line, sender, recipients and dates are not.
- Mail that arrived without end-to-end encryption stays readable to the server. See How we protect your data.
Requirements#
- You need your own keys.
- Each recipient needs a public key. Without one you cannot send them an encrypted message.
- E2EE cannot be combined with an expiring or password-protected message.
Set up on the web#
- Go to Settings > Encryption.
- Choose Generate Keys.
- Enter a passphrase and confirm it.
- Turn on Show E2EE in composer.
Your passphrase is separate from your login password.
Encrypt a message yourself#
- Open the composer.
- Click End-to-End Encrypt. The button reads End-to-End Encrypted when on.
- Write and send as usual.
Received encrypted messages ask for your passphrase to open.
On iPhone and Android#
The app can set encryption up for you. It keeps a random passphrase in the device keychain. Create a recovery phrase when the app offers it: the 12 words are the only way to open your encrypted mail on a new phone or after a reinstall. The Encryption screen also has Auto-Encrypt Replies, which encrypts replies to encrypted emails, and Clear Passphrase Cache.
How it works#
| Part | What is used |
|---|---|
| Message, attachments and inline images | OpenPGP (PGP/MIME), encrypted to each recipient’s key and your own, and signed |
| Keys | Curve25519: Ed25519 for signing, X25519 for encryption |
| Your private key | Encrypted with AES-256-GCM, using a key derived from your passphrase with PBKDF2 (310,000 iterations), and stored on the server |
OpenPGP is an open standard, so the same format works with other OpenPGP software. Messages in the earlier SIPHER-E2EE-V1 format stay readable.
Regenerating keys#
Regenerate Keys replaces your keys. Messages encrypted with the old keys become unreadable. This cannot be undone.