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What we can and can’t see

Lastward is honest about its privacy boundary: The one-line version: we can see that a switch exists and when it fires — never what’s inside.

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How the encryption works

Your files and secrets (and, if you choose, your messages) are zero-knowledge:
1

Encrypted on your device

When you save an encrypted item, your device encrypts it with a strong modern cipher (XChaCha20-Poly1305). The key is derived from a passphrase you choose (via Argon2id). Only the ciphertext ever leaves your device.
2

Share the passphrase out-of-band

You give the passphrase to your recipient outside the app — in a will, a sealed envelope, or in person. We never see it, so we can’t lose it or hand it over.
3

Your recipient decrypts in their browser

When the switch fires, your recipient opens a link and enters the passphrase. Decryption happens entirely in their browser — the passphrase is never sent to us.
Because it’s truly zero-knowledge, if the passphrase is lost, the content cannot be recovered — not even by us. That’s the point. Record it somewhere durable (the same place you’d keep a will) and make sure your recipient will have it.

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Readable messages

Not everything has to be encrypted. For a plain, low-stakes message you can choose readable delivery — a normal email your recipient just reads, no passphrase needed. It’s clearly labelled as not encrypted when you choose it. Files and secrets are always zero-knowledge.

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Your own account

Your account is always recoverable by email, independently of any switch passphrase. So forgetting a passphrase never locks you out of managing your switches — only out of reading that one old encrypted payload.