Security — Syncer

The encryption model

One clipboard key that only your devices hold, Signal-verified pairing, and a relay that can route your clips but never read them.

One key, only on your devices

Every synced clip is sealed with a single clipboard key that lives only on the devices you've paired — and nowhere else. Any of them (your laptop, your phone, even the Syncer keyboard) can open a clip, because they all hold that key.

It's generated on your device and only ever leaves it wrapped — sealed individually for each of your other devices — so the server relays and stores copies it has no way to unwrap. Clips are encrypted with XChaCha20-Poly1305.

Signal secures pairing, not your clips

Syncer uses the Signal Protocol — the vetted encryption behind Signal and WhatsApp — to verify device identities and hand your clipboard key safely from an existing device to a new one.

Your clips themselves aren't Signal messages. Signal's job here is trust and key exchange — not carrying or storing your clipboard.

Device pairing & approval

New devices are added through an explicit pairing step — scan a QR code or enter a 6-digit code, then approve from an existing device. You can compare a safety fingerprint to verify there's no impostor in the middle, and revoke any device's access instantly.

A relay that only sees ciphertext

Our servers relay opaque encrypted blobs and never receive the key to open them. A payload is deleted the moment your device fetches it, and anything unfetched expires from the relay within 7 days.

All the server keeps is what it needs to route sealed data: your public device bundles, the per-device wrapped copies of your clipboard key (which it can't unwrap), and — only if you turn it on — your backup ciphertext.

The honest trade-off

We'd rather tell you where the line is than let you assume.

Syncer's shared clipboard key is not the same as the per-message forward secrecy you get from a 1:1 messenger. In a messenger, every message is sealed with its own fresh key. In Syncer, your devices deliberately share one key so that any of them — including the keyboard, which can't run a full handshake — can read any clip the instant it arrives.

That key rotates periodically — each rotation period is an epoch — so if a key were ever compromised, the exposure is bounded to that window, not your entire history. It's the conscious trade for a clipboard that appears everywhere, instantly, on every surface.

When you need more, you have it: “send as secret” seals a single item to one specific device only, and it's never fanned out to your other devices or included in a backup.

PIN-protected backups

Keep your history if a device is lost — without handing us your keys.

Backups are optional and, like everything else, encrypted on your device. We derive a strong key from your PIN and use it to seal the backup so that only someone with the PIN can restore it.

Your PIN never leaves the device. We never see it, can't reset it, and can't recover a backup without it. The cryptography that protects your backup:

Argon2id key derivation HKDF key expansion AES-256-GCM authenticated encryption

Argon2id makes brute-forcing your PIN deliberately expensive, HKDF derives distinct keys for distinct purposes, and AES-256-GCM both encrypts and authenticates the backup so tampering is detectable.

Built from established, well-studied cryptography

We didn't invent our own crypto. Device pairing and identity use the Signal Protocol — the public, widely scrutinized protocol used by Signal and WhatsApp. Clips are sealed with XChaCha20-Poly1305, and backups with Argon2id and AES-256-GCM — all standard, well-studied primitives. We document exactly how we use each one on this page, because we'd rather show our work than ask you to take it on faith.

Responsible disclosure

Found a vulnerability? Tell us.

We take security seriously and welcome reports from researchers. If you believe you've found a vulnerability in Syncer, please let us know so we can fix it and protect our users.

How to report

Email [email protected] with details and steps to reproduce. This address routes to the team. Please include enough information for us to reproduce and assess the issue, and give us reasonable time to respond before any public disclosure.

Our commitment: we'll acknowledge your report within a few business days, keep you updated as we investigate, and aim to ship a fix for valid issues within 90 days — sooner for anything actively exploitable.

Report to [email protected]

Scope

The Syncer apps (macOS, Windows, Linux, iOS, Android) and the backend relay and API.
Issues affecting the confidentiality, integrity, or availability of user data or the service.

Out of scope: attacks requiring physical access to a victim's unlocked device, social engineering of our staff or users, denial-of-service via traffic volume, and findings in third-party services we don't operate. When in doubt, ask.

Please do

Give us reasonable time to fix the issue before disclosing it publicly.
Only test against your own accounts and devices — avoid accessing, modifying, or deleting other people's data.
Avoid privacy violations, service disruption, and data destruction while testing.

Safe harbor. If you make a good-faith effort to comply with this policy during your research, we will consider your testing authorized, will work with you to understand and resolve the issue quickly, and will not pursue or support legal action against you for that research.

No bounty program (yet)

We're honest about where we are: Syncer does not currently offer a paid bug-bounty program. We deeply appreciate responsible reports and will credit researchers who wish to be acknowledged. If and when we launch a bounty program, we'll announce it here.

A machine-readable contact is published at /.well-known/security.txt. For anything else, email [email protected].