01 — Keys
Keys stay on your devices
Each device makes its own encryption keys when you install sync.photos. Private keys never leave the device, and we never receive a copy.
Security
Security
by design.
Your library moves only between devices you paired yourself. Here is how that works, what our servers can and can’t see, and how to tell us about a problem.
01–06 — Layers
Six layers between your photos and anyone else.
02 — Pairing
Six matching digits
Pairing starts with a QR code and finishes only when you confirm that both screens show the same six digits. A device that shows different digits is not yours: cancel, and nothing is shared.
03 — Encryption
End-to-end encrypted
Photos, videos, dates, places and album names are encrypted on the sending device and can be read only by the paired device receiving them, nearby or over the internet.
04 — Account
No account to steal
There is no email, phone number or password, so there is no login to phish and no account database to breach. Trust lives in the devices you paired.
05 — Exclusions
Filtered before sending
Albums you keep off a device and photos marked Never Sync are filtered out before anything is sent. The other device never learns they exist, not even their names or dates.
06 — Cryptography
No home-made crypto
Every connection uses TLS 1.3, the standard behind secure websites, authenticated with each device’s own Ed25519 key. We do not invent our own cryptography.
07 — What our servers see
A tiny helper, nothing more.
Nearby sync needs no server at all. For internet sync, a small connection service introduces your devices to each other, then steps aside.
Connection service
Introductions only.
It helps two of your devices find each other over the internet. It never receives photos, and it cannot read what your devices send each other.
Handles briefly
- Temporary session IDs
- IP addresses
Never sees
- Photos and videos
- File names, dates and places
- Album names
- Pairing codes
Relay
If a relay is used, it stays encrypted.
Sometimes two devices can’t connect directly over the internet. If relay is enabled, encrypted traffic may pass through a relay server, which forwards data it cannot read and does not store it.
Nearby sync
- Same Wi-Fi, no server involved
- Works with no internet
Internet sync
- Off by default
- Turn it on in Settings
08 — Honest limits
What security can’t promise.
The strongest protection is still the lock on each device.
No remote erase
Removing a device stops future syncs with it as soon as each of your other devices hears about the removal; a device that is offline learns of it the next time it connects. Photos already on the removed device stay there. If it is lost or stolen, erase it with Find My or Google’s Find Hub.
Your device lock matters
Anyone who can unlock a paired device can see the photos on it, like any other photo on that device. Use a passcode or biometric lock.
Other backups follow their own rules
If iCloud Photos or Google Photos backup is on, those services upload what arrives on that device under your account with them.
09 — Technical details
For the curious.
The same answers we would give a security reviewer.
Info — how the encryption worksStandard, reviewed
- Every connection
- TLS 1.3, with X25519 key exchange and AES-GCM or ChaCha20-Poly1305 encryption. Nearby and over the internet alike.
- Device keys
- Each device has its own Ed25519 key, kept in the iOS and macOS Keychain or the Android Keystore. It never leaves the device.
- Pairing
- The QR code carries the devices’ public keys. The six matching digits prove nobody swapped them, and from then on a device only talks to keys it has paired with.
- No internet needed
- On the same Wi-Fi there is no certificate authority, no server and no online lookup. Keys are checked device to device.
- Relays
- If a relay is used for internet sync, it only forwards encrypted packets it cannot read.
- Photo fingerprints
- Duplicates are found with keyed hashes (HMAC-SHA256), so nobody outside your devices can recognise a photo from them.
- Algorithms
- Only standard, publicly reviewed algorithms. No home-made cryptography.
10 — Report a vulnerability
Found a problem? Tell us.
We welcome reports from security researchers and users. Please write to hi@sync.photos. Our contact details are also published in security.txt.
- Describe the issue, the app and platform versions, and the steps to reproduce it.
- Give us reasonable time to investigate and fix it before you share details publicly.
- Never access, change or delete photos that are not yours while testing.
- We will acknowledge your report and keep you updated until it is resolved.