PrivateFamily / Encryption explained
Encryption explained
PrivateFamily is the end-to-end encrypted family photo album: here, step by step, is how we encrypt your photos before they're sent, what the server actually sees, and what's still left to encrypt. No overselling, no unnecessary jargon.
Step by step
Here's precisely what happens, technically, between the moment you tap "send" and the moment your mother opens the photo on her phone.
As soon as you pick a photo, the app splits it into 1 MiB blocks and encrypts each one with your family's secret key — a key generated on that device, never anywhere else. What heads to the server is no longer a photo at all: it's an unreadable string of bytes.
The server receives these encrypted bytes, stores them as they are, and will serve them as they are later on. It doesn't hold the key: it can't open them, generate a preview, or guess what they show.
When a family member opens the album, their phone downloads those same encrypted bytes and decrypts them locally, with its own copy of the family key. The photo never exists unencrypted on any server, at any point.
Two ways to understand it
Two ways to read this, depending on what reassures you most: a simple picture, or the exact cryptographic mechanisms we use.
Picture every photo leaving your phone already locked inside a sealed box. Only the people in your family hold the key to that box — a key made by a phone, never typed on a keyboard, never sent by email.
The server only stacks sealed boxes on a shelf: it can count them, move them around, hand them to the right person. It can't open them. And when you invite someone close to you, it's your phone — never the server — that quietly slips them a copy of the key.
Authenticated encryption with XChaCha20-Poly1305-IETF, via the react-native-libsodium library. The family key ("FDK") is 256 bits (32 bytes), generated at random on the device with randombytes_buf — never derived from a password.
PrivateFamily
Keychain / Android Keystore, via expo-secure-store — never in the app's regular storage, never transmitted over the network.crypto_pwhash, libsodium's INTERACTIVE preset) to recover the family key from the recovery phrase.In full transparency
Encryption protects the content of your photos and videos. It doesn't make the server blind to everything: here, plainly, is the exact line between what's encrypted today and what isn't yet.
Encrypted end to end: the server only stores and serves opaque bytes. It can't generate a single thumbnail, read any EXIF metadata, or know the dimensions except through whatever the app itself declares to it.
Metadata, never the content: the exact date and time each photo was taken (captured_at), the size and SHA-256 hash of the encrypted file, the image dimensions, and who sent, viewed, reacted to, or commented on it — via an internal account ID.
Captions, comments, children's first names and birthdates, growth and milestone notes, family and member names, reaction emojis: end-to-end encrypted, with the same key as your photos.
Two honest nuances: numeric growth values (height, weight) stay in plaintext — only their date and notes are encrypted. Your account name, used to sign you back in on a new device, stays separate and unencrypted; it's the name shown to other members within each family that is.
Another honest limitation: video playback currently downloads and decrypts the entire video before playing it. There's no real-time streaming decryption yet.
Frequently asked questions
The exact capture date (captured_at) is used to automatically sort your photos into the timeline, by month and year — sorting that currently happens server-side, which requires the server to know that date in plaintext. It's metadata about the photo, never its content: it doesn't show anyone what's actually in the picture.
Another admin or co-admin in your family can restore your access within seconds. If you're the only admin, the 12-word recovery phrase you received when the family was created lets you recover everything on a new device.
No, there's no perceptible difference. Encryption happens on your phone, at the same moment the app is already compressing the photo before sending it — a step that happened anyway.
Because a password chosen and remembered by humans is almost always weaker than a 256-bit key generated at random by a device. That key never even needs to be typed day to day: only the recovery phrase exists, as a personal safety net for each admin, meant to be used only if a device is lost.
Yes, since August 31, 2026: captions, comments, children's first names and birthdates, growth and milestone notes, family and member names, and reactions are all end-to-end encrypted with the same key as your photos. The only exceptions, for technical reasons: numeric growth values (height, weight) and your account name (used to sign you back in on a new device) stay in plaintext.
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Free for up to 10 photos. Two minutes to set up your family.
