Is Hejje end-to-end encrypted?

Yes. Activities, routes, workouts, meals, weight, photos, goals and settings are encrypted on the phone with keys that are created there and never sent to Hejje, and the server stores ciphertext it has no key for. A short list stays readable so accounts and following can work, and the server can still see metadata such as when a record was saved and roughly how large it is.

What does end-to-end encrypted mean for a fitness app?

It means your training is locked on your own device, with a key only your devices hold, before it is uploaded. The company stores and moves the data but cannot read it. That is different from encryption in transit and at rest, which most fitness services use: it keeps outsiders out, but the company holds the keys and can read everything.

Which encryption does Hejje use?

Standard, published primitives. AES-256-GCM seals each record with its own random key. Those keys are sealed by a vault key held on your devices, and the vault key is backed up under a 28 character recovery key with 128 bits of randomness. Ed25519 signs every request the phone makes, in place of a password, and X25519 is used to hand a key to someone you share with.

Can Hejje staff see my workouts?

No. There is no admin view of anyone's training and no key to build one with. What staff could see is the readable list: your first name and handle, public key, profile and banner images, who follows whom, and device names, app versions and last-seen times.

Does end-to-end encryption stop the app working offline?

No. Encryption happens on the phone at the moment you save, and the whole app runs from a database on the device, so recording and reading back history work with no signal. Sync catches up, sealed, the next time the phone is online.

Is Hejje open source or audited?

Neither yet. The apps are not open source and the design has not been independently audited, so the encryption claim currently rests on what Hejje publishes: this page, the table of what the server stores in the blog post What our server can actually see, and the privacy policy, which is the document that binds.

End-to-End Encrypted Fitness Tracker: How It Works

What end-to-end encrypted means for a fitness app

End-to-end encryption means your data is locked on your own device, with a key only your devices hold, before it goes anywhere. The company in the middle stores it and moves it, and cannot read it.

Most fitness services describe something else: encryption in transit and at rest. That protects your routes from someone on the same Wi-Fi and from a thief who walks off with a disk. The company still holds the keys, so it can read your training, analyse it, hand it over, or lose it in readable form. Both get called encryption. Only one of them keeps the operator out.

The quick test

If a service can give you back your full history after you have lost every device and reset your password with nothing but an email, it holds a key to your data. Whatever the marketing says, that is not end-to-end encryption.

How Hejje does it: three keys, all made on your phone

Hejje uses envelope encryption, which is keys inside keys. Each layer is locked by the one above it, and our server only ever holds the locked versions.

The three layers of keys in Hejje, and where each one lives.
Key	What it is	Where it lives
Record key	A fresh random key for each thing you save: an activity with its route, a meal, a weigh-in.	Locked by your vault key and stored beside the record it opens.
Vault key	One random key that locks all of your record keys.	On your devices, in Android Keystore or the iOS Keychain, plus a copy locked by your recovery key so a new phone can get back in.
Recovery key	28 characters carrying 128 bits of randomness, shown once when you create your account.	Wherever you wrote it down. Never on our server.

The building blocks are standard, published ones, not anything home-made. AES-256-GCM seals the records. Ed25519 signs every request your phone sends, which is how you log in, because there is no password. X25519 is used to hand a key to someone you choose to share with.

The record key layer is what makes sharing one session possible without exposing the rest: one key can be passed on while every other record stays shut. And because the recovery key is 128 random bits rather than a password you picked, there is no weak secret for anyone to guess. That is why it is long, and why the app shows it to you instead of asking you to choose one.

What is sealed, what is readable, and what is neither

A server that routes accounts and follow requests has to be able to read a little. The useful question is exactly how little, so here is the whole answer in three groups.

Sealed: routes, distance, pace, elevation, heart rate, sets, reps and weights, meals, calories and water, body weight, steps, the photos and videos on an activity, goals and settings, and the contents of anything you share.
Readable, because accounts and following need it: your first name and handle, your public key, profile and banner images, who follows whom, and device names, app versions and last-seen times. If you subscribe to Premium, also the purchase record Google Play sends, which carries no card details and no training data.
Metadata, which encryption does not hide: which kind of record arrived, when it was saved, how many there are and how large each one is, and that you sent something to a given follower.

That last group is the honest limit. We could tell that a run was saved on Thursday evening and a longer one on Sunday morning, without seeing either. Hiding it would mean padding every record to one size and delaying uploads away from when you train, which costs battery and data, and we decided against it. Every row of the server's database is listed in what our server can actually see.

Sharing a session without opening the vault

A follow request is sealed to the other person's public key and signed with yours, so our server can deliver it but can neither read it nor forge one. When they accept, their phone makes a key for that one direction of that one relationship and sends it back, sealed the same way.

From then on, each session you choose to share is sealed with that key and left in a mailbox our server holds and cannot open. Unshare it or delete it and the withdrawal travels the same way. If two people follow each other, that is two unrelated keys, one in each direction.

What end-to-end encryption does not protect

Your phone itself. On the device the app works with your data unlocked, guarded by your screen lock and the phone's own storage encryption, like any other app. End-to-end encryption is about what leaves the phone.
What you share. A follower's app shows them the sessions you sent. From there they can see them, and screenshot them, like anything else on their screen.
The shape of your data. The metadata above.
Our word, for now. Hejje is not open source and the design has not been independently audited, so today the claim rests on this page, the blog post and the privacy policy rather than on code you can read yourself.

What it costs, and what it rules out

The recovery key is the only way back into your vault on a new phone. We never receive it, so we cannot reset it, and if the key and your phone are both gone, the synced history is gone with them. Every service that can reset an account for you can also be pressured, tricked or breached into opening it for someone else. We took the other side of that trade.

Some features need a server that can read everybody's training, so Hejje cannot have them: segment leaderboards, a global heatmap of routes, and cloud-to-cloud links with watch makers, which deliver your workouts to the app's server unencrypted.

How to check any app that says it is end-to-end encrypted

These questions work on any fitness app, including this one. The answers are usually in the privacy policy, or conspicuously missing from it.

Who makes the keys? They should be generated on your device. If the server issues them, it can keep a copy.
What happens if you forget your password? If the answer is an email link and all of your history is still there afterwards, the company can open it.
What can the server read? A serious answer is a list. "Everything is encrypted" with no list is a slogan.
Does it mention metadata? Every app that syncs leaks some. One that says so is more likely to be telling the truth about the rest.
Can it be checked? Open source code or an independent audit beats a promise. By that test Hejje is currently a promise, and says so above.

An end-to-end encrypted fitness tracker, and what that actually covers