Myle is a fitness app where every health metric is encrypted on your phone with fully homomorphic encryption (FHE) before it leaves your device. Even we cannot read your workouts. This policy explains exactly what is collected, where it goes, and what we never see.
Where your encrypted data lives. Myle stores your encrypted records on a public blockchain network operated by independent third parties. Records on the chain are permanent — neither we nor anyone else can alter or delete them. We don't control that network; as with any decentralized infrastructure, its long-term availability is outside our control. See the Terms for details.
Not a cryptocurrency product. Myle does not handle, custody, transfer, or display any token or asset of monetary value, and does not and will not introduce such functionality. The blockchain referenced throughout this policy is used only as an append-only storage substrate for FHE-encrypted health values.
1. What we collect
1.1 Health data (encrypted before transmission)
With your permission, Myle reads workout summaries from Apple HealthKit: total distance, duration, workout type, and start time. These values are encrypted on your phone via the Fhenix CoFHE SDK before anything is sent over the network. The ciphertexts are stored on-chain as ciphertext on a public blockchain. The plaintext values never travel off the device.
We do not read your GPS route, your location, your nutrition data, your sleep, your menstrual data, or any health sample outside the workout summary fields listed above.
1.2 Profile data (you provide)
When you create an account, you choose a public handle and may optionally add a display name, avatar, and short bio. These are stored on our backend so other Myle users can find you by handle.
1.3 Account and authentication data
We use Privy for sign-in via a one-time email code, and to create the on-device key that secures your account. Myle stores your Privy user ID and your account address to associate them with your profile.
We use Pimlico to sponsor all network costs so you never pay a fee. Pimlico sees your account address and transaction calldata when it relays your operations; it does not see plaintext health values.
1.4 Diagnostic data
We do not use any third-party crash-reporting or analytics service. We rely on Apple's built-in App Store crash aggregation (which produces anonymized counts and stack traces) and on your own bug reports. No workout values are ever sent to any analytics or telemetry endpoint.
2. What we never see or store
- Plaintext distance or duration from any workout.
- Your GPS route, location, or any geographic data.
- Any HealthKit category we did not list above.
- Your encryption keys — they live in your Privy-secured account on your device, not on our servers.
- Advertising identifiers (IDFA/IDFV). We do not run advertising.
- Cross-site behavioral profiles. We do not track you across other apps or websites.
3. How encryption works (in one paragraph)
When you log a run, the values are encrypted on your device with the Fhenix CoFHE SDK, bound to your own account. Your phone submits the resulting ciphertext to the on-chainRunsCorecontract. Plaintext never leaves the phone, so our servers only ever see ciphertext and cannot decrypt it. Your aggregate stats (weekly, monthly, and lifetime distance and your personal bests) are computed on your device after you decrypt your own runs — only you hold the key. Achievement proofs are verified on-chain using fully homomorphic encryption, so a threshold like “5K” can be confirmed without ever exposing the underlying value.
4. Third-party services
We rely on these vendors. Their privacy policies are linked.
- Privy — email sign-in and on-device account key. Policy
- Pimlico — ERC-4337 bundler and paymaster. Policy
- Fhenix CoFHE — FHE coprocessor and SDK. Site
- Neon — Postgres database for profiles and friend graph only. No health data. Policy
- Fly.io — backend hosting. Policy
- Apple Push Notification service — message delivery.
5. Sharing with friends
You control who can decrypt your aggregates. When you accept a friend request, you sign an on-chain transaction that grants that friend permission to decrypt the specific metrics you choose. You can revoke access at any time. Revocation prevents future decryptions; data a friend already saw cannot be un-seen — this is a property of cryptography, not a limitation we can fix.
6. Account deletion
You can delete your account from the Profile screen inside the app, or by emailing myle@fhenix.io. Deletion removes your profile row, your friendships, and your push tokens from our backend.
What deletion cannot reverse: the encrypted ciphertexts you previously submitted on-chain. Blockchains are append-only by design. Those records remain on the blockchain indefinitely, but only the holder of the decryption key (you) can decrypt them. If you also lose access to your account, the records become permanently unreadable to everyone.
7. Security
Health values are encrypted before transmission. Our backend communicates over HTTPS only. Production secrets are held in Fly.io's secret store, not in source files.
FHE is a young field of cryptography. We rely on the Fhenix CoFHE protocol for the underlying primitives. No system is unbreakable; if a critical vulnerability is discovered in the FHE stack, we will notify users and may pause the on-chain features.
8. Children
Myle is not directed to children under 17. We do not knowingly collect data from users under 17. If you are a parent or guardian and believe your child has provided us information, please contact us and we will delete it.
9. International users
Our backend operates from Fly.io regions in the United States. Using Myle requires transmitting data into the United States. We do not sell your data and do not have advertising trackers.
10. Changes
We will update this policy as Myle evolves. If we make a material change, we will notify active users by push notification, in-app message, or email associated with your Privy account. The “Effective” date at the top tracks the most recent revision.
11. Contact
All inquiries — privacy, data requests, account deletion, general support, security disclosures — myle@fhenix.io.