PearPetal

PearPetal has no server that stores or reads your data. Your cycle log lives only on your own phones. When you share with a partner, they get only the slice you choose, and they can never edit it or pass it on. Devices talk to each other directly, encrypted end to end. No company, including PeerLoom, can read your cycle. On the rare networks where two devices cannot reach each other directly, the connection is passed along by a relay we run, which carries the same scrambled data and cannot read any of it.

Most cycle trackers send your log to the company's server, and your partner's app reads it from there. The server holds everything. In a peer to peer app, phones talk directly to each other, with no server in the middle reading or keeping anything.

Think of email versus a handwritten letter. Email passes through several companies that could read it. A letter goes from your hand to your recipient's hand. PearPetal works more like the letter.

If there is no central server, how do your phone and your partner's phone find each other?

PearPetal uses a distributed hash table, or DHT, the same technology that powers BitTorrent. A DHT is a phone book that no one company owns. It is spread across thousands of devices around the world. When your phones come online, they ask the DHT for each other and it helps them connect, whether they are on the same Wi-Fi or on opposite sides of the world.

The DHT only helps devices find each other. It never sees the data they exchange.

Sometimes a direct connection cannot be made at all. A few home routers and mobile carriers are set up so that two devices cannot reach each other however many times they try. For those cases PearPetal can route the connection through a relay that PeerLoom runs. It carries the same encrypted traffic the devices would have exchanged directly, it cannot read any of it, it stores nothing and it can be turned off. Like any relay, it can see that two devices are talking and how much data passes between them, but not that the app is PearPetal. It is only tried after a direct connection has already failed. Details: The PeerLoom relay.

PearPetal stores the following on your phone, and on any of your own phones you link:

• Your cycle log: period dates and flow, plus any symptoms, mood, notes or temperatures you record.
• Your goal and cycle preferences, including any conditions or birth control you enter.
• Predictions such as your fertile window and next period, worked out on your phone.
• The name and optional photo you choose for yourself.
• The cryptographic keys that identify your devices, and any partner you share with, to each other.
• App preferences such as your flower and reminder settings.

None of it is uploaded to PeerLoom or any third party.

PearPetal keeps your full log and anything you share in two separate stores, each with its own encryption:

• Your private log only syncs between your own phones. Its key is never given to a partner.
• A shared view for each partner holds only the scope you agreed to: cycle phase only, your fertile window or your full cycle. You write it and your partner can only read it.

Predictions are worked out on your phone and are never put in the shared view or sent over the network. Ending a share stops it from then on. It cannot take back what your partner has already seen, so share deliberately.

• End to end encryption. Everything your devices exchange is encrypted with keys that only those devices hold. Anyone watching your Wi-Fi, your mobile carrier or the wider internet sees scrambled bytes.
• Cryptographic signing. Every entry is signed by the device that wrote it. A partner's phone cannot forge entries in your log.

Most cycle trackers ask you to create an account and upload your log to the company's servers. For health data this sensitive, that has real costs:

• The company can read your cycle, fertility and pregnancy data.
• If the company gets hacked, your log leaks along with everyone else's.
• The company can be asked or forced to hand your data over.
• If the company shuts down, your history may go with it.

PearPetal has no account to hack, no server to leak or hand over and no company holding your history.

• Phones need to be online at the same time to sync. You can always read and edit your own log offline. Changes reach your other phone or your partner the next time both can connect.
• On iPhone, sharing catches up when the app is open, because iOS pauses apps in the background.
• No web dashboard. There is no website where you can log in and see your cycle, because no server holds it. PearPetal is a phone app only.
• No automatic cloud backup. Export a backup file from Settings now and then, so a lost phone does not mean a lost history.

You do not have to take our word for any of this. PearPetal is fully open source. The complete code, including the sync and encryption, is published at github.com/peerloomllc/pearpetal.

• Full privacy policy
• Hypercore Protocol. The peer to peer technology that powers PearPetal sync.