How Personal Sync Encryption Works

Personal Sync encrypts your Brains, documents and chats on your computer before they leave it, and only your own approved devices hold the keys to read them. The sync server stores encrypted data it cannot read.

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What syncs, and what stays on each computer

When you turn on Sync, Elephas tells you: “Brains, documents, and chat history will leave this device as end-to-end encrypted data. Search indexes, AI keys, and app settings stay local.” See What syncs for details.

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How it works

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Encrypted before it leaves

Each piece of synced data is encrypted on your computer with AES-256-GCM. Each Brain has its own key, and your chats have their own. The server receives only the encrypted result.

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Keys never leave your devices unprotected

Every device has its own key pair, created on that device and kept in Keychain (Mac) or Credential Manager (Windows). The private half never leaves the device. When a Brain key needs to reach another of your devices, it is encrypted to that device’s public key first, so the server only ever stores keys it cannot open. Your Elephas account is not the encryption key. Signing in proves who you are to the server; it does not unlock your data. As the warning in Elephas puts it: “Your Elephas account alone cannot unlock it.”

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Approving a new device with five words

A new device can only read your data after one of your existing devices approves it. The five words are computed on both devices from the details of that specific enrollment. Matching words prove that the two devices are talking to each other, and not to someone in the middle, including the sync server. Full steps: Add a device to Sync.

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There is no recovery

Before you turn on Sync, Elephas asks you to confirm: I understand there is no recovery. The reason is stated plainly in the app: there is no password reset and no recovery. If you lose every synced device, your synced data cannot be recovered by anyone, including Elephas. Your Elephas account alone cannot unlock it. This is the tradeoff of end-to-end encryption. Because Elephas does not hold a copy of your keys, Elephas cannot be made to open your data, and it also cannot restore it for you. To stay safe:

• Keep Sync on at least two computers.
• Keep your own backup of the original files you care about.

See Sync recovery.

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What the sync server can see

The server cannot read your documents, file names, Brain names or chats. To deliver data to the right devices, it does see:

• Your account and which devices belong to it, including each device’s name and platform (Mac or Windows)
• Random IDs for Brains, items and devices, and the order of changes
• When changes happen and the size of the encrypted data

Sizes and timing can reveal some information about activity, such as when you add a large file. They do not reveal content.

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Removing a device

Revoking a device cuts off its future access, and Elephas rotates the keys so the removed device cannot read anything new. Data already synced to that device cannot be erased remotely. See Remove a device.

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Sync and AI are separate

Personal Sync moves your knowledge between your own devices as encrypted data. It is separate from cloud AI, which only receives what you send in a chat. See What data is sent to AI.

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Troubleshooting

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