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arXiv · 2507.21122

Kintsugi: Decentralized E2EE Key Recovery

Emilie Ma·Martin Kleppmann
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Abstract

Kintsugi is a protocol for key recovery, allowing a user to regain access to end-to-end encrypted data after they have lost their device, but still have their (potentially low-entropy) password. Existing E2EE key recovery methods, such as those deployed by Signal and WhatsApp, centralize trust by relying on servers administered by a single provider. Kintsugi is decentralized, distributing trust over multiple recovery nodes, which could be servers run by independent parties, or end user devices in a peer-to-peer setting. To recover a user's keys, a threshold $t+1$ of recovery nodes must assist the user in decrypting a shared backup. Kintsugi is password-authenticated and protects against offline brute-force password guessing without requiring any specialized secure hardware. Kintsugi can tolerate up to $t$ honest-but-curious colluding recovery nodes, as well as $n - t - 1$ offline nodes, and operates safely in an asynchronous network model where messages can be arbitrarily delayed.

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Emilie Ma, Martin Kleppmann. 2025-07-18. Kintsugi: Decentralized E2EE Key Recovery. https://arxiv.org/abs/2507.21122

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