Paper 2025/1799 Original: eprint.iacr.org/2025/1799 ↗

Unforgettable Fuzzy Extractor: Practical Construction and Security Model

Abstract

Secure storage of private keys is a challenge. Seed phrases were introduced in 2013 to allow wallet owners to remember a secret without storing it electronically or writing it down. Still, very few people can remember even 12 random words. This paper proposes an alternative recovery option that utilizes lower-than-standard entropy secrets (such as passwords, biometrics, and object extractors). It can be used on its own (in combination with strong key derivation functions) or provide an additional backup option for the existing mnemonics. In this work, we investigate several aspects of secure key derivation: (1) how much entropy different sources can provide; (2) what is the preferred construction of the fuzzy extractor; (3) our key contributions in the selected approach; (4) the main security assumptions and properties of Unforgettable Fuzzy Extractor; (5) economic rationale for parameters (e.g., fuzzy vault size, additional PoW difficulty, secret length, cost of the attack) achieving the optimal solution from both security and time perspectives.