[Research] Chameleon-Hashes

[FantasticoFox]

Source: https://eprint.iacr.org/2017/011.pdf
@phil-jakubeit

Abstract. A chameleon-hash function is a hash function that involves a
trapdoor the knowledge of which allows one to find arbitrary collisions
in the domain of the function. In this paper, we introduce the notion of
chameleon-hash functions with ephemeral trapdoors. Such hash functions
feature additional, i.e., ephemeral, trapdoors which are chosen by the
party computing a hash value. The holder of the main trapdoor is then
unable to find a second pre-image of a hash value unless also provided
with the ephemeral trapdoor used to compute the hash value. We present
a formal security model for this new primitive as well as provably secure
instantiations. The first instantiation is a generic black-box construction
from any secure chameleon-hash function. We further provide three direct
constructions based on standard assumptions. Our new primitive has
some appealing use-cases, including a solution to the long-standing open
problem of invisible sanitizable signatures, which we also present.