We formally study “non-malleable functions” (NMFs), a general cryptographic primitive which simplifies and relaxes “non-malleable one-way/hash functions” (NMOWHFs) introduced by Boldyreva et al. (Asiacrypt 2009) and refined by Baecher et al. (CT-RSA 2010). NMFs focus on basic functions, rather than one-way/hash functions considered in the literature of NMOWHFs. We mainly follow Baecher et al. t...

A new type of signature scheme, called NTRUSign, based on solving the approximately closest vector problem in a NTRU lattice was proposed at CT-RSA’03. However no security proof against chosen messages attack has been made for this scheme. In this paper, we show that NTRUSign signature scheme contains the weakness of malleability. From this, one can derive new valid signatures from any previous...