Abstract— We propose an attack on the recent attempt by Li,
Xing and Yeo to produce a code-based signature scheme using
the Schnorr-Lyubashevsky approach in the Hamming metric, and
verify its effectiveness through numerical simulations. Differently
from other (unsuccessful) proposals, this new scheme exploits
rejection sampling along with dense noise vectors to hide the
secret key structure in produced signatures. We show that
these measures, besides yielding very slow signing times and
rather long signatures, do not succeed in protecting the secret
key. We are indeed able to prove the existence of a strong
correlation between produced signatures, which ultimately leaks
information about the secret key. To support this claim, we use
both theoretical arguments and numerical evidences. Finally,
we employ such a weakness to mount a full key recovery attack,
which is able to recover the secret key after the observation of a
bunch of signatures. Our results show that the considered scheme
may be secure only for one-time usage.
