We present a new lattice-based signature scheme, called ‘ \(\textsf{NTRU}+ \textsf{Sign}\) ’, using the Fiat-Shamir with Aborts framework. The proposed scheme is designed based on a novel NTRU-based key structure that fits well with bimodal distributions, enabling efficiency improvements compared to its predecessor, \(\textsf{BLISS}\) . The novel NTRU-based key structure is characterized by: (1) effectively changing a modulus from 2q to q, which is different from the existing usage of 2q for bimodal distributions, and (2) drastically reducing the magnitude of a secret key, which directly leads to compactness of signature sizes. We provide two concrete parameter sets for \(\textsf{NTRU}+ \textsf{Sign}\) , supporting 93-bit and 211-bit security levels. Using the technique from \(\textsf{GALACTICS}\) (that was suggested as the constant-time implementation of \(\textsf{BLISS}\) ), our analysis shows that \(\textsf{NTRU}+ \textsf{Sign}\) achieves a good balance between computational efficiency and signature compactness, with constant-time implementation. For instance, at the NIST-3 security level, \(\textsf{NTRU}+ \textsf{Sign}\) produces signatures that are significantly smaller than \(\textsf{Dilithium}\) and \(\textsf{HAETAE}\) , while providing faster verification speeds. These advantages position \(\textsf{NTRU}+ \textsf{Sign}\) as a competitive and practical solution for real-world deployments.
