International Association
for Cryptologic Research

We introduce SQISignHD, a new post-quantum digital signature scheme inspired by SQISign. SQISignHD exploits the recent algorithmic breakthrough underlying the attack on SIDH, which allows to efficiently represent isogenies of arbitrary degrees as components of a higher dimensional isogeny. SQISignHD overcomes the main drawbacks of SQISign. First, it scales well to high security levels, since the public parameters for SQISignHD are easy to generate: the characteristic of the underlying field needs only be of the form $2^{f}3^{f'}-1$. Second, the signing procedure is simpler and more efficient. Third, the scheme is easier to analyse, allowing for a much more compelling security reduction. Finally, the signature sizes are even more compact than (the already record-breaking) SQISign, with compressed signatures as small as 105 bytes for the post-quantum NIST-1 level of security. These advantages may come at the expense of the verification, which now requires the computation of an isogeny in dimension $4$, a task whose optimised cost is still uncertain, as it has been the focus of very little attention.