Given $q$ and a matrix $A \in \mathbb{Z}_q^{n \times m}$, the $q$-ary lattice is defined as $$\Lambda(A)=\{x \in \mathbb{Z}^m:Ax=0 \bmod q\} $$ An instance of a q-ary lattice and its short basis is computed in Generating short basis for hard random lattices. Once the short basis $T_A$ for $\Lambda(A)$ is given, computing the short vector $s$ in $\Lambda (A)$ is given in SamplePre algorithm.

Is it possible to find a short basis for $\Lambda(A^T)$, if we are given a short basis of $ \Lambda(A)$?

Basically I want to find the short vector $s^\prime$ such that $A^Ts^\prime=0 \bmod q$.

  • $\begingroup$ It is highly unlikely that such a short (nonzero) vector $s’$ exists, for a uniformly random $A$ and typical dimensions $m \gg n$. $\endgroup$ – Chris Peikert Jul 6 '19 at 14:48

If $n<m$ then for almost all matrices $A$ the columns of $A^T$ will be linearly independent and in that case $\Lambda(A^T)$ is the lattice generated by the basis $qI$ (which is the shortest possible basis for this lattice).

| improve this answer | |
  • $\begingroup$ The basis would not be $qI$ because that does not include the columns of $A^T$. $\endgroup$ – Chris Peikert Jul 6 '19 at 14:50
  • $\begingroup$ The notations are confusing, but the question asks about the kernel lattice of $A^T$, so I don't see why that lattice should include the columns of $A^T$. $\endgroup$ – LeoDucas Jul 9 '19 at 15:12

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