B-2.1 Setup

Let $[0,t-1]$ be the plaintext range, and $[0,q-1]$ the ciphertext range, where $t\ll q$ ($t$ is much smaller than $q$). Randomly pick a vector $\overrightarrow{s}$ of length $k$ comprising $k$ ternary numbers sampled from $\{-1,0,1\}$as a secret key (denoted as $\overrightarrow{s}\underset{}{\overset{\$}{\leftarrow }}{\{-1,0,1\}}^k$). Let $\mathrm{\Delta }={\displaystyle \frac{q}{t}}$, the scaling factor of plaintext.