  We study the equivalence between non-perfect secret sharing (NSS) and
symmetric private information retrieval (SPIR) with colluding and unresponsive
servers. We prove the equivalence between NSS and SPIR in the following two
senses. 1) Given any SPIR protocol, we can construct an NSS protocol. 2) Given
any linear NSS protocol, we can construct a SPIR protocol. From this
equivalence relation, we prove that the capacity of $\mathsf{n}$-server SPIR
with $\mathsf{r}$ responsive servers and $\mathsf{r}$ colluding servers is
$(\mathsf{r}-\mathsf{t})/\mathsf{n}$.
