in src/group/ristretto.rs [136:143]
fn deserialize_scalar(scalar_bits: &[u8]) -> Result<Self::Scalar> {
scalar_bits
.try_into()
.ok()
.and_then(Scalar::from_canonical_bytes)
.filter(|scalar| scalar != &Scalar::zero())
.ok_or(Error::Deserialization)
}