Function generate_trapdoor

pub fn generate_trapdoor<T>(csprng: &mut T) -> Result<Fr, RandError>
where
    T: RngCore + CryptoRng,

Generates a random scalar from the scalar field 𝔽_{r_𝕁}.

The prime order subgroup 𝕁^(r) is the order-r_𝕁 subgroup of 𝕁 that consists of the points whose order divides r. This function is useful when generating the uniform distribution on 𝔽_{r_𝕁} needed for Sapling commitment schemes’ trapdoor generators.

https://zips.z.cash/protocol/protocol.pdf#jubjub