Function oaep_encrypt 

pub fn oaep_encrypt(
    pk: &RsaPublicKey,
    msg: &[u8],
    label: &[u8],
    rng: &mut dyn FnMut(&mut [u8]),
) -> Vec<u8> 

OAEP encrypt a message with RSA.

label can be empty (common case). rng fills buffers with random bytes.