Function hkdf_expand 

pub unsafe extern "C" fn hkdf_expand(
    hash_idx: c_int,
    info: *const c_uchar,
    infolen: c_ulong,
    in_: *const c_uchar,
    inlen: c_ulong,
    out: *mut c_uchar,
    outlen: c_ulong,
) -> c_int