I’m not sure if I fully understand your question; it’d be nice to give more context (e.g. where this “cipher data” comes from, or which package you are trying to use).
Plugins are implemented through .wasm binary files, so, in principle, they have no documentation or source code available unless you know where the binary was compiled, or you can reverse engineer the compiled code.
Usually, however, Typst packages tend to provide high-level functions wrapping plugins instead of plugins themselves, with exceptions.
Which package are you having trouble with? Maybe we can help.