Possible to serialize/deserialize hasher state for later use?

[felstead]

Hey BLAKE3 team - so I am prototyping something akin to a Proof of Data Possession/Proof of Retrievability system over a large number of large files. My thought is to BLAKE3(file_bytes) then serialize the hasher state (which is presumably quite small?) then, when trying to determine if someone owns a file, I provide a unique, random nonce, deserialize the state, then effectively BLAKE3(file_bytes + nonce) and use that to determine ownership. It's not perfect security wise (proof of possession moves from knowing the hash to knowing the hasher state) but I believe it works for my use-case.

To my question - is there a reliable way for me to serialize the state of a Hasher object prior to finalization such that I can load it at an arbitrary later time? There is plenty of stuff in hazmat that looks like it's viable, but I would need a couple of pointers in the right direction to work out how to do it.

Thank you!