Comment by Nerdyfro

This implementation is flawed. Each shard gets a unique substitution cipher making this nothing more than a cryptogram generator. Input "aaaaabbbbbcccccdddddeeeee" with any number of shards/threshold to see.

Taking the message bytes (starting at byte 23), you can run a frequency analysis and recover any sufficiently long english message from a single shard.

I have not come across a good library that implements SSS over finite fields that was easy-to-use, reliable, or robust. Any suggestions would be welcome.