Well, one way is to brute iterate through every potential 256-bit string you dredge out of the canal against the known public key.

If you can dredge up 64kB of fresh data every time, that's 511,744 tests per shovelful which is quite a bit to sift through from a performance perspective but it's also a trivially parallel task.

Additionally, folk might know of even better ways to narrow that down. For example, the data representation in memory might have easy to grep for delimiters.