.... all we need to do is feed different text possibilities into the validator logically. It may be possible to programmatically find the private key with several characters mistranscribed or missing:
- Starts with "5"? No? Add "5" if missing characters; substitute "5" if right length; add "5" and drop other characters if right length;
- Correct Length: substitute alternate upper/lower case for one character, check all positions for one character wrong, then iterate for increasing numbers of multiple incorrect cases, incorrect letters, etc;
- Missing one character? Try adding all Base58 characters at all positions.
Missing two characters? It becomes a slightly harder problem. Adding two characters in all possible positions = 3,956,064 possibilities (if the 5 at the start is correct). Single-threaded python does about 300,000 SHA256 hashes a second on my PC, so probably less than a minute to try all.
This might be an interesting programming project, but I wouldn't bother until it's actually going to recover some Bitcoins.
It sounds like the private key may need more massaging to recover, whether programmatically, or by analysis of what was written down. I would start by analyzing how you transcribed the private key to paper, and think for yourself where you were and how it might have been written in error. Did you lose your place when writing it down, are there any letters close to each other that repeat? Did you make a mistake in lower/upper case when transcribing. Picture yourself with pen and paper in one hand and screen, you will be your own best resource for figuring out how it might have gone wrong.
Programming a solution to "brute force" what was written down now needs to be informed about further possible ways that mistakes were made.
, and it is impossible to recall....