Is it possible to guess missing characters of a wif? Let's say there are 62 characters (lowercase + uppercase + digits) and the last 10 characters are missing. Is it possible to guess the WIF with powerful cloud computing in a reasonable amount of time? Guessing more than 10 characters (when we need to try all combinations) sounds utopic, but how is the WIF generated? Can we infer something about the math behind it to exclude specific combinations?
This would be trivial to brute force, if you had software to do so.
WIF private keys are encoding a number in base 58. If the last 10 characters are missing, that's 5810 = 430,804,206,899,405,824 potential numbers. That's a huge amount, but thankfully, every WIF key also contains a 32-bit checksum. That means that only 1 in 232 of those has to be tried, leaving us with just 100,304,421 keys left. Even fairly naive implementations could compute the corresponding addresses for those in a few hours of CPU time, to see which one might have been used.