1.) Is it possible to recover part of private key, when I have valid address?
For example:
let's say one of my paper wallet is partialy destroyed, and I have lost 5 or more characters from private, like:
pub: 1DrqrF3JEYB9TXWymz4zGoEzM5i75JMLFB
priv: L3Wji4b***4Po3vo2gmi42Y2kbbxtnpAfQ5wJx11BgNr****8v3Q
It is possible as long as exact position of lost characters & it's public key/address are known since 58^5 (656.356.768) combination is small number for GPU these days. But AFAIK this software don't support such feature.
But if the exact position of lost characters & it's public key/address isn't known, time complexity would increase significantly because :
1. If it's public key/address isn't known, you need to check if generated address from bruteforce with partial private key contain Bitcoin and AFAIK it's far slower compared with bruteforce speed
2. If exact position of lost characters isn't known, total possible combination is far higher