Quote from: dadadum on Today at 10:10:07 AM

What i figure out with all the PK i saw is

53 Characters
hex format
no big I or big O letters

and thats it. Somebody a idea ??

Hex uses ONLY the following letters and numbers:
0123456789ABCDEF

That's it, nothing more. Hex doesn't care about capital letters or not, so A is the same as a, and B is the same as b, and so on.
If your key has any letters later in the alphabet than F, then it is NOT hex.

Bitcoin's Base58check encoding uses the following:
123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz

Base58check DOES care about capital letters, so A is different than a, and B is different than b, and so on.

Notice that Base58check does NOT use the number 0 (zero) or the letters capital i (eye), capital o (oh), or lowercase l (elle). If your key has any of those 4 characters then it is NOT Base58check.

Base 64 encoding uses the following:
0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz+/=

If your key has any +, or /, or =, or the number 0 (zero) or the letters capital i (eye), capital o (oh), or lowercase l (elle), then there's a pretty good chance that it is Base 64.

If they were using Bitcoin Core when they successfully used the bitcoins, and then they wrote down what they thought was a private key and stopped using the bitcoins anymore after that... Then unfortunately, it is very possible that they didn't understand what they were doing and accidentally wrote something down that is NOT a private key. If that happened, then you will never be able to access those bitcoins.

If they were writing down the keys in 2017 for a fishing trip, then the format for keys was pretty standard at that time, which means that either they made an expensive mistake and wrote down the wrong thing OR they invented their own process for converting a key into something unrecognizable and you'll need to learn what they did if you want to convert it back to a key.