I should have been more clear.: When I use the word airgapped, without exception I mean permanently airgapped. A computer without an internet connection temporarily is not airgapped.
OK, I understand that, but it's not common for probably the majority of people to dedicate a computer to be permanently offline. A TAILS boot media is safe and trustworthy enough for me for such a task and more practical. YMMV...
I wouldn't make a digital copy. I'd simply copy the private key to a second piece of paper in case something happens to the original.
OK, while doable manual handwriting to copy such data is quite error prone. You'd have to verify very thoroughly no error has been introduced in the manual copy. As I think about it, I likely would copy it by hand, too.
Didn't really think about that.. might be a cool souvenir and a cool story to tell my grandkids ... of the day I found something that sparked an educational sojourn down a rabbit hole I've not been down before,... to be rediscovered in my old age......
... or do I tell them a different story?
There's no easy answer to your dilemma and there's a lot to debate. A Private Key gives you technically the ability to move the coins that are "controlled" by that particular Private Key. Does this automatically grant you ownership of those coins. I doubt that. Think of the analogy if you find a key of a foreign house. I believe the majority of legal systems won't allow you to use the key to legally enter the house and take possession of values therein.
You have almost no verifiable way to determine if the legit owner of the paper wallet is still in possession of the Private Key that you found, except if he or someone else who has a copy of the Private Key moves the coins or signs a message with the Private Key (the latter is possible but wouldn't make much sense in this context). If I were the legit owner of the paper wallet, I would move the coins immediatelly should I discover that I lost the paper wallet or someone else has it, as long as I can do it.
If I were you and with the mindset of an honest finder, I would do the following (I am in the comfortable position to have enough Bitcoin knowledge to do all by myself):
- Publish the Public Address of the paper wallet at places like here, no further details that might be suitable to identify a legit owner of it; pay attention not to expose details to compromise your identity
- Make a verifiably correct manual copy of the Private Key to prevent degradation of the original paper wallet (store safely!)
- Make a transaction of the paper wallet's coins to the same Public Address of the paper wallet and add an output to the transaction like this:
OP_RETURN "See https://bitcointalk.org/index.php?topic=5408263.40"
(A move by someone else, not by the owner, should alarm the legit owner enough. But it's no guarantee to trigger the owner to check in a reasonable time frame.) - HODL... and save a story for my children or grandchildren, it will be a good one, anyway how the outcome will be!
- If I've done necessary steps to comply with rules for a finder and those rules grant me partly or in total ownership of my finding should no legit owner show up usually within some defined time frame governed by law, I would claim the coins after enough time has passed.
(I wouldn't hand over the Private Key to others as they could steal the coins should they be corrupt, not honest, underpaid, whatever the dark side offers for them. My faith in officials is partly deteriorated... - You do you!
Yeah, I know, that sounds too good to be true. Don't tempt me, haha. As we hope for rising Bitcoin exchange rates, there'll be enough temptations in the future... stay humble!