howdoibtc

Wufoo.com -> Demo -> Form Settings -> Pasting the key in the description caused the preview to show the key.

This was sort of finicky to do, I'm not sure how reproducible it is? I also had the BTC key shoved in a bunch of other fields, some of which became partially visible.

That explains why the validator error looked entirely different when I tried to reproduce it locally -- I was wondering about that.

And yeah, it's a CTF, gotta hold onto issues until the flag redemption is back up.

Got it :)

Pasted the private key into the email address field on the Wufoo signup page, and the validator helpfully told me my "email" was invalid, with the whole key included.

Launch Electrum, create a new wallet, "Import Bitcoin addresses or private keys", paste in the recovered key.

If you just paste the raw key, Electrum uses a legacy format, and none of the transactions show up for that private key. Adding the "p2wpkh:" prefix to the key makes the transactions show up, but I realized that well after someone else claimed it.

I don't know if this is an Electrum thing, if this is considered general knowledge now for those who regularly use BTC, or if it's a quirk of how BTC has evolved.

I found the key as well, also used Electrum, and also was (seemingly) unable to do anything with it.

Turns out, you have to prefix the private key with "p2wpkh:", or else it imports it as a legacy key, and generates a completely different public hash.

fwiw I was able to get a private key out of the system, but there's no BTC/transactions associated with it. Dunno if that's an error on my part (although the key has a valid checksum) or the wrong key got uploaded.