Why not simply AES-256 encrypt the private key and be done with it in, like, 3 lines? No password hashing and so on.

I solved puzzle #66 but I'm very afraid to sweep it. Since no one claimed it yet, they definitely belong to me, right? Here's my proof: the encrypted private key is:
First 16 bytes are the IV, then 32 bytes of private key. I removed the padding, since it's 16 bytes of 0x10 (e.g. no bytes in last block).

If anyone steals my prize I will divulge the decryption key.

Or, simply hash it once together with some secret value, you only need to prove you knew the hashed value before anyone else, not to protect the actual data.