Forgot OpenPGP key's passphrase, can I recover key or files somehow?

Question

I had two OpenPGP key files on two separate TAILS OS USB flash drives, but the most recent one fails to boot up. Then I discovered that I don't remember the old keys passphrase on the first USB flash drive.

I still can export the private key and view it, but without the passphrase it's worthless. I can also still mount the USB flash drive that fails to boot and access its files but I can't seem to open the folder where the keys are kept.

Answer 1

The short version

You won't be able to decrypt the files unless you can either brute-force the passphrase, or some future changes to the subject enable you to do so (new cryptographic findings on exploiting the used cryptography, more computing power, likely a combination of both).

The longer explanation

The private key is encrypted with the passphrase. The passphrase protection is to meant to be and implemented as an actual protection -- without the passphrase, you will not be able to decrypt and use the private key. The same applies to the encrypted files.

Without the passphrase, you're in the position of an arbitrary attacker getting hold of the encrypted copy of the key and the encrypted files. To access the files, you have following chances:

• Brute-forcing generally requires vast computational power. You could brute-forcee
  • the passphrase (for a reasonable passphrase, this will be out of scope, especially for a home user without access to a whole data center) -- but might be a thing to try if you know parts of the passphrase and can somehow prune the space of possible passphrases
  • the private key (for RSA 1024 and larger out of scope for the time, might change in future if computing power heavily increases)
  • the session key of each file (considering the computational effort, even worse)
• Exploiting cryptographic weaknesses that might arise in the future.