Yeah. I appreciate you trying to correct me, but I never was saying that this was an instance of “public key encryption”, whichever version you mean. This is

Yeah. I appreciate you trying to correct me, but I never was saying that this was an instance of “public key encryption”, whichever version you mean. This is a scheme by which you can intentionally create a key that can be re-generated in a fixed amount of time, and use it as part of normal symmetric encryption to protect a secret. One usage of that is creating intentionally crackable schemes, such as protecting other signing keys in a way you can later crack if you need to. This allows a device, such as a phone, to emit a masked secret that we have cryptographic guarantees it still takes time to recover. Hashchains for time locking is a studied mechanism, and though it predates crypto currencies, it’s deployed as a mechanism in several kinds of applications there. A second usage is in storing paper copies of master signing keys in a safe, since the key cannot be exposed in the event of a robbery before a certain period of time — giving you time to rekey your system. (Generally, people use multipart keys instead, because they’re less cumbersome to recover; however, if you only have one secure location — multipart keys don’t help. Hash chains still do.) So it’s literally how (part of) modern cryptography works.