If I'm understanding this right, someone can download and cache the decryption key (while it's available) and then decrypt the cipher text at any time they want

If I'm understanding this right, someone can download and cache the decryption key (while it's available) and then decrypt the cipher text at any time they want in the future, right? I don't think it's beyond the NSA's ability to just pre-emptively cache every decryption key, just in case they need it later.