How do you know they're not one-time pads?
What am I missing here?
How many billions of NTLM keys can a Geforce crack in a second? How is this cryptography problem so greatly different than that one?
According to https://hashcat.net/oclhashcat-plus/ , it's approximately 2.5 B.
This corresponds to a one time pad message of just under 4 bytes long. The difference, of course, with NTLM is you know when you've found the right value. With OTPs, all decryptions are possible and equally valid.