The NSA had the capability, and the motivation. How plausible is this theory?
There's also the anagram
I AM A HOST TO NSA OK
And this paper from 1996: How to make a mint: The Cryptography of Anonymous Electronic Cash, Laurie Law, Susan Sabett, Jerry Solinas, NSA Office of Information Security Research and Technology, Cryptology Division, https://groups.csail.mit.edu/mac/classes/6.805/articles/money/nsamint/nsamint.htm