I sometimes don't know where to start with comments like these.
We do in fact know what it is, because no matter what the bits of the secret key are, the use of the key in Microsoft's software is published: the code we're talking about isn't obfuscated.
You say "[l]ogically, we should assume it was a COMSEC backdoor for NSA so Microsoft could make money on exports". You say that as if it was impossible to look at the code and see where the key is used. It obviously isn't. People have done that work. They did it years and years ago. They explained what the key does. But the conspiracy theory about NSAKEY being a secret backdoor keeps coming up.
Once again: the key we're talking about doesn't even make sense as a backdoor. It's a second authentication key, the first of which is a key Microsoft already has, and could already use to the exact same effect.
Given your rep, I'll assume you did thorough research and drop NSAKEY for now. I'll dig up that old work later for verification. If it checks out, I'll pass the correction along to others bringing it up along with modifying Wikipedia article to keep it from confusing others.
We do in fact know what it is, because no matter what the bits of the secret key are, the use of the key in Microsoft's software is published: the code we're talking about isn't obfuscated.
You say "[l]ogically, we should assume it was a COMSEC backdoor for NSA so Microsoft could make money on exports". You say that as if it was impossible to look at the code and see where the key is used. It obviously isn't. People have done that work. They did it years and years ago. They explained what the key does. But the conspiracy theory about NSAKEY being a secret backdoor keeps coming up.
Once again: the key we're talking about doesn't even make sense as a backdoor. It's a second authentication key, the first of which is a key Microsoft already has, and could already use to the exact same effect.