An interesting idea, although highly unpracticable. Sending a binary is nearly impossible. As an example, I have at my disposal (and I log into regularly) at least 6 different platforms. All Unix, but each one would require its own binary!
I assume you mean embedded binary (under radix 64). In Unix land, uudecode could be assumed or a script version of radix decoding could run against itself. You are quite correct in assumption of platform. This is a bummer. The ubiquity of DOS makes this a bother rather than a block. (I'll bet even you at least _see_ a DOS box occasionally! :)
This doesn't mean that your idea has no merit. On the other hand, it is an interesting key distribution model. Except there are a number of problems that I can see. First, anything you know about the person is something that someone else could probably do a little research and find out as well. This inherently means it is not a very secure channel, rather it is only moderately secure.
"Ida, remember our last conversation.... who were we talking about? (Please provide full name properly capitalized.)" "Ida, you and I were reading the newspaper in the break room the other day. We discussed a point of mutual interest. What was it?" The less intimately I know the recipient, the tougher it is to formulate a good question. I agree, moderately secure.
Also, there is no way to meet your goal of "no external binary needed." There may be a few things you can do in lieu of this, but all of them require some knowledge of the recipient hardware system.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Yes. :(
But in a case such as mine, even that wouldn't help (do you send it for an RT, Vax, Decmips, RS6000, Alpha, Linux, Sun386i, Next, ...?)
Like I said, its an interesting key distribution model, but I do not see any way to realize it under your assumptions.
-derek