Re: I have said it once, I will say it AGAIN
One time pad...
Here we go again with the obligatory OTP rubbish.
Sure, works wonderfully and is the only provably secure crypto system known to man.
"only provably secure crypto system known to man" is either wrong or tautological, depending on how specific your definition of the OTP is. The security proof for OTP rests on the fact that all plaintexts of appropriate length are equally likely for a given ciphertext, if the OTP conditions are met. That's a limited proof; it doesn't account for side channels, traffic analysis, etc.
OTP as traditionally described provides only confidentiality; you can use a bit-flipping attack to change the ciphertext and then the recovered plaintext. You have to add a message integrity mechanism to detect alteration. So the OTP "provably secure" claim doesn't cover attack categories outside confidentiality.
Further, if the definition of OTP you're using isn't sufficiently general, then you aren't including some OTP constructs. For example, most people describe OTP using XOR, but EQV works just as well. And an OTP cryptosystem can be decorated in various ways without violating the OTP confidentiality proof, so your definition has to cover those too if you want that "only provably secure" claim to hold up.
And if you're definition's broad enough to cover all the cases, then it covers anything that has the equally-probable plaintext attribute. And so all you're saying then is "all provably perfectly confidential [which is what you meant by 'secure', a meaningless term in this context] cryptosystems are isomorphic to an OTP". So "only" in the sense of "equivalent to all". And that's not a very interesting observation.
Of course all of this is largely irrelevant because the suggestion to use the OTP as a general cryptosystem is stupid. OTP requires a separate secure channel A that's as large as the secure channel B it provides, in order to distribute its key material. So you've just deferred your secure-communications problem, and created a less-secure channel which is open to attack and weakens the theoretical strength of the OTP.