I'd go so far as to say that outside OTP, cryptography is always breakable. You can always just guess keys. The aim of most secret key cryptography is to make

I'd go so far as to say that outside OTP, cryptography is always breakable. You can always just guess keys. The aim of most secret key cryptography is to make sure there aren't much better strategies than that to break it, or if there are that the key sizes are sufficiently big it doesn't matter. With OTP you can't guess keys, as there is a valid key for any possible message. It is unbreakable without the original key.