alt Hacker NewsThere is already a mathematically secure algorithm for securing a message: One Time Pad. The problem is that OTP requires that the length of the key and the length of message must be the same, which is inconvenient for large amounts of data.
So the solution is to find algos that let you use a smaller key, but the side effect is that by pigeonhole principle, your keyspace is smaller than the message space, so it MUST be insecure. The trick is to make it so that it's only insecure enough that it's infeasible to break.
It's inconvenient for any amount of data, because it essentially begs the question; if you can securely transmit N bytes of key pad to a counterparty, just use that mechanism to transmit N bytes of plaintext instead.