jo
But my system was not so secure. My cipher system was this: Take a message and type it on a US Qwerty keyboard, but shift every letter over one place. So `hi` became `jo`. Not very strong. It would easily be cracked with a message consisting of an actual sentence or two.
Now, with Telegraph, it wasn’t just length of the message involved, but additional information; still, the conditions are so narrow that it doesn’t apply to the real world. Just like I’d never simply send you a message that said "hi", Telegraph would be used in ways beyond one simple back-and-forth exchange, so it artificially limits the information available to a cracker. Make sense?
See also: The BEAST attack or the general class of side channel attacks.
Basically, the framework of the contest precludes many avenues of attack to which a given cryptosystem could be vulnerable. The researcher who discovered the vulnerability in the OP used a man-in-the-middle attack, which cannot be used in the Telegram contest.