I don't really find the "because it's difficult" arguments convincing at all. Especially the one claiming it's hard because it requires designing and running a large number of tests and reasoning about the results of each one. That kind of tedious grinding is exactly where LLMs should shine vs humans!
The only convincing argument here is that these things are battle tested (literally in most cases I would guess), with tons of research that never gets published because it's unsuccessful. A whole lot of human effort has gone into trying to break these things. A lot more than went into any of the math problems AI has solved so far. It's going to take a while before LLMs can equal and surpass that amount of human effort. And they might have to surpass it by many, many times to actually break these, if it is even possible, which is not certain.
There are very few computer-era symmetric ciphers that were truly broken. RC4 is probably the worst example.
There are no reasonable attacks even on the good old DES. And by "reasonable" I mean attacks that would bring down the complexity to a practical level if the DES key size were to be extended to something like 128 bits. We can brute-force DES keys trivially, but that's not a fault of the cipher per se.
RC4 is a good example of what Aumasson means when he jokes about weak symmetric cryptography being a quirk of history. It's genuinely weird that RC4 was as popular as it was! DES is broken because it's small, with tiny keys and an 8-byte block. But if it had 16-byte keys and blocks, and presumably a higher round count, the only dealbreaker with it might be that it'd be slow.
RC4 was fast in software for computers with weak CPUs (like 80286 or even 8086, which were still in use during the nineties) and no hardware assistance for cryptography. DES had been designed for computers that had a special DES hardware accelerator.
Moreover, together with RC2 it was approved for export from USA, during a time when this was prohibited, so it was included in browsers from the beginning.
When the export rules were relaxed, it was trivial to increase the key length of RC4, which could be chosen arbitrarily, so that appeared as a simple way to enhance the security of the existing Internet browsers.
This lead to its ubiquity in the early SSL.
I read it as "because there are no viable attacks", which is...fightin' talk I suppose.
What I have seen LLMs do recently is find what turned out to be very basic bugs in encryption and ZK libraries that for some reason humans never saw. In those cases it wasn't that the encryption algorithms were broken per se, but the the implementation was.
This alone seems very worthwhile.
Agreed, we have probably seen only the tip of the iceberg on that. I wouldn't want to be holding niche crypto coins right now.