This comment boils down to: you're wrong and you're stupid.

Also, and quite ironically, you have misinterpreted and are misapplying the D.K. effect. Can you care to explain why the above wouldn't be true? Does an extra layer of bad crypto diminish the effectiveness of the good crypto? It doesn't seem like it would, and OPs statement reads more like a reasonable logical assumption, but I know very little about crypto, which is why I ask.

No, I'm not misapplying DK

> Does an extra layer of bad crypto diminish the effectiveness of the good crypto?

Yes, you can find other children comment with specific examples.

> It doesn't seem like it would

More DK: you don't know enough to evaluate how much you know.

So rot13 will render my aes useless?

Possibly. If your rot13 takes longer to rotate a Z than it does and A, then it will leak your Zs through the AES. Similarly, you might accidentally write your own rot13 heartbleed.

So you just need to add an extra layer on another computer surely, or else I could MITM SSL by encrypting/unencrypting it

It might weaken it, yes.

> You're making the argument "If I apply good crypto plus crypto which might or might not be good, the worst case scenario is that I end up with crypto which is at least as good as the good crypto."

I'm really not seeing how you pulled that argument out of the GP's comment.

I thought that was what he was saying. Maybe I misunderstood it.