[iraqmtpizza]

I'm sure that the people getting hacked care deeply about whether the attack they suffered was sui generis.

Also, zip/deflate etc was not designed to eliminate side channel leakage. Some compression schemes obviously (with padding) can mitigate leaks, but it has to be done deliberately

[zrm]

Any of it has to be done deliberately. The length of the data reveals something about its contents whether it's compressed or not.

The special concern with compression is when attacker-controlled data is compressed against secret data because then the attacker can measure the length multiple times and deduce the secret based not just on the length but on how the length changes when the secret is constant and the attacker-controlled data varies. This can be mitigated with random padding (makes the attack take many times more iterations because it now requires statistical sampling) or prevented by compressing the sensitive data and attacker-controlled data separately.