Re OpenSSL's BN_CONSTTIME_SWAP: Purportedly "constant-time" code should not be written in C, full stop.https://stackoverflow.com/questions/29149058/does-memory-dependence-speculation-prevent-bn-consttime-swap-from-being-constant …
@dakami @daniel_bilar @solardiz Or preferably sleep if power-consumption/cpu-load side-channel attacks are not an issue. Wasting cpu sucks.
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@dakami@daniel_bilar@solardiz Sleep is not an option for internal primitive ops but it's easy to do for the whole client-/user-visible op. -
@RichFelker@dakami@daniel_bilar Unfortunately, sleep fails e.g. when trying to prevent concurrent username probing. Have to waste CPU. -
@solardiz@dakami@daniel_bilar Depends on the usage. E.g. in password hashing that can be solved by system-wide serialization of hashing. -
@RichFelker@dakami@daniel_bilar You'd have to serialize all requests, not just password authentication ones. Usually impractical. -
@solardiz@dakami@daniel_bilar Or dedicate a core/host. You lose computing power but at least don't pay for wasted electricity. -
@RichFelker@dakami@daniel_bilar Dedicating a core might not be good enough because of shared caches, buses, and power and thermal envelope -
@solardiz@RichFelker@daniel_bilar nobody wants to isolate computers and everyone wants isolation of some sort. Weird.
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@RichFelker@daniel_bilar@solardiz wasting CPU sucks in a tight loop. Amdahls law and all thatThanks. Twitter will use this to make your timeline better. UndoUndo
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@RichFelker@daniel_bilar@solardiz issue with sleep is scheduler granularity is terribleThanks. Twitter will use this to make your timeline better. UndoUndo
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@RichFelker@dakami@daniel_bilar@solardiz Sleep might get you constant time (but clocks vary) but it'll show a different power signature. -
@hyc_symas@RichFelker@daniel_bilar@solardiz I have no delusions anything protects against an attacker watching power draw
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@RichFelker@dakami@daniel_bilar Usually, those side-channels are a concern, even if you're not letting attackers run their own codeThanks. Twitter will use this to make your timeline better. UndoUndo
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