Re:Security Update
by tialaramex on Friday May 17, 2019 @05:46AM
(#19937909)
> In a single-target attack, I don't really see the concept of "pre-computation to trade space for time"
In a single-target attack the reason you'd do this is because you expect your target to react in a timely fashion to discovery of some other part of your attack by changing passwords.
e.g. maybe you're sure you can break in to get hashes, but you will trigger a reactive IDS. You figure you have some period of time after that trigger before your target is alerted and changes their password.
Time-space tradeoff lets you avoid doing all the work against the clock _after_ the IDS triggers, instead you can do it all _before_ you have the hashes, and only pull the trigger and set off the alarms when you're ready to quickly break the hash, get in and do whatever your actual attack requires.
It's not a _common_ scenario, but it's important to remember it exists in designing general purpose components like password hashes.
In a single-target attack the reason you'd do this is because you expect your target to react in a timely fashion to discovery of some other part of your attack by changing passwords.
e.g. maybe you're sure you can break in to get hashes, but you will trigger a reactive IDS. You figure you have some period of time after that trigger before your target is alerted and changes their password.
Time-space tradeoff lets you avoid doing all the work against the clock _after_ the IDS triggers, instead you can do it all _before_ you have the hashes, and only pull the trigger and set off the alarms when you're ready to quickly break the hash, get in and do whatever your actual attack requires.
It's not a _common_ scenario, but it's important to remember it exists in designing general purpose components like password hashes.