Date: Sat, 19 Jan 2013 01:39:27 -0800 From: Colin Percival <cperciva@...mni.sfu.ca> To: crypt-dev@...ts.openwall.com CC: Christian Forler <christian.forler@...-weimar.de> Subject: Re: Password Scrambling On 01/19/13 01:18, Christian Forler wrote: > Let's say A has access to multiple CPUs. Then there are two extreme cases: > > 1) A can test one candidate per CPU in parallel or > 2) A can parallelize the KDF function and test the candidates in a > sequential order. > > In both cases, I would assume that the number of computed password > candidates is similar apart a constant factor c. Or is this not the case? If he has enough RAM, yes. But case (1) requires N times as much RAM as case (2), where N is the number of CPUs, since each CPU needs its own memory rather than all the CPUs sharing. Since the point of memory-hard functions is to maximize the area-time cost of the RAM used, this makes a big difference in the overall cost. Colin Percival
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