Date: Thu, 19 Dec 2013 06:31:43 +0400 From: Solar Designer <solar@...nwall.com> To: crypt-dev@...ts.openwall.com Subject: Re: scrypt parallelism vs. area-time vs. TMTO resistance On Thu, Dec 19, 2013 at 06:08:53AM +0400, Solar Designer wrote: > * Classic scrypt is available by setting flags to ESCRYPT_WORM [...] > [...] In this mode, the thread-local memory region (RAM) > * is first sequentially written to and then randomly read from. This > * algorithm is friendly towards time-memory tradeoffs, available both to > * defenders (albeit not in this implementation) and to attackers. > * > * Setting ESCRYPT_RW adds extra random reads and writes to the thread-local > * memory region (RAM), which makes time-memory tradeoffs less efficient. > * This may be used to slow down the kinds of attackers who would otherwise > * benefit from classic scrypt's efficient time-memory tradeoff. I realized the above quote may be confusing in what "thread-local memory region" refers to, so I'd like to clarify: it's about possible use of threads by the calling application, not about possible (additional) use of threads (for p>1) by an optimized implementation of escrypt. [ The comment talks about it because there's also a possible data structure that is shared between the application-level threads (if they exist at all), and is naturally read-only to the threads. ] In other words, this quote's mention of threads is irrelevant to the (different) threads that I was talking about in the previous message. The rest of the source code comment that this quote came from is nevertheless relevant. Alexander
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