Date: Sat, 18 Oct 2008 05:48:05 +0000 (UTC) From: Marc Bevand <m.bevand@...il.com> To: john-users@...ts.openwall.com Subject: Re: Breaking UNIX crypt() on the PlayStation 3 Solar Designer <solar@...> writes: > > Isn't the PPU capable of issuing more instructions per cycle (than the > SPUs)? If not more AltiVec instructions, then maybe more PowerPC > instructions intermixed with AltiVec ones? Oh you are right. The PPU is a dual-issue design. So I guess it could be capable of 140-180% the perf of 1 SPU ! > > [...running sbox-gen for other arches...] > This should probably be done, including for architectures that do have a > mux instruction. Yeah I think I'll try it. > Yes. It is also possible to start with any bit number, not necessarily > bit 1, and proceed to add gates for other bits in any order - then > choose the best solution. This will make the search roughly 4! = 24 > times slower, which is two days instead of two hours. Of course, this > will likely not find the most optimal solution, so this approach can be > combined with what you describe above. sbox-gen already tries the 4! different possibilities of ordering the output bits. And the 6! possibilities for the input bits as well. > BTW, another way to "satisfy" the latencies for the Cell would be by > using 256-bit or longer "virtual" vectors, with repeated instructions. > You have enough registers for that. Something Simon already suggested to me :) In reality I am already using 64 of the 128 registers to store the 32 "left" and 32 "right" bits of each DES Feistel round, and most of the 64 others to implement the S-boxes. So I don't have that many unused registers and couldn't implement that idea. But fortunately I have been very happy with the results of manually reordering the S-box instructions. Only a negligible number of instructions depend on the immediately preceding one (2 or 3 per S-box). > > And maybe not worth > > it because a human can do these optimizations pretty easily, after you > > give him or her a good, low-gate count output of sbox-gen. > > Have you tried doing that for MMX or 8-register SSE2? It's not easy > for a human to do at all. Nope I haven't tried. But you are correct, it was much easier in my case, I had 128 registers... -marc -- To unsubscribe, e-mail john-users-unsubscribe@...ts.openwall.com and reply to the automated confirmation request that will be sent to you.
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