Date: Fri, 8 May 2020 20:03:43 +0200 From: Solar Designer <solar@...nwall.com> To: john-users@...ts.openwall.com Subject: Re: Hashes with different formats in Johnny Hi MA40, On Fri, May 08, 2020 at 06:22:31PM +0200, MA40 wrote: > Using Johnny, when all the hashes are the same format there is no problem. > > My question is whether an attack can be carried out with several hashes at > the same time, but these hashes are of a different format, for example, one > is MD5, the other is SHA-256, etc. I do not succeed. Is this attack > possible? Generally, no. And this is not specific to Johnny, but is how John works. One John session can only load hashes that are recognized as one "format". In some special cases, a format may recognize what you'd possibly consider more than one hash type. In fact, in your very first posting in here you inquired about two variations of Bitcoin wallet "hashes", where we support both in the same "format" and could thus load both variations simultaneously. Another such example are FreeBSD-style md5crypt, Apache apr1, and AIX smd5 hashes, which are similar enough we treat them as one "format", even though they look differently and their computation is also slightly different. There are many more examples like this, but in general they are exceptions and not the rule. Your example with MD5 and SHA-256 isn't one of those exceptions, so you have to run two separate John sessions on those hashes. The good news for you is that often you actually maximize efficiency by running separate attacks on different hash types. That's the case when the different hash types are of very different speed. If you attack such hashes simultaneously (if this were supported), then you'd test unnecessarily few candidate passwords against the faster hashes, because the attack's speed would be limited by the slower hashes. Another way to look at this is that the faster hashes wouldn't get what you'd likely consider their fair share of processing time. For example, if one hash is 99 times faster than the other, it will only receive 1/100th of the processing time when you test a certain number of candidate passwords against both hashes at once. This makes that number unnecessarily low for the faster hash. With an equal split of processing time, such as what you can achieve by running separate attacks, you'd test 50 times more candidate passwords against the faster hash, but only under 2 times fewer of them against the slower hash. Alexander
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