Date: Fri, 27 Nov 2020 14:56:25 +0100 From: magnum <john.magnum@...hmail.com> To: john-users@...ts.openwall.com Subject: Re: PBKDF2-HMAC-* with non-standard bit-length of the derived key? On 2020-11-27 14:30, Vincent wrote: > Is it possible to use a custom bit-length of the derived key (mostly > called dkLen) for the PBKDF2-HMAC-* formats? Do you mean shorter than the native hash length, or longer (multiple or not)? I believe most or all of our PBKDF2 formats already support cracking longer ones (eg. 320 bits of PBKDF2-HMAC-SHA-1). They are clever enough to skip the second pass unless the first matches the 160 first bits. Not sure if they support checking eg. only 128 bits of 160, but that could be implemented of course. In fact, if you need to match somthing longer than native length but not a multiple, such as 170 bits of PBKDF2-HMAC-SHA1, you could simply edit your input file to only keep 160 bits, and all will be fine. You wont get a false positive with these key lengths anyway. magnum
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