Date: Sat, 5 Jan 2002 18:28:48 -0800 (PST) From: Paul Herman <pherman@frenchfries.net> To: Bill Vermillion <bv@wjv.com> Cc: security@FreeBSD.ORG Subject: Blowfish salt generation (was Re: MS5 salt password generation) Message-ID: <200201060228.g062SmL41195@tick.sc.omation.com> In-Reply-To: <20020105224539.GA38820@wjv.com>
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On Sat, 5 Jan 2002, Bill Vermillion wrote: > Blowfish encrypted: > > fp:$2a$04$.d4.6FZpPIj9GC6DRIRDUuJhPWGP059OmLP2IxSgTQ11LWHVGxxbu:1007:1007::0:0:Bogus Name:/home/fp:/bin/ksh93 > > [...] > > So MD5 uses a much larger salt, but blowish generates a much > long encrypted key, 52 vs 22. I have no docs but >if< the salt is > only 2 characters in blowfish - assuming it works as does MD5 Use the source Luke! See /usr/src/secure/lib/libcrypt The "04" in the blowfish password is the number of iterations to generate the hash (actually on the order of 2^4). The cool thing is you can change this "on the fly" without having to recompile libcrypt. Change that and you've just increased the time it would take to do a dictionary attack. The default (and the minimum) is 4, but could be anything. The blowfish salt is included in the hash and stops with the 23rd character. So, the salt above is ".d4.6FZpPIj9GC6DRIRDUuJ" which is about 16 bytes. The rest is the password hash. So, the blowfish salt is indeed larger than MD5's, which I believe is only 6 bytes. -Paul. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message
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