linux-kernel - Re: Where exactly will arch_fast

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20141207100252.6707.qmail@ns.horizon.com>
Date:	7 Dec 2014 05:02:52 -0500
From:	"George Spelvin" <linux@...izon.com>
To:	herbert@...dor.apana.org.au, linux@...izon.com
Cc:	dborkman@...hat.com, hannes@...essinduktion.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org, tgraf@...g.ch
Subject: Re: Where exactly will arch_fast_hash be used

> For a start why don't you print out the hashes of 1-255 and then
> find out how easy it is to deduce the last bit of the hash result.

They're available in lib/crc32table.h, as crc32ctable_le[0].

As a CRC is a linear function, every bit is the XOR of some
selected bits of the input, i.e. the parity of the input and
some bit-specific mask sequence.

Furthermore, CRCs are cyclic, so the mask sequences for adjacent bits are
shifts of each other.

The lsbit of the CRC32c of x is the parity of x & 0x1f.

This is because the LFSR sequence generated by the polynomial
starts 0001111110010001110010101111011000111000011011110010110000100101...

The first bit corresponds to the msbit of the last byte.

How does this implicate the low bits specifically?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/