From: Michael Richardson <mcr@sandelman.ca>
To: linux-crypto@vger.kernel.org
Subject: Re: SHA-2 HMAC support in linux kernel
Date: Mon, 02 Apr 2007 19:04:59 -0400 [thread overview]
Message-ID: <eus26s$8ji$1@sea.gmane.org> (raw)
In-Reply-To: <45FB116C.5080205@certicom.com>
Chinh Nguyen wrote:
> Looking at the source http://lxr.linux.no/source/net/xfrm/xfrm_algo.c,
> it seems to confirm that this is true. In fact, sha-384 and sha-512 are
> not supported at this time and sha-256 is truncated to 96-bit.
That's normal.
HMAC usage in IPsec specifies that we only use 96-bits of the result.
This is a tradeoff in space in the packet vs absolute "security"
In addition should you be able to cause a collision in 96-bits by some
method other than brute force, you can not be sure if you guess the key
properly.
> However, the following ietf draft, which I believe is very closed to
> ratification (it has already been assigned iana numbers), specifies
> sha-256 to use 128-bits as hmac (page 18):
> http://www.ietf.org/internet-drafts/draft-kelly-ipsec-ciph-sha2-01.txt
Yes, but that's the key, not the result.
It is keyed with various sizes of bits, but the results are truncated.
prev parent reply other threads:[~2007-04-02 23:05 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-16 21:51 SHA-2 HMAC support in linux kernel Chinh Nguyen
2007-04-02 23:04 ` Michael Richardson [this message]
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