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Just to be clear on truncation...
I asked Hugo which bits I should chop off for a truncation. Here's his
reply:
Forwarded message:
> From HUGO@watson.ibm.com Thu Feb 20 11:16:02 1997
> From: HUGO@watson.ibm.com
> Message-Id: <199702201915.OAA23526@mailhub1.watson.ibm.com>
> Date: Thu, 20 Feb 97 14:12:39 EST
> To: Dan.McDonald@Eng
> Subject: IPsec Straw Poll results
> content-length: 2071
>
> Ref: Your note of Thu, 20 Feb 1997 11:00:10 -0800 (PST) (attached)
>
> rfc2104 says to leave the leftmost bits, ie. chop off the low bits.
>
> Hugo
>
> PS: you're welcome to post this to ipsec (with your example)
Since Hugo said to post this to IPsec, I figured I would, with my example.
Let's say I start off with the following 128-bit HMAC-MD5 computation:
> 0901 2504 2112 5150 1984 0311 dead beef
The right thing to do is to chop off the low bits, so the above would become:
> 0901 2504 2112 5150 1984 0311 (chop off low bits)
Dan