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From: Greg Carter <firstname.lastname@example.org>
To: "'email@example.com'" <firstname.lastname@example.org>
Cc: "'email@example.com'" <firstname.lastname@example.org>
Subject: RE: How to negotiate key length with ISAKMP?
Date: Tue, 24 Jun 1997 07:43:22 -0400
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>From: Perry E. Metzger[SMTP:email@example.com]
>Sent: Monday, June 23, 1997 3:48 PM
>To: Rodney Thayer
>Subject: Re: How to negotiate key length with ISAKMP?
>Rodney Thayer writes:
>> With CAST (and RC5, and ARCFOUR...) we are going to want to negotiate key
>Not to say that you aren't right about needing to negotiate key
>lengths in general, and certainly with RC4 and RC5, but I believe
>CAST-64 and CAST-128 are really different algorithms, not a single
>algorithm with a variable sized key length.
No they are the same algorithm.
>From the CAST-128 RFC 2144
2.5. Variable Keysize
The CAST-128 encryption algorithm has been designed to allow a key
size that can vary from 40 bits to 128 bits, in 8-bit increments
(that is, the allowable key sizes are 40, 48, 56, 64, ..., 112, 120,
and 128 bits). For variable keysize operation, the specification is
In order to avoid confusion when variable keysize operation is used,
the name CAST-128 is to be considered synonymous with the name CAST5;
this allows a keysize to be appended without ambiguity. Thus, for
example, CAST-128 with a 40-bit key is to be referred to as CAST5-40;
where a 128-bit key is explicitly intended, the name CAST5-128 should