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[kitten] Freshness Security Considerations for minimum/maximum size

Michiko Short <michikos@microsoft.com> Thu, 01 December 2016 17:55 UTC

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From: Michiko Short <michikos@microsoft.com>
To: "kitten@ietf.org" <kitten@ietf.org>
Thread-Topic: Freshness Security Considerations for minimum/maximum size
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Date: Thu, 01 Dec 2016 17:55:34 +0000
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Archived-At: <https://mailarchive.ietf.org/arch/msg/kitten/m0j9HhxMhR5Kn_N9CvwrsjxbJWc>
Subject: [kitten] Freshness Security Considerations for minimum/maximum size
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We have concerns about the lack of guidance about size of the freshness token.


Minimum length

Problematic due to the fact that we intentionally did not specify the format of the freshness token.  Since the structure of the freshness token is left up to the KDC, there is no good way to determine a minimum size.  However, we can add to the security considerations:



Although we don't specify the format of the freshness token, there are a few size considerations based on if the following are used:

-          Nonce: Size is determined by the birthday problem.

-          Symmetric cryptography: Size is determined by properties of the encryption types supported.

-          Asymmetric cryptography: Size is determined by properties of the encryption types supported.

Maximum length
A maximum size makes sense as a way to avoid processing messages that are clearly bad.  Is there an accepted value for a worst case CMS signature?

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