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Re: [kitten] draft-ietf-kitten-kerberos-iana-registries -- KerberosFlags limited to 0..31?

Greg Hudson <ghudson@MIT.EDU> Mon, 21 July 2014 14:43 UTC

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Date: Mon, 21 Jul 2014 10:43:22 -0400
From: Greg Hudson <ghudson@MIT.EDU>
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To: Rick van Rein <rick@openfortress.nl>, tlyu@mit.edu, kitten@ietf.org
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Subject: Re: [kitten] draft-ietf-kitten-kerberos-iana-registries -- KerberosFlags limited to 0..31?
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On 07/21/2014 05:03 AM, Rick van Rein wrote:
> I was surprised to learn that draft-ietf-kitten-kerberos-iana-registries-03 defines
>> 6.1.  AP-REQ options
>>    Valid values:       ASN.1 bit numbers 0 through 31
[...]

I believe this is in deference to implementations which store flag
values in fixed 32-bit flags.  For example, in MIT krb5:

* krb5_flags is a 32-bit integer type.
* A krb5_flags field representing ticket flags is included in krb5_creds.
* krb5_creds is used in several core public APIs such as
krb5_get_credentials.

Although RFC 4120 has a well-specified means of encoding larger flag
values over the wire, there would still be a significant implementation
cost to using larger bit values over the wire.

If the IETF decides that this implementation cost is warranted, the
standards action which assigns the flag value could amend the registry
to accomodate it.

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