Removal of krb4 support...

The attached patch completely removes krb4 support.  The advisory
listed below contains details, but suffice it to say the krb4 protocol
is fundamentally flawed and its use should be highly pessimized, to
the point of complete removal if database integrity is valued.  Taken
from the advisory, the twenty second summary of the krb4 vulnerability
is:

    A cryptographic weakness in version 4 of the Kerberos protocol
    allows an attacker to use a chosen-plaintext attack to impersonate
    any principal in a realm.  Additional cryptographic weaknesses in
    the krb4 implementation included in the MIT krb5 distribution
    permit the use of cut-and-paste attacks to fabricate krb4 tickets
    for unauthorized client principals if triple-DES keys are used to
    key krb4 services.  These attacks can subvert a site's entire
    Kerberos authentication infrastructure.

    Kerberos version 5 does not contain this cryptographic
    vulnerability.  Sites are not vulnerable if they have Kerberos v4
    completely disabled, including the disabling of any krb5 to krb4
    translation services.

For full details:

http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2003-004-krb4.txt

The attached patch includes references to the above advisory as well
as updated release notes and client auth pointing out that support for
krb4 has been removed.

To date, krb4 support has been removed from all four of the BSDs
(Free, Net, Open, and Darwin) and krb4 support has been disabled in
Heimdal and MITs KDCs.  The extent to which the protocol has been
removed from other products is unknown at this time, but is likely
that universally in support is being deorbited quickly.  Commercial
vendors were 2/3rds of the way through their zero day notification for
removal of krb4 when someone posted the vulnerability two months
before the agreed upon disclosure date.

The impact of this patch should be minimal as organizations should
have already moved to krb5 several years ago.

-sc

--
Sean Chittenden