b15cbefc25
git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@3338 ec53bebd-3082-4978-b11e-865c3cabbd6b
75 lines
3.7 KiB
Plaintext
75 lines
3.7 KiB
Plaintext
@node Kerberos 4 issues, Acknowledgments, Setting up a realm, Top
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@comment node-name, next, previous, up
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@chapter Kerberos 4 issues
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If compiled with version 4 support, the KDC can serve requests from a
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Kerberos 4 client. There are a few things you must do for this to work.
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@menu
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* Principal conversion issues::
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* Converting a version 4 database::
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@end menu
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@node Principal conversion issues, Converting a version 4 database, Kerberos 4 issues, Kerberos 4 issues
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@section Principal conversion issues
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First, Kerberos 4 and Kerberos 5 principals are different. A version 4
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principal consists of a name, an instance, and a realm. A version 5
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principal has one or more components, and a realm @footnote{for the
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common case of one and two component principals, we will refer to the
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first component as the ``name'' and the second as the ``instance''}.
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Also, in some cases the name of a version 4 principal differs from the
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first component of the corresponding version 5 principal. One notable
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example is the ``host'' type principals, where the version 4 name is
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@samp{rcmd} (for ``remote command''), and the version 5 name is
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@samp{host}. For the class of principals that has a hostname as
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instance, there is an other major difference, Kerberos 4 uses only the
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first component of the hostname, whereas Kerberos 5 uses the fully
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qualified hostname.
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Because of this it can in the general case can be hard or impossible to
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correctly convert a version 4 principal to a version 5 principal
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@footnote{the other way is not always trivial either, but usually
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easier}. The biggest problem is to know if the conversion resulted in a
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valid principal. To give an example, suppose you want to convert the
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principal @samp{rcmd.foo}.
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The @samp{rcmd} name suggests that the instance is a hostname (even if
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there are exceptions to this rule). To correctly convert the instance
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@samp{foo} to a hostname, you have to know which host it referred to. You
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can to this by either guessing (from the realm) which domain name to
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append, or you have to have a list of possible hostnames. In the
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simplest cases you can cover most principals with the first rule. If you
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have several domains sharing a single realm this will not usually
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work. If the exceptions are few you can probably come by with a lookup
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table for the exceptions.
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In a complex scenario you will need some kind of host lookup mechanism.
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Using DNS for this is tempting, but DNS is error prone, slow and unsafe
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@footnote{at least until secure DNS is commonly available}.
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Fortunately, the KDC has a trump on hand: it can easily tell if a
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principal exists in the database. The KDC will use
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@code{krb5_425_conv_principal_ext} to convert principals.
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@node Converting a version 4 database, , Principal conversion issues, Kerberos 4 issues
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@section Converting a version 4 database
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If you want to convert an existing version 4 database, the principal
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conversion issue arises too.
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If you simply convert a database, this conversion will only take place
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once. It is also possible to run a version 5 KDC as a slave. In this
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case this conversion will happen every time the database is propagated.
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When doing this conversion, there are a few things to look out for. If
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you have stale entries in the database, these entries will not be
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converted. This might be because these principals are not used anymore,
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or it might be just because the principal couldn't be converted.
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You might also see problems with a many-to-one mapping of
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principals. For instance, if you are using DNS lookups and you have two
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principals @samp{rcmd.foo} and @samp{rcmd.bar}, where `foo' is a CNAME
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for `bar', the resulting principals will be the same. Since the
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conversion function can't tell which is correct, these conflicts will
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have to be resolved manually.
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