oysteikt/heimdal
0
0
Fork 0
Code Issues 5 Pull Requests Releases Activity

some more babbling

Browse Source 
git-svn-id: svn://svn.h5l.se/heimdal/trunk/heimdal@4806 ec53bebd-3082-4978-b11e-865c3cabbd6b
This commit is contained in:
Johan Danielsson
1998-04-25 01:58:35 +00:00
parent b507007b14
commit 2e8a383915
1 changed files with 109 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

137
doc/kerberos4.texi
View File

@@ -15,30 +15,28 @@ Kerberos 4 client. There are a few things you must do for this to work.
First, Kerberos 4 and Kerberos 5 principals are different. A version 4
principal consists of a name, an instance, and a realm. A version 5
principal has one or more components, and a realm @footnote{for the
common case of one and two component principals, we will refer to the
first component as the ``name'' and the second as the ``instance''}.
Also, in some cases the name of a version 4 principal differs from the
first component of the corresponding version 5 principal. One notable
example is the ``host'' type principals, where the version 4 name is
@samp{rcmd} (for ``remote command''), and the version 5 name is
@samp{host}. For the class of principals that has a hostname as
instance, there is an other major difference, Kerberos 4 uses only the
first component of the hostname, whereas Kerberos 5 uses the fully
qualified hostname.
principal has one or more components, and a realm (the terms ``name''
and ``instance'' are still used, for the first and second component,
respectively). Also, in some cases the name of a version 4 principal
differs from the first component of the corresponding version 5
principal. One notable example is the ``host'' type principals, where
the version 4 name is @samp{rcmd} (for ``remote command''), and the
version 5 name is @samp{host}. For the class of principals that has a
hostname as instance, there is an other major difference, Kerberos 4
uses only the first component of the hostname, whereas Kerberos 5 uses
the fully qualified hostname.
Because of this it can in the general case can be hard or impossible to
correctly convert a version 4 principal to a version 5 principal
@footnote{the other way is not always trivial either, but usually
easier}. The biggest problem is to know if the conversion resulted in a
valid principal. To give an example, suppose you want to convert the
principal @samp{rcmd.foo}.
Because of this it can be hard or impossible to correctly convert a
version 4 principal to a version 5 principal @footnote{the other way is
not always trivial either, but usually easier}. The biggest problem is
to know if the conversion resulted in a valid principal. To give an
example, suppose you want to convert the principal @samp{rcmd.foo}.
The @samp{rcmd} name suggests that the instance is a hostname (even if
there are exceptions to this rule). To correctly convert the instance
@samp{foo} to a hostname, you have to know which host it referred to. You
can to this by either guessing (from the realm) which domain name to
append, or you have to have a list of possible hostnames. In the
@samp{foo} to a hostname, you have to know which host it is referring
to. You can to this by either guessing (from the realm) which domain
name to append, or you have to have a list of possible hostnames. In the
simplest cases you can cover most principals with the first rule. If you
have several domains sharing a single realm this will not usually
work. If the exceptions are few you can probably come by with a lookup
@@ -50,7 +48,8 @@ Using DNS for this is tempting, but DNS is error prone, slow and unsafe
Fortunately, the KDC has a trump on hand: it can easily tell if a
principal exists in the database. The KDC will use
@code{krb5_425_conv_principal_ext} to convert principals.
@code{krb5_425_conv_principal_ext} to convert principals when handling
to version 4 requests.
@node Converting a version 4 database, , Principal conversion issues, Kerberos 4 issues
@section Converting a version 4 database
@@ -58,13 +57,14 @@ principal exists in the database. The KDC will use
If you want to convert an existing version 4 database, the principal
conversion issue arises too.
If you simply convert a database, this conversion will only take place
once. It is also possible to run a version 5 KDC as a slave. In this
case this conversion will happen every time the database is propagated.
When doing this conversion, there are a few things to look out for. If
you have stale entries in the database, these entries will not be
converted. This might be because these principals are not used anymore,
or it might be just because the principal couldn't be converted.
If you decide to convert your database once and for all, you will only
have to do this conversion once. It is also possible to run a version 5
KDC as a slave to a version 4 KDC. In this case this conversion will
happen every time the database is propagated. When doing this
conversion, there are a few things to look out for. If you have stale
entries in the database, these entries will not be converted. This might
be because these principals are not used anymore, or it might be just
because the principal couldn't be converted.
You might also see problems with a many-to-one mapping of
principals. For instance, if you are using DNS lookups and you have two
@@ -72,3 +72,84 @@ principals @samp{rcmd.foo} and @samp{rcmd.bar}, where `foo' is a CNAME
for `bar', the resulting principals will be the same. Since the
conversion function can't tell which is correct, these conflicts will
have to be resolved manually.
@subsection Conversion example
Given the following set of hosts and services:
@example
foo.se rcmd
mail.foo.se rcmd, pop
ftp.bar.se rcmd, ftp
@end example
you have a database that consists of the following principals:
@samp{rcmd.foo}, @samp{rcmd.mail}, @samp{pop.mail}, @samp{rcmd.ftp}, and
@samp{ftp.ftp}.
lets say you also got these extra principals: @samp{rcmd.gone},
@samp{rcmd.old-mail}, where @samp{gone.foo.se} was a machine that has
now passed away, and @samp{old-mail.foo.se} was an old mail machine that
is now a CNAME for @samp{mail.foo.se}.
When you convert this database you want the following conversions to be
done:
@example
rcmd.foo host/foo.se
rcmd.mail host/mail.foo.se
pop.mail pop/mail.foo.se
rcmd.ftp host/ftp.bar.se
ftp.ftp ftp/ftp.bar.se
rcmd.gone @i{removed}
rcmd.old-mail @i{removed}
@end example
A @file{krb5.conf} that does this looks like:
@example
[realms]
FOO.SE = @{
v4_name_convert = @{
host = @{
ftp = ftp
pop = pop
rcmd = host
@}
@}
v4_instance_convert = @{
foo = foo.se
ftp = ftp.bar.se
@}
default_domain = foo.se
@}
@end example
The @samp{v4_name_convert} section says which names should be considered
having an instance consisting of a hostname, and it also says how the
names should be converted (for instance @samp{rcmd} should be converted
to @samp{host}). The @samp{v4_instance_convert} section says how a
hostname should be qualified (this is just a hosts-file in
disguise). Host-instances that aren't covered by
@samp{v4_instance_convert} are qualified by appending the contents of
the @samp{default_domain}.
Actually, this example doesn't work. Or rather, it works to well. Since
it has no way of knowing which hostnames are valid and which are not, it
will happily convert @samp{rcmd.gone} to @samp{host/gone.foo.se}. This
isn't a big problem, but if you have run your kerberos realm for a few
years, changes are big that you have quite a few `junk' principals.
If you don't want this you can remove the @samp{default_domain}
statement, but then you will have to add entries for @emph{all} your hosts
in the @samp{v4_instance_convert} section.
Instead of doing this you can use DNS to convert instances. This is not
a solution without problems, but it is probably easier than adding lots
of static host entries.
To enable DNS lookup you should turn on @samp{v4_instance_resolve} in
the @samp{[libdefaults]} section.
@emph{And then there are a many more things you can do; more on this in
a later version of this manual. Until then, UTSL.}