[Freeipa-users] FreeIPA Kerberos and Single-DES for OpenAFS

[Andreas Ladanyi]

>
>>>> Hi,
>>>>
>>>> I set up the 389 LDAP server to support des-cbc-crc enctype.
>>>>
>>>> I created a principal for OpenAFS. OpenAFS need des-cbc-crc:v4
>>>> (single-DES). I created the principal with:
>>>>
>>>> kadmin.local -x ipa-setup-override-restrictions
>>> Please don't do this, use the ipa service-add and ipa-getkeytab
>>> commands instead.
>> I cant use ipa service-add, because for OpenAFS i need a service
>> principal called:
>>
>> afs/cellname at REALM , the cellname could be any name. In my case the
>> cellname is the same like the domainname.
> [root at cc21 ~]# ipa host-add --force afs-cellname.ipacloud.test
> ---------------------------------------
> Added host "afs-cellname.ipacloud.test"
> ---------------------------------------
>  Host name: afs-cellname.ipacloud.test
>  Principal name: host/afs-cellname.ipacloud.test at IPACLOUD.TEST
>  Password: False
>  Keytab: False
>  Managed by: afs-cellname.ipacloud.test
> [root at cc21 ~]# ipa service-add --force afs/afs-cellname
> ----------------------------------------------
> Added service "afs/afs-cellname at IPACLOUD.TEST"
> ----------------------------------------------
>  Principal: afs/afs-cellname at IPACLOUD.TEST
>  Managed by: afs-cellname.ipacloud.test
> [root at cc21 ~]# ipa service-show afs/afs-cellname
>  Principal: afs/afs-cellname at IPACLOUD.TEST
>  Keytab: False
>  Managed by: afs-cellname.ipacloud.test
> [root at cc21 ~]# ipa-getkeytab -s `hostname` -p afs/afs-cellname   -k
> /tmp/afs.keytab Keytab successfully retrieved and stored in:
> /tmp/afs.keytab
>
> As you can see there is no problem at all -- all you need is to have a
> host entry with the same name as afs-cellname. Note that the host
> afs-cellname doesn't even need to exist in DNS.
>
> However, your primary problem would be in a different area. You'll need
> to enable weak crypto at KDC server, Kerberos clients, and LDAP servers.
>
> krb5.conf (on both IPA masters and clients):
> [libdefaults]
>  allow_weak_crypto = true
>
> /var/kerberos/krb5kdc/kdc.conf (on IPA masters):
> [realms]
> IPACLOUD.TEST = {
>   supported_enctypes = aes256-cts-hmac-sha1-96:normal
> aes128-cts-hmac-sha1-96:normal des3-cbc-sha1:normal
> arcfour-hmac-md5:normal des-cbc-crc:v4
> }
>
> Finally, you need to modify
> cn=IPACLOUD.TEST,cn=kerberos,dc=ipacloud,dc=test
> and add des-cbc-crc:v4 to supported Kerberos encryption types with
> krbSupportedEncSaltTypes
> attribute. You have to use ldapmodify as cn=Directory Manager for that
> as we don't allow admins to modify these entries directly.
>
> A simplified approach would be to use ipa-ldap-updater with your own
> update file (which should have a name like <number>-<name>.update where
> <number> is something between 01 and 90):
>
> [root at cc21 ~]# cat 20-weak-enctypes.update dn:
> cn=$REALM,cn=kerberos,$SUFFIX
> add: krbSupportedEncSaltTypes: des-cbc-crc:v4
>
> [root at cc21 ~]# ipa-ldap-updater ./20-weak-enctypes.update Directory
> Manager password:
> Parsing update file './20-weak-enctypes.update'
> Updating existing entry:
> cn=IPACLOUD.TEST,cn=kerberos,dc=ipacloud,dc=test
> Done
> The ipa-ldap-updater command was successful
>
> Only after that you'll get ipa-getkeytab to generate weaker encryption
> type-based keys. 

Thats interesting. Now i can receive afs/cellname at REALM service tickets
with des-cbc-crc and aes256 key on the client but only when i execute:

kvno -e des-cbc-crc afs/cellname

If i execute aklog to obtain an afs token from tgt i get a
afs/cellname at REALM service ticket without des-cbc-crc key.

> However, we have a problem in FreeIPA 4.x that an
> attempt to force only a specific encryption type in ipa-getkeytab is
> ignored and instead only enctypes from krbDefaultEncSaltTypes attribute
> are generated. This bug is tracked with
> https://fedorahosted.org/freeipa/ticket/4718
>