Thursday, December 24, 2015

How to manage kerberos keytab file?

1. Use klist to display the keytab file entries:

klist -e -k -t  mykeytabfile.keytab
or klist -ekt nsupdateuser.ktab
or type command:

#ktutil     # execute this command
ktutil:     # this prompt will appear
ktutil: read_kt /etc/apache2/http.keytab   #read keytab file
ktuilt: list                             #list all princples


[root@customer-prod-util-101 utilscripts]# klist -e -k -t  nsupdateuser.ktab
Keytab name: FILE:nsupdateuser.ktab
KVNO Timestamp         Principal
---- ----------------- --------------------------------------------------------
   1 09/08/15 21:50:45 (aes256-cts-hmac-sha1-96)
[root@customer-prod-util-101 utilscripts]#

2. Following is an example of the keytab file creation process using kerberos method :

  > ktutil
  ktutil:  addent -password -p -k 1 -e rc4-hmac
  Password for [enter your password]
  ktutil:  addent -password -p -k 1 -e aes256-cts
  Password for [enter your password]
  ktutil:  wkt username.keytab
  ktutil:  quit

Following is an example using Heimdal Kerberos:

> ktutil -k username.keytab add -p -e arcfour-hmac-md5 -V 1

3. Obtain a ticket-granting ticket using the keytab for testing:

You can check that the keytab contains the appropriate encryption key by attempting to use it to obtain a ticket-granting ticket. This can be done using the kinit command:

#kinit -k -t /etc/nsupdateuser.keytab    # here nsupdate is username exiting in AD. this has privileges to update dns records on win DNS.
#klist                <#will show if ticket is created or not

example :

[root@customer-prod-util-101 ~]#  kinit -k -t /root/utilscripts/nsupdateuser.ktab nsupdate   # uses default domain
[root@customer-prod-util-101 ~]# klist
Ticket cache: FILE:/tmp/krb5cc_0
Default principal:

Valid starting     Expires            Service principal
12/24/15 05:29:49  12/24/15 15:29:49  krbtgt/
        renew until 12/31/15 05:29:49
[root@customer-prod-util-101 ~]#

   Or try to login to test if keytab file works :

Test with out keytab file:

#kinit username@MYDOMAIN.COM
password>     // pass password of username

Test with keytab file:

#kinit username@MYDOMAIN.COM -k -t username.keytab

4. Using a keytab to authenticate scripts:

To execute a script so it has valid Kerberos credentials, use:

  > kinit -k -t mykeytab; myscript

list out principle :

ktutil:  rkt nsupdateuser.ktab
ktuilt: list

5. Merging keytab files:

> ktutil
  ktutil: read_kt mykeytab-1
  ktutil: read_kt mykeytab-2
  ktutil: read_kt mykeytab-3
  ktutil: write_kt krb5.keytab
  ktutil: quit

6. Delete principle:

ktutil: rkt
ktuilt: list
ktutil: delete_entry slot-number
ktuilt: wkt
ktuilt: quit

7. Destroy cached ticket:

kdestroy -A  //all cache will be destroyed
kdestroy -C  //this cache will be deleted only

#kdestroy -c "FILE:/tmp/krb5cc_0"

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