Script Kerberos Ktutil to make keytabs

Question

I want to make a script that will generate the a keytab using ktutil. When running the script I want to use [user]$ script.sh PASSWORD

#script.sh
echo "addent -password -p PRINCIPAL -k 1 -e aes256-cts-hmac-sha1-96" | ktutil

Ktutil than needs a password, here I want to use the PASSWORD argument from above. How would I pass the password arguement?

Flirt

Answer 1

With GNU bash:

user="PRINCIPAL"
pass="topsecret"

printf "%b" "addent -password -p $user -k 1 -e aes256-cts-hmac-sha1-96\n$pass\nwrite_kt $user.keytab" | ktutil

printf "%b" "read_kt $user.keytab\nlist" | ktutil

Output:

slot KVNO Principal
---- ---- ---------------------------------------------------------------------
   1    1                          PRINCIPAL@YOURDOMAIN

Horsley

This is not safe. Password will be visible. – Effluent

Cannot read password while adding new entry – Erenow

@Horsley If there is \n in the environment variable (for example, in a password), the result will be incorrect. – Urine

@Giorgos-Myrianthous Variables of the environment will not be visible. It is safe. Or what do you mean? – Urine

@MaximMandrik environment variables will not be visible, but printf argument will. – Disloyalty

Answer 2

I followed the accepted answer by Cyrus but kept hitting

"Cannot read password while adding new entry" as mentioned by Arrow_Raider

I was able to overcome the error by using the slightly similar result using the below.

   {
    echo "addent -password -p ${user} -k 1 -e RC4-HMAC"
    sleep 1
    echo "${pass}"
    sleep 1
    echo "write_kt my.keytab"
    } |
    ktutil

Memoirs

This answer is underrated, and more simple than using expect. Nice work. – Youngling

Previously I always used the printf "%b" "..\n..\n.." | ktutil, but on one machine I also got hit by addent: Cannot read password while adding new entry. – Auramine

Answer 3

To create the multiple orgs keytabs and default hbase,pipe,hdfs keytab at the same time you can run the below script, which i have just created:

#!/bin/bash
read -p "Please enter space-delimited list of ORGS to create: " NEW_ORGS

clear
#echo "#################  CREATE KEYTABS  ############################"
#echo ""
kdestroy

for i in $NEW_ORGS
do
     printf "%b" "addent -password -p ${i} -k 1 -e aes256-cts-hmac-sha1-96\n${i}\nwrite_kt ${i}.keytab" | ktutil

     printf "%b" "read_kt ${i}.keytab\nlist" | ktutil

done
echo ""


if [ ! -e /home/eip/.keytabs/hbase.keytab ]
then
        printf "%b" "addent -password -p hbase -k 1 -e aes256-cts-hmac-sha1-96\nhbase\nwrite_kt hbase.keytab" | ktutil

        printf "%b" "read_kt hbase.keytab\nlist" | ktutil
fi

exit 0

Wiggs

@Lokendra_Jain If there is \n in the environment variable (for example, in a password), the result will be incorrect. – Urine

Answer 4

A version in Python

https://github.com/Tagar/stuff/blob/master/keytab.py

piping password to ktutil in shell is not secure as password will be visible in list of processes.

Since this Python scripts just interacts with ktutil using pexpect library, it's possible to implement the same as a pure shell script using expect.

Hope this helps.

Tincher

Answer 5

enjoy

import os, getpass
from subprocess import run, PIPE
import sys
userndomain, passwd, enctype = 'username@DOMAIN', 'secret', 'arcfour-hmac-md5'
input_load = f"""add_entry -password -p {userndomain} -k 1 -e {enctype}
{passwd}
write_kt {user}.keytab
quit
"""
p = run(['ktutil'], stdout=PIPE, input=input_load, encoding='ascii')

Elutriate

Answer 6

Use expect to keep the password out of the process list:

expect << EOF
    set timeout 10
    spawn /usr/bin/ktutil
    expect {
       "ktutil: " { send "addent -password -p $PRINCIPAL -k 1 -e $METHOD\r" }
       timeout { puts "Timeout waiting for ktutil prompt."; exit 1; }
    }
    expect {
       -re "Password for \\\\S+: " { send "$PASSWORD\r" }
       timeout { puts "Timeout waiting for password prompt."; exit 1; }
    }
    expect {
       "ktutil: " { send "wkt $KEYTAB_TMP\r" }
    }
    expect {
       "ktutil: " { send "q\r" }
    }
EOF

Or use a <<HERE document to provide stdin, but if addent fails to prompt, you may end up with the password in your stdout:

/usr/bin/ktutil <<EOF
addent -password -p $PRINCIPAL -k 1 -e $METHOD
$PASSWORD
wkt $KEYTAB_TMP
q
EOF

Etana

Probably in the case of expect send: if there is \r in the environment variable (for example, in a password), the result will be incorrect. I like the second example, although also has its drawbacks if the ktutil program will change (but it is unlikely and the problem will be quickly detected, because it will be immediately visible). But in this example, it is possible to use \r and similar in passwords. – Urine

The expect approach doesn't work if kubernetes runs this. It results in a keytab file that is 0 bytes. Not sure about the second. – Erenow