Wireshark-users: Re: [Wireshark-users] TShark -T fields and kerberos decryption
From: Nicolas BONNAND <[email protected]>
Date: Fri, 18 Sep 2009 17:15:36 +0200

I'm facing the same problem as Guy.

What I need:
To write a perl script that uses tshark output to retrieve client name principals in kerberos AS-REQ packets in order to make stats and early detect password attacks. This script triggers an alarm if too many password attempts come from the same host.
In this case, I want to be informed what principal name was used.

I have:
**- capture file with thousands of Kerberos AS-REQ packets.*
*- tshark  1.2.2
- perl
- linux

What I would like:
**To have a tshark 3 columns output with: ipsource, ipdest and clientnameprincipal*
*( This output will be processed by a perl script. )

**What my problem is:
*When using tshark -T fields -e 'ip.src' -e 'ip.dst' -e 'kerberos.name_string', it seems unfortunately that server name is displayed rather than client name principal.
When I analyze my capture file with wireshark, I can see hundreds of 
client name principals.
When I analyze my capture file with tshark **-T fields -e 
'kerberos.name_string' , I can see none of them and get server names and 
realms instead ...  :-(*
I'm only able to see client name principals:
a) while using tshark -V
but I don't want that option because it's far too verbose.
b) while using **tshark -T fields -e 'kerberos.name_string' -w outputfile
but client name principals are lost among binary stuff in outputfile
In both case a) and b)  output data is not simple to parse.
By the way, in wireshark , whether I select "Kerberos AS_REQ/KDC_REQ_BODY / Server Name / Name" or "**Kerberos AS_REQ/KDC_REQ_BODY/Client Name Principal/Name" **and then I click on "apply as filter": I can see that filter has exactly the same name "kerberos.name_string" !!! As far as I understand, **kerberos.name_string is not related to a particular field in kerberos part, it simply means: match to whatever string wherever it is in kerberos part.*
My question is
What is the most correct way, and what are right tshark arguments to use in order to catch **client name principals with tshark ?* *Is it possible to use some syntax looking like **tshark -T fields -e 'kerberos[x:y]' to display only y bytes starting from byte x in kerberos part of packet ?


>From*: [email protected] <mailto:[email protected]>
*>Date*: Sun, 19 Jul 2009 20:10:25 +0200

Hi Guy,

Are you looking for this:
$ tshark -r dc3-dc4_Stream_8364.pcap -T fields -e kerberos.name_string |
sort | uniq

added key in 4
added key in 5
woohoo decrypted keytype:23 in frame:4
woohoo decrypted keytype:23 in frame:5


On Sun, 19 Jul 2009 11:32:56 +0200 Guy Shtub wrote:
I'm using TShark to capture SMB packets, using the "-T fields" flag to get
specific fields of the packets that interest me.
I'm able to decrypt kerberos (krb5) using a keytab file.
I can not find a way to get the decrypted Client Name (Principal) when using
the -T fields option.
If I run TShark in verbose mode -V I can get the client name.
If I run it with -x mode to display all bytes, I get all the bytes encrypted
followed by all the bytes decrypted.

Is there a way to get just the client name field decrypted with the -T
fields option?


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