Pick up the phone 1

Aperi'CTF 2019 - Forensic (50 pts).

Aperi’CTF 2019 - Pick up the phone 1

Challenge details

Event Challenge Category Points Solves
Aperi’CTF 2019 Pick up the phone 1 Forensic 50 34

Le directeur commercial de notre entreprise a été victime d’une attaque au président. Investiguez et rammenez une preuve de cette attaque.

Challenge: call.pcap - md5sum: ab8626c4e8fd088db4b08dc88663fa9a


Replay SIP Stream with wireshark.


Since the file is a pcap file, we can open it with Wireshark

wireshark call.pcap &


The main protocols on the pcap is “SIP” and RTP. SIP is a session protocol mostly used in VoIP communication. We can extract from the pcap the following session (Telephony > VoIP Call/SIP Flow > Flow):

graph.png graph2.png

We can certify that there is only one call of 18.105 seconds (906 packets).

Wireshark has an RTP Player embbed which let us replay the VoIP call. Some of wireshark does’nt have this features. For this I decided to use Wireshark-qt on my debian (Telephony > VoIP Call > Play stream):


Once played we got:

Ok, c'était plutôt simple mais voici le flag en majucule: APRK{S1MPL3_SIP_C4LL}.