Tag Archives: IKE

IKE Solutions

Almost 4 weeks ago I published a pcap file with some challenges – this time four falsified configured IPsec VPN connections. If you have not solved it by now you should first download the pcap file and should give it a try.

Remember the scenario: You need to prove that the wrong VPN settings are not on your side (the four routers) but on the headquarters firewall side. Not an easy job. Now here are the solutions:

Continue reading IKE Solutions

IKEv1 & IKEv2 Capture

It is probably one of the most used protocols in my daily business but I have never captured it in detail: IKE and IPsec/ESP. And since IKEv2 is coming I gave it a try and tcpdumped two VPN session initiations with IKEv1 main mode as well as with IKEv2 to see some basic differences.

Of course I know that all VPN protocols are encrypted – hence you won’t see that much data. But at least you can see the basic message flow such as “only 4 messages with IKEv2” while some more for legacy IKEv1. I won’t go into the protocol details at all. I am merely publishing two pcap files so that anyone can have a look at a VPN session initiation. A few Wireshark screenshots complete the blogpost.

Continue reading IKEv1 & IKEv2 Capture

IKE Challenges

A few month ago I published many Layer 2/3 challenges on my blog. Beside the happy feedback I got some remarks that the challenges were to easy at all because you only needed the display filter at Wireshark while no deep protocol knowledge.

Ok, “challenge excepted” ;) here I have some more protocol related challenges for you: With this post I am publishing a pcap which has four site-to-site IPsec VPN connections inside. On the first half of the pcap all four of them are wrongly configured, hence, not working. –> What are the reasons for that? <–

Continue reading IKE Challenges

Site-to-Site VPNs with Diffie-Hellman Groups 19 & 20 (Elliptic Curve)

Similar to my test with Diffie-Hellman group 14 shown here I tested a VPN connection with the elliptic curve Diffie-Hellman groups 19 and 20. The considerations why to use these DH groups are listed in the just mentioned post – mainly because of the higher security level they offer. I tested the site-to-site IPsec connections with a Juniper ScreenOS firewall and a Fortinet FortiGate firewall. (Currently, neither the Palo Alto nor the Cisco ASA support these groups.)

Continue reading Site-to-Site VPNs with Diffie-Hellman Groups 19 & 20 (Elliptic Curve)

Considerations about IPsec Pre-Shared Keys

Pre-shared keys (PSK) are the most common authentication method for site-to-site IPsec VPN tunnels. So what’s to say about the security of PSKs? What is its role for the network security? How complex should PSKs be? Should they be stored additionally? What happens if an attacker catches my PSKs?

I am listing my best practice steps for generating PSKs.

Continue reading Considerations about IPsec Pre-Shared Keys

Site-to-Site VPNs with Diffie-Hellman Group 14

When talking about VPNs it is almost always clear that they are encrypted. However, it is not so clear on which security level a VPN is established. Since the Perfect Forward Secrecy (PFS) values of “DH group 5” etc. do not clearly specify the “bits of security”, it is a misleadingly assumption that the security is 256 bits due to the symmetric AES-256 cipher. It is not! Diffie-Hellman group 5 has only about 89 bits of security…

Therefore, common firewalls implement DH group 14 which has a least a security level of approximately 103 bits. I tested such a site-to-site VPN tunnel between a Palo Alto and a Juniper ScreenOS firewall which worked without any problems.

Continue reading Site-to-Site VPNs with Diffie-Hellman Group 14