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.)
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.
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.