Tag Archives: PFS

F5 Single DH use

F5 SSL Profile: “Single DH use” not working?

In the paper of the Logjam attack, a sentence about the F5 load balancers confused me a bit: “The F5 BIG-IP load balancers and hardware TLS frontends will reuse g^{b} unless the “Single DH” option is checked.” This sounds like “it does NOT use a fresh/ephemeral diffie-hellman key for new connections”. I always believed, that when a cipher suite with EDH/DHE is chosen, the diffie-hellman key exchange always generates a new b for computing g^{b}. Hm.

Therefore, I tested this “Single DH use” option on my lab F5 unit, in order to find out whether the same public key (as noted in Wireshark) is used for more than one session.

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FRITZ!OS 06.23 IPsec Proposals

FRITZ!OS ab 06.23: IPsec P2 Proposals erweitert

Es geht in eine weitere Runde bei den VPNs von und zur FRITZ!Box. Nach den unglücklichen Änderungen in Version 06.20 hat AVM wieder ein paar Phase 2 Proposals hinzugenommen, die komplett ohne Kompression laufen. Somit ist es wieder möglich, die FRITZ!Box im Aggressive Mode VPN-Verbindungen zu diversen Firewalls aufbauen zu lassen. Komisch nur, dass noch nicht alles ganz wie erwartet funktioniert. Hier kommen meine Testergebnisse.

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Elliptic-Curve

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.)

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FritzBox VPN Diffie-Hellman 14 small

FRITZ!OS ab 06.20: Änderungen bei VPNs

In den Release Notes der neuesten AVM FRITZ!Box Version FRITZ!OS 06.20 stand unter anderem: “VPN-Verbindungen unterstützen jetzt zusätzliche Diffie-Hellman-Gruppen 5, 14 und 15”. Coole Sache, ist doch die Sicherheit bei der Perfect Forward Secrecy mit DH-14 deutlich höher und der heutigen Zeit angemessen. Also habe ich das bei einem meiner VPNs direkt mal eingerichtet und entsprechend getestet. Leider hat sich aber mit der neuen Version die Kompatibilität zu diversen Firewalls/VPN-Gateways deutlich verschlechtert. Es ist also nicht nur Gewinn, die Version 06.20 am laufen zu haben.

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PFS Featured Image

At a Glance: Perfect Forward Secrecy (PFS)

During the last few months the concept of Perfect Forward Secrecy (PFS) was presented on many newspapers and guidelines. This concept is related to the session key generation for SSL/TLS as well as for IPsec tunnels. And even though many of these articles describe the benefit of PFS, I was still missing a picture that shows the main difference between the classical key exchange via RSA and the exchange via Diffie-Hellman with PFS. So, here comes my poster. 😉

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