Re: OpenVPN/IPsec - Sweet32: Birthday attacks

[IT Superhack <itsuperhack@web.de>]

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Hello Erik,

as far as I am concerned, removing ciphers from any software is
always a bit problematic.

For security reasons, it is always better to disable broken or
weak ciphers such as RC4, MD5 or similar. But this may cause
trouble if there are many legacy clients around.

In this case, mainly Windows XP-systems are affected since 3DES
was the only "safe" cipher suite they are able to use. Others
(RC4, DES) went down the drain a long time ago.

With Sweet32, it became impossible to use such a system for _any_
secure connection, no matter if its HTTPS, VPN or something else.

Back to the VPN: It seems like there is a similar problem here,
because the (at least in Germany) very popular Fritz!Box by AVM
cannot handle IPSec VPNs with AES ciphers (source:
http://wiki.ipfire.org/en/configuration/services/ipsec/avm-fritzbox).

In my humble opinion, removing the 3DES cipher is better. First
because it improves the transport security situation, although it
cannot be easily exploited. Second, the more weak techniques and broken ciphers
a legacy system supports are disabled on the majority of the servers,
the sooner people throw the old systems away.

Nevertheless, it should be mentioned in the release notes that
some clients might not work anymore, so users can prepare for this scenario.

Best regards,
Timmothy Wilson


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