Hi all,
You say "disable in the list." Would systems currently running these ciphers have to rebuild their certificates? Or would their system continue to run as is, but new configurations would only have the better options available.
the systems would run further with these ciphers but it won´t be possible to add new clients via WUI without changing the cipher and regarding to OpenVPN this means to change all configurations cause a OpenVPN instance have no variability with ciphers per client.
If it would break any existing systems, I would prefer to not disable it. If there was a way to change the tags in OpenVPN to add a DANGER to the label, that would be sufficent. Maybe even a link between Encyption: and the dropdown pointing to the articles describing the issu e.
I never like to disallow someone from doing something, especially if it can cause their system to not work after an upgrade. I prefer to warn them, and let them make informed decisions.
I think this is also a good idea but as far as i can see OpenSSL for example will treat DES (triple-des) with version 1.1 like RC4 (haven´t seen a similar note with e.g. Blowfish ?) --> https://www.openssl.org/blog/blog/2016/08/24/sweet32/ . So it won´t be compiled by default but you need to activate "enable-weak-ssl-ciphers in config options in the new OpenSSL version. Whereby OpenSSLs new version might fill another discussion round i think cause it seems pretty problematic without patching a lot of other software which are linked against OpenSSL (e.g. failed builds with OpenSSL-1.1 on Debian --> https://breakpoint.cc/openssl-1.1-rebuild-2016-08-26/failed/ ), there seems also to be some strange changes in the API but this only as a beneath info…
In my release 104, I see 128 bit as the lowest option. This vulnerability specifically shows that for 64 bit blocks, the problem exists. To successfully attack a 64 bit block, you would only need to generate 32 gig of traffic; definitely reasonable. However, to successfully attack 128 bit blocks requires reading 256 Exobytes, which is unreasonable to worry about at this time. I'm assuming I'm reading this correctly and BF-CBS (128 bit) actually means it is using 128 bit blocks.
I don´t think so, this problem addresses not the key lenght, it means the fixed-lenght group of bits in the 'block' for these ciphers e.g. --> https://en.wikipedia.org/wiki/Blowfish_(cipher) under 'Cipher detail' .
Finally, OpenVPN 2.4 (still very much in alpha) will support cipher negotiation, where the client and server will dynamically negotiate which cipher to use. Within a short time of its release, the problem will no longer exist since both servers and clients will be able to do behind the scenes negotiation.
Yes, 2.4. brings some hope per default in that manner beneath some other things (ECDH support, …) but who knows when they will release it. Longer time ago i integrated the '--reneg-sec' directive into the WUI for testing purposes which is pretty similar to '--reneg-bytes' but i left it behind cause IPFire serves also the "Additional configuration" possibility so a individual way to adjust both configurations (client/server) is possible.
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.
Not sure about this cause a lot of software ships their own crypto libs and do not use the system crypto, for example while the OpenVPN development time for Core 79 we tested also Windows XP systems positive with the Camellia cipher (AES too but also SHA2-512 was ok) --> http://forum.ipfire.org/viewtopic.php?f=17&t=10008&start=90#p69221 .
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).
Indeed, this is a problem and there are for sure more other problematic constellations out there…
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.
I think this is not completely wide of the mark and it does remind me a little on the RC4, MD5, SHA1 discussions. In fact this problem is known since long time but anyways this ciphers are nowadays nevertheless widely used…
Another good overview causing this topic can be found also here --> https://sweet32.info/SWEET32_CCS16.pdf .
Some thoughts from here.
Greetings,
Erik