On 02/11/17 17:16, Jan Just Keijser wrote: > Hi, > > On 01/11/17 19:37, Simon Deziel wrote: >> On 2017-11-01 02:08 PM, Steffan Karger wrote: >>> On 01-11-17 17:16, Jan Just Keijser wrote: >>>> On 29/10/17 02:49, Jason Haar wrote: >>>>> Best practice would be to routinely rotate secrets, to mitigate >>>>> configuration misuse/loss, etc. >>>>> >>>>> Due to CAs, certificates already support that concept, >>>>> but tls-auth/tls-auth do not. >>>>> >>>>> So wouldn't it be a good idea to allow tls-auth/tls-crypt to contain >>>>> multiple keys, so that the key could be rotated without an outage >>>>> (really like a "major upgrade"). i.e. >>>>> >>>>> 1. replace server key with one containing old + new >>>>> 2. replace client config, replacing old key with new one >>>>> 3. wait weeks/months (probably) until you know all clients are >>>>> reconfigured >>>>> 4. replace server key with just the new one >>>>> 5. rotation is now complete >>>> someone else asked me a similar question just lately, so you're not the >>>> only one facing this issue. >>>> There is something to be said for such a replacement scheme, BUT to do >>>> this properly would require an OpenVPN protocol change, IMHO; the >>>> problem is that if you allow multiple tls-auth/tls-crypt keys that you >>>> end up unhashing EVERY packet with EVERY key to see if there is a >>>> match. >>>> This will kill performance; performance already takes quite a hit with >>>> tls-auth set. >>> The first byte of an openvpn packet contains an opcode that indicates >>> whether a packet is a control channel packet or a data channel packet. >>> Only control channel packets are affected by tls-auth (or tls-crypt). >>> Data channel performance should be impacted by tls-auth. >> Data channel performance should /not/ be impacted by tls-auth. :) >> > of course, Steffan and Simon are absolutely right - I've misread the > docs+code once more: Open mouth, Insert foot. > > However, in my tests I have seen that data channel performance **IS** > impacted by tls-auth. > I've just repeated one test: 2 servers, connected via gigabit ethernet > on a quiet network. > > OpenVPN 2.4.3 and OpenVPN 2.4.4 running: > > Setup 1: > cipher aes-256-cbc > auth sha256 > ncp-disable > > > Setup 2: > tls-auth /etc/openvpn/ta.key 0|1 > cipher aes-256-cbc > auth sha256 > ncp-disable > > then run iperf over the tunnel. > > In setup 1 I consistently get 244 +/- 4 Mbps > In setup 2 I consistently get 232 +/- 3 Mbps > > So even though the impact is not enormous, there DOES seem to be an > impact on performance when using 'tls-auth' ... Could it be related to tunnel renegotiations? It depends of course on the runtime of these tests. It would also be interesting to see the if the amount of control vs data channel packets ratio changes when flipping --tls-auth. And also if there's some changes in the packet sizes.
-- kind regards, David Sommerseth OpenVPN, Inc
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