Hi Hubert, I don't think that the guidance should be "MUST NOT". That would be exceeding the recommendation of BCP 195 and would leave administrators of devices that only support TLS_RSA_WITH_AES_128_CBC_SHA with no interoperability options. Following the guidance of BCP 195 by using "SHOULD NOT" will (hopefully) give an Administrator some pause to think about why that guidance was given. I would prefer that rather than having an Administrator just see that the guidance is "MUST NOT" and then blindly ignore it with no thought given to any consequences.
Best regards, Chris On Wed, Sep 13, 2023 at 8:23 AM Hubert Kario <hka...@redhat.com> wrote: > RSA key exchange are the worst ciphersuites you can possibly use, they > should > be MUST NOT as anything else is an improvement. > > If that's the only interoperable ciphersuite that's available in the > environment > that the administrator is configuring, they'll ignore any guidance anyway. > > On Wednesday, 6 September 2023 22:14:54 CEST, Chris Lonvick wrote: > > Hi Ilari, > > > > If a syslog server MUST NOT offer the only cipher suite that an > > associated client has available then the client will not be able > > to securely convey syslog messages to that server. That would > > break things. Changing that to "SHOULD NOT" allows an > > administrator to evaluate the risks. The administrator would > > then be able to decide if the client has to be upgraded to use a > > secure cipher suite, or if it acceptable for a time to continue > > using a cipher suite with known problems. > > > > Best regards, > > Chris > > > > On Wed, Sep 6, 2023 at 1:07 PM Ilari Liusvaara > > <ilariliusva...@welho.com> wrote: > > On Wed, Sep 06, 2023 at 12:53:39PM -0400, Chris Lonvick wrote: > >> Hi Viktor and all, > >> > >> I see your point. > >> > >> How about if the phrases "MUST NOT offer TLS_RSA_WITH_AES_128_CBC_SHA" > in > >> Sections 4 and 5 be changed to "SHOULD NOT offer..."? > >> > >> This seems to be more consistent with Section 4.2.1 of RFC 9325 (BCP > 195) > >> and will continue to allow devices to offer that algorithm --and allow > log > >> messages to continue to be delivered during a transition. > > > > How would having a MUST NOT break things? Servers are already required > > to ignore any unsupported or disabled ciphersuites. > > > > > > > > > > -Ilari > > > > -- > Regards, > Hubert Kario > Principal Quality Engineer, RHEL Crypto team > Web: www.cz.redhat.com > Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic > >
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