On 02/15/2019 06:07 PM, Christoph Anton Mitterer wrote: > On Fri, 2019-02-15 at 15:57 +1100, Darren Tucker wrote: >> That was the original intent (and it's mentioned in RFC4419) however >> each moduli file we ship (70-80 instances of 6 sizes) takes about 1 >> cpu-month to generate on a lowish-power x86-64 machine. Most of it >> is parallelizable, but even then it'd likely take a few hours to >> generate one of each size. I imagine that'd cause some complaints >> about startup time. > > One way of handling this, at least if the moduli generation was nicely > interruptable, is that distros ship a file, e.g. /etc/ssh/moduli.dist > but by some mean (init script, systemd unit, maybe even sshd itself) a > daemon that does calculation of new moduli values is started whenever > /etc/ssh/moduli (no ".dist") isn't found. I'm (manually) creating the shorter moduli anew for every VM I set up (which may have but one core), but have the longer ones copied after being created *once* for every "platform" (definition subject to practicality). Running *that* much of ssh-keygen already takes longer than people are willing to wait for the VM that's needed oh-so-urgently for a customer-visible change. I can't say that I would be very happy about an out-of-the-box "Hulk smash puny CPU!!" behavior. Considering that the moduli file already varies with the distro, I'ld say that the duty of recognizing it / that situation (and reacting to it) is *not* on the OpenSSH maintainers, beyond maybe suggesting a global mechanism to do so (*). Since /etc/ssh/moduli's syntax supports comment lines, how about having the distro moduli files include one alike # DO-MODULI-WARNING This is an unchanged $DISTRO moduli file. You *want* to (create and) install one of your own (or delete this comment to hide your disgrace and make this OpenSSH shut up). and then have the distro's choice of escalating warnings / countermeasures (**) triggered by a '^# DO-MODULI-WARNING' regexp? (*) I first wanted to suggest recognizing distro's default moduli files by checksum, but that would discourage having it updated / recomputed frequently by the package maintainers (boatload of historic checksums to check for), which is *not* what we want. (**) Say, start with the equivalent of a hardcoded login banner, escalate all the way up to running a *very* niced-down moduli generation when nobody intervened for a year ... Regards, -- Jochen Bern Systemingenieur www.binect.de www.facebook.de/binect
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