On Sun, 20 Sep 2020 at 16:03, Pavel Raiskup <prais...@redhat.com> wrote:
> On Sunday, September 20, 2020 8:52:21 PM CEST Kevin Fenzi wrote: > > On Sun, Sep 20, 2020 at 07:11:29PM +0200, Pavel Raiskup wrote: > > > After upgrade of one of my servers to F33, I noticed that I can not > ssh to > > > one of my other servers running Debian 9 system (relatively freshly > EOLed, > > > I need to do something about it). On F33 I always need to: > > > > > > $ ssh -oPubkeyAcceptedKeyTypes=+ssh-rsa user@debian-9-host > > > > > > The changes in Fedora packages led me to: > > > > > > > https://gitlab.com/redhat-crypto/fedora-crypto-policies/-/commit/b298a9e1 > > > > > > Which led me to: > > > > > > https://fedoraproject.org/wiki/Changes/StrongCryptoSettings2 > > > > > > I'm curious about the effects of the change. It claims that RSA 2048 > >= should > > > stay accepted by DEFAULT, and from what I can tell the host server key > seems to > > > be RSA 2048 (at least that's what is generated by default on Debian 9): > > > > > > $ ssh-keygen -l -f ssh_host_rsa_key.pub > > > 2048 SHA256:<...> root@debian-9-host (RSA) > > > > > > Can anyone translate to me if this is really expected or a bug? > Effect is that > > > Fedora 33 clients can not ssh to Debian 9 hosts by default (I'm not > sure about > > > the supported Debian 10, and the key quality there). > > > > I thought this was actually due to openssh dropping support for > > 'ssh-rsa': > > > > https://www.openssh.com/txt/release-8.3 > > > > (ie, the sha-1 ssh-rsa) > > Well, I did: > > $ cd /etc/ssh > $ rm ssh_host* > $ ssh-keygen -N "" -t rsa-sha2-512 -b 4096 -f /etc/ssh/ssh_host_rsa_key > $ dpkg-reconfigure openssh-server > ... generates the remaining ECDSA and ED25519 ... > > I would just double check that is the file being used for host keys and not something been altered on the hosts /etc/ssh/sshd_config [I banged my head on this recently so it is an off chance it might be the case.] > New host signature detected, but I still get on F33 when trying to ssh: > > $ ssh -vv ... > debug1: Offering public key: /home/praiskup/.ssh/id_rsa RSA SHA256:... > debug1: send_pubkey_test: no mutual signature algorithm > ... > > And still -oPubkeyAcceptedKeyTypes=+ssh-rsa helps... Does that meant that > the > ssh-keygen on Debian 9 is broken? How am I able to tell this is server or > client problem? > > Pavel > sshd -d -p 2222 on the server and then see what it is saying it is doing. look for debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,null> or some similar item. also look to see what grep KexAlgorithms /etc/ssh/sshd_config says if it has a default of ssh-rsa in its list and none of the rsa-sha2 items.. the server will try this anyway. -- Stephen J Smoogen.
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