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maggie

Member

Registered: 2011-02-12

Posts: 255

openssh generates 4 different types of host key but I only want 1 type

I am hardening my sshd and the recommendation is to use only ed25519 and rsa style keys. I can't make sshd only keep them; it regenerates the other styles even when I delete them and uncomment the following lines in sshd_config. What is the trick to disabling the other two?

KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256
Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-ripemd160-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160,umac-128@openssh.com

HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ed25519_key

graysky

Wiki Maintainer

From: :wq

Registered: 2008-12-01

Posts: 10,696

Website

Re: openssh generates 4 different types of host key but I only want 1 type

See /usr/lib/systemd/system/sshdgenkeys.service ... looks like if any key is not on the file system it runs with the `ssh-keygen -A` which generates all 4 of them.  Without masking this service or edited it, I don't see how to accomplish what you want.

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Leonid.I

Member

From: Aethyr

Registered: 2009-03-22

Posts: 999

Re: openssh generates 4 different types of host key but I only want 1 type

So... touch /etc/ssh/ssh_host_{dsa,ecdsa}_key and same for *pub? This will keep sshdgenkeys.service happy and with the proper sshd_config, these empty keys will never be used...

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