Advanced users • SSH - no matching key exchange method

I am trying to SSH from RPi to Centos 4.9 server.
The RPi is running OpenSSH 9.2, the Centos server is running OpenSSH 3.9

I can SSH from a windows 10 machine to the Centos server.
I can SSH from the RPi to another RPi.

When I SSH from the RPI to Centos server I get:
"Unable to negotiate with A.B.C.D port 22: no matching key exchange method found. Their offer: diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1" (where A.B.C.D is the IP address of my server).

ssh -Q kex reports:
diffie-hellman-group1-sha1
diffie-hellman-group14-sha1
diffie-hellman-group14-sha256
diffie-hellman-group16-sha512
diffie-hellman-group18-sha512
diffie-hellman-group-exchange-sha1
diffie-hellman-group-exchange-sha256
ecdh-sha2-nistp256
ecdh-sha2-nistp384
ecdh-sha2-nistp521
curve25519-sha256
curve25519-sha256@libssh.org
sntrup761x25519-sha512@openssh.com

Since that list includes all the key types offered by the server should I not be able to connect?

From other internet posts I tried adding the following line to /etc/ssh/sshd_config, but it had no effect:
KexAlgorithms diffie-hellman-group-exchange-sha1

How can I resolve the connection between these two different versions of OpenSSH?

Right now I don't want to upgrade the Centos machine to a newer OS (that's on the cards but I need to get rsync going between the two machines first so they need to communicate over SSH as they are).

Statistics: Posted by PiPeteC — Sun Mar 24, 2024 11:55 am

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