latest openssh can not connect to older server

[David Balažic]

Hi!

I tried to backup some files from my server with scp and failed:

$ scp  -v  root@the.server:/root/a.file  .
Executing: program /usr/bin/ssh host the.server, user root, command
scp -v -f /root/a.file
OpenSSH_8.2p1, OpenSSL 1.1.1f  31 Mar 2020
debug1: Connecting to the.server [192.168.1.11] port 22.
debug1: Connection established.
debug1: identity file /home/stein/.ssh/id_rsa type -1
debug1: identity file /home/stein/.ssh/id_rsa-cert type -1
debug1: identity file /home/stein/.ssh/id_dsa type -1
debug1: identity file /home/stein/.ssh/id_dsa-cert type -1
debug1: identity file /home/stein/.ssh/id_ecdsa type -1
debug1: identity file /home/stein/.ssh/id_ecdsa-cert type -1
debug1: identity file /home/stein/.ssh/id_ecdsa_sk type -1
debug1: identity file /home/stein/.ssh/id_ecdsa_sk-cert type -1
debug1: identity file /home/stein/.ssh/id_ed25519 type -1
debug1: identity file /home/stein/.ssh/id_ed25519-cert type -1
debug1: identity file /home/stein/.ssh/id_ed25519_sk type -1
debug1: identity file /home/stein/.ssh/id_ed25519_sk-cert type -1
debug1: identity file /home/stein/.ssh/id_xmss type -1
debug1: identity file /home/stein/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_8.2
debug1: Remote protocol version 2.0, remote software version dropbear_2011.54
debug1: no match: dropbear_2011.54
debug1: Authenticating to the.server:22 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: (no match)
Unable to negotiate with 192.168.1.11 port 22: no matching key
exchange method found. Their offer:
diffie-hellman-group1-sha1,diffie-hellman-group14-sha1


I tried OpenSSH_8.0p1-2 which is still available in the cygwin
setup-x86_64.exe wizard and that version works fine.
(the version above is 8.2.p1-1 in the setup wizard)

Regards,
David