2023-12-18

Since several years ago, most up-to-date distributions have had OpenSSH settings that 
prevent them connecting to RHEL6 (RedHat Enterprise Linux 6 ... end-of-life end of 2021) 
systems. 

In the process of retiring such systems, it's particularly convenient to be able to 
copy files to a new computer!  SSH-based methods are handy for this.  
Hence a desire to force compatibility as a simple, transient measure. 


The following worked, found in some useful webpage or two (which I haven't immediately found). 

Do this on the RHEL9 system, to let it connect to the RHEL6. 



# in /etc/ssh/ssh_config  find this original line (as in RHEL9)
Ciphers  aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc
#
# and insert aes256-cbc, at the start: 
Ciphers aes256-cbc,aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc



# make a file (e.g. /tmp/osc ) with this content:
.include /etc/ssl/openssl.cnf
[openssl_init]
alg_section = evp_properties
[evp_properties]
rh-allow-sha1-signatures = yes


# then set this file in the environment when calling ssh, scp, rsync or whatever, 
OPENSSL_CONF=/tmp/osc   ssh  remote.computer.name