To allow specific key type algorithms in the sshd server, use the HostKeyAlgorithms option in /etc/ssh/sshd_config. Even if the server has a DSA key file and that key file is referenced by the HostKey option, it will not be used unless the ssh-dss algorithm is present in the HostKeyAlgorithms list. HostKeyAlgorithms specifies the key type algorithms offered by the server or accepted by the client. There are two separate settings that control the use of key types. In OpenSSH 7.1 and higher, DSA key types are no longer allowed by default.
To allow specific key exchange algorithms in the ssh client, use the same KexAlgorithms option but instead set it in either the global /etc/ssh/ssh_config file or each user's individual $HOME/.ssh/config file. Examples: KexAlgorithms KexAlgorithms +diffie-hellman-group1-sha1 You can specify a list of allowed key exchange algorithms or add individual algorithms with the "+" option. To allow specific key exchange algorithms in the sshd server, use the KexAlgorithms option in /etc/ssh/sshd_config. If the client does not support other key exchange algorithms, the connection will fail with the message "no matching key exchange method found." In OpenSSH 7.1 and higher, the Diffie-Hellman Group 1 SHA1 algorithm is no longer allowed by default. There is a bug in OpenSSH 7.1 (7.1.102.1100) that prevents the "+" option from working it is fixed in OpenSSH 7.5 (7.5.102.1100).The order of ciphers in the list determines their preference, with the highest preference at the beginning.The ciphers in the Ciphers option are separated by commas without spaces.This is the complete list of ciphers supported by OpenSSH as of version 7.5.102.2000. To specify or add ciphers on the ssh client, use the same Ciphers option but instead set it in either the global /etc/ssh/ssh_config file or each user's individual $HOME/.ssh/config file. Examples: Ciphers Ciphers +blowfish-cbc,arcfour256,arcfour128 You can specify a list of allowed ciphers or add individual ciphers with the "+" option. To allow specific or additional ciphers in the sshd server, use the Ciphers option in /etc/ssh/sshd_config. If a client tries to connect with one of the ciphers not on the allowed cipher list and the client doesn't accept any of the ciphers on the allowed cipher list, the server rejects the connection attempt with the error message "no matching cipher found." In the versions of OpenSSH on AIX before 7.1, the default cipher list was the same as the list of allowed ciphers: due to a bug in OpenSSH 7.1.102.1100, the default allowed cipher list contains only these values: other ciphers are still present in ssh, but they are not allowed by default.
To allow root logins with a password, change the PermitRootLogin setting in /etc/ssh/sshd_config to yes: PermitRootLogin yes ssh_dispatch_run_fatal: Connection to X.X.X.X port 22: DH GEX group out of rangeīy default in OpenSSH 7.1 and higher, the root user may log in only with non-interactive methods, such as with a public/private key pair.
HOW TO USE CONFIG FILE FOR SSH ON MAC UPGRADE
To resolve the problem, continue to use OpenSSH 6.x on AIX or upgrade the software on the other side to a level that supports moduli of at least 2048 bits. The following error means that the other side does not support Diffie-Hellman keys based on moduli of at least 2048 bits. Ciphers re-enable root logins with a password, change the PermitRootLogin option in /etc/ssh/sshd_config to yes. To enable the same ciphers as in OpenSSH 6.x (plus the new ciphers available in OpenSSH 7.x), add the following line to /etc/ssh/sshd_config and ssh_config.
HostKeyAlgorithms re-enable the old Diffie-Hellman KEX (key exchange) algorithm, add the following line to /etc/ssh/sshd_config and /etc/ssh/ssh_config.
HOW TO USE CONFIG FILE FOR SSH ON MAC FULL
In this case, set HostKeyAlgorithms in /etc/ssh/ssh_config on the client to the full list of host key types with ssh-dss at the beginning. Note: Because these settings add ssh-dss to the end of the respective options, this change might not resolve the problem on the ssh client side if there are multiple key types in users' known_hosts file for the server. To re-enable DSA keys, add the following lines to /etc/ssh/sshd_config on the server side and just the line PubkeyAcceptedKeyTypes to /etc/ssh/ssh_config on the client side.
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