I've got a secure transmission system where I'm pushing host keys to a database and I'm trying to install keys generated on a Ubuntu 15 machines and install them them on a SLES 11 machine and I'm trying to install keys generated on a Centos 7 machine on that Ubuntu 15 machine.

So, is there a common mechanism for each of these machines to install host keys, this is getting really confusing and I'm thinking I'm being a bit over scrupulous. Everything is supposed to be automated and I'm figured out a decent method for collecting the keys, I just don't know where the right place to put them on the machine

Here's a key on the centos machine:

[root@centos ~]# cat /etc/ssh/ssh_host_ecdsa_key.pub ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBIl8BT33T4sEAgG56CItPWep/N3IKaUaw8Xy6Fn6k9SLsARi9zZk9FAd6H6DfbIxzkz1sjSjfq1JSVyd3slKf4M=

and here's what it looks like when I import it (via ssh manually accepting it) in my knownhosts on my ubuntu machine

root@ubuntu:/home# cat aaron/.ssh/known_hosts |1|F+Hr+T8eulEpFFFhwdJKdcOg6yQ=|yM/XLEkDPFUWO/g9vPOONBkRvtE= ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBIl8BT33T4sEAgG56CItPWep/N3IKaUaw8Xy6Fn6k9SLsARi9zZk9FAd6H6DfbIxzkz1sjSjfq1JSVyd3slKf4M=

So, it looks like the first part is in the known_hosts file is something encrypted and on the SLES machines, that part is not encrypted, so it's a bit simpler.

So my questions are

  1. How do I come up with that encrypted part so I can echo it in to the known_hosts file?
  2. How do I know if a given linux system is expecting the first hunk to be encrypted?

Manual page for sshd describes format of the file:


The /etc/ssh/ssh_known_hosts and ~/.ssh/known_hosts files contain host public keys for all known hosts. The global file should be prepared by the administrator (optional), and the per-user file is maintained automatically: whenever the user connects from an unknown host, its key is added to the per-user file.

Each line in these files contains the following fields: markers (optional), hostnames, bits, exponent, modulus, comment. The fields are separated by spaces.


Alternately, hostnames may be stored in a hashed form which hides host names and addresses should the file's contents be disclosed. Hashed hostnames start with a ‘|’ character. Only one hashed hostname may appear on a single line and none of the above negation or wildcard operators may be applied.

Except the part bits, exponent, modulus is now used together as public key. The hostname is hashed, but you can write it as a string and then run ssh-keygen over the file:

ssh-keygen -H [-f known_hosts_file]

for example ssh-keygen -H -f ~/.ssh/known_hosts

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.