04-23-2018
The files in
/etc/ssh are for the service on the server you are connecting to. it uses them to listen and exchanges keys with the client session so that the data is encrypted.
Your personal keys (as you know in
~/.ssh) provide the reverse.
When you request a connection (before signing on or anything) the server listening (default on port 22) will pass you its public key for the server. This key enables you to encrypt traffic that only the server can decrypt. You can also use this public key to verify that you have connected to the correct server. The first time, you open a connection, you will be asked to confirm the key provided by the server. If you accept, this is stored in
~/.ssh/knwon_hosts so that you can be sure you are connecting the the same server on a later occasion.
See this article for more information -
17.3. Event Sequence of an SSH Connection
I hope that this helps. If not, feel free to ask again.
Kind regards,
Robin
This User Gave Thanks to rbatte1 For This Post:
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LEARN ABOUT REDHAT
ssh-keyscan
SSH-KEYSCAN(1) BSD General Commands Manual SSH-KEYSCAN(1)
NAME
ssh-keyscan -- gather ssh public keys
SYNOPSIS
ssh-keyscan [-v46] [-p port] [-T timeout] [-t type] [-f file] [host | addrlist namelist] [...]
DESCRIPTION
ssh-keyscan is a utility for gathering the public ssh host keys of a number of hosts. It was designed to aid in building and verifying
ssh_known_hosts files. ssh-keyscan provides a minimal interface suitable for use by shell and perl scripts.
ssh-keyscan uses non-blocking socket I/O to contact as many hosts as possible in parallel, so it is very efficient. The keys from a domain
of 1,000 hosts can be collected in tens of seconds, even when some of those hosts are down or do not run ssh. For scanning, one does not
need login access to the machines that are being scanned, nor does the scanning process involve any encryption.
The options are as follows:
-p port
Port to connect to on the remote host.
-T timeout
Set the timeout for connection attempts. If timeout seconds have elapsed since a connection was initiated to a host or since the
last time anything was read from that host, then the connection is closed and the host in question considered unavailable. Default
is 5 seconds.
-t type
Specifies the type of the key to fetch from the scanned hosts. The possible values are ``rsa1'' for protocol version 1 and ``rsa''
or ``dsa'' for protocol version 2. Multiple values may be specified by separating them with commas. The default is ``rsa1''.
-f filename
Read hosts or addrlist namelist pairs from this file, one per line. If - is supplied instead of a filename, ssh-keyscan will read
hosts or addrlist namelist pairs from the standard input.
-v Verbose mode. Causes ssh-keyscan to print debugging messages about its progress.
-4 Forces ssh-keyscan to use IPv4 addresses only.
-6 Forces ssh-keyscan to use IPv6 addresses only.
SECURITY
If a ssh_known_hosts file is constructed using ssh-keyscan without verifying the keys, users will be vulnerable to attacks. On the other
hand, if the security model allows such a risk, ssh-keyscan can help in the detection of tampered keyfiles or man in the middle attacks which
have begun after the ssh_known_hosts file was created.
EXAMPLES
Print the rsa1 host key for machine hostname:
$ ssh-keyscan hostname
Find all hosts from the file ssh_hosts which have new or different keys from those in the sorted file ssh_known_hosts:
$ ssh-keyscan -t rsa,dsa -f ssh_hosts |
sort -u - ssh_known_hosts | diff ssh_known_hosts -
FILES
Input format:
1.2.3.4,1.2.4.4 name.my.domain,name,n.my.domain,n,1.2.3.4,1.2.4.4
Output format for rsa1 keys:
host-or-namelist bits exponent modulus
Output format for rsa and dsa keys:
host-or-namelist keytype base64-encoded-key
Where keytype is either ``ssh-rsa'' or ``ssh-dsa''.
/etc/ssh/ssh_known_hosts
BUGS
It generates "Connection closed by remote host" messages on the consoles of all the machines it scans if the server is older than version
2.9. This is because it opens a connection to the ssh port, reads the public key, and drops the connection as soon as it gets the key.
SEE ALSO
ssh(1), sshd(8)
AUTHORS
David Mazieres <dm@lcs.mit.edu> wrote the initial version, and Wayne Davison <wayned@users.sourceforge.net> added support for protocol ver-
sion 2.
BSD
January 1, 1996 BSD