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<u>'''Establishing a Safe SSH Connection: Public Key Authentication'''</u>
[[Image:spoof.png|thumb|right|485px|If you receive a message like the one displayed above, you should investigate why it is happening as it could indicate a '''serious security issue''', or it could just mean that something on '''the host has changed'''(i.e. the OS was <u>reinstalled</u>)]]
When a user connects to a host using ssh, the host sends a fingerprint or digital signature to the client to establish its identity. The first time a connection is established the identity must be stored for subsequent connections. The fingerprints are stored separately for each user in a file called <code>~/.ssh/known_hosts</code> . <br /><br />From now on when you connect to that host the client will compare the received fingerprint against the list of known hosts before connecting. If the fingerprint does not match it could indicate somebody had setup a system to impersonate the computer you wish to connect to and you would receive a message similar to depicted in the diagram on the right.