Hi,

I guess you are asking for fingerprint checking in the sftp connection. There is a code scatch:

string hostname = "your-host-name";

// get server fingerprint
Sftp client = new Sftp();
client.Connect(hostname);
string fingerprint = client.Fingerprint;

// loading from some storage (defining is up to you)
Dictionary<string,string> approvedFingerprints = LoadApprovedFingerprints();

// check finger print
if (approvedFingerprints.ContainsKey(hostname))
{
    if (fingerprint == approvedFingerprints[hostname])
    {
        // checking OK
    }
    else
    {
        // hostname changed !
        //   if you trust: 
            //     approvedFingerprints[hostname] = fingerprint;
    }
}
else
{
    // new or disaproved hostname
    //   if you trust: approvedFingerprints[hostname] = fingerprint;
}

SaveApprovedFingerprints(approvedFingerprints);

A brief description of fingerprint checking is given in the Rebex SFTP Tutorial, Basics.