How Ssh Works - ZyXEL Communications GS3700 Series User Manual

48.6 How SSH works

The following t able sum m arizes how a secure connect ion is est ablished bet ween t wo rem ot e host s.
Figure 357 How SSH Works
1 Host I dent ificat ion
The SSH client sends a connect ion request t o t he SSH server. The server ident ifies it self wit h a host
key. The client encrypt s a random ly generat ed session key wit h t he host key and server key and
sends t he result back t o t he server.
The client aut om at ically saves any new server public keys. I n subsequent connect ions, t he server
public key is checked against t he saved version on t he client com put er.
2
Encrypt ion Met hod
Once t he ident ificat ion is verified, bot h t he client and server m ust agree on t he t ype of encrypt ion
m et hod t o use.
3
Aut hent icat ion and Dat a Transm ission
Aft er t he ident ificat ion is verified and dat a encrypt ion act ivat ed, a secure t unnel is est ablished
bet ween t he client and t he server. The client t hen sends it s aut hent icat ion inform at ion ( user nam e
and password) t o t he server t o log in t o t he server.
Chapter 48 Access Control
GS3700/XGS3700 Series User's Guide
473