ZyXEL Communications 2WG - Manual (Page 257)

ZyWALL 2WG Support Notes
All contents copyright (c) 2006 ZyXEL Communications Corporation.
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describe the rules governing the different uses of these certificates.
G09. How does a PKI ensure data confidentiality?
Users' public keys are published in an accessible directory. A person wishing to send an encrypted
message uses the recipient's public key to scramble the information in the message. Only the
recipient's private key can decrypt the message.
So, if Bob wants to send a confidential message to Alice, his PKI software finds Alice's public key in
the directory where it is published, and he uses it to encrypt his message. When Alice receives the
encrypted message, she uses her private key to decrypt it. Because Alice keeps her private key secret,
Bob can be assured that, even if his message were to be intercepted, only Alice can read it.
G10. What is a digital signature?
Not to be confused with a digitized signature (a scan of a hand-written signature), a digital signature
can be used with either encrypted or unencrypted messages to confirm the sender's identity and ensure
the recipient that the message content has not been changed in transmission. Digital signatures
incorporate the characteristics of hand-written signatures in that they can only be generated by the
signer, are verifiable, and cannot easily be imitated or repudiated.
G11. How does a digital signature work?
Suppose that the famous Bob and Alice wish to correspond electronically. Bob wants to assure Alice
that he originated the electronic message, and that its contents have not been tampered with. He does
so by signing the message with a digital signature.