ZyXEL Communications Corporation P663HN51 Manual De Usuario
Chapter 17 Certificates
P-663HN-51 User’s Guide
139
17.3.2 Private-Public Certificates
When using public-key cryptology for authentication, each host has two keys. One
key is public and can be made openly available. The other key is private and must
be kept secure.
key is public and can be made openly available. The other key is private and must
be kept secure.
These keys work like a handwritten signature (in fact, certificates are often
referred to as “digital signatures”). Only you can write your signature exactly as it
should look. When people know what your signature looks like, they can verify
whether something was signed by you, or by someone else. In the same way,
your private key “writes” your digital signature and your public key allows people
to verify whether data was signed by you, or by someone else. This process works
as follows.
referred to as “digital signatures”). Only you can write your signature exactly as it
should look. When people know what your signature looks like, they can verify
whether something was signed by you, or by someone else. In the same way,
your private key “writes” your digital signature and your public key allows people
to verify whether data was signed by you, or by someone else. This process works
as follows.
1
Tim wants to send a message to Jenny. He needs her to be sure that it comes
from him, and that the message content has not been altered by anyone else
along the way. Tim generates a public key pair (one public key and one private
key).
from him, and that the message content has not been altered by anyone else
along the way. Tim generates a public key pair (one public key and one private
key).
2
Tim keeps the private key and makes the public key openly available. This means
that anyone who receives a message seeming to come from Tim can read it and
verify whether it is really from him or not.
that anyone who receives a message seeming to come from Tim can read it and
verify whether it is really from him or not.
3
Tim uses his private key to sign the message and sends it to Jenny.
4
Jenny receives the message and uses Tim’s public key to verify it. Jenny knows
that the message is from Tim, and that although other people may have been able
to read the message, no-one can have altered it (because they cannot re-sign the
message with Tim’s private key).
that the message is from Tim, and that although other people may have been able
to read the message, no-one can have altered it (because they cannot re-sign the
message with Tim’s private key).
5
Additionally, Jenny uses her own private key to sign a message and Tim uses
Jenny’s public key to verify the message.
Jenny’s public key to verify the message.
17.3.3 Verifying a Trusted Remote Host’s Certificate
Certificates issued by certification authorities have the certification authority’s
signature for you to check. Self-signed certificates only have the signature of the
host itself. This means that you must be very careful when deciding to import (and
thereby trust) a remote host’s self-signed certificate.
signature for you to check. Self-signed certificates only have the signature of the
host itself. This means that you must be very careful when deciding to import (and
thereby trust) a remote host’s self-signed certificate.
Trusted Remote Host Certificate Fingerprints
A certificate’s fingerprints are message digests calculated using the MD5 or SHA1
algorithms. The following procedure describes how to use a certificate’s fingerprint
to verify that you have the remote host’s correct certificate.
algorithms. The following procedure describes how to use a certificate’s fingerprint
to verify that you have the remote host’s correct certificate.