Let's consider whether we mentioned all the typical applications of public key infrastructure we talked
about E-F technology.
Authentication using a smart card is much safer than authentication using a key chain device because
Kerberos is integrated with public key infrastructure.
We talked about the ATO to doubt one standard for example the radius server we discussed as mine the
digital signing of programs the secure version of Internet Protocol and Web sites network access protection
technology that was briefly mentioned in one of the earlier modules can also be based on certificates.
It's the safer version using this technology we can quarantine computers that are connected to our company
network a given computer will be isolated until its health is confirmed.
Meaning for example that it has security updates and a virus scanner is installed in order to clearly
identify who's isolated.
We need a strong mechanism.
The best is a certificate issued to a given computer or the lack of such.
We also discuss software restriction policies which are mechanisms that enable blocking users from running
programs.
In conclusion the public key infrastructure has a very extensive implementation but at the same time
it's a very functional and easy to use cryptographic system in the Windows environment.
Running this infrastructure is a matter of days rather than a matter of weeks.
Let's consider now how we can trust these certificates in a moment we'll take a look at a few of them.
First certain information must be recorded in the certificate.
Above all we need to be able to read to whom the certificate was issued.
This brings up an interesting problem.
If someone shows a certificate issued to for example March in can we believe that he has really march
in not really we don't know him here.
The issue is our trust in the organization that issued the certificate.
Anyone can use a certificate.
There is no photo.
We need to trust that if an organization has issued someone a certificate that this organization verified
in some way the identity of the person applying for the certificate.
We also need to be able to read the purpose of the certificate.
Is it used for file encryption for network user authentication or the secure exchange of electronic
mail.
Certificates may have a very specific use or they may be certificates that allow the performance of
various operations.
The certificate must have a validity period.
We need to know to and from which states the certificate is valid.
It's not mainly about a certificate that was revoked but the fact that we can't trust someone infinitely
our trust must be limited in some way.
We also need to know who issued the certificate a statement from certification authority X that issued
the certificate is not enough.
We have to be able to verify such a statement.
We need to be able to verify the certification authority that issued certificates certificates may be
revoked a revoked certificate provides for immediately breaking the relationship of trust if the certificate
fell into the wrong hands or if the certification authority fell into the wrong hands.
From now on if someone took control of the certification authority we should not further trust certificates
issued by Therefore there must also be a way to inform system users that certain certificates were revoked.
This is the purpose of the certificate revoke racialist.
We need to be able to check of a specific certificate is on this list.
The user certificate must be authenticated by a digital signature of the certification authority who
issued it.
We do not trust even in our own company directly the certification authority who is responsible.
We need to have a level relationship of trust.
It must start at the root certification authority.
If we rely on a hierarchical model of certification authorities we will incorporate a public key infrastructure
as is designed in the Microsoft operating systems environment.
An alternative solution is the peer to peer network solution BGP is an example of such a solution.
In this solution there is no hierarchy of trust.
There is a person who has some sort of certificate because he knows his coworkers for example Jill insue
he vouches for them.
So they also could get a certificate.
At this point three people already have a certificate.
Joe may also have trusted coworkers for which she vouches and certifies their request to receive a certificate.
Now 12 people have certificates and we all trust each other such a model is very interesting especially
in theory.
In practice there are certain problems if there are lots of acquaintance's research suggests that six
to seven passes are enough.
Consisting of the fact that we know someone who knows someone and so on in order to include in our trust
all inhabitants on our planet seven passes and we find a friend of everyone on the earth.
The network model is great but on a limited scale it simply doesn't work on a large scale.
We would have to trust everybody and then we would not trust anybody.