>> Hi everybody. Continuing with the CIA triad,
let's look at integrity.
When we talk about threats to integrity,
we are concerned about whether a data has been modified.
There are a couple of ways that can happen.
One way is through corruption,
which is accidental or unintentional modification.
Maybe it happens because
there is interference on the line
or something happens as data
traverses great lengths, for example.
Another way is through
malicious modification. That's intentional.
For example, an attacker inserts
malware into a file that gets downloaded,
or somebody captures a package in transit,
and makes modifications to it.
Or maybe they alter communication
and change a session header or a source ID.
All of that is threat against integrity.
Corruption is easier to
detect than malicious modification.
When we're just looking to protect against corruption,
we use hashes or hashing.
Another word for a hash is a message digest,
and another word is a checksum.
Those three words might be used together.
They're all good methods to use
for unintentional modification,
but with malicious modification,
we have to be more robust with our security controls.
That's because if an attacker can modify the data,
they may be able to modify the security controls.
For this, we have a MAC or a message authentication code,
or a digital signature.
We'll cover all of these things in
more detail in the cryptography chapter.
If we want to protect the integrity of
log files and audit records,
we can use write-once media
to make sure they can't be modified.
Baseline images can be put on write-once media also,
and hashes can be used with images as well.
Then the last of the security principles
in the CIA triad is availability.
This means having timely access to resources.
The most common attack against
availability is a denial of service attack.
A denial of service DoS attack has
to do with overwhelming the servers that it is so
busy responding to my illegitimate requests
that it can't respond to a legitimate request.
It could also be
someone on [inaudible] server in the server room,
but the ones we're going to look at
have to do with the resource overload.
Now, if a single system can cause a resource overload,
what about if an attacker took over 10
or 100 or 10,000 systems?
That's what happens in a distributed
denial-of-service or DDoS attack.
The attacker gets malicious software
on the systems without
zombies or botnets which launch downstream attacks,
lots of attacks look like that.
Another type of issue with availability is just failure.
Failure of devices or resources.
It can be caused by natural disaster
like a fire or a hurricane that causes
power outages or even something
like an employee strike can affect availability.
They can also have something like a ransomware attack,
which means your data is not available.
There are all sorts of ways that availability can suffer.
The answer to keeping availability alive is redundancy.
Along with that, go with the ideas
of resiliency and fault tolerance.
The idea there is to withstand an attack and
keep going on even if you have been attacked.
We also list backups here,
but when you think about availability,
you have to be really comprehensive,
and backups only work for data.
We'll talk about other solutions for
availability of hardware and software later.