- [Instructor] Security professionals use cryptography
for several different reasons.
We describe those reasons as the four goals of cryptography.
First, the most common goal of cryptography
is to preserve confidentiality.
Confidentiality ensures that unauthorized individuals
are not able to gain access to sensitive information.
If Alice and Bob are communicating
with each other using encryptions, they want to ensure
that their communication remains private.
And, even if a third party intercepts their communication,
she is unable to read the contents.
The second goal of cryptography, is integrity.
Integrity protects messages
against unauthorized modification.
If Alice and Bob are communicating with each other,
they want to make sure that someone else
is not able to tamper with the message.
Bob wants to know that the message he received,
claiming to be from Alice,
is actually the message that Alice sent.
The third goal of cryptography, is authentication.
Many systems that verify the identity of users,
rely upon the use of encryption.
I won't cover those in this course,
but you can learn more about them
in the CISSP Identity and Access Management course.
The fourth and final goal
of cryptography is nonrepudiation.
Nonrepudiation means that the recipient of a message
can prove to an independent third party
that the message actually came from the alleged sender.
For example, if Alice sends a message to Bob
using an encryption algorithm that supports nonrepudiation,
Bob could then show the message to Charlie
and prove to Charlie that the message
actually came from Alice,
and that Bob simply didn't forge it himself.
The technology that we use to achieve nonrepudiation
is called digital signiatures.
We'll discuss digital signatures later in this course.
Nonrepudiation is only possible
with asymmetric encryption algorithms.
Remember, in symmetric cryptography,
the sender and receiver both know and use the same key.
In this approach, it would be easy for Bob
to forge a message from Alice because Bob knows
the same secret key that Alice does.
If Bob receives a message encrypted with that key,
he does know that it came from Alice
because she is the only other person who has the key.
Bob can't however, prove to Charlie
that the message came from Alice
because Bob could just as easily have created it himself.