So once again what is a symmetric algorithm in a symmetrical algorithm.
The same key is used to encrypt and decrypt the message.
An example of a symmetric key algorithm would be a yes.
Notice both the sender and the receiver using the same algorithm as well as the same key.
This can cause a major problem because both the sender and the receiver must know what the key is and
they need a method to communicate this.
The problem is how do I tell the security what the key is if I don't have a secure tunnel established
as yet I need the key to establish a secure tunnel.
But I cannot establish a secure tunnel until we both know what the key is.
So this means that we need to communicate the key out of band.
I need to phone you.
I need to ask you why I need to use some out-of-band method to tell you what to use.
So as an example if I'm in the UK and you're in the US and we want to set up a private VPN between or
out in the U.K. and Iran in the US I would have to phone me and let you know what key to use.
That's fine when we have a simple VPN but it doesn't scale well when we have thousands of routers.
There is an advantage of a symmetrical algorithm.
The good symmetric ciphers are just secure and easy to implement using modern microprocessors and they
tend to be used for bulk encryption.
There are some examples of symmetric key algorithms these days.
Yes and blowfish going explain data encryption standard or days trippled days an Advanced Encryption
Standard or A-S in more detail in upcoming slides.
But for now please realize that we still use symmetric key algorithms in the peahens today because of
the advantage that they can encrypt bulk data quickly and modern microprocessors so their encryption
standard or does is a symmetric encryption algorithm where the same key is used by the sender and receiver.
So notice the sender uses days with a key of 2:59 and the receiver uses days with the key of 2:59.
It was developed by IBM and the U.S. National Security Agency in 1975.
It has a fixed key length of 56.
Let's remember once again that a close a IP address gives you two to the power of 24 combinations days
give you two to the power 56 combinations.
So the algorithm was good but the key length doesn't meet today's security requirements and it's recommended
that you do not use days in today's corporate environments.
The problem is is that it's susceptible to brute force attacks.
By 1998 it does encrypted message was decrypted with in 56 hours and by 1999 it took just over 22 hours
to crack once again days is not recommended in today's environments.
Around the same time triple days was developed trippled days is also a symmetric key algorithm with
the same the uses triple days and the receiver uses triple days and they have the same set of keys.
In this case there are three keys.
The way triple-B is works is that it takes data is encrypted with key one that encrypted text is then
decrypted with a different key key.
And then it's encrypted with a third key.
In this case key three.
So the data is encrypted then decrypted and then encrypted but with different keys.
Now if key one and key three are the same.
This would result in 112 but key length if key one and key 3 are not the same.
It would result in 168 but coolants as you can see the key length is greater than days which was 56
bits in length.
Please note at s.a.a level it's not expected that you understand the details of all these algorithms
but I mention them here because I find it's easier to understand how the paeans work if you have a bit
of knowledge of how the algorithms function yes or Advanced Encryption Standard is the recommended symmetric
key algorithm to use today in corporate environments once again the sender and the receiver use the
same algorithm as well as the same key as this is the symmetric key algorithm Yes comes in different
variants.
Got eight hundred twenty eight point eight hundred ninety two but an 8 is 256 but yes was announced
in 2001 and became a federal government standard in May of 2002.
It was approved by the NSA for top secret information it once again is the recommended algorithm for
the peons in today's corporate environment.
The details of these three algorithms are available on the internet.
Have a look at Wikipedia and other sources for more detailed information of how the algorithms work
but cannot just have an appreciation that does triple days an ace or symmetric key algorithms that can
be useful both encryption and decryption of data.
Now an asymmetric key algorithm uses a different key to encrypt and decrypt.
So for instance the sender would be using a asymmetric algorithm like RSA.
The receiver would be using an algorithm like RSA.
But please notice different keys are used to encrypt and decrypt the data.
Asymmetric key algorithms.
So many of the longstanding problems with symmetric key algorithms like how do you exchange the secret
keys in the first place with a symmetric key algorithm.
For instance how do we send the decided private key to each other without it being intercepted.
When using a symmetric key algorithm once again without a secure channel there is no way to establish
a secure channel.
I need to securely tell you for instance what the shape key is in a symmetric algorithm but we both
need to know what the shade secret key is to establish a secure channel to be able to securely send
the key to one another.
But we can set up the channel because we don't have a key yet.
That means we have to tell each other what the key is out of.
Like by phoning one another asymmetric key algorithms allow us to solve this problem because different
keys are used encryption versus decryption.
Also note asymmetric key algorithms have key lint's far greater than symmetric key algorithms.
The key lengths vary from 512 bytes to 2048.
That's a lot of this information is out of the scope of the course but it's worth knowing so that you
can understand Hoggy peahens work with an asymmetric key algorithm.
You fusee generate what's called a private key.
Now the word private means that you don't tell anyone else what your key is.
In other words a private key is kept to oneself.
No one else gets told what your private key is a public key is derived from a private key.
So firstly a device like Arata will generate a private key.
It will then generate a public key from its private key Please note a private key cannot be generated
from a public key.
A public key can only be generated from a private key.
Now this is not a math course so we not going to get into the mathematics of public and private keys
or derived.
We as network engineers just need to have an appreciation of how they work and then how to configure
them in networking environments.
So to sum up you create a private key which you keep to yourself.
You then generate a public key from your private key your public key is then shared with the world.
Now something encrypted with your private key can only be decrypted by your public key and something
encrypted with your public key can only be decrypted with your private key.
So for instance if a on the left wants to send something to be on the right the way it works is as follows
B generates a private key a public key is then generated from these private key B then shares his public
key with a when he wants to send something to be a encrypts the data with be public key which now knows
the only key that can decrypt something encrypted with the public key is these private key.
And B is the only person that has these private key.
So a encrypts the data with these public key and sends it to B.
B is the only device or person with these private key.
So only B can decrypt the information can get really confusing.
So let me say it again if I want to send something to you that only you can decrypt I would encrypt
the data with your public key if you want to send something to me that only I can decrypt.
You would encrypt that data with my public key because only my private key would be able to decrypt
something encrypted with my public key.
Now how does this apply to the PM's while in 1976 two gentlemen Duffy and Hellman discovered a way out
of the secure channel dilemma.
In other words the issue we had with the transmission of a shady secret across an insecure medium can
be solved by using Diffie Hellman.
They found out that by using a different key certain one way functions could be undone.
The solution called public key cryptography takes advantage of a characteristic of prime and almost
prime numbers.
Specifically how hard it is to find the two factors of a large number that has only two factors both
of which are prime.
This uses things like quadratic residues and if you're a mathematician that will have no meaning I'm
sure now once again we as network engineers do not need to understand the math behind all of these algorithms.
We just have to know when to apply the algorithms in production environments.
So just understand that Diffie Hellman discovered a way to securely create a secure channel to exchange
a shade secret key which is required by algorithms like a triple days and days a cross an insecure medium
like the Internet securely so that no hacker can find out what the shed secret is.
In brief the way home and works is as follows.
The peers.
In other words the two devices involved in a VPN can yield operate a shared secret key based on the
other peers public value and their own secret.
In other words if you and I are going to set up a VPN and we need to create a shared secret key between
us by using complicated mathematics we can create a shared secret securely without other people being
able to work out what that key is.
You need at least one secret ballot to perform this function or calculation.
Remember secret or private keys are not exchanged with other people.
So the attacker has no secret values and needs to perform a discrete logarithm of a public Valley which
is computationally infeasible.
In other words in theory impossible.
So for example yes MTA takes data that we want to see insecurely using an algorithm like a yes.
Being a symmetric key algorithm requires that the same key be used for encryption and decryption.
We want to be able to work out a shared secret key between the sender and receiver securely across an
insecure medium with all kinds of undesirables trying to sniff the network and work out what the password
is.
So both peers need to establish a shared key securely and Diffie Hellman gives us the ability to do
this.
So by using public key cryptography and other words private and public keys we can work out a shared
secret securely without others being able to see that.
So when two people want to set up a VPN they use Diffie Hellman to work out a shared key.
The reason why we need that shade key is symmetric key algorithms like a require that the same key be
used on both sides.
And the reason why we use ABS is because it's good for bulk encryption.
Once the Diffie Hellman key exchange has taken place we can create a shared secret for eight years and
they a.
And the shade key can be used for bulk encryption of data which can be sent across the insecure Internet
securely and only decrypted by the receiving party.