It's now onto digital signatures now I did you tell signature is a hash value which is here which we
just discussed.
So it's the fixed lenth result of a hash function that is encrypted with the sender's private key to
produce the digital signature or the signed message.
So the digital signature is technically a stamp of approval for the sign.
It is a provider of guarantee over whatever it is that's being signed.
When something is digitally signed it provides authentication because it's been encrypted with the private
key which only the person who has the private key can encrypt with.
So that is the authentication.
It provides non repudiation because again the sender's private key is used and it provides integrity
because we are hashing a digital signature could be used for example with software.
It could be used for drivers within your operating system.
It could be used for certificates to validate that all of those things are genuinely from the person
that they claim to be from and that the integrity of them has been maintained or there's been no changes.
So if we go and have a look here at the chrome install file properties and you'll be able to do this
in any operating system or the equivalent of.
And we look here the digital signatures we click here you can see already some details me view the certificate.
What we can see is this is an issue to Google by Verizon.
So is there a sign the private key has been used to digitally sign this software code is saying this
software is legitimate and it hasn't been changed.
So as it says here in schul software came from software publisher pre-text software from alteration
after publication to know this digital signature is valid.
We have to reverse the original process so we have the digital signature here or the signed message
or the sign software.
We then use the sender's public key.
In that case it would be there a sign to decrypt to reveal the hash which you can then verify yourself.
You'll have a hash value for it.
It will have been taken from the digital signature.
You can then take the file many through the same hashing algorithm and you compare hashes and you can
see that this software has maintained its integrity but when it comes to software.
This is all happening behind the scenes and it's been verified without even knowing if verification
doesn't happen.
You get warning messages and you've seen these before.
Here's an example of them.
Windows cannot verify the publisher.
This driver software that means that it either does not have a digital signature or you see how the
code was the person that verified that digital signature that your operating system doesn't trust very
code and will go in later as to why you might trust very code or not transfer code when we get to certificates.
Windows 10 has introduced new technology called device code which is a way of using digital signatures
to lock down what your operating system will and will not run.
So device God will only allow certain types of signed files to be wrong.
Theory being that then malware cannot be run or rats or trojans because they won't be signed.
Or of course ways around this which we'll discuss later.
That device God is another layer of defense.
So let's get through this just one more time because I think it can be sometimes a little bit tricky.
So a hash value that has been encrypted with the sender or issue is private key.
That is a digital signature.
It provides authentication no repudiation and integrity.
And if you encrypt something and also provide a digital signature then you're also going to get confidentiality
along with authentication repudiation and integrity.
Digital signatures ensure that the software or whatever it is that you've got came from that person
or that publisher and it protects that software or that message from alteration after it has been published
or sent.