Why are root certificates needed?

Question

Digital certificates

A little confused about cause and effect relationships.
Understanding SSL certificates. It seems that I understood that a special center issues certificates, while, in fact, it signs the newly created certificates with its own certificate.
After that, the certificate (freshly created) is installed on the site and allows you to ensure that the site is "real".
It seems that this whole construction is based on the fact that only the certification authority has the only root (?) certificate that all the others are signed with.

Now the question is: why is everyone so afraid that someone will install a left root certificate on their system? And immediately the second question: why does any Fiddler that installs its root certificate into the system work at all?
After all, when entering a site, it will have its own certificate, signed by a very specific root certificate. And not the left that someone planted in the system.
Why do "left" root certificates work at all if no one has signed anything with them yet?

Answer 1

On the example of our state sites
There is a site on which ssl encryption should work. But ours do not want to do it normally, because they are enemies, and they make YOUR ssl certificate, signing it with YOUR certificate center.
As a result, when you go to the site - the browser will swear, because. he sees ssl, but he cannot check who issued it, because. not a public center issued
a certificate. In order to prevent this from happening, it is required to put a root certificate from our certification center into the system. After that, the browser will stop swearing, because. now he can track this site certificate (and check it) to the certification
authority
Because when you go to the site of the same Google, the certificate of the site is checked by the center from Google, and if this site is replaced by the provider, you will know about it in the browser
. But, if you installed the left certificate from the center, and it will issue a certificate for the Google site, and the provider will change this page on its own - the browser will not swear, because it will match the ssl certificate of the site with what is indicated in the root (from the cert center) ...
By the same principle, proxy servers are made in many companies, putting their certificate on the user's PC. This allows them to decrypt all traffic that is encrypted. And as a result - to receive and write down information - what did the user do on the site (from which, in theory, ssl protects, from substitution of the site and interception of information entered on it)

Answer 2

The whole PKI system is hierarchical and built on trust. Nothing else. Only on trust, which is enough to deceive once in order to stop trusting the system as a whole.
There are a number of firms that issue SSL certificates. They are not the best and not the most correct, just one day they got together and decided to stir up business. Why does everyone trust them? Yes, simply because until recently there was no reason to accuse them of fraud - everything is in order (it was) with the "internal police", which threw violators nafig from the beach.
And - most importantly - everyone trusts them, because their root certificates are located in the Windows and Mozilla root certificate stores (Google uses the Windows store).
And all
No exclusivity - just a dumb deal the size of the world. But, since it is always possible to put your own certificates in the root store (except in android, which immediately starts squealing "ahhh, Big Brother controls me!"), This scheme suited everyone.
Until the guys decided to shoot themselves in the foot by stopping the issuance of certificates in the .ru/.su/.by/.rf zones simply for political reasons. Their right is private business - it is such a private business. But then everyone abruptly somehow remembered that all the "global certification centers" are not world-wide at all, but just a bunch of impostors.
And soon we will have state SA, state certificates, state browsers and everything else in the order of import substitution.
Now about how the validity of the certificate is checked. And it is checked very simply - if the certificate is issued by a CA that is on the trusted list - it is valid.
ALL!
You can deploy your CA, put its certificate in the root store on your computer - and all the certificates issued by it - for you - will become valid. Release at least for vk.com, at least for whitehouse.gov.
And that's exactly why everyone is so afraid to put a certificate from some state CA in the root store - because everyonethe certificates issued by him will be considered valid by the system! It makes no difference between a certificate from Thawte and from Comrade Major Inc. - she will accept a certificate from both. And Comrade Major, having received the opportunity to issue certificates that are valid in your system, will issue them on the go and slip them instead of "real ones", gaining access to session keys and thus decrypting https traffic (which is what Fiddler actually does)

Answer 3

Well, let's start with the fact that there are a decent set of root certificates. Not one, and not even a dozen. Example:

64 pieces. And the certificate signed by any of them is considered trusted by the system. This, in fact, is the reason why they are afraid to get an additional root certificate - you don’t know in advance who has the ability to sign with it, and you can distinguish a certificate signed by a new added root (transitively or not) only after you receive it , while most programs do not allow the user to block a connection established using a trusted certificate. That is, at first they will fuck you with him, then you will have to clean up the consequences.
Fiddler installs a freshly created (this is important, a new key pair that no one else has) root certificate in your trusted roots, and uses it to generate certificates on the fly for each site you break into, slipping them into the browser so that did not blather, but he himself performed the role of man-in-the-middle.
The question of trusting the existing "roots" remains on the conscience of the system administrator (that is, you), while updates to the list of root certificates may arrive over the network, after which you again need to check the storage in case of undesirable root certificates for you.

Answer 4

Fiddler intercepts the connection, creates an "intermediate site", with the same name, which is signed with the left certificate. So he can see all the data being sent and HTTPS is no longer secure.
That's why everyone is afraid of left-handed certificates, so that your traffic / passwords / card data / correspondence is not listened to locally or at the provider level.

Answer 5

It seems that this whole construction is based on the fact that only the certification authority has the only root (?) certificate that all the others are signed with.

Exactly. The system is based on trust in the CA.

why is everyone so afraid that someone will install a left root certificate on their system?

Because this will allow an attacker to generate their certificates in arbitrary names, signed by a root certificate that your system trusts and, if possible, redirect traffic, send you to your site or view your https traffic that you think is encrypted.

And immediately the second question: why does any Fiddler that installs its root certificate into the system work at all?

Without installing its root certificate, Fiddler will not be able to intercept https traffic. Anyone who installs Fiddler must understand that a vulnerability arises in the system.

Answer 6

It seems that this whole construction is based on the fact that only the certification authority has the only root (?) certificate that all the others are signed with.

No. Only the certification authority has the private key of this certificate. And the certificate itself is distributed to everyone and even in some cases pre-installed. If a CA leaks its private key, it means that all certificates signed by it are compromised.
And the whole scheme is based on the fact that both sides of the exchange "trust" the certification authority.
About fiddler did not understand the question. Why shouldn't it work? Many applications work with certificates. You can even create your own CA and generate certificates for your friends.

And not the left that someone planted in the system.

For example, by attaching a left CA certificate, you can make a phishing site with a certificate signed by this left CA and everything will be beautiful in your browser. It is unlikely that someone will go to check the details of the certificates. And it can be difficult for phishing sites to get the "correct" certificate. Although now, in my opinion, this is no longer relevant - there are services that generate certificates for everyone.