How does having a custom root certificate installed from school or work cause one to be monitored?

Question

I was reading an article which said that if you install custom root cert from a third party then they can decipher all communication between you and others.

But that doesn't make sense. What I understand is that root cert allows SSL mechanism to verify if a certificate provided by connecting party is legit or not.

So unless someone(company, work, hacker, etc) really tries to impersonate by doing mitm. Only then the compromised root cert will come in play as that would be used to pass fake cert as valid cert.

otherwise just simply having a custom root cert isn't like decrypting all your ssl traffic. Unless the same org has also installed a software that acts as a proxy for all internet traffic. It requires active intercepting, decrypting, and re-encryption of all traffic. So either by installing malware on the computer or monitoring internet traffic.

correct?

Answer 1

I was reading an article which said that if you install custom root cert from a third party then they can decipher all communication between you and others.

I have no idea what you were reading (citations would be helpful). But you are right in that it is not sufficient to just have a custom root CA certificate installed as trusted - the school/work also has to be an active man in the middle in the traffic and use this CA certificate for SSL interception.

So either by installing malware on the computer or monitoring internet traffic.

Not only malware installed on the computer can monitor the traffic. It is actually common that trusted programs like antivirus or parental control software do this.

And when being directly inside the company (or school) network the path to the internet is usually through the companies firewalls and proxies anyway. Even when connecting from remote with a VPN or other access software the traffic is routed and inspected through company controlled firewalls/proxies, either in the company directly but more often also somewhere in the cloud.

Answer 2

If you use https for example to buy stuff from Amazon, Amazon will send you a certificate to prove it’s them, and that works because nobody other than Amazon can get an “Amazon” certificate from one of the companies whose root certificates your device trust.

But if you let me install a root certificate on your device that I created, then I can create an “Amazon” certificate signed by this root certificate, and since your computer installed my root certificate, it would trust this certificate. With a little bit of hacking I can redirect all request intended for Amazon to my site, and because of the root certificate on your device your computer would trust it. Without the root certificate your computer would refuse to touch the fake Amazon site.

And of course that applies to any website. The root certificate makes your computer trust any site I redirect you to.

Answer 3

Unless the same org is also install software that acts as a proxy for all internet traffic. It requires active intercepting, decrypting, and re-encryption of all traffic.

Why else do you think they want you to install their root cert? If it was for a legitimate purpose (securing their own properties), they could obtain certificates from a trusted third-party CA. If they want to become a root, with the ability to sign anything, it's because they want to operate outside of the rules of a legitimate CA — that is, they want to impersonate other sites on the internet in order to monitor your traffic. Software to do so is readily available to all kinds of businesses and organizations. In short, someone who asks you to install their root cert is MITMing you, at least some of the time, and probably at all times when you are connected to their network.

Answer 4

I was reading an article which said that if you install custom root cert from a third party then they can decipher all communication between you and others.

Its common practice for organisations to use internal certificate authorities to decrypt traffic as most internet communication is encrypted now. Although it's theoretically possible to decypher all traffic send and received by you, in practice storing this information would require a huge amount of storage. Usually, packets are inspected using the CA for SSL decryption then if the packet is allowed to pass through the firewall, the decrypted traffic is discarded.

The image below demonstrates the process well:

Without using the internal root CA the companies firewall, IDS/IPS, etc., can only scan a packet's headers to determine if it should be permitted or blocked.

With SSL decryption, the firewall decrypts the entire packet to scan its full contents, known as DPI (Deep Packet Inspection). DPI allows for better protection from malware and can also be used to detect applications that should be blocked using non-standard ports to bypass firewall rules, for example, FTP using port 80 vs 21.

So unless someone(company, work, hacker, etc) really tries to impersonate by doing mitm. Only then the compromised root cert will come in play as that would be used to pass fake cert as valid cert.

That's correct; the process of SSL decryption is a MITM attack.

otherwise just simply having a custom root cert isn't like decrypting all your ssl traffic. Unless the same org has also installed a software that acts as a proxy for all internet traffic. It requires active intercepting, decrypting, and re-encryption of all traffic. So either by installing malware on the computer or monitoring internet traffic.

That's also correct; the certificate alone is just a certificate that's trusted within your machine. The organisation will need to pass your traffic through them somehow to perform the MITM. This is usually through a VPN, proxy or by default if you're connected to the internal network.

If you wish to learn more about how SSL decryption works the following white-paper is good: https://www.paloaltonetworks.com/apps/pan/public/downloadResource?pagePath=/content/pan/en_US/resources/whitepapers/decryption-why-where-and-how

Answer 5

The true answer depends on the fact who possesses the private key corresponding to the certificate, and how much do you trust them?:

• "Normal" trusted CAs don't have the private key they are certifying (their own CA key excepted), so someone having or installing a normal certificate can do no harm. And CAs take great care to keep their private key secret.

• "Normal" private keys are created in a trusted environment and they are protected, so only the owner ("subject") possesses the private key.

• "Normally" policies make sure that the CAs certify only subjects they trust (i.e. the identity had been checked), and clients (server too) will check whether a certificate offered actually matches the subject.

So to be in danger, an adversary has to present a certificate that your client trusts. In turn this means the subject of the certificate has to match, and the certificate has to be signed (issued) by a trusted CA. Here is where your CA comes into play: The owner of a CA can certify anything. If you trust that CA, you trust any certificate issued by that CA.

Even without a bogus CA, a stolen private key of a "normal server certificate" can bring you into trouble (the "man in the middle" attack).

Amazingly my mobile phone complains "your network might be monitored" because of the CA certificate of "Deutsche Telekom Root CA 2"; I'd guess most certificates that are pre-installed are much less trustworthy, but you get the idea...