Selfhosted

AFAIK, the only reason not to use Letsencrypt are when you are not able to automate the process to change the certificate.

As the paid certificates are valid for 12 month, you have to change them less often than a letsencrypt certificate.

At work, we pay something like 30-50€ for a certificate for a year. As changing certificates costs, it is more economical to buy a certificate.

But generally, it is best to use letsencrypt when you can automate the process (e.g. with nginx).

As for the question of trust: The process of issuing certificates is done in a way that the certificate authority never has access to your private key. You don't trust the CA with anything (except your payment data maybe).

Why?

Let's encrypt is free and secure. There is no good reason not to use it.

If you are just self hosting for your own use, just stick with letsencrypt or self signed certificates.

The paid certificates are for businesses where the users need to trust the certificate. They usually come with warranties and identity verification, which is important if you are accepting payments through your website, but it's just a waste of money for personal use.

With paid certificates you can target ancient and unsupported operating systems like windows XP and android 2, letsencrypt is relatively recent and it's not present in the root certificates of those systems

Worked as a sysadmin for years dealing with all kinds of certificates. Liek others have said if you can't automate the process a paid certificate buys you 12 months at a time in validity. Also wildcard certificates are more difficult to do automated with let's encrypt. If you want EV certificates (where the cert company actually calls you up and verifies you're the company you claim to be) you also need to go the paid route

In my experience trustworthyness of certs is not an issue with LE. I sometimes check websites certs and of I see they're LE I'm more like "Good for them"

The main benefits to paying for certs are

• as many said, getting more than 90 days validity for certs that are harder to rotate, or the automation hasn't been done.
• higher rate limits for issuing and renewing certs, you can ask letsencrypt to up limits, but you can still hit them.
• you can get certs for things other than web sites, ie code signing.

The only thing that matters to most people is that they don't get cert errors going to/using a web site, or installing software. Any CA that is in the browsers, OS and various language trust stores is the same to that effect.

The rules for inclusion in the browsers trust stores are strict (many of the Linux distros and language trust stores just use the Mozilla cert set), which is where the trust comes from.

Which CA provider you choose doesn't change your potential attack surface. The question on attack surface seems like it might come from lacking understanding of how certs and signing work.

A cert has 2 parts public cert and private key, CAs sign your sites public cert with their private key, they never have or need your private key. Public certs can be used to verify something was signed by the private key. Public certs can be used to encrypt data such that only the private key can decrypt it.

What exactly are you trusting a cert provider with and what are the security implications?

End users trust the cert provider. The cert provider has a process that they use to determine if they can trust you.

What attack vectors do you open yourself up to when trusting a certificate authority with your websites' certificates?

You’re not really trusting them with your certificates. You don’t give them your private key or anything like that, and the certs are visible to anyone navigating to your website.

Your new vulnerabilities are basically limited to what you do for them - any changes you make to your domain’s DNS config, or anything you host, etc. - and depend on that introducing a vulnerability of its own. You also open a new phishing attack vector, where someone might contact you, posing as the certificate authority, and ask you to make a change that would introduce a vulnerability.

In what way could it benefit security and/or privacy to utilize a paid service?

For most use cases, as far as I know, it doesn’t.

LetsEncrypt doesn’t offer EV or OV certificates, which you may need for your use case. However, these are mostly relevant at the enterprise level. Maybe you have a storefront and want an EV cert?

LetsEncrypt also only offers community support, and if you set something up wrong you could be less secure.

Other CAs may offer services that enhance privacy and security, as well, like scanning your site to confirm your config is sound… but the core offering isn’t really going to be different (aside from LE having intentionally short renewal periods), and theoretically you could get those same services from a different vendor.

The point of paid SSL at this stage in the game are the higher tiers of verification. Instead of just verifying that you own the domain, you can verify that you are who you say you are. These are called Extended Validation and Organizational Validation certificates. This has historically been desirable by businesses. It used to be that these higher tier certs would not only give you a lock icon in the address bar of a web browser, but also a little blurb confirming your organization is legit. Not sure if this is still the case though. You will see the extended validation when you check the sites certificate though for sure.

As far as encryption and security, there’s no difference. Also side note, the Comodo brand still technically exists but it was bought by Sectigo like 7 years ago.

So, the web uses a system called chain of trust. There are public keys stored in your system or browser that are used to validate the public keys given to you by various web sites.

Both letsencrypt and traditional SSL providers work because they have keys on your system in the appropriate place so as to deem them trustworthy.

All that to say, you're always trusting a certificate authority on some level unless you're doing self signed certificates... And then nobody trusts you.

The main advantage to a paid cert authority is a bit more flexibility and a fancier certificate for your website that also perhaps includes the business name.

Realistically... There's not much of a benefit for the average website or even small business.