Since the beginning of this year, Let’s Encrypt rolled out a new shortlived profile for certificates that make them valid for only 160 hours. The intention, as they say, is to encourage automation and reduce the window of certificate compromise (because revocation is somewhat a flakey thing).
Yet, I haven’t seen a lot of news about it since then. Hence the question: is this shorter cert thingy something you considered and deployed for your homelab?
As for me I’ve set up lego-acme with profile: "shortlived" on my rig. Lego runs on a bihourly cronjob, but only renews when a cert has >=3 days to expiry. It’s been pretty much a set-and-forget experience, although some more monitoring would be nice.
Honest, non-techie question: How is it an advantage? Given modern crypto isnt it more likely that a mitm didn’t crack the crypto but instead got somehow else in the middle and just can “ignore” certs renewals?
Several reasons
You make some good arguments so I’m not attacking you at all, just my thoughts on your points. These short renewal times are getting to the point of ridiculousness and creating another point of failure with little time to do anything about it. I find these super short certs less than useful, create many more possible problems, and not really necessary except for a small set of circumstances. And I have been in IT as a web dev/sys admin/systems architect for over 30 years now.
My last job had an Onlineshop, 4years in a row the colleague dealing with ssl wad on vacation when the cert ran out.
Your colleague sucked at automation. Normally, I’d say no one should be bothered on vacation, but in this case you should have called him on his vacation, since he didn’t value anyone else’s time either.
The manager sucked. There’s a lot of solutions to this issue but cross training and proper backup preparation are the most ideal ones.
That was already the case with the 90 day ones. No sane person is going to be manually renewing certificates every 3 months.
Emphasis on “sane”
A private key leaking is bad, since anyone with the private key can decrypt data that was encrypted with it.
Traditionally, the way that leaked certs were handled was via Certificate Revocation Lists (CRL). CRLs contain lists of revoked certificates - their serial number, revocation date, and the reason why they were revoked.
However, CRLs are imperfect. Checking for revoked certificates every time you go to a site would slow things down a lot, as the lists are now too large to check and download real-time. Modern browsers and other TLS clients periodically download the lists in the background. Also, it might take a while between when the certificate is compromised and when the company notices the compromise.
Because of this, the CA/Browser forum (a group with all the major browser and TLS certificate vendors) have started dropping the max lifetime of certificates. The idea is that even if a private key does leak, the time frame that it’s usable for will be significantly shorter and any leaks should (in theory) cause less damage.
All modern deployments, regardless of if they’re using free or paid certs, should have their renewals fully-automated, so in theory the validity period shouldn’t matter as much as it did in the past. All major vendors (Let’s Encrypt, DigiCert, Sectigo, GlobalSign, AWS, SSL .com, etc) support ACME now. Reducing the validity is also a forcing function t o ensure automation is actually implemented.
I’m not sure that’s possible, since an attacker in the middle shouldn’t be able to obtain a valid certificate for the domain. Certificates have a “not valid after” date encoded into them, after which the certificate is considered invalid and you get an error.
The real value is in the agility needed to update certs every six days.
Six days is still too long to leave a compromised key in play, but anyone who can rotate their keys every six days can probably also rotate their keys quite quickly if there’s a comprise.
You’re gonna get different viewpoints, ranging from “yeah, but it’s popular” to “shut up”.