Hi, I’m experimenting with Public Key Pinning (HPKP).
So when I renewed the certificate, HPKP was affected. At this point I’m not sure how to PIN in a way that will never mess up the HPKP whenever there’s a certificate renewal.
Assuming that the website is now not accessible anymore because of the keys in the HPKP having changed during the renewal - in other words a bricked website now.
So I have two questions:
How can I bypass the mess HPKP did, that is, not giving access to the website.
Will a certificate revocation nullify that?
Anyone has a clear guide of how to achieve correct way of doing pinning (HPKP) which will not get messed up whenever there’s a certificate renewal?
You can’t unwind the effect of pinning. If you could then bad guys would also be able to do the same and pinning would be useless.
Revoking your certificate won’t help as it just tells anyone who asks that this certificate isn’t trustworthy after all. If you explain in detail what you did people might have suggestions but it is very possible you’ve bricked it and now it’ll be useless for several months.
I did the pinning on the first-time-issued certificate.
When I renewed the certificate and the pinning was now wrong Letsencrypt has generated new keys
Yes I do have all my keys, I keep a version of all of them.
The link you provided is a very good pointer. I’m surprised I have not landed on that page despite reader some of Scott’s posts. So thank you very much for this.
One doubt that I have is, how to I generate a certificate with letsencrypt by providing it with a CSR? I do things commandline and not if there’s a param to give it a csr. Do you have a link to such an article?
I believe you should be able to use the apache or nginx authenticator with certonly but you may need to take extra steps to install (if your server is not currently pointing to etc/live/directory)
Authenticators are plugins used with the certonly command to obtain a cert. The authenticator validates that you control the domain(s) you are requesting a cert for, obtains a cert for the specified domain(s), and places the cert in the /etc/letsencrypt directory on your machine. The authenticator does not install the cert (it does not edit any of your server’s configuration files to serve the obtained certificate). If you specify multiple domains to authenticate, they will all be listed in a single certificate. To obtain multiple separate certificates you will need to run Certbot multiple times.
wow, thank you so much for the energy & effort to help! awesome !
Yes I’m using certbot, cool.
hey @ahaw021
I have used certbot as you mentioned above to generate a new certificate based on my backup key.
It generated three files:
0000_cert.pem
0000_chain.pem
0001_chain.pem
I have made all the changes, including the PINNING.
I think this 10th time getting my head into this HPKP, I think I could probably have gotten this in my mind straight now. Asking a friend to verify if he can access the website now, which we have set into an “experiment” to understand this HPKP thing.
Since I have manually generated this certificate. Next time when it expired, should I manually generate a new one or ask certbot to renew it? If with certbot renew, what’s the command to use?
@ahaw021, you Sir, deserve a BIG KUDOS for your awesome response and pointers which have helped me understand/consolidate certain things in my mind. CHEERS
@7php, I’m glad that you were able to get things fixed with @ahaw021’s help.
There is a feature that I’m working on (but have been slow to finish) that will re-use the previous key when renewing a certificate in Certbot, if you specify the appropriate option. Currently this can never be done by certbot renew, which always generates a new key every time. One of the main reasons that some users would like the ability to re-use a previous key is indeed for HPKP. So, we know that Certbot could be more helpful in this regard.
Notably, when you use a CSR, the certificate that you get cannot be renewed by certbot renew (you need to use the CSR again and run the same command again to obtain a new version of that certificate).
Hi @schoen thank you for all the awesome effort Certbot and all you do for all of us and LEtsEncrypt community.
Appreciate the info that you gave.
So to confirm, I will need to regenerate a new certificate, but I can use same CSR as follows: certbot certonly --manual --csr previous_csr_file --preferred-challenges "dns"
You confirm?
This would also mean that it will resolve the HPKP issue of not having to change the PINS - am I correct?
When you renew an expired certificate, you are also getting a new one with the same subject names. (Though in current practice, normally not the same key.) However, Certbot will save it in the same place as the old certificate, which may hide the fact that it is actually a new certificate.
A question in general:
Why does renewal of a certificate need to change the Key and not keep “the same old data, same key, initial creation date”, but with just an update on the expiry?
They private key can remain the same.
The public cert (key) will have to be new as the expiration has changed.
Understand that the public cert is cryptographically signed/encrypted - it can’t be modified.
If it could be so easily modified, we would not have much trust in this system.
I.E. What would stop anyone from just changing the expiration date?
Keeping the original creation date is also misrepresenting the facts; as that new cert was just issued (not issued previously).
(Though in current practice, normally not the same key.) However, Certbot will save it in the same place as the old certificate, which may hide the fact that it is actually a new certificate.