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A certificate is essentially a cryptographic key that one entity (the "issuer") asserts was issued to some other entity (the "subject"). Whether that assertion

A certificate is essentially a cryptographic key that one entity (the "issuer") asserts was issued to some other entity (the "subject"). Whether that assertion is true now, was true a day ago, or was never true does not affect the strength or usefulness of that key for cryptography. Other attributes of the key, like its bit length, do matter, but when it was issued and when it "expires" absolutely do not. I find this misleading because the implied value of the certificate to the end user, that "you can be sure you are talking to the entity you think you are talking to and nobody else", is not really what the issuer is promising. They're just saying something like "we verified the company that bought this really is named XYZ". They are NOT saying that "the entity that operates the server you're communicating with is under the control of XYZ corp". It's entirely possible for a certificate to be sold to XYZ corp, which emails the certificate to a IT consultant, which FTPs it to a Word Press hosting company that deploys it to a server run by a cohosting company where it's used to market services that are fulfilled by independent contractors. The issuer doesn't touch on anything beyond the first step in that chain but the browser's freaking out and going full red screen the second the certificate "expires" might make you think that it does.

pathseeker 8y ago
>but when it was issued and when it "expires" absolutely do not. Of course it does. A certificate is more than a key. It's an attestation that the signer verified that the subject was the one receiving the key. Without expiration dates, I only need to control the domain for a short period of time to get a certificate that says I am that domain forever.
femto113 8y ago
A specific example--right now on disasterhousing.gov I get this message in Chrome Your connection is not private Attackers might be trying to steal your information ... This server could not prove that it is disasterhousing.gov; its security certificate expired 21 days ago. This may be caused by a misconfiguration or an attacker intercepting your connection. The first statement is extremely misleading, your connection is as "private" as it ever was, since the cryptography still works and the issuer never validated the end-to-end privacy of your information server in any way. That last statement is so misleading as to be mostly just wrong. 100% of expired certificate problems in my experience are due to an organization failing to renew because of inattention ("Bob bought the certificate 2 years ago and used an email he set up on gmail because we didn't have our own mail server back then but we do now and so no one ever looks at that email so we never saw the renewal notice"). I am not aware of any attack on SSL that leverages a certificate that is valid in every way except that it has expired, other than the possibility that an old certificate fell into the attacker's hands. However it is also entirely possible for an unexpired certificate to fall into attackers' hands, and because unexpired certificates are more valuable it is more likely that is what attackers actually will steal (or forge). I think users would be better served if certificate expiration was a more subtle warning, that perhaps slowly increases its panic-inducing-messaging over long time frames.

pathseeker 8y ago

>but when it was issued and when it "expires" absolutely do not. Of course it does. A certificate is more than a key. It's an attestation that the signer verified that the subject was the one receiving the key. Without expiration dates, I only need to control the domain for a short period of time to get a certificate that says I am that domain forever.

femto113 8y ago

A specific example--right now on disasterhousing.gov I get this message in Chrome Your connection is not private Attackers might be trying to steal your information ... This server could not prove that it is disasterhousing.gov; its security certificate expired 21 days ago. This may be caused by a misconfiguration or an attacker intercepting your connection. The first statement is extremely misleading, your connection is as "private" as it ever was, since the cryptography still works and the issuer never validated the end-to-end privacy of your information server in any way. That last statement is so misleading as to be mostly just wrong. 100% of expired certificate problems in my experience are due to an organization failing to renew because of inattention ("Bob bought the certificate 2 years ago and used an email he set up on gmail because we didn't have our own mail server back then but we do now and so no one ever looks at that email so we never saw the renewal notice"). I am not aware of any attack on SSL that leverages a certificate that is valid in every way except that it has expired, other than the possibility that an old certificate fell into the attacker's hands. However it is also entirely possible for an unexpired certificate to fall into attackers' hands, and because unexpired certificates are more valuable it is more likely that is what attackers actually will steal (or forge). I think users would be better served if certificate expiration was a more subtle warning, that perhaps slowly increases its panic-inducing-messaging over long time frames.