Tag Info

Hot answers tagged

20

The technical reason is to keep CRL size under control: CRL list the serial numbers of revoked certificates, but only for certificates which would otherwise be still valid, and in particular not expired. Without an end-of-validity period, revoked certificates would accumulate indefinitely, leading to huge CRL over time. However, since network bandwidth ...


16

There is no such thing as a non-signed CRL; the signature field is mandatory, and any system that uses the CRL will verify the signature. In pure X.509, a CRL will be deemed "acceptable" as a source of information about the revocation status of a given certificate E if it is signed by an "allowed revocation issuer": the CRL's signature must match the public ...


13

Revocation is the only method by which a certificate authority may propagate the information that a private key has been compromised. It is, in fact, a damage containment system: in the unfortunate event of a private key being stolen, the revocation system will make sure that nobody trusts the corresponding certificate more than one week or so after the ...


12

There's just no way to fix it. Even if the registration period is two years and a one year certificate is issued, you could still sell or drop the registration next week. There's nothing the certificate authority can do about that. (Well, I suppose they could monitor the registrations and if there's a change in registrant, they could revoke the certificate. ...


11

There are several problems with OCSP. Some of them: It puts too strain on the OCSP responder (minor issue) It makes your browser respond slower, as it has to ask the CA before visiting the site. Privacy reasons: The CA gets the serial number requests for all the certificates you ask, so it can pinpoint which sites you visit. Who says it will not sell that ...


10

Although the certificate has a finite validity period it can be revoked at any time. The act of revocation places the serial number of that certificate into a certificate revocation list (CRL). Each certificate will include a link to a location where the latest CRL has been published by the issuer of that certificate. This means that if a certificate is no ...


9

It is a bug of OpenSSL (at least in version 1.0.1c); precisely, a bug of the command-line "ca" option handling. If you look at the apps/ca.c source file in OpenSSL source code, you may see that the MAIN() function begins by parsing the command-line options, then reads the configuration file, then does this: ...


7

Some CA do not offer an OCSP server, relying instead on CRL (notably, full OCSP with support for client nonces is rather expensive for the CA). And among those who do implement OCSP, many botch the job, resulting in OCSP responses which are not, per se, verifiable (e.g. the OCSP response is signed with a dedicated OCSP responder certificate for which the ...


7

Do I have any assurance that the previous owner does not have a valid HTTPS certificate for the site? No, you don't. CAs can issue certificate that are valid after the expiry date of the domain (at the time of issuance). Even if they didn't, a domain could be transferred before its expiry date. In addition, you can't possibly control all the CAs ...


7

Segmenting the space of certificates so that "partial" CRL can be computed is possible and supported, but it must be done properly. One base principle of CRL is that a CRL should be amenable to processing regardless of how it was obtained: that's the whole point of having signed objects. Since a certificate is considered as non-revoked by virtue of not ...


7

About the replay attack, the CRL is time stamped with the date of generation and a date for the next update. The nextUpdate date is mandatory in the PKIX profile. If a certificate is revoked, the old CRL can be replayed before nextUpdate if an unsecure channel is used.


6

A couple fundamental things: The basis of a CRL is a promise for a certain time period. That means a begin time and an end time. Once a CRL is made and signed, it can't be changed, so it lasts as long as it lasts, and can't be trusted after that. In essence, you won't know until you check. A CRL in its regular form is one big list. You can't assume ...


6

I find the question useful, because it is actually hard to find out if a certificate got revoked the right way. If you know who issued the original certificate you can download the CRLs (which contains only the serial numbers and the date of revocation, not the revoked certificate itself). If not you are out of luck. If you know the serial number of the ...


6

The question is... a bit complex. The critical issues are existence and availability of intermediate CA certificates. Consider the following points: Root CA are not "revoked". Revocation is a mechanism by which the issuer for a given certificate specifies, directly or indirectly, that one of its issued certificates is not to be trusted and must not be used ...


6

From RFC 5280 3.3 Revocation An entry MUST NOT be removed from the CRL until it appears on one regularly scheduled CRL issued beyond the revoked certificate's validity period. If you have a lot of changes (people leaving etc.) it's best to not make the certificate validity too long otherwise the CRL can grow large (some CRLs are > 30MB which ...


5

The big one - IMO - is the speed. I've used a couple different plugs and configurations to enable OCSP in browsers, and even in a lab environment where the OCSP server is unburdened and one hop away in a high bandwidth environment, the OCSP checking can be a serious delay in session establishment. I've even gotten plenty of user complaints, even when the ...


5

Since I can't comment, apparently, I want to clarify a couple of points. CT does not require all browsers to use it: there is a herd immunity conferred even if only one browser does it. And, BTW, Chrome's next release includes CT support. Webservers do not have to change to support CT - CAs can include the SCTs in issued certificates. Some CAs already do ...


5

There is no global directory of all issued certificates (X.509 was designed to support the Directory, but it never existed in practice). You will have to contact "all CA" and ask them nicely. Basically, this would mean going to their site, and using the "I lost my password" feature so as to regain control of your account, if it exists. Details vary depending ...


4

EKU is Extended Key Usage; this is a certificate extension described in X.509 (RFC 5280), section 4.2.1.12. As the RFC says: In general, this extension will appear only in end entity certificates. because, contrary to "Certificate Policies", there is no notion of inheritance and propagation of EKU along a certificate path. The EKU extension tells ...


4

"Rekey" is a term which is usually employed when obtaining a new certificate: it means that you want the new certificate to use a newly generated key pair, instead of reusing the same public key as was in a previous certificate. "Revocation" is the act of declaring, on the CA side, that a given certificate should no longer be considered as valid (it is a ...


4

In practice, what software can support is uniformResourceIdentifier. The extension then contains a URI which points to the CRL. http:// and ldap:// URL are rather common; https:// URL for CRL download raise interesting issues since the server certificate must then also be validated (so, in practice, it does not work well, or at all). In situations where ...


4

A CA must indeed publish CRL regularly, and if the CA is offline, then human intervention is needed. Each CRL has an issuance date (thisUpdate) and a provisional date of next publication (nextUpdate) which everybody uses as an end-of-validity date for the CRL. The next CRL must be published before reaching the nextUpdate date of the current CRL; otherwise, ...


4

The first problem I can see is how do you find the first certificate? If you've visited the site before, then I suppose you could, but for anyone that doesn't keep certificates around from all the sites they have visited, we'd need some infrastructure to be able to look up all certificates that resolve for a particular CN. Additionally, such a system might ...


4

The private key of the CA is needed because the revocation must be signed by the CA. Else it would be possible that the revocation is done by any entity.


4

First off, let's be clear: the client certificates are not self-signed. They are signed by a CA, and that CA's certificate is self-signed. This is important, because a self-signed certificate cannot be revoked at all, by definition: revocation is an information coming from the issuing CA; a self-signed certificate is its own CA. A second important point is ...


4

Certificate Transparency is a heuristic defence mechanism which does not detect misissued certificates; instead, it strives to allow faster detection of misissued certificates. The core idea is that of Glasnost. It so happens that most successful attacks rely on an asymmetry of information. Suppose that I want to impersonate Google's server. Through ...


4

A CRL is a signed object, just like a certificate. This is why they need not be covered by the actual document signature. However, for long-term archival, they need to be timestamped. The theoretical background is the following: At a given time T, you may validate certificates and verify signatures by using just-downloaded CRL, which give guarantee about ...


4

You are using the expression "zero-knowledge proof" but it does not mean what you believe it to mean. A ZKP proof is a kind of cryptographic protocol by which a Prover demonstrates to a Verifier a given property on a secret value. The proof is "zero-knowledge" if it does not divulge any extra information to the verifier. For instance, suppose that there is ...


4

Partly solving the underlying problem, you may use Public-Key-Pins header to restrict which certificates are valid for your domain (so a stolen certificate could only be used by a man-in-the-middle if used on the first connection to your site). You can also use Public-Key-Pins-Report-Only to get notifications for failed Pin validation. Both headers are ...


4

From the iOS 7 Deployment Technical Reference document (opens a PDF): Certificate validation The first time a user opens an app, the distribution certificate is validated by contacting Apple’s OCSP server. Unless the certificate has been revoked, the app is allowed to run. Inability to contact or get a response from the OCSP server isn’t ...



Only top voted, non community-wiki answers of a minimum length are eligible