34

CA A revokes CA B, does certificate C become invalid? Yes, revocation cascades down to the tree. If CA certificate is revoked, all certificates below (regardless of how many levels are below CA) are implicitly considered untrusted. Keep in mind that they become *untrusted*, not revoked. CA A gets revoked (somehow), does its revocation cascade all the way ...


17

If Alice keeps her correspondent's public key in a database, spreadsheet, text document; then it's feasible that your scenario would work. However, most (including Alice hopefully) would only trust public keys that have been certified as authentic. There are two mainstream methods by which this is currently done: Certified by a central authority The ...


16

How does Alice know Bob's public key? There are several ways for Alice to verify Bob's public key, each with their own pros and cons. Direct and in person This is probably the most secure approach. Alice and Bob meet in person, exchange and possibly sign each others public keys. This would make it virtually impossible for anyone to tamper this process. ...


16

No, HSTS does not protect against certificate misissuance. HSTS simply tells the browser to only allow connecting to that site over HTTPS, it doesn't have anything to do with checking whether the certificate should be trusted. There are two things that can help with misissuance to some extent, Certificate Transparency (CT) and Certificate Authority ...


15

The subject key identifier (SKID) is an x509 extension and thus actually part of the certificate. The fingerprint instead is not part of the certificate but instead computed from the certificate. A certificate does not need to have an SKID at all and can have at most one SKID. But since the fingerprint is just a computed from the certificate there can be ...


9

While Guntbert's answer was good at the time, it's getting a little outdated. openssl rsa -aes256 creates an encrypted file using the md5 hash of your password as the encryption key, which is weaker than you would expect - and depending on your perspective that may in fact be worse than plaintext. (If you use the same password for your ssh key and your login,...


9

"It depends". The most secure answer is "yes, it revokes the subtree", because once the "B" certificate has been revoked there's no reason to trust any certificate it claims to have issued (or any CRL it has signed, et cetera). But it really depends on what inputs are given to the chain builder (which means it won't be consistent from application to ...


8

What will happen if someone sends me a genuine certificate for authentication which does not really belong to him? A certificate is really just a public key that someone stamped with their approval. With that in mind, the special properties of public/private key pairs (e.g., each can uniquely decode what the other encoded) are used to prove "belonging." ...


8

RFC 5280 states that "Certificate users MUST be able to handle serialNumber values up to 20 octets. Conforming CAs MUST NOT use serialNumber values longer than 20 octets." Of course one doesn't have to conform... Edit: an octet is 8 bits so if you have 20 octets that's 160 bits...for binary we have base 2 bits => 2^160 = 1.4615016e+48 AKA a really ...


8

There's a few different things here. a public key is the product of two large prime numbers That is partially true for RSA, though RSA public keys also contain an additional integer (e, in the algorithm's description). Other public key algorithms, and even public key ciphers, do not work the same way (see ElGamal Encryption, for example.) as long as ...


6

It is solely certificate viewer, nothing else. Microsoft time by time tweak/change certificate viewer. Prior to Windows 10, hex values were printed in octets separated by a space, now they removed space. Though, public keys and public key parameters are printed in octets with spaces. The fact that you see spaces for some certs is related to certificate ...


6

Quantum computing is being developed to attack specific algorithms. Right now there are efforts under way to find algorithms that are resistant to quantum computing attacks. Such algorithms are called post-quantum. The Public Key Infrastructure is built on the concept of certificates, not algorithms. Certificates are documents that are capable of storing ...


6

No, but. Yes, technically you sign (or decrypt) with the privatekey, not with the certificate itself. And a publickey certificate never contains the privatekey. But a lot of software, and thus documentation, and other description, blurs this distinction. We generally use a privatekey with a certificate (with the exception of SSH, where we attach limited ...


5

If someone sends you a certificate that they do not own and you encrypt a message using it, they simply will not be able to decrypt that message without having the private key associated with the certificate. In the context of HTTPS/TLS the client authenticates the host by sending them something only they know (usually random) encrypted with the certificate ...


5

The best I can find is from a draft version 2 of X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP proposal, which later became RFC 2560. It states that: The requester signature is used to authenticate the requester to the OCSP Responder. It is used in conjunction with the requester certificate extension defined ...


4

ADCS has a feature for this. Assuming you have the Certificate Services Client - Auto-Enrollment group policy configured, simply create a new template in the MMC with the correct SAN configuration and add the original template name to the Superseded Templates tab. Group policy will enroll for a new certificate with this template and delete the original for ...


4

This could well be the same key in two different formats. Try extracting the public key for both and compare the fingerprints, for instance using the commands here. The public key is unique and part of the public key / private key pair. The fingerprint over the public key is unique with very high probability. So if the comparison succeeds you've got the ...


4

If your data at any point is in plaintext on user’s machine – you can’t secure it. You can do many things to protect it, but this would only slow down a dedicated attacker: obfuscating source code, encrypting data at rest, rotating encryption keys on server, etc. This is the territory of DRM, and there are many companies that will sell you their solutions. ...


4

Yes, there's a reason; public key encryption is very slow and CPU-intensive, and not at all suitable for encrypting chat data, which may well include images, audio or video as well as text. That's why wherever it's used, it's only used to transmit a shared symmetric encryption key which is then used to encrypt the actual content. But in any case, it's never ...


4

(CW for anyone who wants to add additional cases) The size/strength of ephemeral keys for DHE and ECDHE key exchanges in TLS can depend on the protocol (version) the server-side implementation code (usually a library), and sometimes configuration the client-side implementation (ditto) First, there is a significant difference between TLS 1.0 through 1.2 (...


4

OCSP responses may be signed not only by the CA itself, but also a designated OCSP signer. That's an X.509 certificate issued by that CA with the OCSPSigning (1.3.6.1.5.5.7.3.9) extended key usage. For details see RFC 6960, section 4.2.2.2.


4

How can I validate, that the cert certifies exactly that key? A certificate does not "certify" a key. What you describe is to check if the private key matches the public key in the certificate and thus can be used to prove ownership of the certificate against a third party. And yes, it is enough for this to check that the public key you have in the key pair ...


3

What you are looking at (PEM, text) are just two possible views of the same data. what is my public key here ... is it a continuous large number in hex format A key is a sequence of bytes. Hex format is just a representation of these bytes as text in order to be viewable by a human. There are different kinds of public keys (RSA, ECC,...) and what the ...


3

Yes, the public key size and signature size is smaller when you use a smaller RSA modulus. The RSA public key composed primarily of the product of two very large prime numbers. This product is said to be the modulus, and this is what makes RSA keys so large. RSA 2048 has a 2048-bit modulus. The signature size also depends on the modulus size. In fact, it ...


3

I'd first check the organization for their policies. They may not even allow GPG. I'd use multiple GPG keys, one per organization. An organization may require you to hand over your GPG keys to get to the data encrypted with it. If you change jobs or identities within an organization then you might want to use sub-keys. And, as usual, always keep your ...


3

According to Oracle JRE and JDK Cryptographic Roadmap Symantec Root CAs will be removed in April 2019 release: Date: 2019-04-16 Releases: 12, 11, 8, 7 Action: Distrust TLS server certificates anchored by Symantec Root CAs.


3

The S/MIME standard (RFC 5751) in section 3.2.1 states that the file extensions SHOULD be appropriate: certificate management message: .p7c CompressedData: .p7z SignedData: .p7s SignedData + EnvelopedData: .p7m


3

Websites use x509 certificates which uses public key cryptography (public private keypairs). Even small companies have many different certificates, and many different public private key pairs. The idea is if one system is compromised and a private key is exposed, you wouldn't want to risk traffic on another system. Think of it this way. Would a ...


3

Of course organisations use lots of different keys. Typically a separate key for each service, so each website, ssh server, backup server (and maybe client) etc would have its own key pair. Each employee might have one or more personal keys too, eg email encryption, ssh identity, disk encryption. And yes, key management can be a significant problem too, ...


3

CRL distribution points are location that the client must be able to resolve to a file. If the client is unable to obtain that file, it will go to the next location. In order to obtain that file, the client must be able to: Understand the schema of the endpoint (HTTP, LDAP, File, Whatever...) Resolve the host name (if appropriate). Contact the host name ...


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