Questions tagged [x.509]

X.509 is a standard for a public key infrastructure used for authentication and access control. X.509 specifies standard formats for certificates, revocation lists, attribute certificates, and path validation.

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What is the difference between serial number and thumbprint?

I have problems to understand what is the difference between the serial number of a certificate and its SHA1 hash. The MSDN says: Serial number A number that uniquely identifies the ...
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71 votes
1 answer
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Why is there no certificate error while visiting google.net although it presents a certificate issued to google.com?

The following output shows that google.net is presenting a certificate that has been issued to www.google.com. $ openssl s_client -connect google.net:443 < /dev/null > out.txt 2>&1; cat ...
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65 votes
2 answers
113k views

What's the difference between X.509 and PKCS#7 Certificate?

Am I correct calling file with .p7b file extension saved as 'Cryptographic Message Syntax Standard - PKCS#7 Certificates (.P7B)' in Windows - a 'PKCS#7 certificate'? Or is it better called 'X.509 ...
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51 votes
2 answers
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What is the difference between SSL and X.509 Certificates?

I used openssl to create a X.509 certificate but I don't quite understand the relationship between a X.509 and a SSL certificate. Are they the same? Is a SSL certificate just a X.509 certificate that ...
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46 votes
4 answers
24k views

Determine if private key belongs to certificate?

Given a certificate¹ and a private key file², how can I determine if the public key on the certificate matches the private key? My initial thought was to simply encrypt some text with the public key ...
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43 votes
4 answers
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How to set up OpenSSH to use x509 PKI for authentication?

I do not mean simply putting the public RSA key of a x.509 certificate into ~/.ssh/authorized_keys - I'm looking for a way to set up a ssh such that x.509 certificates signed by a pre-defined CA will ...
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43 votes
2 answers
7k views

Can a SSL certificate have longer validity period than its parent in X.509 chain?

When a X.509 certificate chain is composed of X1, X2 ... Xn and Xn is root CA, Can a certificate in lower level have longer validity period than its parents? I think that lower level should be proper ...
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39 votes
2 answers
17k views

Do SSL / X.509 certs cover all ports for a host?

Or are certs both host- and port-specific (excepting wildcard certs)? I would assume they aren't, because they're supposed to verify a domain, but at the same time I've never seen anyone run HTTPS on ...
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36 votes
7 answers
7k views

Could governments and banks become CAs?

When you apply for a passport, driver's license, home mortgage, bank account, credit card, etc., the issuing organization must verify your identity. In the course of doing so, would it be feasible for ...
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32 votes
1 answer
27k views

Which properties of a X.509 certificate should be critical and which not?

RFC5280's section 4.2 states Each extension in a certificate is designated as either critical or non-critical. A certificate-using system MUST reject the certificate if it encounters a critical ...
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31 votes
1 answer
33k views

Which key usages are required by each key exchange method?

I'm only really concerned with RSA keys, so the exchange methods are RSA (generate a key, encrypt it, and send it over) and [EC]DHE_RSA (generate an ephemeral [EC]DH key, sign it, and use it for key ...
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30 votes
5 answers
37k views

What is the use of cross signing certificates in X.509?

In X.509 architecture what are the uses of cross signing certificates from other hierarchy? Does it just expand trust? So from the answer I am assuming that if CA3 is cross signed by CA2 (from ...
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26 votes
2 answers
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If you revoke a certificate authority's certificate, do all of the certificates it issued become invalid as well?

If you revoke a certificate authority's certificate, do all of the certificates it issued become invalid as well? What about for certificates issued by an authority beneath it? For example, if root ...
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26 votes
4 answers
54k views

Missing X509 extensions with an openssl-generated certificate

My goal is to create a certificate with opensslsimilar to this one generated with cfssl Certificate: Data: Version: 3 (0x2) Serial Number: 60:44:dc:0d:80:f4:54:55:e8:...
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24 votes
3 answers
5k views

Why don't folks seem to use ECC for TLS root certificate signature?

I looked around, and all I see is websites using RSA2048 for Root signature, and a few using ECC for encryption. Are there any reasons folks don't seem to use ECC for TLS root signature? Are there ...
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24 votes
1 answer
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Relationship between RSA, Diffie-Hellman Key Exchange, PKI and X.509?

I am getting confused with RSA, Diffie-Hellman Key Exchange, PKI and X.509v3. I took a look of RSA's mathematics algorithm, it seems like a encryption algorithm, right? Generating public key and ...
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22 votes
4 answers
11k views

Can an intermediate CA be trusted like a self-signed root CA?

Is it possible within the limits of the X.509 specification to mark an intermediate CA as trusted for a specific purpose, e.g. to verify a VPN, HTTPS etc. server key, just like it would work with a ...
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19 votes
1 answer
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The difference between Subject Key Identifier and sha1Fingerprint in X509 Certificates

I have some SW that extracts certificates data and the SW utilizes OpenSSL. I am confused what is the difference between the subjectKeyIdentifier and the sha1Fingerprint. Both are hash values. My ...
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19 votes
2 answers
29k views

How is an X509 certificate signer verified?

Lets say I create a self-signed X509 certificate A and use it to issue certificate B. I put certificate A in my trusted root authorities so that all certificates signed by it are accepted. My question ...
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17 votes
4 answers
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Are SSL certs auto-revoked if their Not-Valid-After date is reached without renewing?

I'm learning about X509 certs used in client-cert authentication to https endpoints. If I have an OCSP checker (Python script that creates, submits, decodes OCSP responses), do I need to check the not-...
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17 votes
2 answers
25k views

Recommended key usage for a client certificate

My program has the following flow: a client sends a CSR to server, the server sends back a client certificate and after that the client communicates with the server to a path that requires a ...
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17 votes
4 answers
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Why is it a good idea that X.509 digital certificates have an expiry date?

What is the benefit of having certificates expire at some fixed date?
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17 votes
4 answers
5k views

CRL over HTTPS: is it really a bad practice?

On the Internet, I can find several statements done over the years claiming that serving a X.509 CRL over HTTPS is a bad practice because either it causes a chicken-and-egg problem when checking for ...
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17 votes
1 answer
25k views

Root certificate key usage (non-self-signed end entity)

This discussion does not include self-signed end entity certificates for hosts like web servers and mail servers. OpenSSL's default configuration for a CA certificate has the following keyUsage: ...
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16 votes
5 answers
51k views

How to validate a client certificate

My understanding is that when using a client certificate for security one issues a private and public key cert (for example X509) of some sort and sends that of to the consumer of the service that one ...
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16 votes
5 answers
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A standard way to manually add a digital signature to a pdf file?

I've created a few certificates to use myself, but I find myself stumped when it comes to creating a certificate which contains a digital signature. First, how would I go about creating a standard ...
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15 votes
2 answers
5k views

How long can X.509 certificate chains be?

Usually, I only see certificate chains with a root CA, an intermediate one, and a third one for the particular SSL/TLS website; but can X.509 certificate chains be deeper than 3 levels? Is there a ...
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14 votes
2 answers
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Definitions for CRL Reasons

Is there any authoritative definition of the various reasons possible in a CRL file? Section 6.3.2(b) of RFC5280 lists a few: unspecified keyCompromise cACompromise affiliationChanged superseded ...
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14 votes
2 answers
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Are certificate authorities required to obey to the signature algorithm (hashing) specified in the CSR?

I was playing a little bit with signature algorithms, trying to determine which CAs among the ones I use are currently issuing SHA2 certificates. I generated a CSR specifying the SHA256 hash (either ...
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13 votes
2 answers
15k views

Validating an SSL certificate chain according to RFC 5280: Am I understanding this correctly?

we're in the process of replacing certificates with SHA1 hash due to Google's move to let them appear less secure in Chrome. The replacement certificates use a different intermediate CA than the ones ...
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13 votes
3 answers
10k views

Why one should prefer EST protocol instead of SCEP?

For many years SCEP was a simple and widely used protocol for obtaining X.509 certificates. However, not too so long ago another protocol called EST (RFC 7030) was developed. What are the main reasons ...
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13 votes
2 answers
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What is the difference of TrustManager PKIX and SunX509?

Java's JSSE provides two different TrustManagers: PKIX and SunX509 I tried to find out what the differences between both are, but couldn't find any in the documentation. Can you tell me the ...
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13 votes
1 answer
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Encrypting local HTTP traffic using a self-signed certificate

For the past couple of hours I've been trying to create a self-signed certificate which I'd like to use to encrypt HTTP traffic between computers and a server on my home network (because I'm paranoid ...
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12 votes
4 answers
2k views

Is it possible to update the contact info (FN/LN, OU, Organization,..) of a certificate?

When creating a self-signed certificate you are asked to enter some information (First Name, Last Name, Organization Unit, Organization, City, State,...). Is it possible to update any of those fields ...
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12 votes
2 answers
3k views

Are X.509 nameConstraints on certificates supported on OS X?

I have the following "chain" of certificates on a test machine right now: A self-signed CA cert, in my Keychain and trusted & trusted by Firefox. A CA cert with with the following, X509v3 Name ...
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12 votes
3 answers
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Creating an X.509 certificate with an invalid signature

Creating an X.509 certificate with a valid signature with OpenSSL is pretty well documented all over the Internet. There are instructions on creating certificates that are signed by themselves and ...
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12 votes
2 answers
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How to use a Yubikey NEO (or any OpenPGP card or GnuPG in general) to sign X.509 CSRs?

Since the Yubikey NEO can be used as an OpenPGP card (see here) with three 2048 bit RSA keys, I thought about creating a CA from one of its public keys. Since the private key cannot be extracted (...
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12 votes
2 answers
293 views

Who was in the first set of CAs

I am currently digging into the history of SSL/TLS. I found that netscape introduced SSL around 1994/1995. They obviously decided to go with a X.509 PKI to mitigate MitM attacks. I, however, could not ...
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12 votes
2 answers
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How to properly create and use cross-signed CAs and certificates

I'm trying to create an environment with cross-signed CAs, and verify a certificate issued against one of the CAs, all using openssl. The best I got so far is getting openssl into an endless loop ...
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11 votes
4 answers
36k views

IP address in SubjectAltName

Is it allowed to specify IP as DNS name for SAN certificate ?
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11 votes
1 answer
21k views

Enhanced Key Usage vs. Extended Key Usage

I've seen both the terms Enhanced Key Usage and Extended Key Usage, and both were abbreviated as EKU. Do both refer to the same extension or property?
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11 votes
3 answers
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Use openssl to individually verify components of a certificate chain

This is related to another question, How to verify a signature of one entity by another using OpenSSL CLI? I used openssl s_client -showcerts -connect www.google.com:443 to collect three certificates ...
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11 votes
1 answer
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Why is the Signature Algorithm listed twice in an x509 Certificate?

Section 4.1 of RFC 5280 defines the contents of an x509 Certificate. Specifically, two fields are listed (signatureAlgorithm and signature) and defined to contain the same information: ...
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10 votes
3 answers
2k views

Allowing the public to generate a CSR from your private key

As a hosting provider, I'd like to make the process of generating a certificate for a customer's domain as convenient as possible. I was pondering creating a webpage where anyone could: generate a ...
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10 votes
4 answers
4k views

Can a revoked certificate be re-instated?

If a certificate is revoked, can it be re-instated, or is the only option to generate a new one?
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10 votes
2 answers
10k views

Extensions for SSL server certificate

I have some question about the X.509 v3 extensions. What extensions should appear in a proper certificate for a SSL server ?
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10 votes
2 answers
1k views

Correct settings to generate private intermediate CA

I am using 'xca' in Linux to set up a private CA. xca only includes templates for the Root CA and End-User CA, no intermediates. What are the correct settings (fields and flags) for an intermediate (...
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9 votes
2 answers
1k views

Why don't banks sign their email using S/MIME?

If email sent by my bank included S/MIME signatures that my mail client can verify, then I would have the assurance that the mail was not tampered with or sent by some malicious third-party. Most ...
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  • 193
9 votes
2 answers
10k views

How TLS certificate chain is verified

Assume the verification of a TLS certificate chain. Suppose the chain has certificates A-B-C-D where D is the root certificate and A is signed by B, B by C, C by D. Suppose the intermediate ...
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9 votes
1 answer
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Which extensions to use for a S/MIME certificate?

Analogously to the SSL server certificate question, which extensions should I use for S/MIME, and should the CA be restricted somehow as well? (I'm using openssl, which at the moment creates CA and ...
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