X.509 is an 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 the difference between the Serial Number of a certificate and its SHA1 Hash is. the MSDN says: Serial number A number that uniquely identifies the ...
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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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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 ...
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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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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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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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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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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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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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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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X.509 certificate policies question

I asked another question about certificate policy mappings. This is a different issue. This is about Certificate Policies. To quote from the X.509 RFC: In an end entity certificate, these ...
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Why do X.509 certificates have “Key Usage” attribute?

I can find their values and all details in the RFC, but I cannot find why it was decided to have this attribute in certificates, instead of leaving them to be multipurposes. Is there a reasoning ...
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Enforce Code/Script Signing

I have both a couple of X.509 Code Signing certificates and a GPG keypair that I can use to sign against code I run on my VPS. Every now and again I write code for iOS, OS X and Windows and always ...
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Limiting the root certificate chain

I'm playing around with the idea of running a mini-CA with my (hobby) website, likely only used internally with a few select developers for internal emails, client authentication, staging/development ...
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Is Man-In-The-Middle necessary for a CA to read HTTP plaintext?

Although I understand the basic theory behind certificates and asymmetric cryptography, I'm not quite sure on the details of the X.509 protocol. I'm wondering what attacker model a given CA requires ...
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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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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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ASN.1: ENUMERATED vs INTEGER

From the X.509 specs: CRLReason ::= ENUMERATED { unspecified (0), keyCompromise (1), cACompromise (2), affiliationChanged (3), ...
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SSL - Null Prefix Attacks Still Possible?

At DEFCON 17 (2009) Moxie Marlinspike gave a talk were he was able to use a malformed certificate signing request to get SSL certs signed for domains he doesn't own. The gist of it was that for the ...
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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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Adding custom data in X.509 certificate

I am using SSL with client authentication. I need to send some extra data while sending the client certificate? Can I send it in the certificate? Can I use the extension fields in certificate for that ...
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What data should I validate when validating X.509 certificates using Java?

Well I began with PKI a year ago with RFID system at school. Now I'm asked to implement this in my job. I understand most part of the idea. The doubt is about the certificate validation. I know it ...
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Which attributes of a X509v3 certificate are never really used?

Are there any extensions/extended key usage attributes of a X.509Certificate that are rarely or never used in practice? Either due to never being part of an issued certificate or because they are ...
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How is an Authenticode timestamp verified?

For an Authenticode signed file to be verifiable by Windows after the original signing certificate has expired (typically 1-3 years after issue), the file also needs to have a cryptographically signed ...
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Is is typical to create both x509 and OpenPGP key pairs?

I'm looking into increasing my use of signed and encrypted "things" - LibreOffice Documents, Off-the-record chat, PDFs, emails, etc. I'm finding that some things only support x509 format-certificates, ...
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ECDHE_RSA and gmail

I'm using Chrome on Ubuntu Linux to connect to Gmail. The connection info says that ECDHE_RSA is used for the https symmetric key exchange. Based on my understanding of TLS and Gmail, my client ...
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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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self-signed certs that aren't the final certificates in the path

The X.509 spec makes frequent statements like this: (b) If certificate i is self-issued and it is not the final certificate in the path, skip this step for certificate i. How can you have ...
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How are possible uses for X.509 (SSL) certificates denoted?

X.509 certificates can be used for servers, clients, email, code signing and more applications. http://twitpic.com/6gdxaq indicates that a certificate can have different of these 'capabilities' on it ...
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Certificate verified using two different paths

StartSSL has an intermediate certificate that they use to sign their EV certificates: sub.class4.server.ca.pem. This certificate's issuer is shown by openssl x509 to be /C=IL/O=StartCom ...
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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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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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X.509 algorithm identifier parameters vs. extension values

From the X.509 specs: AlgorithmIdentifier ::= SEQUENCE { algorithm OBJECT IDENTIFIER, parameters ANY DEFINED BY algorithm OPTIONAL } ...
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Self-signing client certificates and distributing them, is the following a sound procedure?

I have a case at hand as follows: There is a number of clients in Internet (i.e. untrusted channel), initially in hundreds but growing in numbers. There is a server doing processing related to these ...
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where to download revoked certificates from

I don't want the certificate revocation lists - I want actual full on revoked certificates for test purposes. For example, Flame used a signed rogue cert and in 2001 someone posed as Microsoft and ...
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accepted naming convention for public keys/certificates

Is there an accepted naming convention for referring to PKI artifacts? There seems to be a lot of confusion with naming of artifacts. For example, it seems that some people refer to: public keys ...
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how do extended validation X.509 certs work?

https://www.forumatic.com/ uses an extended validation cert. wikipedia.org's entry on extended validation certs says that a cert is known to be an extended validation cert if the OID in the ...
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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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x.509 CRLs: next update?

An X.509 certificate revocation list contains a field specifying when the next such list is expected to be issued. I'm trying to figure out the importance of this field...I know that sometimes ...
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What are the Netscape Cert Type attributes? Why/when are they needed?

What are the Netscape Cert Type attributes in a X.509 Certificate and how are they different with the X509v3 extensions? Example: There is the Client/Server Extended Key Usage (X.509) but there is ...
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Why is the issuer name field signed in X.509?

In the X.509 specification it sais that the issuer name is to be signed. Since we verify the certificate with the authenticated issuer's public key, it seems infeasible to forge the issuer name ...
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Teaching security concepts

I think it would be nice to teach security concepts by giving practical examples. I am looking for some practical cases for x509 certificates, kerberos and SET. How could I know an ecommerse site ...
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How to determine if an X.509 certificate is a renewal of another known certificate?

In my application, the human user accepts the server's X.509 certificate, verifying the fingerprint during the first-time connection. The fingerprint is stored in the client software. At later ...
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parsing the id-ce-keyUsage extension in X.509 certs

I'm trying to decode an X.509 certificate and have a question regarding the decoding of the extensions. In particular, the octet string corresponding to id-ce-keyUsage (OID 2.5.29.15) is as follows: ...
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Why doesn't asn1parse parse all DER encoding strings?

I have a file - crl.txt - that contains the following: MDYwNKAyoDCGLmh0dHA6Ly93d3cyLnB1YmxpYy10cnVzdC5jb20vY3JsL2N0L2N0cm9vdC5jcmw= It's from one of the extensions in a particular X.509 cert. Why ...
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why does the first certificate have a RSA public key in x.509?

Example from http://en.wikipedia.org/wiki/X.509#Extensions_informing_a_specific_usage_of_a_certificate 1st certficate - freesoft 2nd - CA thawte Don't we use the RSA public key from the 2nd ...
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Gmail X.509 certificate chain

I have asked about this on several forums but never got a straight answer. If the root certificate on a certificate chain has a different fingerprint to the root certificate available for download on ...
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distribution mechanisms for CRLs

From the X.509 RFC: DistributionPoint ::= SEQUENCE { distributionPoint [0] DistributionPointName OPTIONAL, reasons [1] ReasonFlags OPTIONAL, cRLIssuer ...
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The reason to insert Subject Alternative Names into CA certificate

I am trying to understand meaning of the Subject Alternative Name extension. The reason of usage it in SSL X.509 certificates or other end-entities certificates is mostly clear for me. However, I ...
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X.509 certificate policy mapping question

So I'm a little confused how X.509 certificate policy mappings work. So let's say the following depicts my cert chain: root CA ---> intermediary CA ---> client cert Would the root CA have a ...