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Understanding X.509 Digital Certificate Thumbprints =LINK=


An X.509 CA certificate is a digital certificate that can sign other certificates. A digital certificate is considered an X.509 certificate if it conforms to the certificate formatting standard prescribed by IETF's RFC 5280 standard. A certificate authority (CA) means that its holder can sign other certificates.




Understanding X.509 digital certificate thumbprints



Company-X needs to register the X.509 CA to IoT Hub where it will serve to authenticate Smart-X-Widgets as they connect. This one-time process enables the ability to authenticate and manage any number of Smart-X-Widget devices. This is a one-time process because of the one-to-many relationship between CA certificate and device certificates that are signed by the CA certificate or an intermediate certificate. This relationship is one of the main advantages of using the X.509 CA authentication method. The alternative would be to upload individual certificate thumbprints for each and every Smart-X-Widget device, thereby adding to operational costs.


The X.509 CA certificate, just like any digital certificate, is public information that is susceptible to eavesdropping. As such, an eavesdropper may intercept a certificate and try to upload it as their own. In our example, IoT Hub has to make sure that the CA certificate Company-X uploaded really belongs to Company-X. It does so by challenging Company-X to prove that they possess the certificate through a proof-of-possession (PoP) flow.


A certificate thumbprint is a hash of a certificate, computed over all certificate data and its signature. Thumbprints are used as unique identifiers for certificates, in applications when making trust decisions, in configuration files, and displayed in interfaces. In this paper we show that thumbprints are not unique in two cases. First, we demonstrate that creating two X.509 certificates with the same thumbprint is possible when the hash function is weak, in particular when chosen-prefix collision attacks are possible. This type of collision attack is now practical for MD5, and expected to be practical for SHA-1 in the near future. Second, we show that certificates may be mauled in a way that they remain valid, but that they have different thumbprints. While these properties may be unexpected, we believe the scenarios where this could lead to a practical attack are limited and require very sophisticated attackers. We also checked the thumbprints of a large dataset of certificates used on the Internet, and found no evidence that would indicate thumbprints of certificates in use today are not unique.


The certificate encodes two very important pieces of information: theserver's public key and a digital signature that can be used to confirmthe certificate's authenticity. Additionally, the certificate willinclude metadata used by the CA to track the certificate and provideguidelines on how the public key can be used.


A hash, often using the SHA256 algorithm, is a digital fingerprint of thedata. If you change a single bit in the data, the hash will change. Bycomputing a hash over the DER-encoded public key section of the certificateand then signing the hash with its own private key, the CA is giving its stampof approval on the certificate. This signed hash value is the signatureappended to the certificate.


The final piece of the puzzle is understanding that the client musttrust the CA explicitly. This is done by adding the CA's public key to theclient's "trusted key store". As the user of common web services,you don't need to think much about certificate authorities. Both youroperating system and your web browser ship with curated lists of authorities,which have been pre-selected as trustworthy for you. Still, from time totime, it may be necessary to install a certificate from a non-standard CA.


A digital certificate provides a link between a public key and an entity (business,domain name etc) that has been verified (signed) by a trusted third party ( A certificate authority)


A domain-validated certificate (DV) is an X.509 digital certificate typically used for Transport Layer Security (TLS) where the identity of the applicant has been validated by proving some control over a DNS domain.-WikI


I hope that this write up has helped to explain how some of the less documented components of the JSON Web Token stack align. As organisations increasingly adopt a system of distributed infrastructure and services, the ability to centrally issue and remotely validate tokens will become more and more valuable. The use of JWT as a token format, and JWK as a format by which to both distribute and store the certificates required to validate these JWTs provides a mechanism by which to enable this. While some of the terms used in the specifications are a little obtuse, and couched security specific language, I would expect to see increased uptake and hope that this helped to at least provide a high-level understanding. Unfortunately, due to the lack of information available on the subject, if you do need more information, you might have to take a deep breath and dive into these RFCs.


X.509 is a standard format for public key certificates, digital documents that securely associate cryptographic key pairs with identities such as websites, individuals, or organizations.


No matter its intended application(s), each X.509 certificate includes a public key, digital signature, and information about both the identity associated with the certificate and its issuing certificate authority (CA):


Digital certificates provide higher levels of identity authentication and document transaction security. Digital certificates cryptography uses Public Key Infrastructure (PKI) technology to issue certificates based on X.509 standards to represent the digital identity of a signer. Standard-based signatures is the DocuSign platform for providing a full range of signature capabilities using digital certificates.


In order to run a certificate-based network, admins need to understand how to create and configure X.509 certificates. X.509 is a cryptography standard for defining a public key certificate. X.509 falls in the X.500 network standards that covers electronic directory services and was developed by Telecommunication Standardization Sector of the International Telecommunications Union (ITU-T) back in 1988. x.509 is the international standard for public key infrastructure (PKI), which is required to operate certificates.


Java developers can use the keytool utility found in the standard JDK to create the public/private key pair and X.509 certificate. keytool is a key and certificate management utility that allows users to administer their own public/private key pairs and associated certificates for use in authentication schemes requiring digital signatures. keytool stores keys and certificates in a "keystore" which for the default implementation is simply a file (".keystore") in the user's home directory. Private keys are guarded with passwords.


A client certificate, or client digital certificate, is a file that is protected with a password. This file is then loaded onto a client application, typically as PKCS12 files with the .p12, .pfx,, or .pem extension. Client certificates are very similar to SFTP keys. They contain important data that is structured using the X.509 standard. This information usually includes digital signature, expiration date, name of client, name of CA certificate (Certificate Authority), revocation status, SSL/TLS version number, and serial number.


A client digital certificate or client certificate is basically a file, usually protected with a password and loaded onto a client application (usually as PKCS12 files with the .p12, .pfx, .pem extension).


Your certificate would typically contain pertinent information like a digital signature, expiration date, name of client, name of CA certificate (Certificate Authority), revocation status, SSL/TLS version number, serial number, and possibly more, all structured using the X.509 standard.


Popular Web browsers like Firefox, Chrome, Safari, and Internet Explorer can readily support client certificates. These digital certificates can also be loaded unto secure file transfer clients like AnyClient as well as to other client applications that support SSL/TLS-protected protocols like HTTPS, FTPS, WebDAVs, and AS2.


Don't confuse client certificates with server certificates. Both are digital certificates that involve client and server applications but they're two different things. A server certificate is sent from the server to the client at the start of a session and is used by the client to authenticate the server. A client certificate, on the other hand, is sent from the client to the server at the start of a session and is used by the server to authenticate the client.


Just like in server certificate authentication, client certificate authentication makes use of digital signatures. For a client certificate to pass a server's validation process, the digital signature found on it should have been signed by a CA recognized by the server. Otherwise, the validation would fail.


In our work, the biometric information is represented by a fingerprint. During the enrolment phase, a fingerprint template of the user is stored in a secure environment (in our solution inside the smartcard). For integrity and authenticity purposes, the (hashed) fingerprint is then inserted in an 'attribute certificate' signed by an Attribute Authority. In the same smartcard we also store an X.509 certificate of the user, which will be used to digitally sign documents.


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