Filename extension | .crl |
---|---|
Internet media type | application/pkix-crl |
Initial release | May 1999 |
Container for | X.509 CRLs |
Standard | RFC 2585 |
Website | https://www.iana.org/assignments/media-types/application/pkix-crl |
In cryptography, a certificate revocation list (CRL) is "a list of digital certificates that have been revoked by the issuing certificate authority (CA) before their scheduled expiration date and should no longer be trusted". [1] CRLs are no longer required by the CA/Browser forum, [2] as alternate certificate revocation technologies (such as OCSP) are increasingly used instead. [3] [4] Nevertheless, CRLs are still widely used by the CAs. [5]
There are two different states of revocation defined in RFC 5280:
Reasons to revoke, hold, or unlist a certificate according to RFC 5280 [6] are:
unspecified
(0)keyCompromise
(1)cACompromise
(2)affiliationChanged
(3)superseded
(4)cessationOfOperation
(5)certificateHold
(6)removeFromCRL
(8)privilegeWithdrawn
(9)aACompromise
(10)Note that value 7 is not used.
A CRL is generated and published periodically, often at a defined interval. A CRL can also be published immediately after a certificate has been revoked. A CRL is issued by a CRL issuer, which is typically the CA which also issued the corresponding certificates, but could alternatively be some other trusted authority. All CRLs have a lifetime during which they are valid; this timeframe is often 24 hours or less. During a CRL's validity period, it may be consulted by a PKI-enabled application to verify a certificate prior to use.
To prevent spoofing or denial-of-service attacks, CRLs usually carry a digital signature associated with the CA by which they are published. To validate a specific CRL prior to relying on it, the certificate of its corresponding CA is needed.
The certificates for which a CRL should be maintained are often X.509/public key certificates, as this format is commonly used by PKI schemes.
Expiration dates are not a substitute for a CRL. While all expired certificates are considered invalid, not all unexpired certificates should be valid. CRLs or other certificate validation techniques are a necessary part of any properly operated PKI, as mistakes in certificate vetting and key management are expected to occur in real world operations.
In a noteworthy example, a certificate for Microsoft was mistakenly issued to an unknown individual, who had successfully posed as Microsoft to the CA contracted to maintain the ActiveX 'publisher certificate' system (VeriSign). [7] Microsoft saw the need to patch their cryptography subsystem so it would check the status of certificates before trusting them. As a short-term fix, a patch was issued for the relevant Microsoft software (most importantly Windows) specifically listing the two certificates in question as "revoked". [8]
Best practices require that wherever and however certificate status is maintained, it must be checked whenever one wants to rely on a certificate. Failing this, a revoked certificate may be incorrectly accepted as valid. This means that to use a PKI effectively, one must have access to current CRLs. This requirement of on-line validation negates one of the original major advantages of PKI over symmetric cryptography protocols, namely that the certificate is "self-authenticating". Symmetric systems such as Kerberos also depend on the existence of on-line services (a key distribution center in the case of Kerberos).
The existence of a CRL implies the need for someone (or some organization) to enforce policy and revoke certificates deemed counter to operational policy. If a certificate is mistakenly revoked, significant problems can arise. As the certificate authority is tasked with enforcing the operational policy for issuing certificates, they typically are responsible for determining if and when revocation is appropriate by interpreting the operational policy.
The necessity of consulting a CRL (or other certificate status service) prior to accepting a certificate raises a potential denial-of-service attack against the PKI. If acceptance of a certificate fails in the absence of an available valid CRL, then no operations depending upon certificate acceptance can take place. This issue exists for Kerberos systems as well, where failure to retrieve a current authentication token will prevent system access.
An alternative to using CRLs is the certificate validation protocol known as Online Certificate Status Protocol (OCSP). OCSP has the primary benefit of requiring less network bandwidth, enabling real-time and near real-time status checks for high volume or high-value operations.
As of Firefox 28, Mozilla has announced they are deprecating CRL in favour of OCSP. [3]
CRL files may grow quite large over time e.g. in US government, for certain institution multiple megabytes. Therefore, incremental CRLs have been designed [9] sometimes referred to as "delta CRLs". However, only a few clients implement them. [10]
An authority revocation list (ARL) is a form of CRL containing revoked certificates issued to certificate authorities, contrary to CRLs which contain revoked end-entity certificates. [11] [12]
Hypertext Transfer Protocol Secure (HTTPS) is an extension of the Hypertext Transfer Protocol (HTTP). It uses encryption for secure communication over a computer network, and is widely used on the Internet. In HTTPS, the communication protocol is encrypted using Transport Layer Security (TLS) or, formerly, Secure Sockets Layer (SSL). The protocol is therefore also referred to as HTTP over TLS, or HTTP over SSL.
Kerberos is a computer-network authentication protocol that works on the basis of tickets to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner. Its designers aimed it primarily at a client–server model, and it provides mutual authentication—both the user and the server verify each other's identity. Kerberos protocol messages are protected against eavesdropping and replay attacks.
A public key infrastructure (PKI) is a set of roles, policies, hardware, software and procedures needed to create, manage, distribute, use, store and revoke digital certificates and manage public-key encryption. The purpose of a PKI is to facilitate the secure electronic transfer of information for a range of network activities such as e-commerce, internet banking and confidential email. It is required for activities where simple passwords are an inadequate authentication method and more rigorous proof is required to confirm the identity of the parties involved in the communication and to validate the information being transferred.
In cryptography, a public key certificate, also known as a digital certificate or identity certificate, is an electronic document used to prove the validity of a public key. The certificate includes the public key and information about it, information about the identity of its owner, and the digital signature of an entity that has verified the certificate's contents. If the device examining the certificate trusts the issuer and finds the signature to be a valid signature of that issuer, then it can use the included public key to communicate securely with the certificate's subject. In email encryption, code signing, and e-signature systems, a certificate's subject is typically a person or organization. However, in Transport Layer Security (TLS) a certificate's subject is typically a computer or other device, though TLS certificates may identify organizations or individuals in addition to their core role in identifying devices. TLS, sometimes called by its older name Secure Sockets Layer (SSL), is notable for being a part of HTTPS, a protocol for securely browsing the web.
In cryptography, X.509 is an International Telecommunication Union (ITU) standard defining the format of public key certificates. X.509 certificates are used in many Internet protocols, including TLS/SSL, which is the basis for HTTPS, the secure protocol for browsing the web. They are also used in offline applications, like electronic signatures.
In cryptography and computer security, a root certificate is a public key certificate that identifies a root certificate authority (CA). Root certificates are self-signed and form the basis of an X.509-based public key infrastructure (PKI). Either it has matched Authority Key Identifier with Subject Key Identifier, in some cases there is no Authority Key identifier, then Issuer string should match with Subject string. For instance, the PKIs supporting HTTPS for secure web browsing and electronic signature schemes depend on a set of root certificates.
In cryptography, a certificate authority or certification authority (CA) is an entity that stores, signs, and issues digital certificates. A digital certificate certifies the ownership of a public key by the named subject of the certificate. This allows others to rely upon signatures or on assertions made about the private key that corresponds to the certified public key. A CA acts as a trusted third party—trusted both by the subject (owner) of the certificate and by the party relying upon the certificate. The format of these certificates is specified by the X.509 or EMV standard.
In cryptography and computer security, self-signed certificates are public key certificates that are not issued by a certificate authority (CA). These self-signed certificates are easy to make and do not cost money. However, they do not provide any trust value.
The certification path validation algorithm is the algorithm which verifies that a given certificate path is valid under a given public key infrastructure (PKI). A path starts with the Subject certificate and proceeds through a number of intermediate certificates up to a trusted root certificate, typically issued by a trusted certificate authority (CA).
The Online Certificate Status Protocol (OCSP) is an Internet protocol used for obtaining the revocation status of an X.509 digital certificate. It is described in RFC 6960 and is on the Internet standards track. It was created as an alternative to certificate revocation lists (CRL), specifically addressing certain problems associated with using CRLs in a public key infrastructure (PKI). Messages communicated via OCSP are encoded in ASN.1 and are usually communicated over HTTP. The "request/response" nature of these messages leads to OCSP servers being termed OCSP responders.
Code signing is the process of digitally signing executables and scripts to confirm the software author and guarantee that the code has not been altered or corrupted since it was signed. The process employs the use of a cryptographic hash to validate authenticity and integrity. Code signing was invented in 1995 by Michael Doyle, as part of the Eolas WebWish browser plug-in, which enabled the use of public-key cryptography to sign downloadable Web app program code using a secret key, so the plug-in code interpreter could then use the corresponding public key to authenticate the code before allowing it access to the code interpreter’s APIs.
Network Security Services (NSS) is a collection of cryptographic computer libraries designed to support cross-platform development of security-enabled client and server applications with optional support for hardware TLS/SSL acceleration on the server side and hardware smart cards on the client side. NSS provides a complete open-source implementation of cryptographic libraries supporting Transport Layer Security (TLS) / Secure Sockets Layer (SSL) and S/MIME. NSS releases prior to version 3.14 are tri-licensed under the Mozilla Public License 1.1, the GNU General Public License, and the GNU Lesser General Public License. Since release 3.14, NSS releases are licensed under GPL-compatible Mozilla Public License 2.0.
The Server-based Certificate Validation Protocol (SCVP) is an Internet protocol for determining the path between an X.509 digital certificate and a trusted root and the validation of that path according to a particular validation policy.
The Certificate Management Protocol (CMP) is an Internet protocol standardized by the IETF used for obtaining X.509 digital certificates in a public key infrastructure (PKI).
The Online Certificate Status Protocol (OCSP) stapling, formally known as the TLS Certificate Status Request extension, is a standard for checking the revocation status of X.509 digital certificates. It allows the presenter of a certificate to bear the resource cost involved in providing Online Certificate Status Protocol (OCSP) responses by appending ("stapling") a time-stamped OCSP response signed by the CA to the initial TLS handshake, eliminating the need for clients to contact the CA, with the aim of improving both security and performance.
An offline root certificate authority is a certificate authority which has been isolated from network access, and is often kept in a powered-down state.
IEC 62351 is a standard developed by WG15 of IEC TC57. This is developed for handling the security of TC 57 series of protocols including IEC 60870-5 series, IEC 60870-6 series, IEC 61850 series, IEC 61970 series & IEC 61968 series. The different security objectives include authentication of data transfer through digital signatures, ensuring only authenticated access, prevention of eavesdropping, prevention of playback and spoofing, and intrusion detection.
Resource Public Key Infrastructure (RPKI), also known as Resource Certification, is a specialized public key infrastructure (PKI) framework to support improved security for the Internet's BGP routing infrastructure.
In public key infrastructure, a validation authority (VA) is an entity that provides a service used to verify the validity or revocation status of a digital certificate per the mechanisms described in the X.509 standard and RFC 5280.
In public key cryptography, a certificate may be revoked before it expires, which signals that it is no longer valid. Without revocation, an attacker could exploit such a compromised or misissued certificate until expiry. Hence, revocation is an important part of a public key infrastructure. Revocation is performed by the issuing certificate authority, which produces a cryptographically authenticated statement of revocation.
In lieu of, or as a supplement to, checking against a periodic CRL, it may be necessary to obtain timely information regarding the revocation status of certificates. ... OCSP may be used to satisfy some of the operational requirements of providing more timely revocation information than is possible with CRLs and may also be used to obtain additional status information.
{{cite book}}
: |work=
ignored (help)