Incryptography andcomputer security, aroot certificate is apublic key certificate that identifies a rootcertificate authority (CA).[1] Root certificates areself-signed (and it is possible for a certificate to have multiple trust paths, say if the certificate was issued by a root that was cross-signed) and form the basis of anX.509-basedpublic 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 (RFC 5280). For instance, the PKIs supportingHTTPS[2] for secureweb browsing andelectronic signature schemes depend on a set of root certificates.
Acertificate authority can issue multiple certificates in the form of atree structure. A root certificate is the top-most certificate of the tree, the private key which is used to "sign" other certificates. All certificates signed by the root certificate, with the "CA" field set to true, inherit the trustworthiness of the root certificate—a signature by a root certificate is somewhat analogous to "notarizing" identity in the physical world. Such a certificate is called an intermediate certificate or subordinate CA certificate. Certificates further down the tree also depend on the trustworthiness of the intermediates.
The root certificate is usually made trustworthy by some mechanism other than a certificate, such as by secure physical distribution. For example, some of the best-known root certificates are distributed in operating systems by their manufacturers.Microsoft distributes root certificates belonging to members of the Microsoft Root Certificate Program toWindows desktops and Windows Phone 8.[2] Apple distributes root certificates belonging to members of its ownroot program.
In 2011, theDutch certificate authorityDigiNotar suffered a security breach. This led to the issuing of various fraudulent certificates, which was among others abused to target Iranian Gmail users. The trust in DigiNotar certificates was retracted and the operational management of the company was taken over by theDutch government.
In 2009, an employee of theChina Internet Network Information Center (CNNIC) applied toMozilla to add CNNIC to Mozilla's root certificate list[3] and was approved. Later,Microsoft also added CNNIC to the root certificate list ofWindows.
In 2015, many users chose not to trust the digital certificates issued by CNNIC because an intermediate CA issued by CNNIC was found to have issued fake certificates for Google domain names[4] and raised concerns about CNNIC's abuse of certificate issuing power.[5]
On April 2, 2015,Google announced that it no longer recognized the electronic certificate issued by CNNIC.[6][7][8] On April 4, following Google, Mozilla also announced that it no longer recognized the electronic certificate issued by CNNIC.[9][10]
In 2016,WoSign,China's largest CA certificate issuer owned byQihoo 360[11] and itsIsraeli subsidiaryStartCom, were denied recognition of their certificates byGoogle.Microsoft removed the relevant certificates in 2017.[12]
WoSign and StartCom issued hundreds of certificates with the same serial number in just five days, as well as issuing backdated certificates.[13] In 2016, a system administrator in Florida was able to get WoSign and StartCom to issue fake certificates for multipleGitHub domains.[14]