Generally, a Certification Authority (CA) shouldn\u2019t directly sign another CA\u2019s certificate. It creates trust issues and defeats the purpose of a hierarchical Public Key Infrastructure (PKI). However, there are specific scenarios like cross-certification where it\u2019s done carefully under controlled conditions.<\/p>\n
Before we dive in, let\u2019s quickly recap:<\/p>\n
Root CA: The top of the trust chain. These are usually self-signed.
\nIntermediate CA: Signed by a Root CA (or another Intermediate). They issue end-entity certificates.
\nEnd-Entity Certificate: Issued to servers, people, or devices.<\/p>\n
Trust is built on the chain of trust \u2013 your browser\/OS verifies that an End-Entity certificate is signed by a trusted Intermediate CA, which in turn is signed by a trusted Root CA.<\/p>\n
Breaks Trust Hierarchy: If CA A signs CA B\u2019s certificate directly, it implies CA A trusts CA B implicitly. This bypasses the need for independent vetting of CA B.
\nCircular Dependency: It can lead to a circular trust loop, making validation difficult and potentially insecure.
\nSecurity Risks: If CA B is compromised, CA A\u2019s reputation is also at risk because it vouched for CA B.<\/p>\n
There are legitimate reasons to allow one CA to sign another CA\u2019s certificate, but these are carefully managed:<\/p>\n
Cross-Certification: This is a formal agreement between two CAs where they vouch for each other\u2019s root certificates. It\u2019s often used when CAs want to expand their trust reach across different ecosystems or geographies.
\nBridging Trust Anchors: To connect separate PKI domains.<\/p>\n
Here\u2019s a simplified breakdown:<\/p>\n
Agreement: CA A and CA B agree to cross-certify each other\u2019s root certificates. This involves thorough due diligence on both sides.
\nCertificate Request: CA A generates a Certificate Signing Request (CSR) for its own root certificate.
\nSigning: CA B signs CA A\u2019s CSR with *its* root certificate, creating a cross-certificate.
\nDistribution: Both CAs distribute the cross-certificates to their respective clients and systems.<\/p>\n
Example using OpenSSL:<\/p>\n
# CA B signs CA A’s CSR (simplified)
\nopenssl ca -config ca_b.cnf -extensions v3_ca -days 3650 -in ca_a_csr.pem -out ca_a_cross.pem<\/p>\n
Clients (browsers, OS) need to be configured with both CAs\u2019 root certificates and cross-certificates to establish trust.<\/p>\n
Browser Trust Stores: Browsers maintain lists of trusted Root CAs.
\nOperating System Certificate Stores: Operating systems have their own certificate stores.<\/p>\n
You can view certificates in your browser by navigating to the site\u2019s security information (usually a padlock icon).<\/p>\n
Due Diligence: Thoroughly vet any CA before cross-certifying.
\nRevocation: Have clear procedures for revoking cross-certificates if necessary.
\nScope: Limit the scope of cross-certification to specific purposes and use cases.<\/p>\n
While directly signing another CA\u2019s certificate is generally discouraged, cross-certification provides a controlled mechanism for establishing trust between CAs when done properly. Always prioritize security best practices and thorough vetting.<\/p>\n
The post CA Signing Other CAs: Is it Possible?<\/a> appeared first on Blog | G5 Cyber Security<\/a>.<\/p>","protected":false},"excerpt":{"rendered":" TL;DR Generally, a Certification Authority (CA) shouldn\u2019t directly sign another CA\u2019s certificate. It creates trust issues and defeats the purpose of a hierarchical Public Key Infrastructure (PKI). However, there are specific scenarios like cross-certification where it\u2019s done carefully under controlled conditions. Understanding CAs and Trust Before we dive in, let\u2019s quickly recap: Root CA: The […]<\/p>\n","protected":false},"author":0,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-6386","post","type-post","status-publish","format-standard","hentry","category-news"],"_links":{"self":[{"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=\/wp\/v2\/posts\/6386"}],"collection":[{"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=6386"}],"version-history":[{"count":0,"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=\/wp\/v2\/posts\/6386\/revisions"}],"wp:attachment":[{"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6386"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6386"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cybersecurityinfocus.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6386"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}