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CASC Releases Minimum Requirements for Code Signing Certificates

The Certificate Authority Security Council (CASC) this week announced that the Code Signing Working Group released a set of minimal requirements that Certificate Authorities (CAs) should use for code signing.

The requirements, which represent the first-ever standardized code signing guidelines, should improve users’ online protection by verifying software authenticity, thus helping them avoid downloading malware and other malicious programs. Through code signing, a certificate-based digital signature is used to sign executables and scripts to verify the author's identity and that the code hasn’t been altered or corrupted.

Before the document (PDF) was released (under the name of Minimum Requirements for the Issuance and Management of Publicly-Trusted Code Signing Certificates), no standards were used, which allowed companies to submit their applications to different CAs if one CA already rejected them.

Part of the CA/Browser Forum, a voluntary group of CAs, Internet browser software vendors, and suppliers of other applications that use X.509 v.3 digital certificates for SSL/TLS and code signing, and comprised of CASC members, the Code Signing Working Group worked together with CAs, application software suppliers and the security community for over two years to devise the requirements.

The guidelines were initially rejected within the CA/Browser Forum, but in July it was decided to bring the document outside of the forum to finalize it as part of the CA Security Council. The document will continue to be improved and maintained by the CASC members and others.

The new minimum requirements should help businesses defend their IT systems and information stores from cyber-attacks by offering features such as increased protection for private keys (the use of a FIPS 140-2 Level 2 HSM or equivalent), certificate revocation (after receiving a request, CAs should revoke the certificate within two days, or alert the requestor that it has launched an investigation), and improved code signatures time-stamping (the standard allows for 135-month time-stamping certificates).

As part of the new guidelines, companies are required to store keys in hardware kept on premise hardware, or to store them in secure cloud-based code signing services. CAs, on the other hand, are forced to act more swiftly on certificate revocation requests, which usually come from malware researchers or application software suppliers. Moreover, they also have to provide a time-stamping authority (TSA), and the new document specifies the requirements for the TSA and the time-stamping certificates.

One other main idea behind creating the requirements is to help users stay informed when it comes to the purpose of signed code, as well as to make informed decisions when relying on certificates. Overall, the guidelines are expected to improve the trustworthiness of software platforms, while also limit the spread of malware.

Microsoft, which has already adopted the new guidelines, will require all CAs that issue code signing certificates for Windows platforms to adopt the minimum requirements starting on Feb. 1, 2017.

“Microsoft is committed to continuously improving the security of our products and services. These new baseline requirements will further our goal by ensuring that our certificate authority partners follow a standard set of rules when issuing certificates to software developers,” Jody Cloutier, Senior Security Program Manager, Microsoft Cryptographic Ecosystem, said.

Given that Microsoft’s Windows platform accounts for around 90% of the desktop operating system market, its decision to adopt the new guidelines and to ask CAs follow them is will likely have a great influence on other application software suppliers, which might follow suit, Jeremy Rowley, Executive Vice President of Emerging Markets, DigiCert, believes.

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