SSL Certificates Now Need Mandatory Authorization Checks

April 13, 2017 @ 7:30 AM
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2 min read

Generating SSL certificates will undergo some method changes starting Sept. 8. Members of the CA/Browser Forum, which includes both certificate authorities (CA) and browser creators, voted in March to run mandatory certificate authority authorization (CAA) checks before issuing any certificate. Before this requirement, CAs implemented CAA checking on an opt-in basis.

Delving Into CAA Records

The system allows domain name holders to specify multiple CAs that can authorize certificates for a domain. By applying this specification, the domain effectively prevents CAs from issuing an authorized certificate in its name. Through the use of this CAA, the domain owner can control the policy on every level, such as specify which CA can issue Wildcard certificates and report issues.

Let’s say some popular CA issues several certificates for a well-known domain in violation of the domain’s wishes. Previously, the domain was limited in how it could stop the CA from this practice. With this new process, the domain owner regains control over the certificates he or she trusts.

SecurityWeek noted that CAA checking isn’t required in specific scenarios, such as “certificates for which a certificate transparency pre-certificate was created and logged in at least two public logs, and for which CAA was checked.”

Setting a New Standard for SSL Certificates

While mandatory CAA checking does offer some boundaries on whether a certificate can or should be issued, there are a few complications. For example, there is no clearly defined policy for how CAA checking will work with the CNAME records stored in the CAA. This means that when given two different CAs on a certificate, it may be unclear which controls issuance. While a check should trace through aliases to be valid, the approved proposal doesn’t specify just how this tracing should occur.

But the real industry issue is the lack of software that supports CAA at the DNS and CA level. This will likely hit smaller CA outfits particularly hard, since they may not have the tools to actually run the check by September.

This is an incremental change in the security of TLS certificates for the better. However, these certificates are still only part of the overall security solution and need to be treated carefully.

Larry Loeb
Principal, PBC Enterprises

Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE mag...
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