DNS Certification Authority Authorization

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DNS Certification Authority Authorization
AbbreviationCAA
Status
RFC 8659
November 2019
OrganizationIETF
Authors

DNS Certification Authority Authorization (CAA) is an

resource record
.

It was drafted by computer scientists Phillip Hallam-Baker and Rob Stradling in response to increasing concerns about the security of publicly trusted certificate authorities. It is an Internet Engineering Task Force (IETF) proposed standard.

Background

A

client-side, and CAA to block mis-issuance on the certificate authority side.[4]

The first draft of CAA was written by

Comodo, failed to implement CAA before the deadline.[10] A 2017 study by the Technical University of Munich found many instances where certificate authorities failed to correctly implement some part of the standard.[4]

In September 2017, Jacob Hoffman-Andrews submitted an Internet Draft intended to simplify the CAA standard. This was improved by the LAMPS Working Group, and approved as

RFC 8659, a Proposed Standard, in November 2019.[11]

As of January 2020[update], Qualys reports that still, only 6.8% of the 150,000 most popular TLS-supporting websites use CAA records.[12]

Record

Certificate authorities implementing CAA perform a

digital certificate. Each CAA resource record consists of the following components:[11]

flag
A
extensible signaling system for future use. As of 2018, only the issuer critical flag has been defined, which instructs certificate authorities that they must understand the corresponding property tag before issuing a certificate.[11] This flag allows the protocol to be extended in the future with mandatory extensions,[4] similar to critical extensions in X.509 certificates
.
tag
One of the following property:
issue
This property authorizes the holder of the domain specified in associated property value to issue certificates for the domain for which the property is published.
issuewild
This property acts like issue but only authorizes the issuance of wildcard certificates, and takes precedence over the issue property for wildcard certificate requests.
iodef
This property specifies a method for certificate authorities to report invalid certificate requests to the domain name holder using the Incident Object Description Exchange Format. As of 2018, not all certificate authorities support this tag, so there is no guarantee that all certificate issuances will be reported.
contactemail
Increasingly, contact information is not available in WHOIS due to concerns about potential GDPR violations. This property allows domain holders to publish contact information in DNS.[13][14]
contactphone
As above, for phone numbers.[15]
value
The value associated with the chosen property tag.

The lack of any CAA records authorizes normal unrestricted issuance, and the presence of a single blank issue tag disallows all issuance.[11][9][16]

Third parties monitoring certificate authority behavior might check newly issued certificates against the domain's CAA records.

RFC 8659 states; CAA records MAY be used by Certificate Evaluators as a possible indicator of a security policy violation. Such use SHOULD take into account the possibility that published CAA records changed between the time a certificate was issued and the time at which the certificate was observed by the Certificate Evaluator.[11]

Extensions

ACME protocol
. For example, website administrator can bind a domain they control to particular account registered with their desired Certification Authority.

History

A draft of the first extension to the CAA standard was published on October 26, 2016, proposing a new account-uri token to the end of the issue property, which ties a domain to a specific

Automated Certificate Management Environment account.[17] This was amended on August 30, 2017, to also include a new validation-methods token, which ties a domain to a specific validation method,[18] and then further amended on June 21, 2018, to remove the hyphen in account-uri and validation-methods making them instead accounturi and validationmethods.[19]

Examples

To indicate that only the certificate authority identified by ca.example.net is authorized to issue certificates for example.com and all subdomains, one may use this CAA record:[11]

example.com.  IN  CAA 0 issue "ca.example.net"

To disallow any certificate issuance, one may allow issuance only to an empty issuer list:

example.com.  IN  CAA  0 issue ";"

To indicate that certificate authorities should report invalid certificate requests to an

Real-time Inter-network Defense
endpoint:

example.com.  IN  CAA 0 iodef "mailto:[email protected]"
example.com.  IN  CAA 0 iodef "http://iodef.example.com/"

To use a future extension of the protocol, for example, one which defines a new future property, which needs to be understood by the certificate authority before they can safely proceed, one may set the issuer critical flag:

example.com.  IN  CAA  0 issue "ca.example.net"
example.com.  IN  CAA  128 future "value"

Incidents

In 2017, Camerfirma was found to improperly validate CAA records. Camerfirma claimed to have misunderstood the CA/Browser Forum Baseline Requirements describing CAA validation.[20][4]

In early 2020, Let's Encrypt disclosed that their software improperly queried and validated CAA records potentially affecting over 3 million certificates.[21] Let's Encrypt worked with customers and site operators to replace over 1.7 million certificates, but decided not to revoke the rest to avoid client downtime and since the affected certificates would all expire in less than 90 days.[22]

See also

References

  1. ^ Ristić, Ivan. "SSL/TLS and PKI History". Feisty Duck. Retrieved June 8, 2018.
  2. ^ Bright, Peter (August 30, 2011). "Another fraudulent certificate raises the same old questions about certificate authorities". Ars Technica. Retrieved February 10, 2018.
  3. S2CID 5027899
    .
  4. ^ .
  5. ^ Hallam-Baker, Phillip; Stradling, Rob (October 18, 2010). DNS Certification Authority Authorization (CAA) Resource Record. IETF. I-D draft-hallambaker-donotissue-00.
  6. ^ Hallam-Baker, Phillip; Stradling, Rob; Ben, Laurie (June 2, 2011). DNS Certification Authority Authorization (CAA) Resource Record. IETF. I-D draft-ietf-pkix-caa-00.
  7. .
  8. ^ Hall, Kirk (March 8, 2017). "Results on Ballot 187 - Make CAA Checking Mandatory". CA/Browser Forum. Retrieved January 7, 2018.
  9. ^ a b Beattie, Doug (August 22, 2017). "What is CAA (Certificate Authority Authorization)?". GlobalSign. Retrieved February 2, 2018.
  10. ^ Cimpanu, Catalin (September 11, 2017). "Comodo Caught Breaking New CAA Standard One Day After It Went Into Effect". Bleeping Computer. Retrieved January 8, 2018.
  11. ^ .
  12. ^ "SSL Pulse". SSL Labs. Qualys. January 3, 2020. Retrieved January 31, 2020.
  13. ^ "Public Key Infrastructure using X.509 (PKIX) Parameters". www.iana.org. Retrieved August 22, 2020.
  14. ^ https://cabforum.org/wp-content/uploads/CA-Browser-Forum-BR-1.6.3.pdf[bare URL PDF]
  15. ^ Beattie, Doug (January 7, 2019). "Ballot SC14: CAA Contact Property and Associated Phone Validation Methods". CA/Browser Forum (Mailing list). Retrieved October 19, 2020.
  16. Symantec
    . Retrieved January 8, 2018.
  17. ^ Landau, Hugo (October 26, 2016). CAA Record Extensions for Account URI and ACME Method Binding. IETF. I-D draft-ietf-acme-caa-00.
  18. ^ Landau, Hugo (August 30, 2017). CAA Record Extensions for Account URI and ACME Method Binding. IETF. I-D draft-ietf-acme-caa-04.
  19. ^ Landau, Hugo (June 21, 2018). CAA Record Extensions for Account URI and ACME Method Binding. IETF. I-D draft-ietf-acme-caa-05.
  20. ^ "CA:Camerfirma Issues - MozillaWiki". wiki.mozilla.org. Retrieved April 27, 2021.
  21. ^ Claburn, Thomas (March 3, 2020). "Let's Encrypt? Let's revoke 3 million HTTPS certificates on Wednesday, more like: Check code loop blunder strikes". www.theregister.com. Archived from the original on May 31, 2020. Retrieved April 27, 2021.
  22. ISSN 1059-1028
    . Retrieved April 27, 2021.

External links