[Servercert-wg] SCXX Ballot - Debian Weak Keys (and related vulnerabilities)

Chris Kemmerer chris at ssl.com
Fri Jul 1 19:13:04 UTC 2022


Thanks to all who participated in the very useful discussion regarding this proposed ballot in our June 23 2022 call.

An important point was raised about how to handle external links to recommended (but not required) resources. In "Section Subscriber Key Pair Generation" of the proposed language, we require CAs to reject requests for certificates with "industry demonstrated weak Private Keys" (as "SHALL" and "MUST" directives), then provide links to "Suggested tools that CAs MAY use" to judge requests.


The questions here are:

  *   If we direct issuers to external resources in CABF documents, what level of CABF-level vetting should be required or expected for those links?
  *   And is the ballot process itself sufficient vetting for such links?


We are assuming that for, weak key detection, we DO want to provide useful links to help guide certificate issuers (see sidebar below). Note that the current BR language already includes one such link, to a page maintained by Debian (https://wiki.debian.org/SSLkeys), though with a vetted status unknown to us.

Our proposed ballot language also adds a requirement to reject keys "identified by the tools available at https://github.com/crocs-muni/roca or equivalent". As we recall it, this resource was suggested by a CABF participant now departed, and again the status of vetting for this link is unknown.

For what it's worth, a quick scan of the BRs shows that, apart from weak key guidance, we do include links to other external resources which are presumably foundational enough to not require vetting. These include:

  *   IETF (various RFCs, ex. http://tools.ietf.org/html/rfc5890)
  *   IANA (registry information, ex. https://www.iana.org/assignments/iana-ipv4-special-registry/iana-ipv4-special-registry.xhtml)
  *   NIST (publications, ex. http://csrc.nist.gov/publications/nistpubs/800-89/SP-800-89_November2006.pdf)
  *   and the Mozilla Foundation (the Public Suffix List, https://publicsuffix.org/).


As Dimitris stated in the call, the two other links included as resources which MAY be utilized:

  *   https://github.com/CVE-2008-0166
  *   https://github.com/HARICA-official/debian-weak-keys

... have been "cross-vetted" by their respective providers (HARICA and Sectigo).

This discussion was spurred by a suggestion from Adriano Santoni to consider adding a third resource (Hanno Böck's badkeys tool):

  *   https://github.com/badkeys/badkeys (web version: https://badkeys.info/)

...for which no such CABF-level "cross-vetting" has been performed (as far as we know).

We ourselves very much appreciate the effort that went into creating these tools and intend to utilize them. However:


  *   Is the ballot process itself considered adequate vetting for external links in CABF documents?
  *   If not, what vetting would we consider adequate?


  *   In the June 23 call, an external, CABF-supported resource (i.e. a separate web page with appropriate links) was considered, discussed, and rejected as likely to increase overhead and decrease reliability. Based on this, our sense is that any links deemed useful should indeed be included in the actual ballot language itself.
  *   And finally, as raised in previous discussions: Would some sort of disclaimer be appropriate for external links, and if so should it extend beyond the links to cover external resources more generally?


From: Servercert-wg <servercert-wg-bounces at cabforum.org> on behalf of Adriano Santoni via Servercert-wg <servercert-wg at cabforum.org>
Sent: Sunday, June 12, 2022 7:11 PM
To: servercert-wg at cabforum.org <servercert-wg at cabforum.org>
Cc: Hanno Böck <hanno at hboeck.de>
Subject: Re: [Servercert-wg] SCXX Ballot - Debian Weak Keys (and related vulnerabilities)

Might a third option be the tool developed by Hanno Boeck?


>From our point of view it's an effective tool.


Il 09/06/2022 15:18, Chris Kemmerer via Servercert-wg ha scritto:
Suggested tools that CAs MAY use to obtain lists of Debian weak keys include:

  - https://github.com/CVE-2008-0166<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FCVE-2008-0166&data=05%7C01%7Cchris%40ssl.com%7C8641292420c44f04613b08da4cd14ed0%7C7741372af1ae4cc7b93ce6c2c138b2bb%7C0%7C0%7C637906759104963939%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=zfjpsiplLaqFzwkKzciu7cQTRzDeeqBP0XFs3zn5OJg%3D&reserved=0> provides a generator, for the complete set of parameters listed above, that runs on any modern 64-bit Linux system; it also provides complete sets of pregenerated keys for the most common RSA key sizes.
  - https://github.com/HARICA-official/debian-weak-keys<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FHARICA-official%2Fdebian-weak-keys&data=05%7C01%7Cchris%40ssl.com%7C8641292420c44f04613b08da4cd14ed0%7C7741372af1ae4cc7b93ce6c2c138b2bb%7C0%7C0%7C637906759104963939%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=JAHix0XFgxltAzN0FGh58bZkHVRLacTP8rUK35Ymn0c%3D&reserved=0> provides a generator, for a subset of the parameters listed above, that can take advantage of a computer cluster.
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