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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>We’re talking the former (re-signing a key used in a previous cert that was revoked by the CA itself for key compromise). There isn’t an obligation for a CA to check to see if a key is compromised. The current process just kicks off a perpetual 24 hour revocation period as long as the public can find the compromised key. <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>“Thus, I would expect that CAs are checking for reuse of compromised private keys prior to issuance.”<o:p></o:p></p><p class=MsoNormal>This is definitely not happening. <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>“<span lang=EN-CA style='color:#1F497D'>My assumption is a certificate which has been revoked due to compromise has a “weak Private Key.” As such, based on the current BRs, a CA should reject certificate requests using a key from a certificate that they revoked due to compromise.”</span><span lang=EN-CA>This also doesn’t happen across CAs. Too ambiguous on what is a “weak Private Key”, although this is mixed results (all CAs seem to prevent 1024 bit certs but not all fail for Heartbleed issues) <span style='color:#1F497D'><o:p></o:p></span></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><b>From:</b> Wayne Thayer <wthayer@mozilla.com> <br><b>Sent:</b> Tuesday, August 21, 2018 3:56 PM<br><b>To:</b> Bruce Morton <Bruce.Morton@entrustdatacard.com>; CA/Browser Forum Public Discussion List <public@cabforum.org><br><b>Cc:</b> Tim Hollebeek <tim.hollebeek@digicert.com>; Jeremy Rowley <jeremy.rowley@digicert.com>; Ryan Sleevi <sleevi@google.com><br><b>Subject:</b> Re: [cabfpub] [EXTERNAL]Re: Issuance of certificates for keys reported as compromised<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On Tue, Aug 21, 2018 at 2:15 PM Bruce Morton via Public <<a href="mailto:public@cabforum.org">public@cabforum.org</a>> wrote:<o:p></o:p></p><div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in'><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-CA style='color:#1F497D'>BR 6.1.1.3 states “The CA SHALL reject a certificate request if the requested Public Key does not meet the requirements set forth in Sections 6.1.5 and 6.1.6 or if it has a known weak Private Key (such as a Debian weak key, see <a href="http://wiki.debian.org/SSLkeys)" target="_blank">http://wiki.debian.org/SSLkeys)</a>.” </span><span lang=EN-CA><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-CA style='color:#1F497D'> </span><span lang=EN-CA><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-CA style='color:#1F497D'>My assumption is a certificate which has been revoked due to compromise has a “weak Private Key.” As such, based on the current BRs, a CA should reject certificate requests using a key from a certificate that they revoked due to compromise.</span><span lang=EN-CA><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-CA style='color:#1F497D'> </span><span lang=EN-CA><o:p></o:p></span></p></div></div></blockquote><div><p class=MsoNormal>If we're talking about the same CA re-signing a key previously used in a certificate that the CA revoked due to key compromise, then [if nothing else] the CA must revoke the new certificate within 24 hours per 4.9.1.1(3). Thus, I would expect that CAs are checking for reuse of compromised private keys prior to issuance.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>If we're talking about other CAs rejecting the compromised key, then I have to question whether there is enough benefit to offset the substantial effort involved in designing and running a system that isn't susceptible to the concerns Ryan raised. It'd be interesting to see a proposal.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;margin-left:4.8pt;margin-right:0in'><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-CA style='color:#1F497D'>Bruce.</span><span lang=EN-CA><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-CA style='color:#1F497D'> </span><span lang=EN-CA><o:p></o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b>From:</b> Public [mailto:<a href="mailto:public-bounces@cabforum.org" target="_blank">public-bounces@cabforum.org</a>] <b>On Behalf Of </b>Tim Hollebeek via Public<br><b>Sent:</b> August 21, 2018 4:55 PM<br><b>To:</b> Jeremy Rowley <<a href="mailto:jeremy.rowley@digicert.com" target="_blank">jeremy.rowley@digicert.com</a>>; Ryan Sleevi <<a href="mailto:sleevi@google.com" target="_blank">sleevi@google.com</a>>; CA/Browser Forum Public Discussion List <<a href="mailto:public@cabforum.org" target="_blank">public@cabforum.org</a>><br><b>Subject:</b> [EXTERNAL]Re: [cabfpub] Issuance of certificates for keys reported as compromised<span lang=EN-CA><o:p></o:p></span></p></div></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-CA> <o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Yes, certainly, at a minimum, CAs should not be issuing new certificates for keys they themselves have previously determined to be compromised.<span lang=EN-CA><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <span lang=EN-CA><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>As you correctly note, this is currently a fairly common occurrence.<span lang=EN-CA><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <span lang=EN-CA><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>-Tim<span lang=EN-CA><o:p></o:p></span></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span lang=EN-CA><o:p> </o:p></span></p></div></div></blockquote></div></div></div></body></html>