<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">The point of the extension OID is to allow an auditor to distinguish between different types of CA blunder. Specifically a CA that fails to produce sufficient randomness and a CA that tries rigid construction and does it wrong.</div><div class=""><br class=""></div><div class="">I would not expect it to be verified in the client end point, the only place where I would expect it to be used is in CertSentry and similar.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">And just responding to Dean’s point. Yes, we did have a vote etc. But then there was a mis-issue that called into question the approach originally proposed. We are now in an incident response mode. </div><div class=""><br class=""></div><div class="">Even if it is too late to change matters this time round, this incident caused me to significantly change my thinking on the value of random vs rigid construction. I think it is useful to consider the strengths of the different approaches.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">The point of ‘randomizing’ the serial number is not that there is a value in unguessability, it is to prevent attacks on the compression function that depend on related keys. </div><div class=""><br class=""></div><div class="">If you really wanted belt and braces you could add a nonce generated by the CA to the phb-sha1-hack extension. That would then ensure that the serial number contained the necessary 64 bits of randomness as per the spec while preserving the ability to audit the scheme.</div><div class=""><br class=""></div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Jul 20, 2016, at 3:13 AM, Ryan Sleevi <<a href="mailto:sleevi@google.com" class="">sleevi@google.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><br class=""><div class="gmail_extra"><br class=""><div class="gmail_quote">On Mon, Jul 18, 2016 at 10:36 AM, <a href="mailto:philliph@comodo.com" class="">philliph@comodo.com</a> <span dir="ltr" class=""><<a href="mailto:philliph@comodo.com" target="_blank" class="">philliph@comodo.com</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">1) Generate the tbsCertificate with the Serial number field containing the bytes [0x01 … 0x01], minimum of 16 bytes. This is just a fixed value placeholder. Also add an extension OID for ‘phb-sha1-hack'<br class=""></blockquote><div class=""><br class=""></div><div class="">Objectively speaking, what value does 'phb-sha1-hack' add? </div><div class=""><br class=""></div><div class="">It would only seem to add value if someone wanted to continue trusting new SHA-1 certificates and programatically evaluate those that contain such an extension.</div><div class=""><br class=""></div><div class="">That doesn't seem to be a thing we should encourage, given that the very argument for the need for these is that they're not to be publicly trusted and on systems that cannot be updated.</div><div class=""><br class=""></div><div class="">Have I missed some other use case?</div></div></div></div>
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