<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=utf-8"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style><!--
/* Font Definitions */
@font-face
{font-family:Helvetica;
panose-1:2 11 6 4 2 2 2 2 2 4;}
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
pre
{mso-style-priority:99;
mso-style-link:"HTML Preformatted Char";
margin:0in;
margin-bottom:.0001pt;
font-size:10.0pt;
font-family:"Courier New";}
p.msonormal0, li.msonormal0, div.msonormal0
{mso-style-name:msonormal;
mso-margin-top-alt:auto;
margin-right:0in;
mso-margin-bottom-alt:auto;
margin-left:0in;
font-size:12.0pt;
font-family:"Times New Roman",serif;}
span.HTMLPreformattedChar
{mso-style-name:"HTML Preformatted Char";
mso-style-priority:99;
mso-style-link:"HTML Preformatted";
font-family:Consolas;}
span.EmailStyle20
{mso-style-type:personal-reply;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Sure. <o:p></o:p></span></p><p class=MsoNormal><a name="_MailEndCompose"><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><o:p> </o:p></span></a></p><span style='mso-bookmark:_MailEndCompose'></span><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Jacob Hoffman-Andrews [mailto:jsha@letsencrypt.org] <br><b>Sent:</b> Thursday, June 23, 2016 3:30 PM<br><b>To:</b> Ben Wilson <ben.wilson@digicert.com><br><b>Cc:</b> CABFPub <public@cabforum.org><br><b>Subject:</b> Re: [cabfpub] FW: Pre-Ballot 164 - Certificate Serial Number Entropy<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><div><div><pre>Hi Ben,<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Discussion seems to have petered out, and I think we are pretty close to<o:p></o:p></pre><pre>a workable ballot. Would you be interested in modifying this ballot to<o:p></o:p></pre><pre>the below and posting it as a final ballot for a vote?<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>-- Motion Begins --<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>Statement of intent:<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>As demonstrated in<o:p></o:p></pre><pre><a href="https://events.ccc.de/congress/2008/Fahrplan/attachments/1251_md5-collisions-1.0.pdf">https://events.ccc.de/congress/2008/Fahrplan/attachments/1251_md5-collisions-1.0.pdf</a>,<o:p></o:p></pre><pre>hash collisions can allow an attacker to forge a signature on the<o:p></o:p></pre><pre>certificate of their choosing. The birthday paradox means that, in the<o:p></o:p></pre><pre>absence of random bits, the security level of a hash function is half<o:p></o:p></pre><pre>what it should be. Adding random bits to issued certificates mitigates<o:p></o:p></pre><pre>collision attacks and means that an attacker must be capable of a much<o:p></o:p></pre><pre>harder preimage attack. For a long time the BRs have encouraged adding<o:p></o:p></pre><pre>random bits to the serial number of a certificate, and it is now common<o:p></o:p></pre><pre>practice. This ballot makes that best practice required, which will make<o:p></o:p></pre><pre>the Web PKI much more robust against all future weaknesses in hash<o:p></o:p></pre><pre>functions. Additionally, it replaces "entropy" with "CSPRNG" to make the<o:p></o:p></pre><pre>requirement clearer and easier to audit, and clarifies that serial<o:p></o:p></pre><pre>number must be positive.<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>In Section 1.6.1 of the Baseline Requirements,<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>ADD<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>CSPRNG: A random number generator intended for use in cryptographic system.<o:p></o:p></pre><pre><o:p> </o:p></pre><pre><o:p> </o:p></pre><pre>In Section 7.1 of the Baseline Requirements,<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>REPLACE<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>"CAs SHOULD generate non-sequential Certificate serial numbers that<o:p></o:p></pre><pre>exhibit at least 20 bits of entropy."<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>WITH<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>"Effective September 30, 2016, CAs SHALL generate Certificate serial<o:p></o:p></pre><pre>numbers greater than zero (0) containing at least 64 bits of output from<o:p></o:p></pre><pre>a CSPRNG."<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>-- Motion Ends --<o:p></o:p></pre><pre><o:p> </o:p></pre><pre>GitHub pull request: <a href="https://github.com/cabforum/documents/pull/24">https://github.com/cabforum/documents/pull/24</a><o:p></o:p></pre></div></div><div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal>On Mon, Apr 18, 2016 at 3:45 PM, Ben Wilson <<a href="mailto:ben.wilson@digicert.com" target="_blank">ben.wilson@digicert.com</a>> wrote:<o:p></o:p></p><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 style='font-size:11.0pt;font-family:"Calibri",sans-serif'>On the cablint report for the 20 bits of entropy, <a href="https://crt.sh/?cablint=38" target="_blank">https://crt.sh/?cablint=38</a>, there are 20 certificates that were listed. If this changes to 64 bits, how many more certificates will be on the list?</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><a name="m_-6300246916968660747__MailEndCompose"><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> </span></a><o:p></o:p></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><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> <a href="mailto:public-bounces@cabforum.org" target="_blank">public-bounces@cabforum.org</a> [mailto:<a href="mailto:public-bounces@cabforum.org" target="_blank">public-bounces@cabforum.org</a>] <b>On Behalf Of </b>Ben Wilson<br><b>Sent:</b> Monday, April 18, 2016 10:25 AM<br><b>To:</b> CABFPub <<a href="mailto:public@cabforum.org" target="_blank">public@cabforum.org</a>><br><b>Subject:</b> [cabfpub] FW: Pre-Ballot 164 - Certificate Serial Number Entropy</span><o:p></o:p></p></div></div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Forwarding</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Kane York [<a href="mailto:kanepyork@gmail.com" target="_blank">mailto:kanepyork@gmail.com</a>] <br><b>Sent:</b> Monday, April 18, 2016 10:23 AM<br><b>To:</b> Ben Wilson <<a href="mailto:ben.wilson@digicert.com" target="_blank">ben.wilson@digicert.com</a>>; Erwann Abalea <<a href="mailto:Erwann.Abalea@docusign.com" target="_blank">Erwann.Abalea@docusign.com</a>><br><b>Cc:</b> <a href="mailto:questions@cabforum.org" target="_blank">questions@cabforum.org</a><br><b>Subject:</b> Re: [cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy</span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><div><div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>On Fri, Apr 15, 2016 at 7:52 AM Ben Wilson <<a href="mailto:ben.wilson@digicert.com" target="_blank">ben.wilson@digicert.com</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-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>I didn’t think it was that simple. For instance, see <a href="https://en.wikipedia.org/wiki/Password_strength" target="_blank">https://en.wikipedia.org/wiki/Password_strength</a> </span><o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> </span><o:p></o:p></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><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Erwann Abalea [mailto:<a href="mailto:Erwann.Abalea@docusign.com" target="_blank">Erwann.Abalea@docusign.com</a>] <br><b>Sent:</b> Friday, April 15, 2016 8:44 AM<br><b>To:</b> Ben Wilson <<a href="mailto:ben.wilson@digicert.com" target="_blank">ben.wilson@digicert.com</a>><br><b>Cc:</b> CABFPub <<a href="mailto:public@cabforum.org" target="_blank">public@cabforum.org</a>></span><o:p></o:p></p></div></div></div></div><div><div><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'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><br><b>Subject:</b> Re: [cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy</span><o:p></o:p></p></div></div></div></div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Bonjour, <o:p></o:p></p><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>20 bits of entropy is the same as 20 bits unpredictable bits.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Whence, 64 bits of entropy is a higher requirement than 20 bits of entropy.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Cordialement,<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Erwann Abalea<o:p></o:p></p></div></div></div></div></div></blockquote><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>No, it definitely is that simple.<o:p></o:p></p><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>I think the confusion here is the definition of "hex characters".<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>> <span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Our CA issues certificates with 32 hexadecimal characters for the serial number.</span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>This is not possible - you cannot have 32 ASCII characters in the serial number.<o:p></o:p></p><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>The most likely truth given that explanation is that you have <b>16 fully random bytes</b>. Which would be 16 * 8 = 128 random bits, satisfying the entropy requirements.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>3 fully random bytes would satisfy the 20-bit requirement.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>6 fully random hexadecimal ASCII characters encoded in the serial number would satisfy the 20-bit requirement.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>8 fully random bytes is required to satisfy the 64-bit requirement.<o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>16 bytes with 4 bits of entropy each, which ASCII-encoded hexadecimal would be, would satisfy the entropy requirement and leave you 3.875 bytes left over for other information.<o:p></o:p></p></div></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <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-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'><div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>Le 15 avr. 2016 à 16:32, Ben Wilson <<a href="mailto:ben.wilson@digicert.com" target="_blank">ben.wilson@digicert.com</a>> a écrit :<o:p></o:p></p></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Forwarding</span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> </span><o:p></o:p></p></div><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Man Ho (Certizen) [<a href="mailto:manho@certizen.com" target="_blank"><span style='color:purple'>mailto:manho@certizen.com</span></a>] <br><b>Sent:</b> Thursday, April 14, 2016 7:51 PM<br><b>To:</b> Ben Wilson <<a href="mailto:ben.wilson@digicert.com" target="_blank"><span style='color:purple'>ben.wilson@digicert.com</span></a>>; Ryan Sleevi <<a href="mailto:sleevi@google.com" target="_blank"><span style='color:purple'>sleevi@google.com</span></a>><br><b>Cc:</b> <a href="mailto:public@cabforum.org" target="_blank"><span style='color:purple'>public@cabforum.org</span></a><br><b>Subject:</b> Re: [cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy</span><o:p></o:p></p></div></div></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'> <o:p></o:p></p></div><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt;background:white'>Ben,<br><br>We had already changed our system to issue SSL certificates with 20 hexadecimal characters of at least 20-bit of entropy since 2014. I'm just wondering why the requirement is changed from "bits of entropy" to "unpredictable bits", which I don't understand the conversion (like "cm" to "inch" :). I don't know whether our software vendor understands it.<br><br>Man<o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'>On 4/15/2016 4:24 AM, Ben Wilson wrote:<o:p></o:p></p></div></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>You’re right, given a randomly generated 20-byte serial number, you have 159 unpredictable bits. </span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> </span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Ryan Sleevi [<a href="mailto:sleevi@google.com" target="_blank"><span style='color:purple'>mailto:sleevi@google.com</span></a>] <br><b>Sent:</b> Thursday, April 14, 2016 2:03 PM<br><b>To:</b> Ben Wilson <a href="mailto:ben.wilson@digicert.com" target="_blank"><span style='color:purple'><ben.wilson@digicert.com></span></a><br><b>Cc:</b> Man Ho (Certizen) <a href="mailto:manho@certizen.com" target="_blank"><span style='color:purple'><manho@certizen.com></span></a>; <a href="mailto:public@cabforum.org" target="_blank"><span style='color:purple'>public@cabforum.org</span></a><br><b>Subject:</b> Re: [cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy</span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'> <o:p></o:p></p></div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'>Ben:<o:p></o:p></p></div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'> <o:p></o:p></p></div></div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'>Are you sure your math is correct? A serial number is 20 bytes, with the high bit needing to be 1 (for the encoding of positive INTEGERS within DER). This leaves 159 bits for entropy. So you certainly can't have more unpredictable bits than that :)<o:p></o:p></p></div></div></div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'> <o:p></o:p></p></div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'>On Thu, Apr 14, 2016 at 12:59 PM, Ben Wilson <<a href="mailto:ben.wilson@digicert.com" target="_blank"><span style='color:purple'>ben.wilson@digicert.com</span></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-top:5.0pt;margin-right:0in;margin-bottom:5.0pt'><div><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Man,</span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Have you had a chance to do further research on the capabilities of your system? Our CA issues certificates with 32 hexadecimal characters for the serial number. There are 4 bits of entropy for each hexadecimal character. Therefore, our serial numbers have 128 bits of entropy and 16*32= 512 unpredictable bits. An 8-hexadecimal character serial number would have 32 bits of entropy and 128 unpredictable bits. A 20-bit entropy would be equal to 5 hexadecimal characters, or 80 unpredictable bits, so this seems like this is a downgrade to go to 64 unpredictable bits. Am I right?</span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>Ben</span><o:p></o:p></p></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><a name="m_-6300246916968660747_m_-52385512724017"><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> </span></a><o:p></o:p></p></div><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'> Man Ho (Certizen) [mailto:<a href="mailto:manho@certizen.com" target="_blank"><span style='color:purple'>manho@certizen.com</span></a>] <br><b>Sent:</b> Wednesday, March 23, 2016 12:27 AM<br><b>To:</b> Ben Wilson <<a href="mailto:ben.wilson@digicert.com" target="_blank"><span style='color:purple'>ben.wilson@digicert.com</span></a>>; </span><a href="mailto:public@cabforum.org" target="_blank"><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:purple'>public@cabforum.org</span></a><span style='font-size:11.0pt;font-family:"Calibri",sans-serif'><br><b>Subject:</b> Re: [cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy</span><o:p></o:p></p></div></div></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'> <o:p></o:p></p></div><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt;background:white'>Hi all,<br><br>Is the meaning of "at least 64 unpredictable bits" setting the same or a higher requirement than "at least 20 bits of entropy" ? I'm not quite sure whether our certificate generation software has this setting in itself.<br><br>Cheers<br>Man<o:p></o:p></p><div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'>On 3/1/2016 12:21 AM, Ben Wilson wrote:<o:p></o:p></p></div></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'>REPLACE <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'>"CAs SHOULD generate non-sequential Certificate serial numbers that exhibit at least 20 bits of entropy" <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'>WITH <o:p></o:p></p><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'>"Effective April 1, 2016, CAs SHALL use a Certificate serialNumber greater than zero (0) that contains at least 64 unpredictable bits." <o:p></o:p></p></blockquote><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'> <o:p></o:p></p></div></div></div><p class=MsoNormal style='mso-margin-top-alt:auto;margin-bottom:12.0pt;background:white'><br>_______________________________________________<br>Public mailing list<br><a href="mailto:Public@cabforum.org" target="_blank"><span style='color:purple'>Public@cabforum.org</span></a><br><a href="https://cabforum.org/mailman/listinfo/public" target="_blank"><span style='color:purple'>https://cabforum.org/mailman/listinfo/public</span></a><o:p></o:p></p></blockquote></div><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'> <o:p></o:p></p></div></div></blockquote><div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;background:white'> <o:p></o:p></p></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'><span style='font-size:9.0pt;font-family:"Helvetica",sans-serif;background:white'>_______________________________________________</span><span style='font-size:9.0pt;font-family:"Helvetica",sans-serif'><br><span style='background:white'>Public mailing list</span><br></span><a href="mailto:Public@cabforum.org" target="_blank"><span style='font-size:9.0pt;font-family:"Helvetica",sans-serif;color:purple;background:white'>Public@cabforum.org</span></a><span style='font-size:9.0pt;font-family:"Helvetica",sans-serif'><br></span><a href="https://cabforum.org/mailman/listinfo/public" target="_blank"><span style='font-size:9.0pt;font-family:"Helvetica",sans-serif;color:purple;background:white'>https://cabforum.org/mailman/listinfo/public</span></a><o:p></o:p></p></div></blockquote></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'> <o:p></o:p></p></div></div></div><p class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto'>_______________________________________________<br>Public mailing list<br><a href="mailto:Public@cabforum.org" target="_blank">Public@cabforum.org</a><br><a href="https://cabforum.org/mailman/listinfo/public" target="_blank">https://cabforum.org/mailman/listinfo/public</a><o:p></o:p></p></blockquote></div></div></div></div></div></div></div></div></div><p class=MsoNormal style='margin-bottom:12.0pt'><br>_______________________________________________<br>Public mailing list<br><a href="mailto:Public@cabforum.org">Public@cabforum.org</a><br><a href="https://cabforum.org/mailman/listinfo/public" target="_blank">https://cabforum.org/mailman/listinfo/public</a><o:p></o:p></p></blockquote></div><p class=MsoNormal><o:p> </o:p></p></div></div></body></html>