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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'>Man,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'>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?<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'>Ben<o:p></o:p></span></p><p class=MsoNormal><a name="_MailEndCompose"><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'><o:p> </o:p></span></a></p><span style='mso-bookmark:_MailEndCompose'></span><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'>From:</span></b><span style='font-size:11.0pt;font-family:"Calibri",sans-serif;color:windowtext'> Man Ho (Certizen) [mailto:manho@certizen.com] <br><b>Sent:</b> Wednesday, March 23, 2016 12:27 AM<br><b>To:</b> Ben Wilson <ben.wilson@digicert.com>; public@cabforum.org<br><b>Subject:</b> Re: [cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>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><p class=MsoNormal>On 3/1/2016 12:21 AM, Ben Wilson wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=line874>REPLACE <o:p></o:p></p><p class=line874>"CAs SHOULD generate non-sequential Certificate serial numbers that exhibit at least 20 bits of entropy" <o:p></o:p></p><p class=line874>WITH <o:p></o:p></p><p class=line874>"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><p class=MsoNormal><o:p> </o:p></p></div></body></html>