Bonjour, 20 bits of entropy is the same as 20 bits unpredictable bits.
Whence, 64 bits of entropy is a higher requirement than 20 bits of entropy. Cordialement, Erwann Abalea Le 15 avr. 2016 à 16:32, Ben Wilson <[email protected]<mailto:[email protected]>> a écrit : Forwarding From: Man Ho (Certizen) [mailto:[email protected]] Sent: Thursday, April 14, 2016 7:51 PM To: Ben Wilson <[email protected]<mailto:[email protected]>>; Ryan Sleevi <[email protected]<mailto:[email protected]>> Cc: [email protected]<mailto:[email protected]> Subject: Re: [cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy Ben, 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. Man On 4/15/2016 4:24 AM, Ben Wilson wrote: You’re right, given a randomly generated 20-byte serial number, you have 159 unpredictable bits. From: Ryan Sleevi [mailto:[email protected]] Sent: Thursday, April 14, 2016 2:03 PM To: Ben Wilson <[email protected]><mailto:[email protected]> Cc: Man Ho (Certizen) <[email protected]><mailto:[email protected]>; [email protected]<mailto:[email protected]> Subject: Re: [cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy Ben: 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 :) On Thu, Apr 14, 2016 at 12:59 PM, Ben Wilson <[email protected]<mailto:[email protected]>> wrote: Man, 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? Ben From: Man Ho (Certizen) [mailto:[email protected]<mailto:[email protected]>] Sent: Wednesday, March 23, 2016 12:27 AM To: Ben Wilson <[email protected]<mailto:[email protected]>>; [email protected]<mailto:[email protected]> Subject: Re: [cabfpub] Pre-Ballot 164 - Certificate Serial Number Entropy Hi all, 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. Cheers Man On 3/1/2016 12:21 AM, Ben Wilson wrote: REPLACE "CAs SHOULD generate non-sequential Certificate serial numbers that exhibit at least 20 bits of entropy" WITH "Effective April 1, 2016, CAs SHALL use a Certificate serialNumber greater than zero (0) that contains at least 64 unpredictable bits." _______________________________________________ Public mailing list [email protected]<mailto:[email protected]> https://cabforum.org/mailman/listinfo/public _______________________________________________ Public mailing list [email protected]<mailto:[email protected]> https://cabforum.org/mailman/listinfo/public
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