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diff --git a/chromium/docs/website/site/developers/md5-certificate-statistics/index.md b/chromium/docs/website/site/developers/md5-certificate-statistics/index.md new file mode 100644 index 00000000000..aaf0b6f974c --- /dev/null +++ b/chromium/docs/website/site/developers/md5-certificate-statistics/index.md @@ -0,0 +1,94 @@ +--- +breadcrumbs: +- - /developers + - For Developers +page_name: md5-certificate-statistics +title: MD5 Certificate Statistics +--- + +Thursday, February 19, 2009 + +Last December, a group of security researchers published a practical attack on +CAs that issue certificates signed with MD5-based signatures +(<http://www.win.tue.nl/hashclash/rogue-ca/>). As a result, some browser +developers are planning to drop support of MD5 certificates at some point. The +exact time frame depends in part on how many HTTPS websites are still using MD5 +certificates. Johnathan Nightingale of Mozilla crawled the top 1 million HTTPS +sites and published his findings +(<http://blog.johnath.com/2009/01/21/ssl-information-wants-to-be-free/>). With +Google Chrome's usage statistics collection service, we can help answer this +usage question by measuring how often Google Chrome users are encountering MD5 +certificates. We'd like to share these measurements with other browser +developers. + +The following statistics were gathered on our Dev channel releases, which are +weekly releases based on the tip of the Chromium source tree. Also note that +only Google Chrome users who opted in to usage statistics collection send their +numbers to us. + +The counts shown below reflect periods of time on the order of a week, but +didn't seem to vary significantly across over a month of investigating. For each +kind of certificate, we collected two counts. One count reflects the number of +SSL connections made to sites using that kind of certificate, while the other +count reflects the number of Google Chrome sessions involving that kind of +certificate. The latter can provide an estimator of the percentage of users that +would be impacted by dropping MD5 certificate support. Note that we ignore the +root CA certificates because the signatures in the root CA certificates are +irrelevant to an attack of this sort. + +1. The number of SSL connections with certain kinds of certificates. Note that +an HTTP keep-alive connection is counted once even though multiple HTTP requests +may be sent over it. + +* The number of all SSL connections: 16408141 +* The number of SSL connections with an MD5 (end entity or + intermediate CA) certificate in the certificate chain: 365152 +* The number of SSL connections with an MD2 (end entity or + intermediate CA) certificate in the certificate chain: 47 +* The number of SSL connections with an MD4 (end entity or + intermediate CA) certificate in the certificate chain: 0 +* The number of SSL connections with an MD5 intermediate CA + certificate in the certificate chain: 480 +* The number of SSL connections with an MD2 intermediate CA + certificate in the certificate chain: 25 + +2. The number of Google Chrome sessions in which the user has seen certain kinds +of certificates. + +* The number of all Google Chrome sessions: 542846 +* The number of Google Chrome sessions that used SSL: 496090 +* The number of Google Chrome sessions that saw an MD5 (end entity or + intermediate CA) certificate: 33134 +* The number of Google Chrome sessions that saw an MD2 (end entity or + intermediate CA) certificate: 14 +* The number of Google Chrome sessions that saw an MD4 (end entity or + intermediate CA) certificate: 0 +* The number of Google Chrome sessions that saw an MD5 intermediate CA + certificate: 58 +* The number of Google Chrome sessions that saw an MD2 intermediate CA + certificate: 10 + +The percentage of MD5 certificates of the secure Web, weighted by site +popularity and reported by users of Google Chrome's Dev channel releases who +opted in to usage statistics collection, is 365152/16408141 = 2.23%. Looking at +the per session statistics, we see that the number of user sessions that would +be impacted by no longer supporting MD5 certificates would be 33134/542846 = +6.1%. Either of these percentages, though significantly smaller than reported by +Nightingale, suggests that there would be a large user impact if MD5 certificate +support were suddenly removed. + +A second alternative being considered is to remove support for MD5 intermediate +CA certificates. Although this would not completely preclude an attack, it would +significantly raise the cost of attacks. The percentage of MD5 intermediate CA +certificates is notably lower, at 480/16408141 < 0.003%. Looking at a per +session statistics, we can see that only 58/542846 = .011% would be impacted by +such a change. As a result, it should be possible for browsers to drop support +of MD5 intermediate CA certificates sooner, which will make the MD5 certificate +attack much more expensive. + +In the future we hope to use the statistics collection service to gather other +information of interest to crypto practitioners, such as which SSL cipher suites +are being used in practice and how many HTTPS sites use certificates with +certification path validation errors. + +Posted by Wan-Teh Chang and Jim Roskind, Software Engineers
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