{"id":51,"date":"2005-03-04T18:09:00","date_gmt":"2005-03-05T01:09:00","guid":{"rendered":"http:\/\/www.elbeno.com\/blog\/?p=51"},"modified":"2005-03-04T18:09:00","modified_gmt":"2005-03-05T01:09:00","slug":"another-blow-against-internet-anonymity","status":"publish","type":"post","link":"https:\/\/www.elbeno.com\/blog\/?p=51","title":{"rendered":"Another blow against Internet anonymity"},"content":{"rendered":"<p>Via Slashdot: A San Diego research team has developed a <a href=\"http:\/\/www.caida.org\/outreach\/papers\/2005\/fingerprinting\/\">method<\/a> for extracting information about a machine from the timestamps contained in the TCP packets it sends. In summary:<\/p>\n<ul>\n<li>Machines will include timestamps in each TCP packet as an option (<a href=\"http:\/\/www.faqs.org\/rfcs\/rfc1323.html\">RFC 1323: TCP Extensions for High Performance<\/a>) which for most machines is negotiated by default.\n<li>Windows machines don&apos;t negotiate this option by default in their intial <i>SYN<\/i>, but will turn it on if the <i>SYN\/ACK<\/i> sets it (breaking the RFC protocol deliberately).\n<li>By comparing the TCP timestamps to a local clock, and allowing for network latency and other factors, you can obtain a fairly accurate estimate of the remote machine&apos;s clock skew (how the clock drifts over time), expressed in \u00c2\u00b5s\/s.\n<li>A given machine has a constant clock skew, and different machines have different clock skews.\n<li>Synchronising the machine&apos;s system time (e.g. by <a href=\"http:\/\/www.faqs.org\/rfcs\/rfc1305.html\">NTP<\/a>) doesn&apos;t help, because the TCP timestamp clock is separate from the system clock (TCP makes very few demands about how the TCP timestamp needs to follow actual time).\n<\/ul>\n<p>This clock skew estimation technique works with any protocol that leaks clock information, not just TCP. It doesn&apos;t provide a positive identification on its own (there are millions of machines on the Internet, many of them have identical clock skews within measurable limits). It can provide a negative result though: one can say that two traces with different clock skews belong to two different machines. There are applications in honeypot detection and counting machines behind NATs that the paper mentions.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Via Slashdot: A San Diego research team has developed a method for extracting information about a machine from the timestamps contained in the TCP packets it sends. In summary: Machines will include timestamps in each TCP packet as an option (RFC 1323: TCP Extensions for High Performance) which for most&#8230;<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-51","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/www.elbeno.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/51","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.elbeno.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.elbeno.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.elbeno.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.elbeno.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=51"}],"version-history":[{"count":0,"href":"https:\/\/www.elbeno.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/51\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.elbeno.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=51"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.elbeno.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=51"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.elbeno.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=51"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}