X-Git-Url: http://pere.pagekite.me/gitweb/homepage.git/blobdiff_plain/db23c334417fbc93be4e1b04abd0aceb32354fd0..8988e891075fcfb7c3c36b99a9bc41e725cd6dcd:/blog/archive/2014/03/03.rss diff --git a/blog/archive/2014/03/03.rss b/blog/archive/2014/03/03.rss index f825bdf398..9ab9ccdd4a 100644 --- a/blog/archive/2014/03/03.rss +++ b/blog/archive/2014/03/03.rss @@ -6,6 +6,150 @@ http://people.skolelinux.org/pere/blog/ + + Public Trusted Timestamping services for everyone + http://people.skolelinux.org/pere/blog/Public_Trusted_Timestamping_services_for_everyone.html + http://people.skolelinux.org/pere/blog/Public_Trusted_Timestamping_services_for_everyone.html + Tue, 25 Mar 2014 12:50:00 +0100 + <p>Did you ever need to store logs or other files in a way that would +allow it to be used as evidence in court, and needed a way to +demonstrate without reasonable doubt that the file had not been +changed since it was created? Or, did you ever need to document that +a given document was received at some point in time, like some +archived document or the answer to an exam, and not changed after it +was received? The problem in these settings is to remove the need to +trust yourself and your computers, while still being able to prove +that a file is the same as it was at some given time in the past.</p> + +<p>A solution to these problems is to have a trusted third party +"stamp" the document and verify that at some given time the document +looked a given way. Such +<a href="https://en.wikipedia.org/wiki/Notarius">notarius</a> service +have been around for thousands of years, and its digital equivalent is +called a +<a href="http://en.wikipedia.org/wiki/Trusted_timestamping">trusted +timestamping service</a>. <a href="http://www.ietf.org/">The Internet +Engineering Task Force</a> standardised how such service could work a +few years ago as <a href="http://tools.ietf.org/html/rfc3161">RFC +3161</a>. The mechanism is simple. Create a hash of the file in +question, send it to a trusted third party which add a time stamp to +the hash and sign the result with its private key, and send back the +signed hash + timestamp. Both email, FTP and HTTP can be used to +request such signature, depending on what is provided by the service +used. Anyone with the document and the signature can then verify that +the document matches the signature by creating their own hash and +checking the signature using the trusted third party public key. +There are several commercial services around providing such +timestamping. A quick search for +"<a href="https://duckduckgo.com/?q=rfc+3161+service">rfc 3161 +service</a>" pointed me to at least +<a href="https://www.digistamp.com/technical/how-a-digital-time-stamp-works/">DigiStamp</a>, +<a href="http://www.quovadisglobal.co.uk/CertificateServices/SigningServices/TimeStamp.aspx">Quo +Vadis</a>, +<a href="https://www.globalsign.com/timestamp-service/">Global Sign</a> +and <a href="http://www.globaltrustfinder.com/TSADefault.aspx">Global +Trust Finder</a>. The system work as long as the private key of the +trusted third party is not compromised.</p> + +<p>But as far as I can tell, there are very few public trusted +timestamp services available for everyone. I've been looking for one +for a while now. But yesterday I found one over at +<a href="https://www.pki.dfn.de/zeitstempeldienst/">Deutches +Forschungsnetz</a> mentioned in +<a href="http://www.d-mueller.de/blog/dealing-with-trusted-timestamps-in-php-rfc-3161/">a +blog by David Müller</a>. I then found +<a href="http://www.rz.uni-greifswald.de/support/dfn-pki-zertifikate/zeitstempeldienst.html">a +good recipe on how to use the service</a> over at the University of +Greifswald.</p> + +<p><a href="http://www.openssl.org/">The OpenSSL library</a> contain +both server and tools to use and set up your own signing service. See +the ts(1SSL), tsget(1SSL) manual pages for more details. The +following shell script demonstrate how to extract a signed timestamp +for any file on the disk in a Debian environment:</p> + +<p><blockquote><pre> +#!/bin/sh +set -e +url="http://zeitstempel.dfn.de" +caurl="https://pki.pca.dfn.de/global-services-ca/pub/cacert/chain.txt" +reqfile=$(mktemp -t tmp.XXXXXXXXXX.tsq) +resfile=$(mktemp -t tmp.XXXXXXXXXX.tsr) +cafile=chain.txt +if [ ! -f $cafile ] ; then + wget -O $cafile "$caurl" +fi +openssl ts -query -data "$1" -cert | tee "$reqfile" \ + | /usr/lib/ssl/misc/tsget -h "$url" -o "$resfile" +openssl ts -reply -in "$resfile" -text 1>&2 +openssl ts -verify -data "$1" -in "$resfile" -CAfile "$cafile" 1>&2 +base64 < "$resfile" +rm "$reqfile" "$resfile" +</pre></blockquote></p> + +<p>The argument to the script is the file to timestamp, and the output +is a base64 encoded version of the signature to STDOUT and details +about the signature to STDERR. Note that due to +<a href="http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=742553">a bug +in the tsget script</a>, you might need to modify the included script +and remove the last line. Or just write your own HTTP uploader using +curl. :) Now you too can prove and verify that files have not been +changed.</p> + +<p>But the Internet need more public trusted timestamp services. +Perhaps something for <a href="http://www.uninett.no/">Uninett</a> or +my work place the <a href="http://www.uio.no/">University of Oslo</a> +to set up?</p> + + + + + Video DVD reader library / python-dvdvideo - nice free software + http://people.skolelinux.org/pere/blog/Video_DVD_reader_library___python_dvdvideo___nice_free_software.html + http://people.skolelinux.org/pere/blog/Video_DVD_reader_library___python_dvdvideo___nice_free_software.html + Fri, 21 Mar 2014 15:25:00 +0100 + <p>Keeping your DVD collection safe from scratches and curious +children fingers while still having it available when you want to see a +movie is not straight forward. My preferred method at the moment is +to store a full copy of the ISO on a hard drive, and use VLC, Popcorn +Hour or other useful players to view the resulting file. This way the +subtitles and bonus material are still available and using the ISO is +just like inserting the original DVD record in the DVD player.</p> + +<p>Earlier I used dd for taking security copies, but it do not handle +DVDs giving read errors (which are quite a few of them). I've also +tried using +<a href="http://people.skolelinux.org/pere/blog/Ripping_problematic_DVDs_using_dvdbackup_and_genisoimage.html">dvdbackup +and genisoimage</a>, but these days I use the marvellous python library +and program +<a href="http://bblank.thinkmo.de/blog/new-software-python-dvdvideo">python-dvdvideo</a> +written by Bastian Blank. It is +<a href="http://packages.qa.debian.org/p/python-dvdvideo.html">in Debian +already</a> and the binary package name is python3-dvdvideo. Instead +of trying to read every block from the DVD, it parses the file +structure and figure out which block on the DVD is actually in used, +and only read those blocks from the DVD. This work surprisingly well, +and I have been able to almost backup my entire DVD collection using +this method.</p> So far, python-dvdvideo have failed on between 10 and +20 DVDs, which is a small fraction of my collection. The most common +problem is +<a href="https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=720831">DVDs +using UTF-16 instead of UTF-8 characters</a>, which according to +Bastian is against the DVD specification (and seem to cause some +players to fail too). A rarer problem is what seem to be inconsistent +DVD structures, as the python library +<a href="https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=723079">claim +there is a overlap between objects</a>. An equally rare problem claim +<a href="https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=741878">some +value is out of range</a>. No idea what is going on there. I wish I +knew enough about the DVD format to fix these, to ensure my movie +collection will stay with me in the future.</p> + +<p>So, if you need to keep your DVDs safe, back them up using +python-dvdvideo. :)</p> + + + Norsk utgave av Alaveteli / WhatDoTheyKnow på trappene http://people.skolelinux.org/pere/blog/Norsk_utgave_av_Alaveteli___WhatDoTheyKnow_p__trappene.html @@ -46,7 +190,7 @@ sette opp tjenesten) på maskinen <a href="http://alaveteli-dev.nuug.no/">alaveteli-dev.nuug.no</a>, der en kan se hvordan de oversatte meldingen blir seende ut på nettsiden. Når tjenesten lanseres vil den hete -<a href="http://www.mimesbrønn.no/">Mimes brønn</a>, etter +<a href="https://www.mimesbrønn.no/">Mimes brønn</a>, etter visdomskilden som Odin måtte gi øyet sitt for å få drikke i. Den nettsiden er er ennå ikke klar til bruk.</p>