blog/data/2016-04-02-trusted-timestamping-syslog.txt

   1 Title: syslog-trusted-timestamp - chain of trusted timestamps for your syslog
   2 Tags: english, sikkerhet
   3 Date: 2016-04-02 09:50
   4
   5 <p>Two years ago, I had
   6 <a href="http://www.hungry.com/~pere/blog/Public_Trusted_Timestamping_services_for_everyone.html">a
   7 look at trusted timestamping options available</a>, and among
   8 other things noted a still open
   9 <a href="https://bugs.debian.org/742553">bug in the tsget script</a>
  10 included in openssl that made it harder than necessary to use openssl
  11 as a trusted timestamping client.  A few days ago I was told
  12 <a href="https:/www.difi.no/">the Norwegian government office DIFI</a> is
  13 close to releasing their own trusted timestamp service, and in the
  14 process I was happy to learn about a replacement for the tsget script
  15 using only curl:</p>
  16
  17 <p><pre>
  18 openssl ts -query -data "/etc/shells" -cert -sha256 -no_nonce \
  19   | curl -s -H "Content-Type: application/timestamp-query" \
  20          --data-binary "@-" http://zeitstempel.dfn.de > etc-shells.tsr
  21 openssl ts -reply -text -in etc-shells.tsr
  22 </pre></p>
  23
  24 <p>This produces a binary timestamp file (etc-shells.tsr) which can be
  25 used to verify that the content of the file /etc/shell with the
  26 calculated sha256 hash existed at the point in time when the request
  27 was made.  The last command extract the content of the etc-shells.tsr
  28 in human readable form.  The idea behind such timestamp is to be able
  29 to prove using cryptography that the content of a file have not
  30 changed since the file was stamped.</p>
  31
  32 <p>To verify that the file on disk match the public key signature in
  33 the timestamp file, run the following commands.  It make sure you have
  34 the required certificate for the trusted timestamp service available
  35 and use it to compare the file content with the timestamp.  In
  36 production, one should of course use a better method to verify the
  37 service certificate.</p>
  38
  39 <p><pre>
  40 wget -O ca-cert.txt https://pki.pca.dfn.de/global-services-ca/pub/cacert/chain.txt
  41 openssl ts -verify -data /etc/shells -in etc-shells.tsr -CAfile ca-cert.txt -text
  42 </pre></p>
  43
  44 <p>Wikipedia have a lot more information about
  45 <a href="https://en.wikipedia.org/wiki/Trusted_timestamping">trusted
  46 Timestamping</a> and
  47 <a href="https://en.wikipedia.org/wiki/Linked_timestamping">linked
  48 timestamping</a>, and there are several trusted timestamping services
  49 around, both as commercial services and as free and public services.
  50 Among the latter is
  51 <a href="https://www.pki.dfn.de/zeitstempeldienst/">the
  52 zeitstempel.dfn.de service</a> mentioned above and
  53 <a href="https://freetsa.org/">freetsa.org service</a> linked to from the
  54 wikipedia web site.  I believe the DIFI service should show up on
  55 https://tsa.difi.no, but it is not available to the public at the
  56 moment.  I hope this will change when it is into production.  The
  57 <a href="https://tools.ietf.org/html/rfc3161">RFC 3161</a> trusted
  58 timestamping protocol standard is even implemented in LibreOffice,
  59 Microsoft Office and Adobe Acrobat, making it possible to verify when
  60 a document was created.</p>
  61
  62 <p>I would find it useful to be able to use such trusted timestamp
  63 service to make it possible to verify that my stored syslog files have
  64 not been tampered with.  This is not a new idea.  I found one example
  65 implemented on the Endian network appliances where
  66 <a href="http://help.endian.com/entries/21518508-Enabling-Timestamping-on-log-files-">the
  67 configuration of such feature was described in 2012</a>.</p>
  68
  69 <p>But I could not find any free implementation of such feature when I
  70 searched, so I decided to try to
  71 <a href="https://github.com/petterreinholdtsen/syslog-trusted-timestamp">build
  72 a prototype named syslog-trusted-timestamp</a>.  My idea is to
  73 generate a timestamp of the old log files after they are rotated, and
  74 store the timestamp in the new log file just after rotation.  This
  75 will form a chain that would make it possible to see if any old log
  76 files are tampered with.  But syslog is bad at handling kilobytes of
  77 binary data, so I decided to base64 encode the timestamp and add an ID
  78 and line sequence numbers to the base64 data to make it possible to
  79 reassemble the timestamp file again.  To use it, simply run it like
  80 this:
  81
  82 <p><pre>
  83 syslog-trusted-timestamp /path/to/list-of-log-files
  84 </pre></p>
  85
  86 <p>This will send a timestamp from one or more timestamp services (not
  87 yet decided nor implemented) for each listed file to the syslog using
  88 logger(1).  To verify the timestamp, the same program is used with the
  89 --verify option:</p>
  90
  91 <p><pre>
  92 syslog-trusted-timestamp --verify /path/to/log-file /path/to/log-with-timestamp
  93 </pre></p>
  94
  95 <p>The verification step is not yet well designed.  The current
  96 implementation depend on the file path being unique and unchanging,
  97 and this is not a solid assumption.  It also uses process number as
  98 timestamp ID, and this is bound to create ID collisions.  I hope to
  99 have time to come up with a better way to handle timestamp IDs and
 100 verification later.</p>
 101
 102 <p>Please check out
 103 <a href="https://github.com/petterreinholdtsen/syslog-trusted-timestamp">the
 104 prototype for syslog-trusted-timestamp on github</a> and send
 105 suggestions and improvement, or let me know if there already exist a
 106 similar system for timestamping logs already to allow me to join
 107 forces with others with the same interest.</p>
 108
 109 <p>As usual, if you use Bitcoin and want to show your support of my
 110 activities, please send Bitcoin donations to my address
 111 <b><a href="bitcoin:15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b">15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b</a></b>.</p>