blog/Public_Trusted_Timestamping_services_for_everyone.html

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   6     <title>Petter Reinholdtsen: Public Trusted Timestamping services for everyone</title>
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  14  <h1>
  15      <a href="http://people.skolelinux.org/pere/blog/">Petter Reinholdtsen</a>
  16
  17  </h1>
  18
  19 </div>
  20
  21
  22     <div class="entry">
  23       <div class="title">Public Trusted Timestamping services for everyone</div>
  24       <div class="date">25th March 2014</div>
  25       <div class="body"><p>Did you ever need to store logs or other files in a way that would
  26 allow it to be used as evidence in court, and needed a way to
  27 demonstrate without reasonable doubt that the file had not been
  28 changed since it was created?  Or, did you ever need to document that
  29 a given document was received at some point in time, like some
  30 archived document or the answer to an exam, and not changed after it
  31 was received?  The problem in these settings is to remove the need to
  32 trust yourself and your computers, while still being able to prove
  33 that a file is the same as it was at some given time in the past.</p>
  34
  35 <p>A solution to these problems is to have a trusted third party
  36 "stamp" the document and verify that at some given time the document
  37 looked a given way.  Such
  38 <a href="https://en.wikipedia.org/wiki/Notarius">notarius</a> service
  39 have been around for thousands of years, and its digital equivalent is
  40 called a
  41 <a href="http://en.wikipedia.org/wiki/Trusted_timestamping">trusted
  42 timestamping service</a>.  <a href="http://www.ietf.org/">The Internet
  43 Engineering Task Force</a> standardised how such service could work a
  44 few years ago as <a href="http://tools.ietf.org/html/rfc3161">RFC
  45 3161</a>.  The mechanism is simple.  Create a hash of the file in
  46 question, send it to a trusted third party which add a time stamp to
  47 the hash and sign the result with its private key, and send back the
  48 signed hash + timestamp.  Both email, FTP and HTTP can be used to
  49 request such signature, depending on what is provided by the service
  50 used. Anyone with the document and the signature can then verify that
  51 the document matches the signature by creating their own hash and
  52 checking the signature using the trusted third party public key.
  53 There are several commercial services around providing such
  54 timestamping.  A quick search for
  55 "<a href="https://duckduckgo.com/?q=rfc+3161+service">rfc 3161
  56 service</a>" pointed me to at least
  57 <a href="https://www.digistamp.com/technical/how-a-digital-time-stamp-works/">DigiStamp</a>,
  58 <a href="http://www.quovadisglobal.co.uk/CertificateServices/SigningServices/TimeStamp.aspx">Quo
  59 Vadis</a>,
  60 <a href="https://www.globalsign.com/timestamp-service/">Global Sign</a>
  61 and <a href="http://www.globaltrustfinder.com/TSADefault.aspx">Global
  62 Trust Finder</a>.  The system work as long as the private key of the
  63 trusted third party is not compromised.</p>
  64
  65 <p>But as far as I can tell, there are very few public trusted
  66 timestamp services available for everyone.  I've been looking for one
  67 for a while now. But yesterday I found one over at
  68 <a href="https://www.pki.dfn.de/zeitstempeldienst/">Deutches
  69 Forschungsnetz</a> mentioned in
  70 <a href="http://www.d-mueller.de/blog/dealing-with-trusted-timestamps-in-php-rfc-3161/">a
  71 blog by David Müller</a>.  I then found
  72 <a href="http://www.rz.uni-greifswald.de/support/dfn-pki-zertifikate/zeitstempeldienst.html">a
  73 good recipe on how to use the service</a> over at the University of
  74 Greifswald.</p>
  75
  76 <p><a href="http://www.openssl.org/">The OpenSSL library</a> contain
  77 both server and tools to use and set up your own signing service.  See
  78 the ts(1SSL), tsget(1SSL) manual pages for more details.  The
  79 following shell script demonstrate how to extract a signed timestamp
  80 for any file on the disk in a Debian environment:</p>
  81
  82 <p><blockquote><pre>
  83 #!/bin/sh
  84 set -e
  85 url="http://zeitstempel.dfn.de"
  86 caurl="https://pki.pca.dfn.de/global-services-ca/pub/cacert/chain.txt"
  87 reqfile=$(mktemp -t tmp.XXXXXXXXXX.tsq)
  88 resfile=$(mktemp -t tmp.XXXXXXXXXX.tsr)
  89 cafile=chain.txt
  90 if [ ! -f $cafile ] ; then
  91     wget -O $cafile "$caurl"
  92 fi
  93 openssl ts -query -data "$1" -cert | tee "$reqfile" \
  94     | /usr/lib/ssl/misc/tsget -h "$url" -o "$resfile"
  95 openssl ts -reply -in "$resfile" -text 1>&2
  96 openssl ts -verify -data "$1" -in "$resfile" -CAfile "$cafile" 1>&2
  97 base64 < "$resfile"
  98 rm "$reqfile" "$resfile"
  99 </pre></blockquote></p>
 100
 101 <p>The argument to the script is the file to timestamp, and the output
 102 is a base64 encoded version of the signature to STDOUT and details
 103 about the signature to STDERR.  Note that due to
 104 <a href="http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=742553">a bug
 105 in the tsget script</a>, you might need to modify the included script
 106 and remove the last line.  Or just write your own HTTP uploader using
 107 curl. :) Now you too can prove and verify that files have not been
 108 changed.</p>
 109
 110 <p>But the Internet need more public trusted timestamp services.
 111 Perhaps something for <a href="http://www.uninett.no/">Uninett</a> or
 112 my work place the <a href="http://www.uio.no/">University of Oslo</a>
 113 to set up?</p>
 114 </div>
 115
 116       <div class="tags">Tags: <a href="http://people.skolelinux.org/pere/blog/tags/english">english</a>, <a href="http://people.skolelinux.org/pere/blog/tags/sikkerhet">sikkerhet</a>.</div>
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 260 <li>2014
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 313
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 315
 316 </ul></li>
 317
 318 <li>2012
 319 <ul>
 320
 321 <li><a href="http://people.skolelinux.org/pere/blog/archive/2012/01/">January (7)</a></li>
 322
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 324
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 330
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 334
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 336
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 340
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 342
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 344
 345 </ul></li>
 346
 347 <li>2011
 348 <ul>
 349
 350 <li><a href="http://people.skolelinux.org/pere/blog/archive/2011/01/">January (16)</a></li>
 351
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 355
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 357
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 361
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 363
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 367
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 369
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 371
 372 <li><a href="http://people.skolelinux.org/pere/blog/archive/2011/12/">December (1)</a></li>
 373
 374 </ul></li>
 375
 376 <li>2010
 377 <ul>
 378
 379 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/01/">January (2)</a></li>
 380
 381 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/02/">February (1)</a></li>
 382
 383 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/03/">March (3)</a></li>
 384
 385 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/04/">April (3)</a></li>
 386
 387 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/05/">May (9)</a></li>
 388
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 390
 391 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/07/">July (12)</a></li>
 392
 393 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/08/">August (13)</a></li>
 394
 395 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/09/">September (7)</a></li>
 396
 397 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/10/">October (9)</a></li>
 398
 399 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/11/">November (13)</a></li>
 400
 401 <li><a href="http://people.skolelinux.org/pere/blog/archive/2010/12/">December (12)</a></li>
 402
 403 </ul></li>
 404
 405 <li>2009
 406 <ul>
 407
 408 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/01/">January (8)</a></li>
 409
 410 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/02/">February (8)</a></li>
 411
 412 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/03/">March (12)</a></li>
 413
 414 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/04/">April (10)</a></li>
 415
 416 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/05/">May (9)</a></li>
 417
 418 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/06/">June (3)</a></li>
 419
 420 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/07/">July (4)</a></li>
 421
 422 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/08/">August (3)</a></li>
 423
 424 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/09/">September (1)</a></li>
 425
 426 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/10/">October (2)</a></li>
 427
 428 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/11/">November (3)</a></li>
 429
 430 <li><a href="http://people.skolelinux.org/pere/blog/archive/2009/12/">December (3)</a></li>
 431
 432 </ul></li>
 433
 434 <li>2008
 435 <ul>
 436
 437 <li><a href="http://people.skolelinux.org/pere/blog/archive/2008/11/">November (5)</a></li>
 438
 439 <li><a href="http://people.skolelinux.org/pere/blog/archive/2008/12/">December (7)</a></li>
 440
 441 </ul></li>
 442
 443 </ul>
 444
 445
 446
 447 <h2>Tags</h2>
 448 <ul>
 449
 450  <li><a href="http://people.skolelinux.org/pere/blog/tags/3d-printer">3d-printer (16)</a></li>
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 455
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 457
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 459
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 461
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 463
 464  <li><a href="http://people.skolelinux.org/pere/blog/tags/bsa">bsa (2)</a></li>
 465
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 467
 468  <li><a href="http://people.skolelinux.org/pere/blog/tags/debian">debian (168)</a></li>
 469
 470  <li><a href="http://people.skolelinux.org/pere/blog/tags/debian edu">debian edu (158)</a></li>
 471
 472  <li><a href="http://people.skolelinux.org/pere/blog/tags/debian-handbook">debian-handbook (4)</a></li>
 473
 474  <li><a href="http://people.skolelinux.org/pere/blog/tags/digistan">digistan (11)</a></li>
 475
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 581     </div>
 582     <p style="text-align: right">
 583  Created by <a href="http://steve.org.uk/Software/chronicle">Chronicle v4.6</a>
 584 </p>
 585
 586   </body>
 587 </html>