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[homepage.git] / blog / index.rss

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+++ b/blog/index.rss
@@ -6,6 +6,112 @@
                 <link>http://people.skolelinux.org/pere/blog/</link>
                 <atom:link href="http://people.skolelinux.org/pere/blog/index.rss" rel="self" type="application/rss+xml" />
        
                 <link>http://people.skolelinux.org/pere/blog/</link>
                 <atom:link href="http://people.skolelinux.org/pere/blog/index.rss" rel="self" type="application/rss+xml" />
        

+       <item>
+               <title>Fetching trusted timestamps using the rfc3161ng python module</title>
+               <link>http://people.skolelinux.org/pere/blog/Fetching_trusted_timestamps_using_the_rfc3161ng_python_module.html</link>
+               <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Fetching_trusted_timestamps_using_the_rfc3161ng_python_module.html</guid>
+                <pubDate>Mon, 8 Oct 2018 12:30:00 +0200</pubDate>
+               <description>&lt;p&gt;I have  earlier covered the basics of trusted timestamping using the
+&#39;openssl ts&#39; client.  See blog post for
+&lt;a href=&quot;http://people.skolelinux.org/pere/blog/Public_Trusted_Timestamping_services_for_everyone.html&quot;&gt;2014&lt;/a&gt;,
+&lt;a href=&quot;http://people.skolelinux.org/pere/blog/syslog_trusted_timestamp___chain_of_trusted_timestamps_for_your_syslog.html&quot;&gt;2016&lt;/a&gt;
+and
+&lt;a href=&quot;http://people.skolelinux.org/pere/blog/Idea_for_storing_trusted_timestamps_in_a_Noark_5_archive.html&quot;&gt;2017&lt;/a&gt;
+for those stories.  But some times I want to integrate the timestamping
+in other code, and recently I needed to integrate it into Python.
+After searching a bit, I found
+&lt;a href=&quot;https://dev.entrouvert.org/projects/python-rfc3161&quot;&gt;the
+rfc3161 library&lt;/a&gt; which seemed like a good fit, but I soon
+discovered it only worked for python version 2, and I needed something
+that work with python version 3.  Luckily I next came across
+&lt;a href=&quot;https://github.com/trbs/rfc3161ng/&quot;&gt;the rfc3161ng library&lt;/a&gt;,
+a fork of the original rfc3161 library.  Not only is it working with
+python 3, it have fixed a few of the bugs in the original library, and
+it has an active maintainer.  I decided to wrap it up and make it
+&lt;a href=&quot;https://tracker.debian.org/pkg/python-rfc3161ng&quot;&gt;available in
+Debian&lt;/a&gt;, and a few days ago it entered Debian unstable and testing.&lt;/p&gt;
+
+&lt;p&gt;Using the library is fairly straight forward.  The only slightly
+problematic step is to fetch the required certificates to verify the
+timestamp.  For some services it is straight forward, while for others
+I have not yet figured out how to do it.  Here is a small standalone
+code example based on of the integration tests in the library code:&lt;/p&gt;
+
+&lt;pre&gt;
+#!/usr/bin/python3
+
+&quot;&quot;&quot;
+
+Python 3 script demonstrating how to use the rfc3161ng module to
+get trusted timestamps.
+
+The license of this code is the same as the license of the rfc3161ng
+library, ie MIT/BSD.
+
+&quot;&quot;&quot;
+
+import os
+import pyasn1.codec.der
+import rfc3161ng
+import subprocess
+import tempfile
+import urllib.request
+
+def store(f, data):
+    f.write(data)
+    f.flush()
+    f.seek(0)
+
+def fetch(url, f=None):
+    response = urllib.request.urlopen(url)
+    data = response.read()
+    if f:
+        store(f, data)
+    return data
+
+def main():
+    with tempfile.NamedTemporaryFile() as cert_f,\
+        tempfile.NamedTemporaryFile() as ca_f,\
+        tempfile.NamedTemporaryFile() as msg_f,\
+        tempfile.NamedTemporaryFile() as tsr_f:
+
+        # First fetch certificates used by service
+        certificate_data = fetch(&#39;https://freetsa.org/files/tsa.crt&#39;, cert_f)
+        ca_data_data = fetch(&#39;https://freetsa.org/files/cacert.pem&#39;, ca_f)
+
+        # Then timestamp the message
+        timestamper = \
+            rfc3161ng.RemoteTimestamper(&#39;http://freetsa.org/tsr&#39;,
+                                        certificate=certificate_data)
+        data = b&quot;Python forever!\n&quot;
+        tsr = timestamper(data=data, return_tsr=True)
+
+        # Finally, convert message and response to something &#39;openssl ts&#39; can verify
+        store(msg_f, data)
+        store(tsr_f, pyasn1.codec.der.encoder.encode(tsr))
+        args = [&quot;openssl&quot;, &quot;ts&quot;, &quot;-verify&quot;,
+                &quot;-data&quot;, msg_f.name,
+               &quot;-in&quot;, tsr_f.name,
+               &quot;-CAfile&quot;, ca_f.name,
+                &quot;-untrusted&quot;, cert_f.name]
+        subprocess.check_call(args)
+
+if &#39;__main__&#39; == __name__:
+   main()
+&lt;/pre&gt;
+
+&lt;p&gt;The code fetches the required certificates, store them as temporary
+files, timestamp a simple message, store the message and timestamp to
+disk and ask &#39;openssl ts&#39; to verify the timestamp.  A timestamp is
+around 1.5 kiB in size, and should be fairly easy to store for future
+use.&lt;/p&gt;
+
+&lt;p&gt;As usual, if you use Bitcoin and want to show your support of my
+activities, please send Bitcoin donations to my address
+&lt;b&gt;&lt;a href=&quot;bitcoin:15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b&quot;&gt;15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b&lt;/a&gt;&lt;/b&gt;.&lt;/p&gt;
+</description>
+       </item>
+       

        <item>
                <title>Automatic Google Drive sync using grive in Debian</title>
                <link>http://people.skolelinux.org/pere/blog/Automatic_Google_Drive_sync_using_grive_in_Debian.html</link>
        <item>
                <title>Automatic Google Drive sync using grive in Debian</title>
                <link>http://people.skolelinux.org/pere/blog/Automatic_Google_Drive_sync_using_grive_in_Debian.html</link>


@@ -572,153 +678,6 @@ wait &quot;$gstpid&quot;
 
 &lt;p&gt;I hope you find the approach useful.  I know I do.&lt;/p&gt;
 
 
 &lt;p&gt;I hope you find the approach useful.  I know I do.&lt;/p&gt;
 

-&lt;p&gt;As usual, if you use Bitcoin and want to show your support of my
-activities, please send Bitcoin donations to my address
-&lt;b&gt;&lt;a href=&quot;bitcoin:15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b&quot;&gt;15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b&lt;/a&gt;&lt;/b&gt;.&lt;/p&gt;
-</description>
-       </item>
-       
-       <item>
-               <title>Streaming the Linux desktop to Kodi using VLC and RTSP</title>
-               <link>http://people.skolelinux.org/pere/blog/Streaming_the_Linux_desktop_to_Kodi_using_VLC_and_RTSP.html</link>
-               <guid isPermaLink="true">http://people.skolelinux.org/pere/blog/Streaming_the_Linux_desktop_to_Kodi_using_VLC_and_RTSP.html</guid>
-                <pubDate>Thu, 12 Jul 2018 02:00:00 +0200</pubDate>
-               <description>&lt;p&gt;PS: See
-&lt;ahref=&quot;http://people.skolelinux.org/pere/blog/Simple_streaming_the_Linux_desktop_to_Kodi_using_GStreamer_and_RTP.html&quot;&gt;the
-followup post&lt;/a&gt; for a even better approach.&lt;/p&gt;
-
-&lt;p&gt;A while back, I was asked by a friend how to stream the desktop to
-my projector connected to Kodi.  I sadly had to admit that I had no
-idea, as it was a task I never had tried.  Since then, I have been
-looking for a way to do so, preferable without much extra software to
-install on either side.  Today I found a way that seem to kind of
-work.  Not great, but it is a start.&lt;/p&gt;
-
-&lt;p&gt;I had a look at several approaches, for example
-&lt;a href=&quot;https://github.com/mfoetsch/dlna_live_streaming&quot;&gt;using uPnP
-DLNA as described in 2011&lt;/a&gt;, but it required a uPnP server, fuse and
-local storage enough to store the stream locally.  This is not going
-to work well for me, lacking enough free space, and it would
-impossible for my friend to get working.&lt;/p&gt;
-
-&lt;p&gt;Next, it occurred to me that perhaps I could use VLC to create a
-video stream that Kodi could play.  Preferably using
-broadcast/multicast, to avoid having to change any setup on the Kodi
-side when starting such stream.  Unfortunately, the only recipe I
-could find using multicast used the rtp protocol, and this protocol
-seem to not be supported by Kodi.&lt;/p&gt;
-
-&lt;p&gt;On the other hand, the rtsp protocol is working!  Unfortunately I
-have to specify the IP address of the streaming machine in both the
-sending command and the file on the Kodi server.  But it is showing my
-desktop, and thus allow us to have a shared look on the big screen at
-the programs I work on.&lt;/p&gt;
-
-&lt;p&gt;I did not spend much time investigating codeces.  I combined the
-rtp and rtsp recipes from
-&lt;a href=&quot;https://wiki.videolan.org/Documentation:Streaming_HowTo/Command_Line_Examples/&quot;&gt;the
-VLC Streaming HowTo/Command Line Examples&lt;/a&gt;, and was able to get
-this working on the desktop/streaming end.&lt;/p&gt;
-
-&lt;blockquote&gt;&lt;pre&gt;
-vlc screen:// --sout \
-  &#39;#transcode{vcodec=mp4v,acodec=mpga,vb=800,ab=128}:rtp{dst=projector.local,port=1234,sdp=rtsp://192.168.11.4:8080/test.sdp}&#39;
-&lt;/pre&gt;&lt;/blockquote&gt;
-
-&lt;p&gt;I ssh-ed into my Kodi box and created a file like this with the
-same IP address:&lt;/p&gt;
-
-&lt;blockquote&gt;&lt;pre&gt;
-echo rtsp://192.168.11.4:8080/test.sdp \
-  &gt; /storage/videos/screenstream.m3u
-&lt;/pre&gt;&lt;/blockquote&gt;
-
-&lt;p&gt;Note the 192.168.11.4 IP address is my desktops IP address.  As far
-as I can tell the IP must be hardcoded for this to work.  In other
-words, if someone elses machine is going to do the steaming, you have
-to update screenstream.m3u on the Kodi machine and adjust the vlc
-recipe.  To get started, locate the file in Kodi and select the m3u
-file while the VLC stream is running.  The desktop then show up in my
-big screen. :)&lt;/p&gt;
-
-&lt;p&gt;When using the same technique to stream a video file with audio,
-the audio quality is really bad.  No idea if the problem is package
-loss or bad parameters for the transcode.  I do not know VLC nor Kodi
-enough to tell.&lt;/p&gt;
-
-&lt;p&gt;&lt;strong&gt;Update 2018-07-12&lt;/strong&gt;: Johannes Schauer send me a few
-succestions and reminded me about an important step.  The &quot;screen:&quot;
-input source is only available once the vlc-plugin-access-extra
-package is installed on Debian.  Without it, you will see this error
-message: &quot;VLC is unable to open the MRL &#39;screen://&#39;.  Check the log
-for details.&quot;  He further found that it is possible to drop some parts
-of the VLC command line to reduce the amount of hardcoded information.
-It is also useful to consider using cvlc to avoid having the VLC
-window in the desktop view.  In sum, this give us this command line on
-the source end
-
-&lt;blockquote&gt;&lt;pre&gt;
-cvlc screen:// --sout \
-  &#39;#transcode{vcodec=mp4v,acodec=mpga,vb=800,ab=128}:rtp{sdp=rtsp://:8080/}&#39;
-&lt;/pre&gt;&lt;/blockquote&gt;
-
-&lt;p&gt;and this on the Kodi end&lt;p&gt;
-
-&lt;blockquote&gt;&lt;pre&gt;
-echo rtsp://192.168.11.4:8080/ \
-  &gt; /storage/videos/screenstream.m3u
-&lt;/pre&gt;&lt;/blockquote&gt;
-
-&lt;p&gt;Still bad image quality, though.  But I did discover that streaming
-a DVD using dvdsimple:///dev/dvd as the source had excellent video and
-audio quality, so I guess the issue is in the input or transcoding
-parts, not the rtsp part.  I&#39;ve tried to change the vb and ab
-parameters to use more bandwidth, but it did not make a
-difference.&lt;/p&gt;
-
-&lt;p&gt;I further received a suggestion from Einar Haraldseid to try using
-gstreamer instead of VLC, and this proved to work great!  He also
-provided me with the trick to get Kodi to use a multicast stream as
-its source.  By using this monstrous oneliner, I can stream my desktop
-with good video quality in reasonable framerate to the 239.255.0.1
-multicast address on port 1234:
-
-&lt;blockquote&gt;&lt;pre&gt;
-gst-launch-1.0 ximagesrc use-damage=0 ! video/x-raw,framerate=30/1 ! \
-  videoconvert ! queue2 ! \
-  x264enc bitrate=8000 speed-preset=superfast tune=zerolatency qp-min=30 \
-  key-int-max=15 bframes=2 ! video/x-h264,profile=high ! queue2 ! \
-  mpegtsmux alignment=7 name=mux ! rndbuffersize max=1316 min=1316 ! \
-  udpsink host=239.255.0.1 port=1234 ttl-mc=1 auto-multicast=1 sync=0 \
-  pulsesrc device=$(pactl list | grep -A2 &#39;Source #&#39; | \
-    grep &#39;Name: .*\.monitor$&#39; |  cut -d&quot; &quot; -f2|head -1) ! \
-  audioconvert ! queue2 ! avenc_aac ! queue2 ! mux.
-&lt;/pre&gt;&lt;/blockquote&gt;
-
-&lt;p&gt;and this on the Kodi end&lt;p&gt;
-
-&lt;blockquote&gt;&lt;pre&gt;
-echo udp://@239.255.0.1:1234 \
-  &gt; /storage/videos/screenstream.m3u
-&lt;/pre&gt;&lt;/blockquote&gt;
-
-&lt;p&gt;Note the trick to pick a valid pulseaudio source.  It might not
-pick the one you need.  This approach will of course lead to trouble
-if more than one source uses the same multicast port and address.
-Note the ttl-mc=1 setting, which limit the multicast packages to the
-local network.  If the value is increased, your screen will be
-broadcasted further, one network &quot;hop&quot; for each increase (read up on
-multicast to learn more. :)!&lt;/p&gt;
-
-&lt;p&gt;Having cracked how to get Kodi to receive multicast streams, I
-could use this VLC command to stream to the same multicast address.
-The image quality is way better than the rtsp approach, but gstreamer
-seem to be doing a better job.&lt;/p&gt;
-
-&lt;blockquote&gt;&lt;pre&gt;
-cvlc screen:// --sout &#39;#transcode{vcodec=mp4v,acodec=mpga,vb=800,ab=128}:rtp{mux=ts,dst=239.255.0.1,port=1234,sdp=sap}&#39;
-&lt;/pre&gt;&lt;/blockquote&gt;
-

 &lt;p&gt;As usual, if you use Bitcoin and want to show your support of my
 activities, please send Bitcoin donations to my address
 &lt;b&gt;&lt;a href=&quot;bitcoin:15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b&quot;&gt;15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b&lt;/a&gt;&lt;/b&gt;.&lt;/p&gt;
 &lt;p&gt;As usual, if you use Bitcoin and want to show your support of my
 activities, please send Bitcoin donations to my address
 &lt;b&gt;&lt;a href=&quot;bitcoin:15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b&quot;&gt;15oWEoG9dUPovwmUL9KWAnYRtNJEkP1u1b&lt;/a&gt;&lt;/b&gt;.&lt;/p&gt;