today, we had to put down our oldest cat, tomtom. (two years after his brother.)
rest in peace, tomtom!
posts for 2017.
four days ago, arch linux switched to openssl 1.1.0. openssl 1.1.0 was originally released at the end of last august, but since it has some breaking api changes, it's only slowly creeping into new linux distributions.
this also means that i can finally test my let's encrypt library, let's encrypt ansible role and ocspbot against openssl 1.1.0. the let's encrypt code worked out of the box (i've already incorporated a change somewhen earlier, even without being able to properly test it), but ocspbot needed a bit more work. there's a command line syntax change between 1.0.x and 1.1.0 when specifying http headers to ocsp calls; the old syntax was -header name value, the new one is -header name=value. so i had to add a version detection (i.e. parsing the output of openssl version) to use the correct syntax depending on the used version. but now it works with both openssl 1.0.x and 1.1.0!
using openssl 1.1.0 on my server also allowed me to use x25519, using daniel j. bernstein's curve25519 in edwards form, for secret key negotation (i.e. ephemeral diffie-hellman). using it in nginx is pretty easy:
this uses x25519 as the default curve/key exchange, followed by the fallsbacks using ecdhe with a 521-bit nist curve and then a 384-bit nist curve as a third fallback. (btw, note the uppercase x in x25519 — if you use the lowercase variant, nginx won't load the config.) the third curve is the only one supported by almost every browser; only a few support the 521-bit one, and right now only chrome supports x25519.
assume you want to allow users (or programs) to upload files/data/... to your website without having to write a script/cgi/... which handles the uploading. something very simple, which just stores the files somewhere so you can analyze them later. this is for example very useful to create a reporting endpoint for a content security policy without using specialized software.
if you use nginx as your webserver, there's a simple solution for this. the idea is to use the client_body_in_file_only directive, which allows you to dump uploads to disk to pass the filename to a reverse proxy, instead of asking nginx to cache the upload and pass it on to the reverse proxy, so that it looks like a regular post/put to the reverse proxy.
unfortunately, this doesn't work if you use a return xxx; instead of proxy_pass yyy;, which would have been my preferred solution. but there's a little trick: you can ask nginx to also listen on another port, say 4000, and simply return a fixed message there. then, for the main listener (on ports 80/443), you use client_body_in_file_only directive combined with proxy_pass http://127.0.0.1:4000. this looks as follows:
server { listen 127.0.0.1:4000; location / { return 200 "Thank you for your report.\n"; } } limit_req_zone $binary_remote_addr zone=peripzone:10m rate=5r/m; server { listen *:80; location = /csp-reporting { # We just allow POST actions. Add PUT if you want to # support PUT as well. (Not needed for CSP reports.) limit_except POST { deny all; } # Where to store the files on disk client_body_temp_path /var/www/reports/csp/; # Store the file on disk, and don't delete it, no matter # what the proxy returns. client_body_in_file_only on; # Store at most 64k on disk. That should be sufficient # for CSP reports. client_body_buffer_size 64K; client_max_body_size 64K; # Give the client 10 seconds to upload. client_body_timeout 10s; # Do rate limiting limit_req zone=peripzone burst=20 nodelay; # Now proxy to the small internal server we started # above, and don't pass the uploaded file to it. proxy_set_body off; proxy_pass http://127.0.0.1:4000/; } }
note that i added rate limiting (see the ngx_http_limit_req_module module), allowing on average five uploads per second for remote ips, with bursts up to 10 uploads. see the ngx_http_limit_req_module module's documentation for more information on adding more rate limiting. you can for example also add limits per server, instead of just one per remote ip.
introduction
classically, revokation of certificates was accomplished with certificate revokation lists (crls). the idea was that browsers regularly download crls from the certificate authorities (cas) and check whether certificates they see are on the list. this doesn't scale well, though. nowadays, there are many cas trusted by browsers in their default configuration, and crls tend to get huge.
a better solution is the online certificate status protocol (ocsp): a browser, when encountering a new certificate, asks the ocsp server of the browser (the url for it is contained in the certificate) whether the certificate is still valid. this has several downsides as well: first, ocsp servers are not always reliable. if a browser cannot connect to it (or doesn't get a reply), what should it do? deny access to the site? besides that, there's another large downside: privacy. the ocsp server knows which page you are visiting, because the browser tells it by asking whether its certificate is valid.
ocsp stapling was invented to improve upon this: the idea is that the webserver itself asks the ocsp server for the status of its certificate, and delivers the answer together with the certificate to the connecting browser. as the ocsp response is signed by the cas certificate, the browser can verify that the response is valid. also, the expiration time of ocsp responses is much less than the one for certificates, so if a certificate is revoked, existing ocsp responses will only be valid for a couple of more days.
this is pretty good already, except that a malicious webserver could simply not send the ocsp response with its certificate. if a browser cannot contact the ocsp server itself, it has no way to know whether the certificate is revoked or not. to overcome this, ocsp must-staple was invented. this is a flag in the certificate itself which says that the certificate is only valid with a valid and good ocsp response. so if a browser encounters a certificate with this flag, and the webserver isn't ocsp stapling, the browser knows that something is fishy.
unfortunately, there are some downsides. first, most the most common webservers for linux, apache and nginx, while having ocsp stapling support, do in some situations send replies without ocsp stapling. if the certificate has the ocsp must-staple flag set, these answers result in error pages shown in browsers. and that's something you really want to avoid, that visitors of your page thing there's something bad happening.
fortunately, at least for nginx, you can specify a file containing an ocsp response directly with the ssl_stapling_file directive. unfortunately, you have to make sure you always have a good and valid ocsp response at that place, and reload nginx in case the response is updated. other programs allow to specify an ocsp response in a similar way, such as exim with the tls_ocsp_file directive, and thus have the same problem. to solve this problem, i've started creating ocsp bot:
ocsp bot
ocsp bot is a python script which should be called frequently (as in: once per hour or so), which checks a set of x.509 certificates to obtain up-to-date ocsp responses. in case the current ocsp responses will expire soon, or aren't there, it will try to get a new response. it will only copy the new response to the correct place if it is valid and good. calling it frequently will ensure that in case of problems getting a new response, it will retry every hour (or so) until a good and valid response could have been obtained. so a user response is only necessary if the process fails several times in a row.
ocsp bot will signal with its exit code whether responses have been updated, allowing to reload/restart the corresponding service to use the new response.
you can install ocsp bot with pip install ocsp from pypi.
integration with ansible
i'm using ansible to configure my server. to copy certificates and obtain ocsp responses, i'm using a custom role.
the ansible tasks for the role are as follows. ocsp bot is installed in /var/www/ocsp:
- name: Create OCSP log folder file: dest=/var/www/ocsp/logs state=directory - name: Create OCSP response folder file: dest=/var/www/ocsp/responses state=directory - name: Install pyyaml pip: name=pyyaml - name: Install OCSP response utility copy: src=ocspbot.py dest=/var/www/ocsp/ocspbot.py mode=0755 # ocspbot.py is ocspbot/__main__.py from https://github.com/felixfontein/ocspbot/ - name: Install OCSP bash script template: src=ocspbot.sh.j2 dest=/var/www/ocsp/ocspbot.sh mode=0755 - name: Install OCSP response utility configurations template: src=ocspbot.yaml.j2 dest=/var/www/ocsp/ocspbot-{{ item.key }}.yaml with_dict: "{{ certificates }}" - name: Install OCSP response cronjob cron: name="Update OCSP responses" hour=* minute=0 job=/var/www/ocsp/ocspbot.sh state=present
the variable certificates is defined as follows:
certificates: nginx: domains: - example.com - example.net reload: - nginx key_owner: root key_group: root key_mode: "0400" mailserver: domains: - mail.example.com reload: - dovecot - exim key_owner: root key_group: exim key_mode: "0440"
The template for ocspbot.sh:
#!/bin/bash RC=0 {% for name, data in certificates|dictsort %} # Renew OCSP responses for {{ name }} /var/www/ocsp/ocspbot.py /home/ocsp/ocspbot-{{ name }}.yaml RESULT=$? if [ $RESULT -gt 0 ]; then {% for service in data.reload %} systemctl reload {{ service }} {% endfor %} elif [ $RESULT -lt 0 ]; then RC=1 fi {% endfor %} exit $RC
the template for the configuration yaml files:
make_backups: True minimum_validity: 3d minimum_validity_percentage: 42.8 ocsp_folder: /var/www/ocsp/responses output_log: /var/www/ocsp/logs/{{ item.key }}-{year}{month}{day}-{hour}{minute}{second}.log domains: {% for domain in item.value.domains|sort %} {{ domain }}: cert: /var/www/certs/{{ domain }}.pem chain: /var/www/certs/{{ domain }}-chain.pem rootchain: /var/www/certs/{{ domain }}-rootchain.pem ocsp: {{ domain }}.ocsp-resp {% endfor %}
the certificates are copied with the following ansible tasks:
- name: copy private keys copy: src=keys/{{ item.1 }}.key dest=/var/www/keys/{{ item.1 }}.key owner={{ item.0.value.key_owner }} group={{ item.0.value.key_group }} mode={{ item.0.value.key_mode }} with_dependent: - "certificates" - "item.0.value.domains" notify: update OCSP responses - name: copy certificates copy: src=keys/{{ item.1 }}{{ item.2 }} dest=/var/www/certs/{{ item.1 }}{{ item.2 }} owner=root group=root mode=0444 with_dependent: - "certificates" - "item.0.value.domains" - '["-rootchain.pem", "-fullchain.pem", "-chain.pem", ".pem"]' notify: update OCSP responses
(here, the dependent loop lookup plugin is used.)
the handler update OCSP responses is defined as follows:
- name: update OCSP responses command: /var/www/ocsp/ocspbot.sh register: result failed_when: result.rc != 0 notify: - reload nginx - reload exim - reload dovecot
i'm using this setup for some weeks now, and it seems to work fine. so far, i'm not using ocsp must-staple certificates (except for some test subdomains). if everything seems to be fine for some time, i'll switch to ocsp must-staple certificates.
a couple days after the previous stroll, i repeated the stroll. this time, there's a lot of snow!
today, i've added two new plugins to nikola: sidebar and static tag cloud. these, together with filetreesubs, a doit-based file tree synchronization and text-based substitution tool, allow to use nikola to create a more dynamic-looking blog with a sidebar having current information, without the need to rebuild every single page every time something changes. (which can take a very long time for a large blog such as spielwiese).
the plugins create html fragments and, for the tag clouds, css files, which have to be included in all generated blog pages. one way to do this is to use javascript, but that wouldn't yield a proper static blog as i imagine it. the sidebar and the tag cloud should always be there, and not depend on javascript being enabled. (i for myself use noscript and javascript in my browser is off by default.)
for spielwiese, a small tag cloud is created (one per language) and included in the sidebar. a large tag cloud is created and included in the tag overview page (chde version). also, a small and large place cloud is created and included in the sidebar and place overview page, respectively.
the configuration for the static tag cloud plugin looks as follows:
RENDER_STATIC_TAG_CLOUDS = { # Small tag cloud 'small': { 'name': 'tcs-{0}', 'filename': 'tagcloud-{0}.inc', 'taxonomy_type': 'tag', 'style_filename': 'assets/css/tagcloud-{0}-small.css', 'max_number_of_levels': 15, 'max_tags': 40, 'minimal_number_of_appearances': 5, 'colors': ((0.4,0.4,0.4), (1.0,1.0,1.0)), 'background_colors': ((0.133, 0.133, 0.133), ), 'border_colors': ((0.2, 0.2, 0.2), ), 'font_sizes': (6, 20), 'round_factor': 0.6, }, # Large tag cloud 'large': { 'name': 'tcl-{0}', 'filename': 'tagcloud-{0}-large.inc', 'taxonomy_type': 'tag', 'style_filename': 'assets/css/tagcloud-{0}-large.css', 'max_number_of_levels': 100, 'minimal_number_of_appearances': 3, 'colors': ((0.25,0.25,0.25), (1.0,1.0,1.0)), 'background_colors': ((0.133, 0.133, 0.133), ), 'border_colors': ((0.2, 0.2, 0.2), ), 'font_sizes': (8, 35), 'round_factor': 0.3, }, # Small place cloud 'places-small': { 'name': 'pcs-{0}', 'filename': 'placecloud-{0}.inc', 'taxonomy_type': 'place', 'style_filename': 'assets/css/placecloud-{0}-small.css', 'max_number_of_levels': 15, 'max_tags': 40, 'minimal_number_of_appearances': 3, 'colors': ((0.4,0.4,0.4), (1.0,1.0,1.0)), 'background_colors': ((0.133, 0.133, 0.133), ), 'border_colors': ((0.2, 0.2, 0.2), ), 'font_sizes': (6, 20), 'round_factor': 0.6, }, # Large place cloud 'places-large': { 'name': 'pcl-{0}', 'filename': 'placecloud-{0}-large.inc', 'taxonomy_type': 'place', 'style_filename': 'assets/css/placecloud-{0}-large.css', 'max_number_of_levels': 100, 'minimal_number_of_appearances': 2, 'colors': ((0.25,0.25,0.25), (1.0,1.0,1.0)), 'background_colors': ((0.133, 0.133, 0.133), ), 'border_colors': ((0.2, 0.2, 0.2), ), 'font_sizes': (8, 35), 'round_factor': 0.3, }, }
the generated css file for the large tag cloud can be found here; the generated html fragments aren't uploaded as filetreesubs doesn't copy them to the output folder.
the configuration for filetreesubs looks as follows:
source: output-spielwiese destination: final-spielwiese # Substitutions substitutes: # For all HTML pages: include sidebar '.*\.html': '<!-- include:sidebar-en -->': file: sidebar-en.inc '<!-- include:sidebar-chde -->': file: sidebar-chde.inc # For specific pages, also include tag/place clouds 'tag/index.html': '<!-- include:tagcloud:en:large -->': file: tagcloud-en-large.inc 'place/index.html': '<!-- include:placecloud:en:large -->': file: placecloud-en-large.inc 'chde/schlagwort/index.html': '<!-- include:tagcloud:chde:large -->': file: tagcloud-chde-large.inc 'chde/ort/index.html': '<!-- include:placecloud:chde:large -->': file: placecloud-chde-large.inc # The substitution chains allow the sidebar to include # the small tag and place clouds. substitute_chains: - template: sidebar-en.inc substitutes: '<!-- include:tagcloud:en -->': file: tagcloud-en.inc '<!-- include:placecloud:en -->': file: placecloud-en.inc - template: sidebar-chde.inc substitutes: '<!-- include:tagcloud:chde -->': file: tagcloud-chde.inc '<!-- include:placecloud:chde -->': file: placecloud-chde.inc # Create index.html files in all folders which don't have one yet. create_index_filename: index.html create_index_content: | <!DOCTYPE html> <html lang="en"> <head> <title>there's nothing to see here.</title> <meta name="robots" content="noindex"> <meta http-equiv="refresh" content="0; url=.."> </head> <body style="background-color:black; color:white;"> <div style="position:absolute; top:0; left:0; right:0; bottom:0;"> <div style="width:100%; height:100%; display:table;"> <div style="display:table-cell; text-align:center; vertical-align:middle;"> there's nothing to see here. go <a href=".." style="color:#AAA;">here</a> instead. </div> </div> </div> </body> </html> # Everything is UTF-8. encoding: utf-8 # I want to be able to run different things in parallel. doit_config: dep_file: '.doit-spielwiese-subs.db'
this allows me to use html-style comments such as <!-- include:tagcloud:en --> to indicate where the html fragments should be included. i also create index files in foldes which otherwise would be empty, such as /photos/ (see here for how it looks). the result is, from my point of view, a much more polished version of the blog than the raw version produced by nikola without postprocessing.
this should give you an idea on how to produce a similar result with nikola, my plugins and filetreesubs.
on new year's day, we enjoyed a peaceful stroll through the nearby forest.
