Kushal Das

FOSS and life. Kushal Das talks here.

kushal76uaid62oup5774umh654scnu5dwzh4u2534qxhcbi4wbab3ad.onion

Get a TLS certificate for your onion service

For a long time, I wanted to have a certificate for the onion address of my blog. Digicert was the only CA who was providing those certificates with an Extended Validation. Those are costly and suitable for an organization to get, but not for me personally, especially due to the cost.

TLS certificate working

A few days ago, on IRC, I found out that Harica is providing Domain validation for the onion sites for around €30 per year. I jumped in to get one. At the same time, ahf was also getting his certificate. He helped me with the configuration for nginx.

How to get your own certificate?

  • Make sure you have your site running as Tor v3 onion service
  • Create an account at https://cm.harica.gr/
  • Goto server certificates on the left bar, and make a new request for your domain, provide the onion address as requested in the form.
  • It will give you the option to upload a CSR Certificate Signing Request. You can generate one by openssl req -newkey rsa:4096 -keyout kushaldas.in.onion.key -out csr.csr. For the common name, provide the same onion address.
  • After the click on the website, it will ask you to download a file and put it in your web root inside of .well-known/pki-validation/ directory. Make sure that you can access the file over Tor Browser.
  • When you click the final submission button, the system will take some time to verify the domain. After payment, you should be able to download the certificate with the full chain (the file ending with .p7b). There are 3 options on the webpage, so please remember to download the correct file :)
  • You will have to convert it into PEM format, I used the command ahf showed me: openssl pkcs7 -inform pem -in kushaldas.in.p7b -print_certs -out kushaldas.in.onion.chain.pem -outform pem

Setting up nginx

This part will be the same as any other standard nginx configuration. The following is what I use. Please uncomment the Strict-Transport-Security header line only after you are sure everything is working fine.

server {
	listen unix:/var/run/tor-hs-kushal.sock;

    server_name kushal76uaid62oup5774umh654scnu5dwzh4u2534qxhcbi4wbab3ad.onion;
    access_log /var/log/nginx/kushal_onion-access.log;

    location / {
	return 301 https://$host$request_uri;
    }

}

server {
    listen unix:/var/run/tor-hs-kushal-https.sock ssl http2;

    server_name kushal76uaid62oup5774umh654scnu5dwzh4u2534qxhcbi4wbab3ad.onion;
    access_log /var/log/nginx/kushal_onion-access.log;

    ssl_certificate /etc/pki/kushaldas.in.onion.chain.pem;
	ssl_certificate_key /etc/pki/kushaldas.in.onion.open.key;

    #add_header Strict-Transport-Security "max-age=63072000; includeSubdomains";
	add_header X-Frame-Options DENY;
	add_header X-Content-Type-Options nosniff;
    # Turn on OCSP stapling as recommended at
    # https://community.letsencrypt.org/t/integration-guide/13123
    # requires nginx version >= 1.3.7
    ssl_stapling on;
    ssl_stapling_verify on;

    # modern configuration. tweak to your needs.
    ssl_protocols TLSv1.2;
    ssl_ciphers 'ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256';
    ssl_prefer_server_ciphers on;

	index index.html;
	root /var/www/kushaldas.in;

	location / {
		try_files $uri $uri/ =404;
	}
}

I also have the following configuration in the /etc/tor/torrc file to use the unix socket files.

HiddenServiceDir /var/lib/tor/hs-kushal/
HiddenServiceVersion 3
HiddenServicePort 80 unix:/var/run/tor-hs-kushal-me.sock
HiddenServicePort 443 unix:/var/run/tor-hs-kushal-https.sock

In case you want to know more about why do you need the certificate for your onion address, the Tor Project has a very nice explanation.

Defending against side channel attacks via dependencies

Yesterday Alex Birsan posted a blog explaining how he made a supply chain attack on various companies via dependencies. I was waiting for this blog from last August when we noticed the mentioned packages on PyPI (and removed). I reached out to Alex to figure out more about the packages, and he said he will write a blog post.

This is the same time when @rsobers also tweeted about how any similar attack works via DNS.

dns data exfiltration

At SecureDrop project, we spend a lot of time figuring out a way to defend against similar attacks. My PyCon US 2019 talk explained the full process. In simple words, we are doing the following:

  • Verify the source of every python dependency before adding/updating them. This is a manual step done by human eyes.
  • Build wheels from the verified source and store them into a package repository along with OpenPGP signed sha256sums.
  • Before building the Debian package, make sure to verify the OpenPGP signature, and also install only from the known package repository using verified (again via OpenPGP signature) wheel hashes (from the wheels we built ourselves).

Now, in the last few months, we modified these steps, and made it even easier. Now, all of our wheels are build from same known sources, and all of the wheels are then built as reproducible and stored in git (via LFS). The final Debian packages are again reproducible. Along with this and the above mentioned OpenPGP signature + package sha256sums verification via pip. We also pass --no-index the argument to pip now, to make sure that all the dependencies are getting picked up from the local directory.

Oh, and I also forgot to mention that all of the project source tarballs used in SecureDrop workstation package building are also reproducible. If you are interested in using the same in your Python project (or actually for any project's source tarball), feel free to have a look at this function.

There is also diff-review mailing list (very low volume), where we post a signed message of any source package update we review.

Introducing Tumpa, to make OpenPGP simple with smartcards

Generating OpenPGP keys in an offline air-gapped system and then moving them into a smart card is always a difficult task for me. To remember the steps and command-line options of gpg2 correctly and then following them in the same order is difficult, and I had trouble enough number of times in doing so when I think about someone who is not into the command line that much, how difficult these steps are for them.

While having a chat with Saptak a few weeks ago, we came up with the idea of writing a small desktop tool to help. I started adding more features into my Johnnycanencrypt for the same. The OpenPGP operations are possible due to the amazing Sequoia project.

Introducing Tumpa

The work on the main application started during the holiday break, and today I am happy to release 0.1.0 version of Tumpa to make specific OpenPGP operations simple to use. It uses Johnnycanencrypt inside, and does not depend on the gpg.

Here is a small demo of the application running in a Tails (VM) environment. I am creating a new OpenPGP key with encryption and signing subkeys, and then putting them into a Yubikey. We are also setting the card holder's name via our tool.

Tumpa demo

We can also reset any Yubikey with just a click.

Reset Yubikey

You can download the Debian Buster package for Tails from the release page from Github. You can run from the source in Mac or Fedora too. But, if you are doing any real key generation, then you should try to do it in an air-gapped system.

You can install the package as dpkg -i ./tumpa_0.1.0+buster+nmu1_all.deb inside of Tails.

What are the current available features?

  • We can create a new OpenPGP key along with selected subkeys using Curve25519. By default, the tool will add three years for the expiration of the subkeys.
  • We can move the subkeys to a smart card. We tested only against Yubikeys as that is what we have.
  • We can set the name and public key URL on the card.
  • We can set the user pin and the admin pin of the smart card
  • We can reset a Yubikey.
  • We can export the public key for a selected key.

What is next?

A lot of work :) This is just the beginning. There are a ton of features we planned, and we will slowly add those. The UI also requires a lot of work and touch from a real UX person.

The default application will be very simple to use, and we will also have many advanced features, say changing subkey expiration dates, creating new subkeys, etc. for the advanced users.

We are also conducting user interviews (which takes around 20 minutes of time). If you have some time to spare to talk to us and provide feedback, please feel free to ping us via Twitter/mastodon/IRC.

We are available on #tumpa channel on Freenode. Come over and say hi :)

There are a lot of people I should thank for this release. Here is a quick list at random. Maybe I miss many names here, but you know that we could not do this without your help and guidance.

  • Sequoia team for all the guidance on OpenPGP.
  • Milosch Meriac for providing the guidance (and a ton of hardware).
  • Vincent Breitmoser, for keep explaining OpenKeyChain codebase to me to understand smart card operations
  • Anwesha Das for fixing the CI failures for Johnnycanencrypt, and documentation PRs.
  • Harlo and Micah, for all the amazing input for months.
  • Saptak Sengupta for being the amazing co-maintainer.

PrivChat with Tor: 2020-12-11 Tor advancing human rights

Tomorrow, on 11th December, 2020 at 18:00UTC, Tor will host the third edition of the PrivChat event, to discuss with some real life Tor users and talk about how Tor helps them to defend human rights. You can watch it live on Youtube.

image of snowden

The event will be hosted by Edward Snowden, President, Freedom of the Press Foundation. We have Alison Macrina (Founder, Library Freedom Project), Berhan Taye ( Africa Policy Manager and Global Internet Shutdowns Lead, Access Now) and Ramy Raoof (Security Labs Technologist, Amnesty International) as participants in the discussion.