Zcash deterministic builds
Gitian provides a way to be reasonably certain that the Zcash executables are really built from the exact source on GitHub and have not been tampered with. It also makes sure that the same, tested dependencies are used and statically built into the executable.
Multiple developers build from source code by following a specific descriptor ("recipe"), cryptographically sign the result, and upload the resulting signature. These results are compared and only if they match is the build accepted.
More independent Gitian builders are needed, which is why this guide exists.
6GB of RAM, four cores.
Note: This project uses VirtualBox to run a virtual machine. If you are running this inside a virtual machine, you'll likely need to enable a feature such as “nested virtualization”, “VT-x”, or similar in your virtualization software's settings for that virtual machine.
If you're using one of the following platforms, see the linked instructions for that platform:
If you're not using one of the platforms that we have specific instructions for, this is the list of dependencies we want. Please document the steps involved and we can add another platform to the list above!
- Vagrant 2.0.3 or higher
- GnuPG 2.x (2.11.18 or greater)
- Python 3.x (with
venvsupport in case that is packaged separately)
- direnv (Optional/Recommended)
We want a configuration file in the home directory of the account you'll be working in. This will determine how you are identified on the projects you contribute to. These settings can be overridden on a per-project basis.
Git provides some convenient command options for setting this up:
$ git config --global user.name "Harry Potter" $ git config --global user.email "firstname.lastname@example.org"
Checking that this worked:
$ git config user.name Harry Potter $ git config user.email email@example.com
This is all the git configuration needed for the steps below, but here is a good reference for further reading on configuring git:
Decide on an ssh keypair to use when uploading build signatures to github
You can generate a keypair specifically for connecting to github like this:
$ ssh-keygen -t rsa -b 4096 -C "firstname.lastname@example.org" -f ~/.ssh/github_id_rsa -N '' Generating public/private rsa key pair. Your identification has been saved in /Users/hpotter/.ssh/github_id_rsa. Your public key has been saved in /Users/hpotter/.ssh/github_id_rsa.pub. The key fingerprint is: SHA256:w1ZAgf+Ge+R662PU18ASqx8sZYfg9OxKhE/ZFf9zwvE email@example.com The key's randomart image is: +---[RSA 2048]----+ | o+. .. | | . .o . .. | | . +.* *. .| | .o.= X.+o.| | S* B oo+E| | ...X = ..+| | B + o | | . B . | | .*oo | +----[SHA256]-----+
Some explanation of the arguments used in the above example:
-t rsa Use a key type of RSA -C "firstname.lastname@example.org" Provide an identity to associate with the key (default is user@host in the local environment) -f ~/.ssh/github_id_rsa Path to the private key to generate. The corresponding public key will be saved at ~/.ssh/github_id_rsa.pub -N '' Passphrase for the generated key. An empty string as shown here means save the private key unencrypted.
Set up your ssh keypair for use with github
Add an entry to
~/.ssh/config (create this file if necessary) telling ssh to use the keypair you
generated above when connecting to github.com.
Host github.com User harrypotter PreferredAuthentications publickey IdentityFile /home/hpotter/.ssh/github_id_rsa AddKeysToAgent yes
The 'User' entry should match your github username.
Test that ssh will successfully use your new key to connect to github.
$ ssh -T email@example.com The authenticity of host 'github.com (22.214.171.124)' can't be established. RSA key fingerprint is SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8. Are you sure you want to continue connecting (yes/no)? yes Warning: Permanently added 'github.com,126.96.36.199' (RSA) to the list of known hosts. Hi harrypotter! You've successfully authenticated, but GitHub does not provide shell access. $
Clone this git project on your machine
From a location where you want to place your local clone of this repository (e.g.
there's a possibility you'll want to make and contribute changes, consider forking the repository
and cloning from your fork.
cd into the project repo
$ cd zcash-gitian zcash-gitian
Copy example environment configuration files
.envrc.example are tracked in the repo as example configurations you
should be able to use to get started. The filenames
.gitignore'd to allow
you to easily make local customizations that don't show up as untracked changes.
.envrc is probably only useful if you are using
direnv. If you're not, you can ignore
that file and the places below that talk about it, and use your preferred way of managing
environment variables instead.
zcash-gitian$ cp .env.example .env zcash-gitian$ cp .envrc.example .envrc direnv: error .envrc is blocked. Run `direnv allow` to approve its content. zcash-gitian$
More on that above message in the following section...
Enable auto-execution of .envrc
If you installed and activated
direnv, it will detect when
.envrc is created in your current
directory, as shown above. As a security precaution, it won't automatically run it without your
approval (to prevent untrusted code from doing something malicious). Let's take a look at what's in
zcash-gitian$ cat .envrc source_up dotenv export GIT_NAME=`git config user.name` export GIT_EMAIL=`git config user.email` direnv: error .envrc is blocked. Run `direnv allow` to approve its content. zcash-gitian$
Some explanation of the lines in the above
`source_up` Load any .envrc higher up in the folder structure. So if for example you place an `.envrc` in your home directory, variables set there will still be available within this project, rather than being overridden by this project's `.envrc`. `dotenv` Set the environment variables defined in `.env`. Think of `.envrc` as code (it runs in a bash interpreter with some extra functions added) and `.env` as data (you can basically just set literal values, and each update to it doesn't require approval). export GIT_NAME=`git config user.name` export GIT_EMAIL=`git config user.email` Use your local git configuration values for the name and email that will be used to add build signatures inside the virtual environment.
If you're ok with running
.envrc, follow the directions in the prompt to allow it.
zcash-gitian$ echo $ZCASH_GIT_REPO_URL direnv: error .envrc is blocked. Run `direnv allow` to approve its content. zcash-gitian$ direnv allow direnv: loading .envrc direnv: export +GIT_EMAIL +GIT_NAME +GPG_KEY_ID +GPG_KEY_NAME +ZCASH_GIT_REPO_URL +ZCASH_VERSION zcash-gitian$ echo $ZCASH_GIT_REPO_URL https://github.com/zcash/zcash zcash-gitian$
A variable defined in
.env is now active in our environment. If we leave this project, it is
unloaded. When we return, it is reloaded:
zcash-gitian$ cd .. direnv: unloading $ echo $ZCASH_GIT_REPO_URL $ cd zcash-gitian/ direnv: loading .envrc direnv: export +GIT_EMAIL +GIT_NAME +GPG_KEY_ID +GPG_KEY_NAME +ZCASH_GIT_REPO_URL +ZCASH_VERSION zcash-gitian$ echo $ZCASH_GIT_REPO_URL https://github.com/zcash/zcash zcash-gitian$
Project-specific environment settings will come in handy in the next step, when we'll create an isolated python virtual environment specifically for use with this project.
Create a python virtual environment for this project
Note: The main purpose of this part is to get a current version of ansible, and keep it locally within this project. If you already installed ansible (e.g. from an OS package manager like apt), you can skip this part and the following parts about pip and pip packages.
When creating a virtual environment, call the python executable you want the virtual environment to
use. The location and version will depend on your specific setup -- your OS may provide a suitably
current python interpreter, or you may have built and installed one yourself. If it's in your PATH,
a command like
type python3 should tell you where it is installed on your system. For example:
zcash-gitian$ type python3 python3 is /usr/local/bin/python3 zcash-gitian$ /usr/local/python3 --version Python 3.7.3
You may also want to check if the
PATH is a symlink to a versioned location, if you
are using a system (like
brew) that can manage multiple installed versions. This way, our virtual
environment will remain pinned to a specific python version even after a newer python version is
$ ls -n /usr/local/bin/python3 lrwxr-xr-x 1 501 20 34 Mar 30 09:35 /usr/local/bin/python3 -> ../Cellar/python/3.7.3/bin/python3
We can use python's built-in
venv module to create a virtual environment:
zcash-gitian$ /usr/local/Cellar/python/3.7.3/bin/python3 -m venv local/python_v3.7.3_venv
Translation: "Create a virtual environment at ./local/python_v3.7.3_venv".
The project subdirectory
.gitignored to provide a convenient location for files we
don't want to commit and track in version control.
You should now have a tree of directories and files in
zcash-gitian$ ls -F local/python_v3.7.3_venv/ bin/ include/ lib/ pyvenv.cfg
bin directory, among other things, are the entries
python3, which are
symlinks that point back to the
python3 executable we used to create this environment:
zcash-gitian$ ls -F local/python_v3.7.3_venv/bin/ activate activate.fish easy_install-3.7* pip3* python@ activate.csh easy_install* pip* pip3.7* python3@
A python virtual environment is 'active' if the python interpreter being executed is run from its
path inside the environment's
bin directory. Even though the file being executed is the same
whether run directly or via a symlink, it pays attention to the path of the command that was used to
activate script is provided, and you can use that, but if you're using
direnv you can set up
a simple automatic activation for the project directory by adding the following line to
load_prefix is provided by
direnv to modify a whole set of common "path" variables
(including PATH) according to a common unix pattern.
Let's add that line now:
zcash-gitian$ echo "load_prefix local/python_v3.7.3_venv" >> .envrc direnv: error .envrc is blocked. Run `direnv allow` to approve its content. zcash-gitian$ direnv allow direnv: loading .envrc direnv: export +CPATH +GIT_EMAIL +GIT_NAME +GPG_KEY_ID +GPG_KEY_NAME +LD_LIBRARY_PATH +LIBRARY_PATH +MANPATH +PKG_CONFIG_PATH +ZCASH_GIT_REPO_URL +ZCASH_VERSION ~PATH zcash-gitian$
When the content of
.envrc is changed, it needs to be approved again (another security
precaution). Then, several variables were set or updated to add paths within our virtual environment
directory at the front (left side) of the list. Let's look at PATH and its effect on which
locations we default to:
zcash-gitian$ echo $PATH /Users/harrypotter/Projects/zcash-gitian/local/python_v3.7.3_venv/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games zcash-gitian$ type python python is /Users/harrypotter/Projects/zcash-gitian/local/python_v3.7.3_venv/bin/python zcash-gitian$ type python3 python3 is /Users/harrypotter/Projects/zcash-gitian/local/python_v3.7.3_venv/bin/python3
python3 commands will now run from the locations we've installed into our
project's virtual environment while we are in the project directory, we can consider the virtual
environment active when using a shell at (or below) that location.
pip has a command to upgrade itself. Let's go ahead and run that:
zcash-gitian$ pip install --upgrade pip Collecting pip [...] Successfully installed pip-19.1.1
Install pip packages
We have some dependencies to install as python packages, using the pip package manager installed
above. The set we need, with version numbers managed via git, is in
requirements-pip.lock; we can
pip install with that file as input:
zcash-gitian$ pip install --requirement requirements-pip.lock
Check that you can run
ansible from the command line:
zcash-gitian$ ansible --version ansible 2.7.10 [...] zcash-gitian$
Decide on a gpg keypair to use for gitian
You can generate a keypair specifically for zcash gitian builds with a command like the one below.
zcash-gitian$ gpg --quick-generate-key --batch --passphrase '' "Harry Potter (zcash gitian) <firstname.lastname@example.org>" gpg: key 3F0C2117D53A4A49 marked as ultimately trusted gpg: directory '/home/hpotter/.gnupg/openpgp-revocs.d' created gpg: revocation certificate stored as '/home/hpotter/.gnupg/openpgp-revocs.d/3F14A629C06FA31D59C64FE93F0C2117D53A4A49.rev'
Some explanation of the arguments used in the above example:
--quick-generate-key --batch This combination of options allows options to be given on the command line. Other key generation options use interative prompts. --passphrase '' Passphrase for the generated key. An empty string as shown here means save the private key unencrypted. "Name (Comment) <Email>" The user id (also called uid) to associate with the generated keys. Concatenating a name, an optional comment, and an email address using this format is a gpg convention.
You can check that the key was generated and added to your local gpg key database, and see its fingerprint value, like this:
zcash-gitian$ gpg --list-keys /home/hpotter/.gnupg/pubring.kbx ---------------------------------- pub rsa2048 2018-04-23 [SC] [expires: 2020-04-22] 3F14A629C06FA31D59C64FE93F0C2117D53A4A49 uid [ultimate] Harry Potter (zcash gitian) <email@example.com> sub rsa2048 2018-04-23 [E]
GPG_KEY_NAME variables in
.env as follows:
GPG_KEY_ID: In the example output shown here, this is the 40 character string
3F14A629C06FA31D59C64FE93F0C2117D53A4A49. Some versions of gpg may truncate this value, e.g. to 8 or 16 characters. You should be able to use the truncated value.
GPG_KEY_NAME: This is passed as the '--signer' argument to Gitian, and used as the name of a directory for your signatures in our
gitian.sigsrepository. We suggest using the username portion of the email address associated with your GPG key. In our example this is
Install Vagrant plugins
This project uses some 3rd party Vagrant plugins. These dependencies are specified in
We can install them locally in the
.vagrant directory with the following command:
zcash-gitian$ vagrant plugin install --local
Configure the version of zcash you want to build and sign
Set the value of the
ZCASH_VERSION variable in
.env to point to the zcash commit you want to
create a signature for. Likely you want the name of a git tag, such as
Provision a virtual machine
From the project root directory, run:
zcash-gitian$ vagrant up zcash-build
This will provision a Gitian host virtual machine that uses a Linux container (LXC) guest to perform the actual builds.
Load your ssh key into ssh-agent
Load your ssh key (for pushing signatures to github) into ssh-agent. The approach here is to allow
programs in the zcash-build VM to connect to ssh-agent to perform operations with the private key.
This way, we don't need to copy ssh keys into the VM. You can verify that the key is loaded by
zcash-gitian$ ssh-add -l The agent has no identities. zcash-gitian$ ssh-add ~/.ssh/github_id_rsa Identity added: /home/hpotter/.ssh/github_id_rsa (/home/hpotter/.ssh/github_id_rsa) zcash-gitian$ ssh-add -l 4096 SHA256:4fFdwJ71VIpF5cW0dqrsU7jxjctaFcAKmdQZPEqR0Y4 /home/hpotter/.ssh/github_id_rsa (RSA)
SSH into the VM
Vagrant should now show that the new VM is in the 'running' state:
zcash-gitian$ vagrant status Current machine states: zcash-build running (virtualbox) The VM is running. To stop this VM, you can run `vagrant halt` to shut it down forcefully, or you can run `vagrant suspend` to simply suspend the virtual machine. In either case, to restart it again, simply run `vagrant up`.
vagrant ssh command to start a shell session in the VM. Once in that session, you can use
ssh-add again to see that your forwarded key is available, and check that you can use that key to
authenticate to github.
zcash-gitian$ vagrant ssh zcash-build [...] # on the virtualbox vm vagrant@zcash-build:~$ ssh-add -l 4096 d1:43:75:a7:95:65:9e:d4:8e:57:d8:98:58:7d:92:4c /home/hpotter/.ssh/github_id_rsa (RSA) vagrant@zcash-build:~$ ssh -T firstname.lastname@example.org Warning: Permanently added the RSA host key for IP address '188.8.131.52' to the list of known hosts. Hi harrypotter! You've successfully authenticated, but GitHub does not provide shell access.
Once in a shell session in the VM, we're ready to run the gitian build.
# on the virtualbox vm vagrant@zcash-build:~$ ./gitian-build.sh
The output from
gbuild is informative. There are some common warnings which can be ignored, e.g. if you get an intermittent privileges error related to LXC then just execute the script again. The most important thing is that one reaches the step which says
Running build script (log in var/build.log). If not, then something else is wrong and you should let us know.
Take a look at the variables near the top of
~/gitian-build.sh and get familiar with its functioning, as it can handle most tasks.
It's also a good idea to regularly
git pull on this repository to obtain updates and re-run the entire VM provisioning for each release, to ensure current and consistent state for your builder.
Generating and uploading signatures
After the build successfully completes, the gitian command
gsign will be called, which will
generate signatures, and a commit will be added. You can cd into the gitian.sigs directory, set the
repository to point to your fork of zcash/gitian.sigs, push
your updates to a branch, and then make a pull request on github.
cd gitian.sigs git remote rename origin upstream git remote add origin email@example.com:harrypotter/gitian.sigs.git git checkout -b v2.0.4 git push origin v2.0.4
Signatures can be verified by running
gitian-build.sh --verify, but set
build=false in the script to skip building. Run a
git pull beforehand on
gitian.sigs so you have the latest. The provisioning includes a task which imports Zcash developer public keys to the Vagrant user's keyring and sets them to ultimately trusted, but they can also be found at
contrib/gitian-downloader within the Zcash source repository.
Working with GPG
We provide two options for automatically importing keys into the VM, or you may choose to copy them manually. GPG keys are needed to sign the manifests which get pushed to gitian.sigs.
GPG is tricky, especially if you use a smartcard and can't copy the secret key. We have a script intended to forward the gpg-agent socket into the VM,
forward_gpg_agent.sh, but it is not currently working. If you want your full keyring to be available, you can use the following workaround involving
sshfs and synced folders:
vagrant plugin install vagrant-sshfs
Uncomment the line beginning with
gitian.vm.synced_folder "~/.gnupg" in
Vagrantfile. Ensure the destination mount point is empty. Then run:
vagrant sshfs --mount zcash-build
Vagrant synced folders may also work natively with
vboxfs if you install VirtualBox Guest Additions into the VM from
contrib, but that's not as easy to setup.
To copy files to the VM:
vagrant scp file_on_host.txt :file_on_vm.txt
To copy files from the VM:
vagrant scp :file_on_vm.txt file_on_host.txt
Port 2200 on the host machine should be forwarded to port 22 on the guest virtual machine.
The automation and configuration management assumes that VirtualBox will assign the IP address
10.0.2.15 to the Gitian host Vagrant VM.