Zcash deterministic builds

This is a deterministic build environment for Zcash that uses Gitian.

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.

Requirements

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.

Install Dependencies

If you're using one of the following platforms, see the linked instructions for that platform:

• Debian 9.x
• Ubuntu 18.04.x
• macOS

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!

• Git
• VirtualBox
• Vagrant 2.0.3 or higher
• GnuPG 2.x (2.11.18 or greater)
• Python 3.x (with venv support in case that is packaged separately)
• direnv (Optional/Recommended)

Configuration

Configure git

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 "hpotter@hogwarts.wiz"

Checking that this worked:

$ git config user.name
Harry Potter
$ git config user.email
hpotter@hogwarts.wiz

This is all the git configuration needed for the steps below, but here is a good reference for further reading on configuring git:

https://git-scm.com/book/en/v2/Customizing-Git-Git-Configuration

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 ed25519 -C "hpotter@hogwarts.wiz" -f ~/.ssh/github_id_rsa -N ''
Generating public/private ed25519 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:qBCOybcJkgs1xdNoocYlsZz3jNQhGgOymreQAQRyh0c hpotter@hogwarts.wiz
The key's randomart image is:
+--[ED25519 256]--+
|Oo*=E+.          |
|+=.%*o..         |
|o %oo..          |
|o@ = + .         |
|@o+.. + S        |
|o+ooo.           |
|. .o.            |
|                 |
|                 |
+----[SHA256]-----+

Some explanation of the arguments used in the above example:

    -t ed25519                     Use a key type of ed25519

    -C "hpotter@hogwarts.wiz"      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 the new key to your github account.

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.

For instance:

Host github.com
  User harrypotter
  PreferredAuthentications publickey
  IdentityFile /home/hpotter/.ssh/github_id_rsa
  AddKeysToAgent yes

The 'User' entry should match your github username.

If using macOS, the IdentityFile path will be:

/Users/yourusername/.ssh/github_id_rsa

If you do generate a new ssh config file you'll need to set its permission bits appropriately. On a Unix system you may do so with a command like this:

chmod 400 ~/.ssh/config

Test that ssh will successfully use your new key to connect to github.

$ ssh -T git@github.com
The authenticity of host 'github.com (192.30.253.112)' 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,192.30.253.112' (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. ~/Projects). If there's a possibility you'll want to make and contribute changes, consider forking the repository and cloning from your fork. For example:

git clone git@github.com:harrypotter/zcash-gitian.git

cd into the project repo

$ cd zcash-gitian
zcash-gitian

Copy example environment configuration files

The files .env.example and .envrc.example are tracked in the repo as example configurations you should be able to use to get started. The filenames .env and .envrc are .gitignore'd to allow you to easily make local customizations that don't show up as untracked changes.

Note that .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 the file:

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 .envrc file:

`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:

% type python3
python3 is /usr/bin/python3
% /usr/bin/python3 --version
Python 3.9.7

We can use python's built-in venv module to create a virtual environment:

zcash-gitian % /usr/bin/python3 -m venv ./local/python_v3.9.7_venv

Translation: "Create a virtual environment at ./local/python_v3.9.7_venv".

The project subdirectory local is .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 local/python_v3.9.7_venv:

zcash-gitian % ls -F ./local/python_v3.9.7_venv
bin/		include/	lib/		pyvenv.cfg

Inside the bin directory, among other things, are the entries python and python3, which are symlinks that point back to the python3 executable we used to create this environment:

zcash-gitian % ls -F ./local/python_v3.9.7_venv/bin/
Activate.ps1	activate.csh	pip*		pip3.9*		python3@
activate	activate.fish	pip3*		python@		python3.9@

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 run it.

An 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 .envrc:

load_prefix local/python_v3.9.7_venv

The command 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_v3.9.7_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 python locations we default to:

zcash-gitian$ echo $PATH
/Users/harrypotter/Projects/zcash-gitian/local/python_v3.9.7_venv/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
zcash-gitian$ type python
python is /Users/harrypotter/Projects/zcash-gitian/local/python_v3.9.7_venv/bin/python
zcash-gitian$ type python3
python3 is /Users/harrypotter/Projects/zcash-gitian/local/python_v3.9.7_venv/bin/python3

Since the python and 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.

Upgrade pip

pip3 has a command to upgrade itself. Let's go ahead and run that:

zcash-gitian % pip3 install --upgrade pip
Requirement already satisfied: pip in ./local/python_v3.9.7_venv/lib/python3.9/site-packages (21.2.4)

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 run pip3 install with that file as input:

zcash-gitian$ pip3 install --requirement requirements-pip.lock

Check that you can run ansible from the command line:

zcash-gitian % ansible --version
ansible [core 2.11.5]
[...]
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) <hpotter@hogwarts.wiz>"
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) <hpotter@hogwarts.wiz>
sub   rsa2048 2018-04-23 [E]

Update your GPG_KEY_ID and 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.sigs repository. We suggest using the username portion of the email address associated with your GPG key. In our example this is hpotter.

For more info about updating or revoking gpg keys, see Notes on updating or revoking GPG keys

Publish your GPG public key

There is a network of key servers that we can use to quickly and easily make your key available for others to find, download, and use to verify any signatures you publish for gitian builds. These keyservers won't let you delete a key you upload, but as long as you have the private key you can post a revocation of a key you've previously uploaded.

The keyservers (mostly) synchronize with one another using (mostly) SKS Keyserver so it may not matter very much which one you upload your key to. That said, at the time of writing, gitian-builder's gverify command uses pgp.mit.edu as its keyserver so it makes sense in this case to upload there.

You can upload your public key like this:

$ gpg --keyserver pgp.mit.edu --send-keys 3F14A629C06FA31D59C64FE93F0C2117D53A4A49
gpg: sending key 3F0C2117D53A4A49 to hkp://pgp.mit.edu

Some explanation of the arguments used in the above example:

--keyserver pgp.mit.edu        Specify the keyserver to use. gpg will use a default server if
                               you don't provide one here or one that has been defined in
                               gpg.conf

--send-keys 3F14A629C06FA31D59C64FE93F0C2117D53A4A49
                               The gpg_key_id for the key to upload.

You can verify that the key was successfully uploaded like this:

$ gpg --keyserver pgp.mit.edu --receive-keys 3F14A629C06FA31D59C64FE93F0C2117D53A4A49
gpg: key 3F0C2117D53A4A49: "Harry Potter (zcash gitian) <hpotter@hogwarts.wiz>" not changed
gpg: Total number processed: 1
gpg:              unchanged: 1

Install Vagrant plugins

This project uses some 3rd party Vagrant plugins. These dependencies are specified in Vagrantfile. 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-tagged zcash version, usually the most recent released version.

Provision a virtual machine

Edit the Vagrantfile so the v.memory and v.cpus values are a bit lower than the memory and CPU count in the actual physical machine. If they're set too high then you might badly wedge your 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.

If you don't already have an ssh-agent running you may need to start one. For example, you might be able to start one like this:

eval `ssh-agent -s`

You can verify that the key is loaded by running ssh-add -l.

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`.

Use the 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 git@github.com
Warning: Permanently added the RSA host key for IP address '192.30.253.112' to the list of known hosts.
Hi harrypotter! You've successfully authenticated, but GitHub does not provide shell access.

Building Zcash

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

If you want to run a parallel build, invoke ./gitian-parallel-build.sh instead.

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

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.

After the build successfully completes, the gitian command gsign will be called, which will generate signatures, and a commit will be added.

Fork the zcash/gitian.sigs repository by following the link and clicking "fork".

Now 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 git@github.com:harrypotter/gitian.sigs.git
git checkout -b v2.0.6
git push origin v2.0.6

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.

Copying files

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

Other notes

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.