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.

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 10.13.x

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) and make sure it is callable via gpg2
• Python 3.x (with venv support in case that is packaged separately)
• direnv (Optional/Recommended)

Install the vagrant-disksize plugin to support resize of the start up disk:

$ vagrant plugin install vagrant-disksize

Most recently tested 2019-03-21 with the following vagrant-disksize release:

$ vagrant plugin list
vagrant-disksize (0.1.3, global)

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 rsa -C "hpotter@hogwarts.wiz" -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 hpotter@hogwarts.wiz
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 "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.

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)

$ git clone git@github.com:zcash/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 +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 +ZCASH_GIT_REPO_URL +ZCASH_VERSION
zcash-gitian$ echo $ZCASH_GIT_REPO_URL
https://github.com/zcash/zcash
zcash-gitian$

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.

$ gpg2 --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:

$ gpg2 --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 the gpg_key_id and gpg_key_name entries in gitian.yml 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: the part before the @ symbol of the associated email address. In our example this is hpotter.

Provision a virtual machine

From the project root directory, run:

$ vagrant up --provision zcash-build

This will provision a Gitian host virtual machine that uses a Linux container (LXC) guest to perform the actual builds.

Use git stash to save one's local customizations to gitian.yml.

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 running ssh-add -l.

$ ssh-add -l
The agent has no identities.

$ ssh-add ~/.ssh/github_id_rsa
Identity added: /home/hpotter/.ssh/github_id_rsa (/home/hpotter/.ssh/github_id_rsa)

$ 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:

$ 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.

$ vagrant ssh zcash-build
[...]

# on the virtualbox vm
$ 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)

$ 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
$ ./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. Commit and push your signatures (both the .assert and .assert.sig files) to the zcash/gitian.sigs repository, or if that's not possible then create a pull request.

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.

Copying files

The easiest way to do it is with a plugin.

vagrant plugin install vagrant-scp

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.