Securing Alice's, Bob's and Carl's software supply chain using in-toto
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final_product
functionary_bob
functionary_carl
owner_alice
README.md
requirements.txt
run_demo.py

README.md

in-toto demo

In this demo, we will use in-toto to secure a software supply chain with a very simple workflow. Bob is a developer for a project, Carl packages the software, and Alice oversees the project. So, using in-toto's names for the parties, Alice is the project owner - she creates and signs the software supply chain layout with her private key - and Bob and Carl are project functionaries - they carry out the steps of the software supply chain as defined in the layout.

For the sake of demonstrating in-toto, we will have you run all parts of the software supply chain. This is, you will perform the commands on behalf of Alice, Bob and Carl as well as the client who verifies the final product.

Download and setup in-toto on *NIX (Linux, OS X, ..)

Virtual Environments (optional)

We highly recommend to install in-toto and its dependencies in a virtualenv. Just copy-paste the following snippet to install virtualenvwrapper and create a virtual environment:

# Install virtualenvwrapper
pip install virtualenvwrapper

# Create directory for your virtualenvs, default is
mkdir -p ~/.virtualenvs

# Source the scripts (you may want to add this to your shell startup file)
source /usr/local/bin/virtualenvwrapper.sh

# Create and change into a virtual environment, e.g. "in-toto-demo"
# This will add the prefix "(in-toto-demo)" to your shell prompt
mkvirtualenv in-toto-demo

Get demo files and install in-toto

# Fetch the demo repo using git
git clone https://github.com/in-toto/demo.git

# Change into the demo directory
cd demo

# Install a compatible version of in-toto
pip install -r requirements.txt

Note: If you are having troubles installing in-toto, make sure you have all the dependencies installed on your system.

Inside the demo directory you will find four directories: owner_alice, functionary_bob, functionary_carl and final_product. Alice, Bob and Carl already have RSA keys in each of their directories. This is what you see:

tree  # If you don't have tree, try 'find .' instead
# the tree command gives you the following output
# ├── README.md
# ├── final_product
# ├── functionary_bob
# │   ├── bob
# │   └── bob.pub
# ├── functionary_carl
# │   ├── carl
# │   └── carl.pub
# ├── owner_alice
# │   ├── alice
# │   ├── alice.pub
# │   └── create_layout.py
# └── run_demo.py

Define software supply chain layout (Alice)

First, we will need to define the software supply chain layout. To simplify this process, we provide a script that generates a simple layout for the purpose of the demo.

In this software supply chain layout, we have Alice, who is the project owner that creates the layout, Bob, who clones the project's repo and performs some pre-packaging editing (update version number), and Carl, who uses tar to package the project sources into a tarball, which together with the in-toto metadata composes the final product that will eventually be installed and verified by the end user.

# Create and sign the software supply chain layout on behalf of Alice
cd owner_alice
python create_layout.py

The script will create a layout, add Bob's and Carl's public keys (fetched from their directories), sign it with Alice's private key and dump it to root.layout. In root.layout, you will find that (besides the signature and other information) there are three steps, clone, update-version and package, that the functionaries Bob and Carl, identified by their public keys, are authorized to perform.

Clone project source code (Bob)

Now, we will take the role of the functionary Bob and perform the step clone on his behalf, that is we use in-toto to clone the project repo from GitHub and record metadata for what we do. Execute the following commands to change to Bob's directory and perform the step.

cd ../functionary_bob
in-toto-run --step-name clone --products demo-project/foo.py --key bob -- git clone https://github.com/in-toto/demo-project.git

Here is what happens behind the scenes:

  1. In-toto wraps the command git clone https://github.com/in-toto/demo-project.git,
  2. hashes the contents of the source code, i.e. demo-project/foo.py,
  3. adds the hash together with other information to a metadata file,
  4. signs the metadata with Bob's private key, and
  5. stores everything to clone.[Bob's keyid].link.

Update version number (Bob)

Before Carl packages the source code, Bob will update a version number hard-coded into foo.py. He does this using the in-toto-record command, which produces the same link metadata file as above but does not require Bob to wrap his action in a single command. So first Bob records the state of the files he will modify:

# In functionary_bob directory
in-toto-record --step-name update-version --key bob start --materials demo-project/foo.py

Then Bob uses an editor of his choice to update the version number in demo-project/foo.py, e.g.:

# In demo-project/foo.py
VERSION = "foo-v1"

And finally he records the state of files after the modification and produces a link metadata file called update-version.[Bob's keyid].link.

# In functionary_bob directory
in-toto-record --step-name update-version --key bob stop --products demo-project/foo.py

Bob has done his work and can send over the sources to Carl, who will create the package for the user.

# Bob has to send the update sources to Carl so that he can package them
cp -r demo-project ../functionary_carl/

Package (Carl)

Now, we will perform Carl’s package step by executing the following commands to change to Carl's directory and create a package of the software project

cd ../functionary_carl
in-toto-run --step-name package --materials demo-project/foo.py --products demo-project.tar.gz --key carl -- tar --exclude ".git" -zcvf demo-project.tar.gz demo-project

This will create another step link metadata file, called package.[Carl's keyid].link. It's time to release our software now.

Verify final product (client)

Let's first copy all relevant files into the final_product that is our software package demo-project.tar.gz and the related metadata files root.layout, clone.[Bob's keyid].link, update-version.[Bob's keyid].link and package.[Carl's keyid].link:

cd ..
cp owner_alice/root.layout functionary_bob/clone.776a00e2.link functionary_bob/update-version.776a00e2.link functionary_carl/package.2f89b927.link functionary_carl/demo-project.tar.gz final_product/

And now run verification on behalf of the client:

cd final_product
# Fetch Alice's public key from a trusted source to verify the layout signature
# Note: The functionary public keys are fetched from the layout
cp ../owner_alice/alice.pub .
in-toto-verify --layout root.layout --layout-key alice.pub

This command will verify that

  1. the layout has not expired,
  2. was signed with Alice’s private key,
    and that according to the definitions in the layout
  3. each step was performed and signed by the authorized functionary
  4. the recorded materials and products follow the artifact rules and
  5. the inspection untar finds what it expects.

From it, you will see the meaningful output PASSING and a return value of 0, that indicates verification worked out well:

echo $?
# should output 0

Tampering with the software supply chain

Now, let’s try to tamper with the software supply chain. Imagine that someone got a hold of the source code before Carl could package it. We will simulate this by changing demo-project/foo.py on Carl's machine (in functionary_carl directory) and then let Carl package and ship the malicious code.

cd ../functionary_carl
echo "something evil" >> demo-project/foo.py

Carl thought that this is the sane code he got from Bob and unwittingly packages the tampered version of foo.py

in-toto-run --step-name package --materials demo-project/foo.py --products demo-project.tar.gz --key carl -- tar --exclude '.git' -zcvf demo-project.tar.gz demo-project

and ships everything out as final product to the client:

cd ..
cp owner_alice/root.layout functionary_bob/clone.776a00e2.link functionary_bob/update-version.776a00e2.link functionary_carl/package.2f89b927.link functionary_carl/demo-project.tar.gz final_product/

Verifying the malicious product

cd final_product
in-toto-verify --layout root.layout --layout-key alice.pub

This time, in-toto will detect that the product foo.py from Bob's update-version step was not used as material in Carl's package step (the verified hashes won't match) and therefore will fail verification an return a non-zero value:

echo $?
# should output 1

Wrapping up

Congratulations! You have completed the in-toto demo! This exercise shows a very simple case in how in-toto can protect the different steps within the software supply chain. More complex software supply chains that contain more steps can be created in a similar way. You can read more about what in-toto protects against and how to use it on in-toto's Github page.

Clean slate

If you want to run the demo again, you can use the following script to remove all the files you created above.

cd .. # You have to be the demo directory
python run_demo.py -c

Tired of copy-pasting commands?

The same script can be used to sequentially execute all commands listed above. Just change into the demo directory, run python run_demo.py without flags and observe the output.

# In the demo directory
python run_demo.py