TAS Agent

TAS Agent is a Rust program that runs inside a Confidential Virtual Machine (CVM). It attests the state of the CVM to a remote TAS server using a hardware Trusted Execution Environment (TEE) attestation report, and receives encrypted secrets in return.

The TAS Server is configured such that a CVM only receives the secrets, such as a LUKS passphrase to unlock the root volume, if it is successfully verified.

How it works:

1. The agent creates a temporary key pair.
2. It collects a hardware TEE attestation report from the CPU (AMD SEV-SNP or Intel TDX).
3. It sends the report and the public key to the TAS server.
4. The server checks the report. If valid, it encrypts the secrets with the public key and sends them back.

TAS Agent uses the Linux configfs/tsm subsystem to collect CPU attestation reports. This kernel interface works the same way for all supported CPU types, so the agent does not need vendor-specific code. It currently supports AMD SEV-SNP and Intel TDX TEE attestation. Nvidia GPU attestation is coming soon.

Use Cases

• LUKS volume unlocking — Automatically unlock LUKS-encrypted volumes at boot using TEE attestation instead of a password. Supports dracut, initramfs-tools, and systemd.
• Secret retrieval — Fetch any TAS-managed secret for use by applications running inside a CVM.
• X.509 certificate issuance (coming soon) — Generate a CSR and submit it alongside a TEE attestation report to a compatible TAS server. After passing verification, the server issues an X.509 certificate that can be used for (m)TLS and to fetch secrets.

Quick Start

cargo build --release

The tas_agent application is configured via a configuration file (config.toml) and/or command-line arguments. Command-line arguments take precedence over the configuration file.

Run the tas_agent program with a config file:

sudo ./target/debug/tas_agent -c config/config.toml

Example output:

Policy-ID: 771e76e7924348899ef751d0754c9060dd805928d03043f29a065275f4f883c8
Value: "30786465616462656566"

Configuration

Configuration File

Default path: /etc/tas_agent/config.toml

# The URI of the TAS REST service (http:// or https://)
server_uri = "https://tas.example.com:5000"

# Path to the API key for the TAS REST service
api_key = "/etc/tas_agent/api-key"

# Path to the CA root certificate signing the TAS REST service cert
# (only required for https:// URIs)
cert_path = "/etc/tas_agent/root_cert.pem"

# Policy ID to request from the TAS REST service
policy_id = "..."

# Maximum number of retry attempts for HTTP requests (default: 3)
# max_retries = 3

# Minimum backoff time in seconds between retries (default: 1)
# retry_min_backoff_secs = 1

# Maximum backoff time in seconds between retries (default: 30)
# retry_max_backoff_secs = 30

If using TLS, ensure that server_uri specifies https.

Command-Line Options

Option	Description
-d, --debug	Display debugging messages (do not use in production — logs sensitive data)
-c, --config <FILE>	Path to the config file (default: /etc/tas_agent/config.toml)
--server-uri <URI>	The URI of the TAS REST service
--api-key <FILE>	Path to the API key for the TAS REST service
--policy-id <ID>	Policy ID to request from the TAS REST service
--cert-path <FILE>	Path to the CA root certificate signing the TAS REST service cert (HTTPS only)
--max-retries <N>	Maximum number of retry attempts for HTTP requests (default: 3)
--retry-min-backoff-secs <SECS>	Minimum backoff time in seconds between retries (default: 1)
--retry-max-backoff-secs <SECS>	Maximum backoff time in seconds between retries (default: 30)
--no-key-binding	Disable public-key binding in TEE report data (for legacy TAS servers)
--gpu-attestation <MODE>	GPU attestation mode: auto (default) or disabled (requires gpu-attestation feature)
--askpass	systemd ask-password watcher mode (requires askpass feature)
--passfifo	initramfs-tools passfifo watcher mode (requires passfifo feature)

Build Instructions

Default (CPU-only attestation)

The default build includes CPU TEE attestation (AMD SEV-SNP / Intel TDX) with public-key binding. This produces the smallest binary, suitable for resource-constrained environments such as pre-boot attestation from an initrd

cargo build --release

With Askpass Support (LUKS unlock via dracut/systemd)

Adds a systemd ask-password watcher that polls /run/systemd/ask-password during early boot, fetches the LUKS passphrase from the TAS server, and replies via the systemd socket. Used with dracut-based initrd on Fedora and Ubuntu.

cargo build --release --features askpass

With Passfifo Support (LUKS unlock via initramfs-tools)

Adds an initramfs-tools passfifo watcher that detects the cryptsetup FIFO and writes the LUKS passphrase directly. Used with initramfs-tools-based initrd on Ubuntu.

cargo build --release --features passfifo

With GPU Attestation Support

cargo build --release --features gpu-attestation

Note: GPU attestation is currently a stub. The GpuEvidenceProvider trait is in place, but no concrete GPU provider is functional yet.

Package Build

Package installation is the preferred deployment method with askpass and passfifo. The .deb and .rpm packages include the expected initramfs and systemd integration artifacts and run the usual package-manager lifecycle hooks.

Prerequisites

# Debian/Ubuntu — install build dependencies (for .deb packages)
sudo apt-get install -y dpkg-dev debhelper fakeroot cargo rustc pkg-config libssl-dev

# Debian/Ubuntu — install additional dependencies for .rpm builds
sudo apt-get install -y rpm elfutils

# Fedora/RHEL — install build dependencies
sudo dnf install -y rpm-build cargo rust pkg-config openssl-devel

Build Packages

# Debian/Ubuntu (.deb)
./build.sh --deb

# Fedora/RHEL (.rpm)
./build.sh --rpm

Tarball Build

Running ./build.sh --tarball produces a tarball at target/package/tas_agent.tar.gz.

The -d, -r, -e, and -a options apply to the tarball build. Use them to change the tarball output directory or the config files bundled into the tarball build.

Use the tarball only for manual installation, local testing, or debugging. It is not the preferred installation path; package installs are preferred because they better match the supported deployment flow.

Testing

Unit Tests

cargo test --features askpass,passfifo

Integration Tests

Integration tests live in a separate repository: TEE-Attestation/tas_agent_tests.

Clone it under the project root:

cd tas_agent
git clone [email protected]:TEE-Attestation/tas_agent_tests.git testing

Then follow the instructions in testing/README.md:

# Chroot-based VM tests (SEV-SNP / TDX)
cd testing && python3 run_tests.py --initrd ubuntu-dracut --test all

# Interactive VM launcher (for debugging, manual passphrase entry)
cd testing && python3 launch_tdx.py --console --image tas-agent-test-ubuntu-dracut.qcow2

Contributing

See CONTRIBUTING.md.