Azure Code Signer

Azure Code Signer is a command line tool that allows you to code sign files using a code signing certificate stored in Azure Key Vault. This tool is designed to work across multiple platforms, including Linux, macOS, and Windows.

Features

• Authenticate with Azure Key Vault to retrieve code signing certificates
• Sign files using certificates from Azure Key Vault
• Generate detached signature files (.sig)
• Verify file signatures
• Cross-platform compatibility (Windows, macOS, Linux)
• Support for various certificate formats (PEM, DER, PKCS#12)

Prerequisites

• Python 3.7 or higher
• An Azure account with access to Azure Key Vault
• A code signing certificate stored in Azure Key Vault

Installation

Using pip (recommended)

pip install azure-code-signer

From source

git clone https://github.com/yourusername/azure-code-signer.git
cd azure-code-signer
pip install -e .

Authentication with Azure

The tool uses Azure's DefaultAzureCredential for authentication, which tries multiple authentication methods in the following order:

1. Environment variables
2. Managed Identity
3. Visual Studio Code credentials
4. Azure CLI credentials
5. Interactive browser authentication

Authentication via Environment Variables

To authenticate using environment variables, set the following:

# Required for service principal authentication
AZURE_TENANT_ID=your-tenant-id
AZURE_CLIENT_ID=your-client-id
AZURE_CLIENT_SECRET=your-client-secret

# Optional - to specify which subscription to use
AZURE_SUBSCRIPTION_ID=your-subscription-id

Setting Up a Service Principal

1. Create a service principal in Azure:

   az ad sp create-for-rbac --name "AzureCodeSigner" --skip-assignment
   

   This will output JSON containing your appId (client ID), password (client secret), and tenant.

2. Grant Key Vault access to your service principal:

   az keyvault set-policy --name your-keyvault-name \
     --object-id <service-principal-object-id> \
     --certificate-permissions get list \
     --secret-permissions get list
   

Setting Environment Variables

Linux/macOS:

export AZURE_TENANT_ID=your-tenant-id
export AZURE_CLIENT_ID=your-client-id
export AZURE_CLIENT_SECRET=your-client-secret

Windows (Command Prompt):

set AZURE_TENANT_ID=your-tenant-id
set AZURE_CLIENT_ID=your-client-id
set AZURE_CLIENT_SECRET=your-client-secret

Windows (PowerShell):

$env:AZURE_TENANT_ID = "your-tenant-id"
$env:AZURE_CLIENT_ID = "your-client-id"
$env:AZURE_CLIENT_SECRET = "your-client-secret"

Authentication via Azure CLI

If you prefer interactive authentication, you can use Azure CLI:

# Login with Azure CLI
az login

# Set your subscription (if necessary)
az account set --subscription <subscription-id>

Usage

Basic usage

azure-code-signer --vault-url https://your-vault.vault.azure.net/ --cert-name your-cert-name --file path/to/file

Command line arguments

Signing a file

azure-code-signer --vault-url https://your-vault.vault.azure.net/ --cert-name your-cert-name --file path/to/file

This will create a detached signature file at path/to/file.sig.

Verifying a signature

azure-code-signer --vault-url https://your-vault.vault.azure.net/ --cert-name your-cert-name --file path/to/file --verify

Specifying a signature output path

azure-code-signer --vault-url https://your-vault.vault.azure.net/ --cert-name your-cert-name --file path/to/file --output path/to/custom-signature.sig

Working with password-protected certificates

If your certificate in Azure Key Vault is password-protected:

azure-code-signer --vault-url https://your-vault.vault.azure.net/ --cert-name your-cert-name --file path/to/file --pkcs12-password your-password

Certificate Formats

Azure Code Signer automatically handles various certificate formats:

• Certificates in Azure Key Vault (native format)
• PKCS#12 (PFX) format with or without password protection
• PEM format certificates and keys
• Base64-encoded certificates
• Raw certificate data with missing headers

The tool will attempt to detect and convert between formats as needed.

Troubleshooting

Enable verbose logging

For detailed debugging information:

azure-code-signer --vault-url https://your-vault.vault.azure.net/ --cert-name your-cert-name --file path/to/file --verbose

Permission errors

Ensure your Azure account has the following permissions on the Key Vault:

• get permission for certificates
• get permission for secrets

Certificate format issues

If you encounter errors like "Failed to load certificate and/or private key", check:

• Is the certificate in the expected format?
• Does it require a password? (Use --pkcs12-password)
• Does the service principal have access to both certificate and secret?

Authentication errors

If authentication fails:

• Check that environment variables are correctly set and spelled
• Verify the service principal has appropriate permissions
• Try using Azure CLI authentication with az login
• Ensure your client secret hasn't expired

Error: bytearray object cannot be converted to PyBytes

This error is typically resolved by newer versions of the tool. Update to the latest version:

pip install --upgrade azure-code-signer

Security Considerations

• Never commit environment variables with secrets to source control
• Consider using a secure secrets manager to store service principal credentials
• For CI/CD pipelines, use the pipeline's built-in secrets management
• Limit the permissions of your service principal to only what's needed
• Rotate your client secrets regularly

Azure Key Vault Setup

1. Create a Key Vault in Azure Portal
2. Import or generate a code signing certificate
3. Add a secret with the same name as your certificate
4. Grant your user or service principal access to the Key Vault

Contributing

Contributions are welcome! Please open an issue or submit a pull request for any improvements or bug fixes.

License

This project is licensed under the MIT License. See the LICENSE file for more details.