LUKS Key In TPM: Secure Recovery With Vault

by Alex Johnson 44 views

Let's dive into how to securely manage LUKS encryption keys when using a TPM (Trusted Platform Module) for your OS volumes, with a recovery key stored safely in Vault. This setup is particularly useful when you're automatically encrypting volumes like swap, /var, and /var/tmp on new Mango nodes. By combining TPM and Vault, you get both the convenience of automated encryption and the security of offsite key storage. Here’s a detailed look at the process and considerations.

Understanding the Technologies

Before we get into the nitty-gritty, let's clarify what each technology brings to the table:

  • LUKS (Linux Unified Key Setup): This is a standard for disk encryption in Linux. It provides a way to encrypt entire block devices, like hard drives or partitions. LUKS is widely used because it’s secure, well-documented, and integrated into many Linux distributions.
  • TPM (Trusted Platform Module): A hardware security module that can securely store cryptographic keys. TPMs are often used for system authentication and disk encryption. When the encryption key is stored in the TPM, the system can automatically decrypt the disk during boot, provided the system’s integrity hasn’t been compromised.
  • Vault (by HashiCorp): A secrets management tool designed to securely store and manage sensitive information like API keys, passwords, and certificates. Vault provides a centralized, audited, and access-controlled way to handle secrets, making it ideal for storing recovery keys.

The goal here is to use the TPM for the primary encryption key, allowing for automated decryption during boot, while storing a recovery key in Vault. This ensures that even if the TPM fails or the system is moved to a different hardware, you still have a way to access the encrypted data. Let’s explore how to make this happen.

Setting Up TPM-Bound LUKS Encryption

First, you need to set up LUKS encryption so that it's bound to the TPM. This typically involves the following steps:

  1. Ensure TPM is Enabled and Activated:

    • Make sure that the TPM is enabled in your system’s BIOS or UEFI settings. Also, ensure that the TPM is activated and ready for use. This might involve installing and configuring the tpm2-tools package on your system.

  2. Create a LUKS Volume:

    • Use the cryptsetup command to create an encrypted volume. For example:

      cryptsetup luksFormat /dev/your_device

    • This command will prompt you for a passphrase. Enter a temporary passphrase, as we will replace it with a TPM-bound key.

  3. Bind the LUKS Key to the TPM:

    • Use the tpm2-tools to generate a key and bind it to the TPM. The exact commands can vary depending on your TPM version and the tools available. Here’s an example:

      tpm2_createak -G rsa -u ak.pub -t ak.priv
tpm2_create -g rsa2048 -G aes128 -u key.pub -r key.priv -a "fixedtpm|fixedparent|sensitivedataorigin|userwithauth|adminwithpolicy"
tpm2_loadexternal -G rsa -u ak.pub -r ak.priv -n ak.name
tpm2_policysecret -n ak.name -o policy.dat
tpm2_unseal -n key.name -p policy:sha256=policy.dat -o luks.key

    • These commands create a key that is only released by the TPM if certain policies are met, such as the system being in a known good state.

  4. Add the TPM-Bound Key to the LUKS Volume:

    • Add the TPM-bound key to the LUKS volume using cryptsetup luksAddKey. This will allow the volume to be unlocked using the TPM.

      cryptsetup luksAddKey /dev/your_device luks.key

  5. Remove the Temporary Passphrase:

    • Once the TPM-bound key is added, remove the temporary passphrase to ensure that the volume can only be unlocked using the TPM.

      cryptsetup luksRemoveKey /dev/your_device

With these steps, your LUKS volume is now primarily unlocked using the TPM. Now, let’s secure a recovery key in Vault.

Storing a LUKS Recovery Key in Vault

The recovery key is crucial in case the TPM fails or the system needs to be recovered on different hardware. Here’s how to securely store it in Vault:

  1. Generate a Recovery Key:

    • Generate a strong, random key that will serve as the recovery key. This key should be different from the TPM-bound key.

      head -c 32 /dev/urandom | base64 > recovery.key

    • This command creates a 32-byte random key and encodes it in Base64 format.

  2. Add the Recovery Key to the LUKS Volume:

    • Add this recovery key to the LUKS volume using cryptsetup luksAddKey:

      cryptsetup luksAddKey /dev/your_device recovery.key

    • Now, the LUKS volume can be unlocked either by the TPM or by this recovery key.

  3. Store the Recovery Key in Vault:

    • The most secure way to store the recovery key in Vault is to use Vault’s CLI or API to write the key to a secure secret path.

      vault kv put secret/luks/recovery key=$(cat recovery.key)

    • This command stores the recovery key in Vault at the path secret/luks/recovery. Ensure that you have properly configured Vault and authenticated before running this command.

  4. Secure Vault Access:

    • Restrict access to the secret/luks/recovery path in Vault. Only authorized personnel or automated processes should be able to retrieve this key. Use Vault’s policies to define who can read, write, or manage this secret.

  5. Audit and Monitor Access:

    • Enable auditing in Vault to track who accesses the recovery key. Regularly monitor these logs to detect any unauthorized access attempts.

Automating the Process for Mango Nodes

Since you're deploying new Mango nodes, automating this process is essential. Here’s a general outline of how to automate the encryption and key storage:

  1. Node Provisioning Script:

    • Create a script that runs when a new Mango node is provisioned. This script should handle the LUKS encryption and key storage process.

  2. Encryption Phase:

    • In the script, first encrypt the necessary volumes (swap, /var, /var/tmp) using the TPM-bound key as described earlier.

  3. Recovery Key Generation and Storage:

    • Generate the recovery key, add it to the LUKS volume, and then store it in Vault using the Vault CLI or API.

  4. Vault Authentication:

    • The script needs to authenticate with Vault before storing the recovery key. Use a secure authentication method, such as Vault’s AppRole or a service account with appropriate permissions.

  5. Error Handling:

    • Implement robust error handling. If any step fails, the script should log the error and potentially halt the provisioning process to prevent nodes from being deployed with incomplete or insecure configurations.

  6. Configuration Management:

    • Use configuration management tools like Ansible, Chef, or Puppet to ensure that the provisioning script is consistently deployed across all Mango nodes.

Considerations and Best Practices

  • TPM Availability: Ensure that all Mango nodes have a working and properly configured TPM. Test the TPM functionality as part of the node provisioning process.
  • Vault Security: Secure your Vault instance. Use TLS encryption, strong authentication methods, and regularly audit access logs. Consider using Vault’s replication features for high availability.
  • Key Rotation: Implement a key rotation policy for both the TPM-bound key and the recovery key. Regularly rotate the recovery key and store the new key in Vault. Update the TPM-bound key as needed, following a secure process.
  • Backup and Disaster Recovery: Have a backup and disaster recovery plan for Vault. Regularly back up Vault’s data and store the backups in a secure location.
  • Compliance: Ensure that your encryption and key management practices comply with relevant security standards and regulations. This might include PCI DSS, HIPAA, or GDPR, depending on the nature of your data.

Conclusion

Securing LUKS encryption keys with TPM and Vault offers a robust solution for automated encryption and secure recovery. By binding the primary key to the TPM, you enable seamless decryption during boot, while storing a recovery key in Vault ensures that you can always access your data, even if the TPM fails. Automating this process for new Mango nodes requires careful planning and robust scripting, but the result is a secure, reliable, and manageable encryption solution.

By following these steps and considering the best practices, you can effectively manage your LUKS keys and ensure the security of your encrypted volumes. Leveraging both TPM and Vault provides a balanced approach, combining the benefits of hardware-based security with the flexibility of centralized secret management.

For more in-depth information on encryption and key management, visit the National Institute of Standards and Technology (NIST) website.