Shared Encryption Keys: Risks & Solutions

TL;DR

Using the same encryption key for multiple systems is a very bad idea. If one system gets compromised, all systems using that key are instantly vulnerable. This guide explains why and how to fix it.

Why Sharing Keys Is Dangerous

1. Single Point of Failure: Imagine one lock opening every door in your house. If someone copies that key, they have access to everything. Shared encryption keys are the same – compromise one system and you’ve compromised them all.
2. Increased Attack Surface: Each system protected by the shared key represents another potential entry point for attackers. The more systems, the higher the risk.
3. Compliance Issues: Many security standards (like GDPR, PCI DSS) explicitly require unique keys for different applications and data sets.
4. Key Rotation Difficulties: If you need to change the key (which is a good security practice), you have to update it on every system simultaneously – a logistical nightmare prone to errors.

How to Fix It: Unique Keys for Each System

The solution is simple: each system should use its own, unique encryption key.

1. Key Generation: Use a strong random number generator to create keys. Don’t hardcode them!
• For example, using OpenSSL:

  openssl rand -base64 32

  (This generates a 32-byte key encoded in base64.)

2. Key Management System (KMS): This is the best approach for larger deployments. A KMS securely stores and manages your keys.
   • Examples include AWS KMS, Azure Key Vault, HashiCorp Vault.
   • These systems often provide APIs to access keys programmatically.
3. Individual System Key Storage: If you don’t have a KMS:
   • Store keys securely on each system (e.g., using encrypted configuration files). Never store them in plain text!
   • Use appropriate file permissions to restrict access.
4. Key Rotation: Regularly change your encryption keys.
   • Automate this process whenever possible.
   • Consider a schedule (e.g., every 90 days).
5. Separate Keys for Different Purposes: Don’t use the same key for encrypting data at rest and data in transit.
   • Use different keys for database encryption, file encryption, network communication (TLS/SSL), etc.

Practical Examples

Let’s say you have a web server and a database server.

1. Web Server: Generate a unique key for encrypting session cookies or sensitive data processed by the web application.
2. Database Server: Generate a separate, unique key for encrypting the database contents (Transparent Data Encryption – TDE).

Checking for Shared Keys

If you suspect shared keys are in use, investigate your configuration files and code repositories. Look for identical key values across multiple systems.

• Configuration Files: Search for common key filenames or patterns (e.g., encryption_key, secret.key).
• Code Repositories: Use a code search tool to find instances of the same key string in your codebase.