How do you implement a secure key rotation policy and schedule?

1 Why rotate keys?

Key rotation is a good practice for several reasons. First, it reduces the risk of key exposure or theft, as you limit the time window that a key is valid and usable. Second, it increases the security of your data, as you prevent attackers from decrypting old data with a compromised key. Third, it complies with regulatory and industry standards, such as PCI DSS, HIPAA, or GDPR, that require periodic key changes.

2 How often to rotate keys?

The frequency of key rotation varies based on several factors, such as the type of encryption, the sensitivity of the data, the threat level, and the operational costs. Generally speaking, symmetric keys (like AES or DES) should be rotated every 90 days or less, or after encrypting a certain amount of data (like 1 TB). Asymmetric keys (such as RSA or ECC) should be rotated annually or less, or after signing a certain number of messages (like 10,000). Master keys (such as KMS or HSM keys) should be rotated every two years or less, or after generating a certain number of subkeys (like 100). However, it is important to rotate keys more frequently if there is suspicion of a breach, if you are changing your encryption algorithm, or if you have high-risk data.

3 How to rotate keys?

The process of key rotation involves four steps: generating new keys, distributing new keys, switching to new keys, and retiring old keys. Each step must be properly planned and executed to prevent data loss or corruption. When generating new keys, use a secure random number generator (RNG) and store them in a secure location such as a KMS or HSM. Do not reuse old keys or derive new keys from them. When distributing new keys, use a secure channel like TLS or VPN and verify the identity and integrity of the recipients. Do not send new keys via plain text or email. To switch to new keys, use a coordinated and synchronized approach and test the encryption and decryption functionality before and after the switch. Do not switch to new keys during peak hours or without backup. Finally, to retire old keys, use a secure method like shredding or overwriting and revoke their access and permissions. Do not keep old keys indefinitely or reuse them for other purposes.

5 How to handle key rotation challenges?

Key rotation can be difficult due to complexity, compatibility, and cost. To balance the security benefits with the operational impacts and risks, use a centralized and automated system (such as KMS or HSM) to manage your keys, and standard and consistent formats and protocols (such as JSON or KMIP) to exchange them. Additionally, use backward and forward compatible encryption schemes (such as envelope encryption or versioned encryption) to ensure that you can decrypt old data with new keys. Furthermore, employ a risk-based and data-driven approach to determine the optimal key rotation frequency and scope. Lastly, use scalable and efficient encryption methods (such as streaming encryption or compression) to reduce the encryption overhead.