Usage and management of symmetric keys and asymmetric keys (for example, AWS KMS)

Can you explain the difference between symmetric and asymmetric encryption and when you’d typically use one over the other within the context of AWS KMS?

Symmetric encryption uses the same key to encrypt and decrypt data and is faster and more efficient for large amounts of data. Asymmetric encryption uses a pair of keys, a public key for encryption, and a private key for decryption, and is more secure for scenarios like key exchange. In AWS KMS, symmetric keys are generally used for data encryption tasks due to performance benefits, while asymmetric keys are often employed in situations where key exchange or digital signature validation is necessary for additional security layers.

How does AWS KMS help ensure the security and durability of your cryptographic keys?

AWS KMS employs hardware security modules (HSMs) to protect the confidentiality and integrity of keys. It is integrated with AWS CloudTrail to provide logs of all key usage for auditing, and it supports automatic key rotation to enhance security. Also, AWS KMS is designed to be highly available and durable, storing multiple copies of keys across different physical locations within an AWS Region.

What is the process for rotating keys in AWS KMS, and why is this practice important?

Key rotation in AWS KMS involves creating new cryptographic material for an existing key and phasing out the old material without changing the key ID. This practice mitigates the risk of the key being compromised over time, limits the amount of data encrypted with one key version, and helps comply with security best practices and regulatory requirements. AWS KMS supports automatic rotation for AWS managed keys and manual rotation for customer-managed keys.

How are permissions managed for AWS KMS keys, and what is the significance of the ‘least privilege’ principle in this context?

Permissions for AWS KMS keys are managed through IAM policies, key policies, and grants. The least privilege principle is crucial because it ensures that only necessary permissions are granted to users, roles, and AWS services, limiting the potential for unauthorized access or operations on the keys and thereby reducing security risks.

When creating a new customer-managed key in AWS KMS, what considerations should be taken into account in terms of key policy and usage?

When creating a new customer-managed key, you should consider who needs access to the key, what actions they should be allowed to perform, and which AWS services can use it. Ensure that the key policy reflects business and security requirements and adheres to the principle of least privilege, granting only necessary permissions to required entities.

In AWS KMS, how would you securely share an encrypted data key with another party?

You would use the AWS KMS GenerateDataKey API to generate a plaintext data key and its corresponding encrypted version. You can keep the plaintext key in memory, use it to encrypt data locally, and then delete it. To share the key with another party, you send them the encrypted data key. Since only someone with the appropriate KMS permissions can decrypt it, this allows secure key sharing.

What are some ways to ensure high availability and disaster recovery for keys stored in AWS KMS?

AWS KMS is designed for high availability by automatically replicating keys across multiple physical locations within a region. For disaster recovery, you should enable multi-region keys or replicate keys and their policies to other regions, and regularly back up key material and relevant configurations using AWS services like AWS Backup.

Can you explain how AWS KMS supports hybrid encryption and why this approach is beneficial?

AWS KMS supports hybrid encryption by using asymmetric keys to securely transfer a symmetric data key. The asymmetric keys (public/private key pair) are used to encrypt and decrypt the symmetric key, which can then be used to encrypt and decrypt data efficiently. This approach combines the security of asymmetric encryption for key exchange with the performance of symmetric encryption for data processing.

How do you manage the automatic rotation of AWS KMS keys, and what is the default rotation period for managed keys?

Automatic rotation of KMS keys can be managed through the AWS KMS console or APIs by enabling or disabling the key rotation feature. The default rotation period for AWS managed keys is three years, but for customer-managed keys, you need to manually enable rotation, with rotation occurring annually once enabled.

What role do AWS KMS custom key stores play, and what are some situations where you might use them?

AWS KMS custom key stores are used to gain more control over key storage by utilizing an AWS CloudHSM cluster. You might use custom key stores when you have requirements for single-tenant HSMs, need to meet certain compliance standards, or have a policy that mandates the use of dedicated physical hardware for cryptographic operations.

How can you monitor the usage of your KMS keys, and what AWS service would you typically use for this purpose?

You can monitor the usage of KMS keys by enabling AWS CloudTrail, which provides logs for every use of the key, including API calls. This service helps in conducting security analysis, resource change tracking, and compliance auditing.

Discuss the importance of AWS KMS in a multi-account strategy, and how do you use it to manage keys across different AWS accounts?

AWS KMS plays a critical role in a multi-account strategy by allowing central management of keys while enabling secure access across multiple accounts through key policies and cross-account permissions. You manage keys across different AWS accounts by creating resource-based policies that permit other accounts to use certain KMS operations, facilitating consistent and secure encryption practices across an organization’s accounts.