Which service provides secure cryptographic key storage within the AWS Cloud?

AWS Key Management Service (KMS) is designed to provide secure cryptographic key storage and management within the AWS Cloud. It allows users to create, import, and manage keys used to encrypt data across a range of AWS services and applications. KMS includes features such as fine-grained access control, audit logs, and integration with other AWS services, making it a powerful option for organizations that need to manage encryption keys securely and efficiently.

On the other hand, AWS CloudHSM is a hardware security module that allows customers to manage their own encryption keys while providing a dedicated appliance for cryptographic operations. Although it provides a high level of security, it's designed for specific use cases that require physical or virtual HSMs, making it less comprehensive than KMS for general key management.

AWS Certificate Manager focuses on managing SSL/TLS certificates to secure communication, which is different from key storage and management. Lastly, Amazon GuardDuty is a threat detection service that continuously monitors for malicious activity and unauthorized behavior, but it does not relate to key storage.

Overall, AWS KMS stands out as the service specifically tailored for secure cryptographic key storage, making it the most appropriate choice in this context.