Encryption is a fundamental principle for securing data in the cloud. Within the cloud's shared responsibility model, the customer is responsible for protecting their data. Since the customer does not control the physical infrastructure, encryption serves as the primary technical control to ensure data confidentiality and integrity. By encrypting data at rest (while stored on disks) and in transit (as it moves across networks), the data remains unreadable and protected from unauthorized access, even in the event of a breach of the underlying cloud infrastructure. This principle is a cornerstone of modern cloud security frameworks and compliance standards.

A. Implementing strong physical security measures is the responsibility of the Cloud Service Provider (CSP), not the cloud customer, as defined by the shared responsibility model.

C. Using complex passwords is a specific identity and access management control, but it is not as foundational a principle for data protection as encryption.

D. Limiting access from specific IP addresses is a network-level control tactic, not a universal, core principle for securing the data itself in all cloud environments.

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1. National Institute of Standards and Technology (NIST). (2011). Special Publication 800-144: Guidelines on Security and Privacy in Public Cloud Computing.

Section 6.3, Data Protection, Page 29: "Organizations should ensure that data is protected while at rest, in transit, and in use... Cryptographic mechanisms are the primary means of providing this protection." This document establishes encryption as the main tool for data protection in the cloud.

2. Cisco. (2020). Cisco SAFE Reference Guide.

Chapter: Cloud Security, Section: Data Security: This guide emphasizes that a key capability for securing cloud data is "Data encryption (in transit, at rest, in use)." It positions encryption as a core component of Cisco's security architecture for the cloud.

3. Chow, R., et al. (2009). Controlling Data in the Cloud: Outsourcing Computation without Outsourcing Control. Proceedings of the 2009 ACM workshop on Cloud computing security.

Section 3.1, Encryption: "The most basic protection for data confidentiality is encryption... Data should be encrypted when it is sent to the cloud, and should be stored encrypted in the cloud." This peer-reviewed paper highlights encryption as the most fundamental protection mechanism. (DOI: https://doi.org/10.1145/1655008.1655020)