Encryption is a method of transforming data in a way that makes it unreadable without a secret key necessary to decrypt the data back into plaintext. Encryption is one of the most common and effective ways to protect data at rest, as it prevents unauthorized access, modification, or theft of the data. Encryption can be applied to different types of data at rest, such as block storage, object storage, databases, archives, and so on. Hashing, tokenization, and segmentation are not methods of rendering data at rest unreadable, but rather of protecting data in other ways. Hashing is a one-way function that generates a fixed-length output, called a hash or digest, from an input, such that the input cannot be recovered from the output. Hashing is used to verify the integrity and authenticity of data, but not to encrypt it. Tokenization is a process that replaces sensitive data with non-sensitive substitutes, called tokens, that have no meaning or value on their own. Tokenization is used to reduce the exposure and compliance scope of sensitive data, but not to encrypt it. Segmentation is a technique that divides a network or a system into smaller, isolated units, called segments, that have different levels of access and security. Segmentation is used to limit the attack surface and contain the impact of a breach, but not to encrypt data at rest. References: CompTIA Security+ Study Guide: Exam SY0-701, 9th Edition, pages 77-781; Protecting data at rest - Security Pillar3
