Secure Hash Algorithm 256 (SHA-256) is a cryptographic hash function designed to ensure data integrity. It processes a digital document of any size and produces a unique, fixed-length 256-bit "hash" or "digest." If even a single bit in the original document is altered, the resulting hash will be completely different. By comparing the original hash with a newly computed hash of the document, one can reliably verify that the document has not been tampered with. This property makes it ideal for detecting unauthorized modifications and ensuring the integrity of digital files.

A. Data Encryption Standard (DES): DES is a symmetric-key encryption algorithm designed for confidentiality, not integrity. It is also considered insecure for modern applications.

C. Advanced Encryption Standard (AES): AES is a symmetric-key encryption algorithm that provides confidentiality by scrambling data. Its primary function is not integrity verification.

D. Rivest-Shamir-Adleman (RSA): RSA is an asymmetric algorithm used for encryption or creating digital signatures. While digital signatures provide integrity, RSA itself is the public-key mechanism that signs a hash, not the algorithm that creates it.

1. National Institute of Standards and Technology (NIST). (2015). FIPS PUB 180-4, Secure Hash Standard (SHS). This publication defines the Secure Hash Algorithms, including SHA-256. Section 4, "SECURE HASH ALGORITHMS," states their purpose is to generate a condensed representation of a message, known as a message digest. The security of the algorithm ensures that "it is computationally infeasible to... find two different messages that hash to the same value." This property is fundamental to integrity verification. (Available at: https://doi.org/10.6028/NIST.FIPS.180-4)

2. Katz, J., & Lindell, Y. (2014). Introduction to Modern Cryptography (2nd ed.). Chapman and Hall/CRC. Chapter 5, "Hash Functions and Applications," explains that a primary application of cryptographic hash functions is for verifying data integrity. It details how comparing a stored hash value with a freshly computed one can detect any modifications to a file.

3. Rivest, R. L. (2006). Lecture Notes, 6.857 Computer and Network Security. MIT OpenCourseWare. Lecture 7, "Hashing," describes the properties of cryptographic hash functions, including collision resistance, which is essential for integrity. It explicitly contrasts hashing for integrity with encryption for confidentiality. (Available at: https://ocw.mit.edu/courses/6-857-computer-and-network-security-spring-2017/resources/lecture-7-hashing/)

4. National Institute of Standards and Technology (NIST). (2001). FIPS PUB 197, Advanced Encryption Standard (AES). This document specifies the AES algorithm. The introduction (Section 1) clearly states that "This standard specifies the Rijndael algorithm... for use by Federal departments and agencies to protect sensitive information," establishing its primary purpose as confidentiality. (Available at: https://doi.org/10.6028/NIST.FIPS.197)