What does a checksum help verify?

A checksum is a value derived from the contents of a file, created through a mathematical algorithm that generates a unique string of characters based on the data. This value can be used to verify the integrity of that file. When a file is transmitted or stored, its original checksum can be calculated and compared against a checksum calculated later. If the two checksums match, it indicates that the file has not been altered, providing assurance that the file remains intact and unmodified. This is particularly important for detecting unauthorized changes that may occur due to malicious activity, errors during transmission, or data corruption.

The other options do not directly relate to the purpose of a checksum. For instance, while software installations could potentially be verified with checksums, the direct focus of a checksum is not on installation correctness but rather on the integrity of the data itself. Authenticity of user credentials typically involves different mechanisms such as hashing passwords, while network connection speed is unrelated to checksums, instead being measured by bandwidth and latency considerations. Thus, the usage of a checksum is specifically centered on confirming that a file has not been maliciously altered.