Which of the following is used to ensure a downloaded file has not been altered?

To ensure that a downloaded file has not been altered, a hash is utilized. A hash is a fixed-length string generated by a hashing algorithm from input data, such as the contents of a file. When a file is downloaded, it can be hashed both on the server and on the client-side after downloading. By comparing the two hash values, you can verify whether the file remains unchanged during transmission. If the hash values match, it indicates that the file has not been altered; if they differ, it means the file may have been tampered with.

This method provides a reliable way to detect any changes to the file, such as corruption or malicious modifications, which is crucial for maintaining data integrity. Hash functions are designed to be quick to compute yet hard to reverse-engineer, enhancing security.

In contrast, asymmetric encryption and symmetric encryption are primarily used for securing data in transit and for confidentiality, rather than integrity verification of files. A private key is a component of asymmetric encryption and is not directly related to ensuring the integrity of a downloaded file.