What is the main purpose of using a hashing algorithm in password storage?

The main purpose of using a hashing algorithm in password storage is to secure passwords by storing their hash value. When a password is hashed, it is transformed into a fixed-size string of characters that appears random and is irreversible. This means that the original password cannot be easily retrieved from the hashed value, which significantly enhances security.

Storing only the hashed value provides a protective measure such that even if an attacker gains access to the password database, they would only obtain the hash, not the actual passwords. This makes it much more challenging for unauthorized users to access the original passwords, as they would need to employ techniques such as brute force or dictionary attacks to attempt to discover the original input that resulted in the hash they have.

Additionally, hashing algorithms are designed to be fast to compute for legitimate users, while being time-consuming for attackers attempting to guess from many different possibilities. This further strengthens the protection of the stored passwords, making option D the best choice in this context.