What access control level can prevent users from retrieving passwords in OpenLDAP?

The correct choice is "none" because setting the access control level to "none" effectively prevents any operations, including the retrieval of passwords, on the specified attributes or entries within OpenLDAP. Access control in OpenLDAP is defined in terms of permissions granted based on LDAP entries and their attributes.

When a user is assigned "none" access control, it means they cannot read, write, or perform any other actions on the protected data, which includes sensitive information like passwords. This is crucial for maintaining security within a directory service, as it restricts unauthorized users from accessing confidential data.

In contrast, other access control levels like "read," "write," and "full" each allow varying degrees of access. "Read" would permit users to read the data, including passwords if they had visibility into the entry, while "write" allows for modification of the data. "Full" would grant complete access for reading, writing, and modifying. Thus, setting access to "none" is the only way to ensure that users cannot retrieve passwords or any other sensitive information, underscoring its role in protecting user credentials and maintaining the integrity of the directory service.