User authentication avoiding exposure of information about enumerable system resources

Abstract

Authentication employs a classification that monitors content of authentication requests and results and assigns and records risk values identifying low-risk sources making normal authentication requests and high-risk sources making abnormal authentication requests indicative of fraud activity. Then for low-risk sources, a normal authentication process is employed having differential success/fail behavior exposing information about an enumerable system resource, such as a user account. Example differential behavior includes (a) granting access when a request identifies a valid user account, and (b) otherwise denying access, enabling an attacker to learn whether a guessed value identifies an existing account. For high-risk sources, a false authentication process is employed having non-differential success/fail response behavior that does not expose the information, such as consistent presentation of a service denial message irrespective of whether the request identifies a valid existing user account, preventing an enumeration attack.