In software engineering, a functional requirement defines a function of a software system or its module used. A function is defined as a set of inputs, the behavior, and outputs. Functional requirements may be calculations, technical details, data handling and processing and other specific functionality that define what a system is supposed to achieve.

Behavioral requirements describing all the cases where the system uses the functional requirements are captured in use cases.Here, the system has to do the following tasks:• Take user id and password along with secret key, match it with corresponding database entries. If a match is found then continue else raise an error message.• Encrypt the file to form a new encrypted file by using an encryption algorithm.• Must be able to retrieve the original file from the encrypted file using the corresponding decryption algorithm.• If any modification is performed on encrypted file, owner of the file should be notified.