Passwords are not generally stored in plaintext form. crypt() is a one way hash function that expects a plaintext password and a salt value for input and then outputs a hash with the salt value prepended to it. This hash is mathematically irreversible ,meaning that it is impossible to determine the original password using only the hash. So if user wants to authenticate user will enter the password and then hash corresponding to that password will be generated ,and if the hash matches with the hash stored in file ,then user entered the correct password .In this way without storing the password in plaintext form we can have authentication here. With this mechanism ,we can think of that the even encrypted password stored in the file is useful ,so we can have a dictionary attack here by hashing each word in the wordlist and compare it with the hash stored in the file ,so in this way we can crack the password. Dictionary Attack program will just needs to read word from file ,hash each...