Improvement On Password Cracking Methods Based On Dictionaries

In the field of security, all the possible password cracking methods have to be taken into account to create a secure password. The study of password cracking methods can promote the development of encryption and authentication systems.First of all, the BRT3 method based on dictionaries is presented to crack hash encryption algorithms. This method combines the TY table structure and the rainbow table algorithm. First, this method uses optimal table structure to generate the pre-computed rainbow tables; then the pre-computed tables are structured and sorted; finally when given an end point, a hash search process will be performed to find the right password.When in a real attack, the BRT3 method can achieve a 50% reduction in the storage requirement and an 11% increase in the success rate compared to the rainbow table method. It also can achieve a 32% reduction in the storage requirement and a 9% increase in the success rate compared with another improved rainbow table method.This thesis also presents the IPCPT method to crack general encryption algorithms, which can learn and extract the features in the passwords. First, this method adds the character alternative technologies to expand the rules of John the Ripper; secondly, the method extracts the keyboard-pattern password and gets the structure division probability in the trainning process; finally, this method generates the guesses according to the context-free gammer and the priority queue.When compared to the password cracking using probabilistic context-free grammars methods, the IPCPT method can achieve a 300% increasing in the coverage of the test set and a 2500% increasing in the the number of guesses. Compared with the password cracking method based on structure division probability, it can achieve a 20% increasing in the coverage of the test set and a 300% increasing in the number of guesses.