Telematic/Audiovisual Syst./Communication Syst. Engineering

Systems Architecture

September 2017 - January 2018

16.9.5.  Emergency: We need the password to enter


  • Folder Crack_passwd in your space shared with Subversion.

Work Plan

A phone call arrives to SAUCEM Inc. from a customer in Singapur that just installed one of your application in the company mobile phones (about 100 of them). The application requires a 9 digit user identifier and a password to enter. The passwords are always the same because they are generated by the application based on the 9 digits of the identifier. The customer has lost the document with the correspondence between the identifiers and the keys, and therefore, none of the 100 mobile phones can use this application.

Luckily, you have the file checkentry.c in the folder Crack_passwd with the code used to read an identifier, a key and compare it with the generated one. Here is the plan:

  • Compile and execute the checkentry.c program in the folder Crack_passwd. Use your NIA (student ID) for these tests.

  • You cannot, I repeat cannot, modify the code.

  • Use the debugger to analyze what is done in the program and obtain the set of chars that make the generated password.

  • It would be great to be able to modify some variables while the program is running using the debugger. Find out how to do such thing.

  • Once you have the key to enter with your student Id, show the execution to the teacher.


Upload a file with name keys.txt in the Crack_passwd folder in your work space containing the keys that you guessed.