BitLocker is a full-disk encryption feature included in recent Windows versions. It is designed to protect data by providing encryption for entire volumes, by using a number of different authentication methods. In this paper we present a solution, named BitCracker, to try the decryption, by means of a dictionary attack, of memory units encrypted by BitLocker with a user supplied password. To that purpose, we resort to GPU (Graphics Processing Units) that are, by now, widely used as general-purpose coprocessors in high performance computing applications. BitLocker decryption process requires the execution of a large number of SHA-256 hashes and also AES, so we propose a very fast solution, highly tuned for Nvidia GPU, for both of them. To evaluate BitCracker performance we made a comparison with oclHashcat and John the Ripper password crackers.