Fast password recovery attack: application to APOP

In this paper, we improve the password recovery attack to Authentication Post Office Protocol (APOP) from two aspects. First, we propose new tunnels to control more fixed bits of MD5 collision, hence, we can recover passwords with more characters, for example, as long as 43 characters can be recovered practically. Second, we propose a group satisfaction scheme, apply divide-and-conquer strategy and a new suitable MD5 collision attack, to greatly reduce the computational complexity in collision searching with high number of chosen bits. We propose a fast password recovery attack to application APOP in local that can recover a password with 11 characters in >1 min, recover a password with 31 characters extremely fast, about 6 min, and for 43 characters in practical time. These attacks truly simulate the practical password recovery attacks launched by malware in real life, and further confirm that the security of APOP is totally broken.