Why John the Ripper is so slow with simple password?

Question

I'm using John the Ripper version 1.7.8 on Linux Ubuntu to crack Linux user passwords as an exercise. I run the Linux on a virtual machine. I created a user called "User1" to the system and set a password "axby" for it. Then I got the password hash with the usual command:

root@machine:~# unshadow /etc/passwd /etc/shadow > filetocrack

Then I run John with command:

root@machine:~# john filetocrack

As I'm writing this question the program has run like 30 minutes trying to guess a simple 4-letter password. Is this normal? Or have I done something wrong? Any suggestions to speed things up would be appreciated.

Solution

Yes, that is pretty common since John uses either a Dictionary Attack or Brute-force. Neither of which are terribly fast, especially against many modern hashing algorithms running on a single thread (running some hashes is expensive, as @DavidSchwartz mentions).

John without arguments also uses pretty slow methods, from the FAQ:

Q: How long should I expect John to run?

A: It primarily depends on the cracking mode(s) and on your password files (in particular, the type of hashes and the number of different salts, if applicable). Most importantly, you should note that the "incremental" mode, which a default John run (with no command line options) proceeds with after being done with the quicker checks, is not supposed to terminate in a reasonable time.

One option to try to squeeze out better performance is to enable parallelization with --fork=N (N is number of processes) or --node. See the options list for details on those.

Theoretically, if you have two threads running semi-intelligently - your execution time should be cut in ~half. (Note the qualifier "theoretically", YMMV in the real world)

Comments

[David Schwartz]

Your system probably uses a very secure password hash that makes each trial expensive. What are your JtR speed metrics?

[JZ555]

175 comparisons per second on the average. I don't know much about the security of the password hash. When I run John it says: "Loaded 1 password hashes with 1 different salts (generic crypt(3) [?/64])". Does that say anything to you?

[David Schwartz]

At 175 comparisons per second, even if it knew the password consisted of precisely four lower case letters, it would still take 43 minutes to try them all.

[JZ555]

So basically what happens with my password is that John tries searching it very slowly from the dictionary and after 20 minutes or so the incremental mode kicks in. But without any restrictions the incremental mode is pretty much useless since the logic is to start testing with 8-letter words. Maybe I should just try another tool for the job... Any suggestions?

[nerdwaller]

Are you going for speed or simply academic reasons of verifying your own security? I can give any great suggestions other than running in parallel and being more explicit in John's parameters.