Tuesday, 26 February 2013

Cracking Postgres Passwords


This article is a brief overview of using HashCat to recover a Postgres 8.4 password.

Hash Format

The format for Postgres is md5(secret || username) where || denotes string concatenation. 


HashCat as a tool is more traditionally associated with oclHashCat-lite and oclHashCat-plus, which delegates the work to the GPU, significantly increasing the cracking speed.

At this point, I am using HashCat because of it's simplicity and flexibility in attack modes and hashing algorithms, however, most of what is written here could be translated for a suitably configured oclHashCat-lite and run on the GPU.

Retrieving the Hashes

In Postgres, if you have read access to pg_roles, you can simply use:

SELECT username,passwd FROM pg_roles;

This will show you a result like:

   usename   |               passwd                |
 postgres    | md50f7e63611a98a9936285c7d609b044da |

The field "md50f7e63611a98a9936285c7d609b044da" is the md5 hash. Simply strip it down to just the hash (removing the "md5" from the front to), and that is what you're attacking.

Using HashCat

If you download HashCat from their site, you'll likely be able to follow these instructions exactly, but these instructions were written using HashCat v0.42.

First, you must make a hash file:

echo 0f7e63611a98a9936285c7d609b044da:postgres > hashfile

Then you may run HashCat:

./hashcat-cli32.bin -m 10 hashfile -a 3 ?a?a?a?a?a?a

The flags we're using are as follows:
  • -m 10 : Use the hashing scheme md5(pass.salt)
  • -a 3 : Use the brute-force attack mode.
  • ?a?a?a?a?a?a?a : Search all passwords up to 7 characters from the character set [a-zA-Z0-9] + symbols.


Mine is still running vs. a password of my choosing, but after around 10 minutes, HashCat reported that it was now trying to crack all 6-character passwords and would take on the order of 16 hours to try them all.

HashCat's current status is that it's trying 12.22M words on my CPU every second. I'll update this blog when real results are found. I suspect at this rate, I'll give up after a couple of days, as all 7 character passwords will take on the order of 2 months.


Having finished running HashCat on my machine with the above arguments, the search finished after a full 15 hours, however, it did not find the password, as it was longer than 6 chars. For this experiment, I mainly wanted to confirm that I could get HashCat to run and attempt to crack a password. The hash given above is for a *very* long password, that actually has more entropy than an MD5 hash!

Wednesday, 6 February 2013

Doing Passwords Wrong with PayPal

What They've Done Wrong

PayPal do a lot to argue that their system is secure, however, their outward-facing practices don't necessarily live up to their own hype. If you can't make a security conscious user feel secure about their password policy, how do you think that one might feel about them having my EMV card details?

Let's look at the problems with their passwords.

Minimum Length

PayPal's minimum length is too low at 8 chars. This gives the minimal password an entropy of approximately 38-bits. Most folks can brute-force that on their phone these days. Even DES thought that 56-bits was good enough in '77. Times have changed (no, they haven't gone backwards!)

Maximum Length

They enforce a maximum length which is too low (it exists!?): 20 chars. This gives the absolute maximum entropy of a password of around 132 bits. I like to make my passwords around 256 bits. It's 2013, let me make a passphrase that's more than 20 characters, it's not that big of a performance hit!

No Copy Paste

In my opinion, this is a huge sin. As a person who uses a password manager, I use an application to generate a very long (~257 bits of entropy), very random password. I then copy and paste this password (having never seen it) into the password field.

This allows me to easily avoid re-using passwords across multiple sites, and ensures that I always pick a strong password.

Allowing Bad Passwords

PayPal does not (client-side!) check if the password you have types is a bad password. In fact, it allows 'password' and '12345678' as passwords. Yes it labels these as "weak", but it doesn't prevent you using them.

Dense Strength Checker

The strength checker offers a false sense of security. I can make it claim an 8 character password is strong. It simply is not! Even the best 8 character password is at most 53-bits of entropy.

What They Should be Doing

  • Minimum length: 12 chars
  • No Maximum Length
  • Allow Copy/Paste for users who use password managers (such as myself)
  • DropBox keeps a list of really bad passwords, and warns against them by checking client-side.

How To Deal With This

you only (unfortunately) have two options:

  • Complain to PayPal. I already have done, and I'll post the follow up.
  • Leave PayPal.
If PayPal don't correct these simple issues, I will most likely be leaving PayPal, as I do not trust them with my details if they can't manage passwords correctly.