Gchq can you crack it solved

The government organisation, Government Communications Headquarters, is responsible for intelligence and security in the UK. They aim to disrupt threats to the country such as terrorism and cyber warfare by using technology and coding.

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Poppy Logo. FB house promo. It is bare code which you can't just run on any modern OS. I could have added headers to it but I decided to write cyber. I used mmap to map a padded version of the code so I could get the code and the stack under my control and examine it after the code had exited:.

Running the code, it seemed to be early terminating - needing 0x or "BBBB" on the end to continue according to this bit of code:. I tried padding with "BBBB" and it core dumped this time. After studying the disassembly some more and experimenting I noted that it needed "BBBB" and a 4 byte length. Running that it appears to decrypt something on the stack this time, so I'm getting somewhere. But what to decrypt? I needed a string starting with "BBBB".

I recursively downloaded the entire website and grepped it for "BBBB" without success. However on really close examination of a hex dump of cyber. That string "QkJCQj I then modified cyber. After it had ran I examined the stack in the cyber. I saw this:. The downloaded file 15bde1ffaade5d0b It has a very realistic and amusing initial commment!

It also says "stage 2 of 3" which is the first indication how long this challenge is going to be. Otherwise it seems a reasonably straightforward job to implement the VM and I got cracking on vm.

Note that it has 8 bytes of 'firmware' which don't seem to fit in anywhere which is a bit puzzling. Wasted a lot of time trying to get the VM to work. Tried poking the firmware in various imaginitive places.

Found a few bugs then finally re-read the doc again - Ah-ha it is 16 byte segment size, not a 16 bit register Found this in the memory in final. I looked in dafe15cbd4ceecfbdaa5. It seems to be using the cygcrypt dll from cygwin and the crypt function. I then set John the Ripper and crack off on it for good measure to find the encrypted password.

John the Ripper found the password cyberwin in 2 hours. The easy one was my test to make sure it was working:. After installing cygwin with the "crypt" package which has the correct dll in, I copied cygcrypt The exe now runs and gives:. Looking through the keygen. The first hint as to who set this puzzle!

Putting "gchqcyberwin" into the license. Alastairkendall Offline. Jepcb25 Offline. Reply to Alastairkendall. NOP Offline. Me Offline. Peter Offline. Dancereden Offline. Reply to Peter. ExTraTor Offline. It should be this or something similar….

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