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Thursday, December 8, 2016

[Pwnable.kr/Toddler's Bottle] collision ( Solved 16.12.08 )


# Problem.


  This problem is about the MD5 hash Collision.


# How To Solve.

  first. connect the server ssh col@pwnable.kr -p2222
  and open the col.c using vi.


  look the check_password code. we notice that this code returns a res by adding the input value five times. 
  now at the main part, hashcode == check_password(argv[1]) 
Because the hashcode is 0x21DD09EC, the value of the finished check_password must also be 0x21dd093c.
therefore, we divide 0x21DD09EC by 0x05, the following formula is calculated.

0x21DD093C = 0x6C5CEC8 *5 + 4

Therefore, the value that we need to input to find the flag is as follows.

then, we can find the flag.


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