![]() The behavior you are observing is due to the way integer overflow is handled in numpy. You will still experience integer wrapping, but at least the operation will be accurate. If you want understandable behaviour, you should at least use float64 here. So you are using it outside of its acceptable precision zone: and here things are clear: everything going outside of the mantissa is silently dropped. This type only has a 24 bits mantissa (ref: IEEE 754). Long story made short: INT_MAX 1 gives INT_MIN. In common implementations (specifically in the ones used by numpy) integer types use 2-complement for negative values, and process overflow by reinterpreting the value as if it was unsigned, do the operation as unsigned (meaning wrapping around 2**32 for a 32 bits types) and convert back the unsigned representation to the signed type. But for example np.int32 is a C-like 32 bits integer and has nothing to do with a multiprecision Python integer.Īnd C language clearly states that overflow over a signed type invokes a so called Undefined Behaviour (anything can be expected.). If you’re Brisbane based, or find yourself here be sure to check out SecTalks.Numpy is not Python! Numpy is a bunch of C library interfaced with the Python language. I hope this helped you to better understand integer overflows. group ( 2 )) overflow = int (( 2 ** 32 destination ) / multiplier ) # encode and transferĬlient. search ( '(\d ) = (\d )', decoded ) multiplier = int ( match. search ( '', decoded ): continue # select integers and store into capture groups If SENTINEL in decoded : break # skip loop until we see our X * Y = Z line Print ( decoded ) # our flag contains flag, once it's revealed print recevied data and exit decode ( 'utf-8' ) # print out response packet recv ( MAXBUF ) data = chunk if len ( chunk ) < MAXBUF : break # store decoded data for future usageĭecoded = data. connect ( CTF_BOT ) while True : data = b '' # receive and store data Import socket import re import operator import sys MAXBUF = 4096 SENTINEL = 'flag' CTF_BOT = ( '', 43981 ) if _name_ = '_main_' : client = socket. Putting this boilerplate together looks like the following: #!/usr/bin/python3 We can use regular expressions to identify this packet stream from the equals sign, and then split our values out into capture groups using another expression. ![]() They’re both present on the line reflected as: Splitting our variables out of the calculation is quite easy. We’ve also been asked in the banner of our connection to limit our calculations to 4 bytes, so we’ll make sure we limit what we request at a time. First is forming an open connection and identifying our destination and multiplier from the data that comes back. There are a few core processes to this part of the exercise. Manual answers are great, but this is classified as a coding challenge, not a mathematical one! Under some circumstances, we would then be able to pipe our answer into a new ncat session but since our variables change on each connection we need to do this manually to verify it’s correct: This generated the answer of 536875645 as follows: To generate our answer, I used the following: python - c 'print((2**32 destination)/multiplier)' ![]() I turned this into a proof of concept by generating a new ncat session, which asked the following: Solve for X, where:
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