Plaid CTF 2012 – Addition is Hard

Addition is hard!
0x0+0x7068703f = ?
Answer in decimal

This is an easy trivia question, it even comes with a hint hidden in the second operand:

$ python2 -c "print ('%x' % 0x7068703f).decode('hex')"

Which refers to PHP bug.

Using an affected PHP binary to compute the sum yields: 3771785342

More info on the PHP bug: https://bugs.php.net/bug.php?id=61095

In case you do not have the affected PHP version you can just do this by hand as well:

7068703f = 1885892671
2 x 1885892671 = 3771785342

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