This is a straightforward reversing problem. The program asks for a large number of command line arguments, each one a single byte. It then performs checks on them, three characters at a time. Here is the first check in Hopper.
The program only checks 3 bytes at a time, and performs the same calculations, only requiring different results for each one. This checks were solved using z3, giving us the flag.
from z3 import *
def solve(a1, a2, a3):
a = Int('a')
b = Int('b')
c = Int('c')
s = Solver()
s.add(b + a - c == a1)
s.add(a - b + c == a2)
s.add(b - a + c == a3)
assert s.check() == sat
m = s.model()
return chr(m[a].as_long()) + chr(m[b].as_long()) + chr(m[c].as_long())
res = solve(81, 53, 87)
res += solve(90, 156, 66)
res += solve(98, 140, 92)
res += solve(38, 170, 60)
res += solve(29, 161, 69)
res += solve(163, 27, 69)
res += solve(147, 43, 59)
res += solve(146, 86, 44)
res += solve(67, 89, 75)
res += solve(117, 125, 125)
print res