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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _calcCTRBUF(self):
 """Calculates one block of CTR keystream"""

        self.ctr_cks = self.encrypt(struct.pack("Q", self.ctr_iv)) # keystream block
        self.ctr_iv += 1
        self.ctr_pos = 0