After having talked to Alfred follow the same path towards the exit from Bane's HQ. return to the sewers [Park Row - Sewers] and listen to the police communication concerning the appearance of the Firefly near the Pioneers Bridge. Use the glue grenade on the water reservoir again, jump onto the small platform and make it over to the other end of the reservoir, using the claw. After you reach the other end, [Park Row - Sewers Access] your character will automatically select from the inventory the Cryptographic Sequencer. Position the crosshair within the orange circle and hold down the key/button displayed on the screen to decrypt the transmission.