Scream: A software-efficient stream cipher. We report on the design of Scream, a new software-efficient stream cipher, which was designed to be a “more secure SEAL”. Following SEAL, the design of Scream resembles in many ways a block-cipher design. The new cipher is roughly as fast as SEAL, but we believe that it offers a significantly higher security level. In the process of designing this cipher, we re-visit the SEAL design paradigm, exhibiting some tradeoffs and limitations