in 2011, a group of german researchers released an attack on csa as used in the dvb system. by noting that mpeg-2 padding frequently requires long series of zeroes, leading to entire 183-byte cells being encrypted with zeroes only, it is possible to build up a rainbow table recovering the key from such a known-zero block. (a block would be known to be zero if two blocks with the same ciphertext were found, since presumably both would be zero blocks.) the attack described would require about 7.9 tb of storage, and enable an attacker with a gpu to recover a key in about seven seconds with 96.8% certainty. however, the attack is only effective when such all-zero padding blocks are present (i.e., in scenes with very little movement or noise), and it would be easily mitigated by for instance sending such all-zero cells unencrypted.