what is the primary weakness of the des block cipher
Block cipher Due to a block cipher's characteristic as an invertible function, its output becomes distinguishable from a truly random output string over time due to the birthday attack. This property results in the cipher's security degrading quadratically, and needs to be taken into account when selecting a block size. There is a trade-off though as large block sizes can result in the algorithm becoming inefficient to operate.[28] Earlier block ciphers such as the DES have typically selected a 64-bit block size, while newer designs such as the AES support block sizes of 128 bits or more, with some ciphers supporting a range of different block sizes.[29]
Captain America's shield Captain America's shield is virtually indestructible under normal conditions.[1] While cosmic and magical or godly opponents have broken the shield, the shield proves strong enough to absorb Hulk's strength, and repel an attack from Thor's mystical hammer Mjölnir without any visible damage. Due to its construction of a vibranium and proto-adamantium alloy, it is able to absorb all kinetic energy and transfers very little energy from each impact, preventing Captain America from feeling recoil or transferred impact forces when blocking attacks. This alloy also allows him to deflect adamantium blades without damage to the shield. These physical properties also means the shield can bounce off of most smooth surfaces, ricocheting multiple times with minimal loss in aerodynamic stability or velocity. The shield can also absorb the kinetic impact of a fall, allowing Captain America to land safely even when jumping off of several stories, a demonstrated in Captain America: Winter Soldier.[volume & issue needed]