<Table> <Tr> <Td> </Td> <Td> This section needs expansion with: Impact of key size and block size, discuss time--memory--data trade - offs...You can help by adding to it . (April 2012) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section needs expansion with: Impact of key size and block size, discuss time--memory--data trade - offs...You can help by adding to it . (April 2012) </Td> </Tr> <P> 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 . 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 . </P> <Table> <Tr> <Td> </Td> <Td> This section needs expansion . You can help by adding to it . (April 2012) </Td> </Tr> </Table>

What is the primary weakness of the des block cipher