Network Management - Quiz 5 Assignment Example | Topics and Well Written Essays - 250 words

Network Management - Quiz 5 - Assignment Example A strong encryption algorithm is needed such that even if an opponent who knows the algorithm and has access to one or more cipher-texts would be unable to decipher the cipher-text or figure out the key. The secrecy of the key should be maintained and only known to only the source and the destination and protect an attacker from knowing the key. If an opponent knows the secret key then the symmetry cryptosystem is compromised. The attacker also knows the encryption algorithm, which means that he can generate the decryption algorithm by simply reversing the encryption algorithm. Therefore, knowing the encryption algorithm translates into knowing the decryption algorithm. Chosen-cipher-text can be termed as a special form of the chosen-plaintext analysis since the attacker selects the cipher-text together with its corresponding plaintext, thus the plaintext is chosen indirectly. The plaintext block is divided into two halves, L and R. The two halves of the data pass through n rounds of processing and then combine to produce the cipher-text block. The 64-bit plaintext goes through an initial permutation (IP) that rearranges the bits to produce the permuted input. A phase consisting of sixteen rounds of the same function follows, which involves both permutation and substitution functions. Substitution is performed on the left half of the data by applying a round function F to the right half of the data and then taking the exclusive-OR (XOR) of the output of that function and the left half of the data. A sequence of plaintext elements is replaced by a permutation of that sequence. No elements are added or deleted or replaced in the sequence, rather the order in which the elements appear in the sequence is changed. The permutation function implemented in each round is the same but the sub-key changes in each round. Each of the sixteen rounds produces a sub-key by the combination of a left shift and permutation. The output of the last (sixteenth) round