Contemporary Symmetric Ciphers

Jordan University of Science and Technology Computer engineering Department Cryptography & Net release bail CPE (541) HW5 Contemporary Symmetric Ciphers (Double- stilbestrol, Triple-DES & Blowfish) administrate by Dr Loai Tawalbeh Eng. Sulaiman Al-Basheer Simsam R. Hijjawi 20022171043 Review Problems 6. 1 What is the terzetto encryption? It is a triad-stages encryption with three different calls, to avoid costly requirements arises from exploitation three different keys with total space of 356 = 186 bits a trinity encryption with two keys maybe employment. 6. 2 What is the meet in the middle sharpshoot?Its that attack doesnt depend on every particular property of the DES, kind of, it will work against any type of block noughts. For the double-DES cipher & a given (P,C) pit, this attack whole works as follow 1. Encrypt the plain textual matterual matterbook P with all possibilities of K1, store the results in a table, & sort that table by the valuate of X. 2. Decrypt C with all executable cherishs of K2, take aim individually resulted value with the entries in the table, in case of match, check these two keys against an otherwise known pair (P1,C1), if match, accept them as the correct keys. 6. wherefore is the middle portion of 3DES is a decoding rather than an encryption ? 1. Its a decoding process in order to salmagundi the traditional nature of the DES, if its an encryption, itll stay a DES but with long key size. 2. In the cryptography, there is no implication of use the decipherment in the middle stage, the only advantage of doing so is to take into account users of 3DES to decrypt data encrypted by the users of the fourth-year adept DES ( C = Ek1Dk2Ek1P = Ek1P. compute that the middle portion is decryption instead of encryption, ( C = Ek1Ek2Ek1PThe previous assumption in equating 1 will not be ever met. On the other hand 3. If an encryption process is through with(p) instead of decryption the meet-in-the-middle attack bec omes possible. 6. 6 What primitive operations are used in Blowfish? addendum Addition the words, it is performed modulo 232. Bitwise exclusive-OR. Problems 6. 1 For the two creation go aboutes introduced in the textbook, which is the preferred in the succeeding(a)s tint the suggested block cipher in my considerations at a lower place is DES. security. The unity loop compact access code single CBC loop is much catch, this is because the EDE block contains the encryption function C = E k1D k2Ek1P without simplifications, this makes the cryptanalysis like derivative instrument coefficient attack to a greater extent difficult than doing it on a simple loop with encryption or decryption process because to each one loop in the second burn up appears like a simple DES that may be attacked alone in a chosen plain-text attack i. e. derivative instrument attack. performance.The second 3 simple arise is the preferred from the performance wise locate of view, this is because each block in each loop contains each encryption or decryption processes so it is faster than the prototypal climb up. But as I mentioned above, it is more vulnerable to cryptanalysis than the first approach because each loop is a single DES with differential attack possibility. We lav also distinguish between the two approaches based on error propagation. 6. 2 Can you suggest security improvements to either option, using three DES chips & more or less number of XOR functions? Assume you are hushed limited to two keys.Changing the method sounds a good solution 1. For the first approach that contain only a single independent loop, using Counter path seems to be simpler, because we deal with counters that less longer than plain texts & have no analogue or statistical relationship, this may addition the performance of the 3DES in this case. 2. For the second approach, the dependance between stages prevents using the counter mode as an enhancement, a more secure mode is requi red in this case, using the CFB may eliminate the possibility of differential cryptanalysis because chosen plain text attack is not worth. . 4 institute that the puffer decryption is the inverse of the sea squab encryption. Taking in consideration the next The decryption process is applied in the same(p) direction as the encryption but with reverse order use of the sub keys. Encryption 1. Assume the following plain text P with E-PL0 & E-PR0 portions. 2. by and by the ith calendar method, the output of that round will be E-PRi = E-PLi Xor Pi (1) E-PLi = F E-PRi Xor E-PRi-1 (2) 3. The cipher text will be E-PR17 = E-PL16 Xor P18 E-PL17 = E-PR16 Xor P17 C = E-PR17 + E-PL17+ support is a concatenationIt will be the input of the decryption algorithm which is the same as the encryption algorithm but with reverse order key fashion. decipherment 1. Assume the following cipher text C with D-CL0 & D-CR0 portions. 2. After the ith round, the output of that round will be D-CRi = D-CLi X or P19-I . (3) D-CLi = F D-CRi Xor D-CRi-1 . (4) 3. the outputs of equating 1 & equation 3 and equation 2 & equation 4 are the same for each round, this implies the reversibility in the blowfish algorithm between the encryption & the decryption algorithms.