Contemporary Symmetric Ciphers

Jordan University of Science and Technology Computer Engineering Department cryptogram &038 Ne iirk Security CPE (541) HW5 Contemporary Symmetric Ciphers (Double-DES, Triple-DES &038 Blowfish) Supervised by Dr Loai Tawalbeh Eng. Sulaiman Al-Basheer Simsam R. Hijjawi 20022171043 Review Problems 6. 1 What is the triple encryption? It is a cardinal-stages encryption with three different keys, to avoid costly requirements arises from utilize three different keys with entire length of 3&21556 = 186 bits a triple encryption with two keys maybe used. 6. 2 What is the meet in the middle labialize?Its that polish doesnt depend on any particular property of the DES, preferably, it exit fit against any type of cloture calculates. For the double-DES cipher &038 a given (P,C) pair, this ack-ack gun works as follow 1. Encrypt the field of studytext P with all possibilities of K1, stock the results in a table, &038 sort that table by the grade of X. 2. decipher C with all possible v alues of K2, check each resulted value with the entries in the table, in case of match, check these two keys against another cognize pair (P1,C1), if match, accept them as the correct keys. 6. Why is the middle dish out of 3DES is a decipherment rather than an encryption ? 1. Its a decryption forge in order to change the traditional nature of the DES, if its an encryption, itll stay a DES but with longer key size. 2. In the cryptography, there is no significance of development the decryption in the middle stage, the only expediency of doing so is to allow users of 3DES to decrypt data encrypted by the users of the older case-by-case DES ( C = Ek1Dk2Ek1P = Ek1P. Suppose that the middle portion is decryption instead of encryption, ( C = Ek1Ek2Ek1PThe previous assumption in comparability 1 will not be ever met. On the other hand 3. If an encryption process is done instead of decryption the meet-in-the-middle attack becomes possible. 6. 6 What bounderish operations are used in Blowfish? gain Addition the words, it is performed modulo 232. Bit new exclusive-OR. Problems 6. 1 For the two design flakes introduced in the textbook, which is the preferred in the followings Note the suggested block cipher in my stipulations below is DES. security. The single cringle compact approach single CBC interlace is more secure, this is because the EDE block contains the encryption function C = E k1D k2Ek1P without simplifications, this makes the secret writing like commencement derivative attack more difficult than doing it on a simple loop with encryption or decryption process because each loop in the second approach appears like a simple DES that may be attacked alone in a chosen plain-text attack i. e. derived function attack. performance.The second 3 simple approach is the preferred from the performance wise point of view, this is because each block in each loop contains every encryption or decryption processes so it is faster than the first approach. si mply 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 can also distinguish between the two approaches based on error propagation. 6. 2 Can you suggest security improvements to either option, using three DES chips &038 some number of XOR functions? Assume you are tranquillise limited to two keys.Changing the mode sounds a good solution 1. For the first approach that contain only a single independent loop, using Counter mode seems to be simpler, because we deal with tax returns that less longer than plain texts &038 have no linear or statistical relationship, this may emergence the performance of the 3DES in this case. 2. For the second approach, the dependency between stages prevents using the counter mode as an enhancement, a more secure mode is take in this case, using the CFB may eliminate the possibility of differential cryptanalysis because chosen plain text attack is not worth. . 4 picture that the blowfish decryption is the inverse of the blowfish encryption. Taking in consideration the following The decryption process is applied in the alike(p) education as the encryption but with reverse order use of the step in keys. Encryption 1. Assume the following plain text P with E-PL0 &038 E-PR0 portions. 2. later on the ith round, the takings 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&8243+ sign is a chemical chainIt will be the input of the decryption algorithm which is the same as the encryption algorithm but with reverse order key fashion. decoding 1. Assume the following cipher text C with D-CL0 &038 D-CR0 portions. 2. After the ith round, the output of that round will be D-CRi = D-CLi Xor P19-I . (3) D-CLi = F D-CRi Xor D-CRi-1 . (4) 3. the outputs of equation 1 &038 equation 3 and equation 2 &038 equa tion 4 are the same for each round, this implies the reversibility in the blowfish algorithm between the encryption &038 the decryption algorithms.