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| Teaching Since: | May 2017 |
| Last Sign in: | 398 Weeks Ago, 5 Days Ago |
| Questions Answered: | 66690 |
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MCS,PHD
Argosy University/ Phoniex University/
Nov-2005 - Oct-2011
Professor
Phoniex University
Oct-2001 - Nov-2016
Consider a Feistel cipher composed of sixteen rounds with a block length of 128 bits and a key length of 128 bits. Suppose that, for a given , the key scheduling algorithm determines values for the first eight round keys, , k1,k2, … k8 , and then sets
k9= k8, k10= k7, k11= k6, … ,k16= k1
Suppose you have a ciphertext . Explain how, with access to an encryption oracle, you can decrypt and determine using just a single oracle query. This shows that such a cipher is vulnerable to a chosen plaintext attack. (An encryption oracle can be thought of as a device that, when given a plaintext, returns the corresponding cipher text.
The internal details of the device are not known to you and you cannot break open the device. You can only gain information from the oracle by making queries to it and observing its responses.)
Hel-----------lo -----------Sir-----------/Ma-----------dam-----------Tha-----------nk -----------You----------- fo-----------r u-----------sin-----------g o-----------ur -----------web-----------sit-----------e a-----------nd -----------and----------- ac-----------qui-----------sit-----------ion----------- of----------- my----------- po-----------ste-----------d s-----------olu-----------tio-----------n.P-----------lea-----------se -----------pin-----------g m-----------e o-----------n c-----------hat----------- I -----------am -----------onl-----------ine----------- or----------- in-----------box----------- me----------- a -----------mes-----------sag-----------e I----------- wi-----------ll