564_hasan_chowdhury_Assignment3.doc - Course 60475 Assignment 3 Name Hasan M Chowdhury ID 101938596 Calculation of question Name hasanchowdhury Ascii

# 564_hasan_chowdhury_Assignment3.doc - Course 60475...

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Course # 60475 Assignment # 3 Name : Hasan M Chowdhury ID # 101938596 Calculation of question # Name: hasanchowdhury Ascii and the total: 104 + 97 + 115 + 97 + 110 + 99 + 104 + 111 + 119 + 100 + 104 + 117 + 114 + 121 = 1512 1512 mod 23 = 17 17+1=18 Question # 18 9.18 The problem illustrates a simple application of the chosen ciphertext attack. Bob intercepts a ciphertext C intended for Alice and encrypted with Alice's public key e. Bob want to obtain the original message M = C d mod n. Bob chooses a random value r less than n and computes Unformatted text preview: Z = r e mod n X = ZC mod n t = r 1 mod n Next, Bob gets Alice to authenticate (sign) X with her private key (as in Figure 9.3 ), thereby decrypting X. Alice returns Y = X d mod n. Show how Bob can use the information now available to him to determine M. Solution: Z = r e mod n X = ZC mod n t = r 1 mod n Y = X d mod n Therefore, r = Z d mod n So the computation is as follows: tY mod n = r-1 . X d mod n = r-1 . Z d . C d mod n = r-1 . r . C d mod n = C d mod n = M...
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