Cryp Essay
4.2 Consider a "CCAtype" extension of the deﬁnition of secure message authentication codes where the adversary is provided with both a Mac and Vrfy oracle. (a) Provide a formal deﬁnition and explain why such a notion may make sense. (b) Show that when the Mac scheme is deterministic, your deﬁnition is equivalent to Definition 4.2. (c) Show that when the Mac scheme may be probabilistic, the deﬁnitions are not equivalent. (That is, show that there exists a probabilistic scheme that is secure by Deﬁnition 4.2 but not by your deﬁnition.) Consideration The message authentication experiment Macforge, Π(n):
1. A random key k ← {0, 1}n is chosen. 2. The adversary is given oracle access to Mack (·) and Vrfyk (·, ·) and outputs a …show more content…
4.3 Prove that Construction 4.5 remains secure for each of the following modiﬁcations: (a) Instead of using a pseudorandom function, use any ﬁxedlength MAC with the appropriate parameters. (b) Instead of including d in every block, set t i = Fk (r b i m i ) where b is a single bit such that b = 0 in all blocks but the last one, and b =

biography of Alan Turing Essay
3963 Words  16 PagesBombe(see below) The people at Bletchley also needed to work out the internal wiring of the wheels but this, at least, would be constant once discovered. At some stage the Germans decided that these sterotyped words were to be avoided( had their cryp.. been heard at last. ?) Told to start and end with some un related word like e.g. lawn mower or clothes cupboard. Now mesages were composed by some one of rank; radio operators sending them neede some brain power but the enigmaa operater only had…

Cryp Essay
1833 Words  8 PagesHomework 5 4.2 Consider a "CCAtype" extension of the deﬁnition of secure message authentication codes where the adversary is provided with both a Mac and Vrfy oracle. (a) Provide a formal deﬁnition and explain why such a notion may make sense. (b) Show that when the Mac scheme is deterministic, your deﬁnition is equivalent to Definition 4.2. (c) Show that when the Mac scheme may be probabilistic, the deﬁnitions are not equivalent. (That is, show that there exists a probabilistic scheme that is…
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