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Authors:
James F. Kurose, Keith W. Ross
Chapter:
Security In Computer Networks
Exercise:
Problems
Question:5 | ISBN:9780132856201 | Edition: 6

Question

Consider the block cipher in Figure 8.5. For a given “key” Alice and Bob would need to keep eight tables, each 8 bits by 8 bits. For Alice (or Bob) to store all eight tables, how many bits of storage are necessary? How does this number compare with the number of bits required for a full-table 64- bit block cipher?

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Answer

(a)      For Alice and Bob to store all eight tables how many bits of storage are necessary?

  • # of table*size each entry  

= 8*2^8*8

= (2^3)(2^8)(2^3)

= 2^14 bits

(b)      How does this number compare with the number of bits required for a full-table 64-bit block cipher? (3 pts) (Referenced)

  • Bits 2^14 bits are far smaller if compared with the number of bits required for a full table 64 bit block cipher (2^71)
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