Invitation to Computer Science 8th Edition

Published by Cengage Learning
ISBN 10: 1337561916
ISBN 13: 978-1-33756-191-4

Chapter 8 - 8.3 - Encryption - Practice Problems - Page 412: 3b

Answer

\begin{array}{l} {\text { Step } 1 . \text { Apply the S mapping to }(U\ L) \text { to get }(21\ 12) .} \\ {\text { Step } 2 . \text { Multiply result times } M^{\prime} :(21\ 12) \times\left[\begin{array}{cc}{23} & {5} \\ {2} & {23}\end{array}\right]} \\ {\qquad=(21 \times 23 +12 \times 2\ \ \ \ \ 21 \times 12+23 \times 3)=(507 \ \ 381) \rightarrow(13\ \ 17)} \\ \\ {\text { Step } 3 . \text { Apply $S^{\prime}$ to $(13\ 17)$ to get $(M\ Q)$} } \end{array}

Work Step by Step

\begin{array}{l} {\text { Step } 1 . \text { Apply the S mapping to }(U\ L) \text { to get }(21\ 12) .} \\ {\text { Step } 2 . \text { Multiply result times } M^{\prime} :(21\ 12) \times\left[\begin{array}{cc}{23} & {5} \\ {2} & {23}\end{array}\right]} \\ {\qquad=(21 \times 23 +12 \times 2\ \ \ \ \ 21 \times 12+23 \times 3)=(507 \ \ 381) \rightarrow(13\ \ 17)} \\ \\ {\text { Step } 3 . \text { Apply $S^{\prime}$ to $(13\ 17)$ to get $(M\ Q)$} } \end{array}
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