(Application of linearity)
(Can Eve decrypt the message without finding the inverse of the secret matrix?)
 
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= Application of linearity =
 
= Application of linearity =
 
== How can Bob decrypt the message? ==
 
== How can Bob decrypt the message? ==
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Assuming that Matrix A is what Alice wants to say, and matix B is a 3-by-3 matrix to encrypt Alice's message, and matrix C is the encoded messange.
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It can be expressed A*B=C.
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In order to find A, Bob needs to find the inverse matrix of B.
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A*B*B`= C*B`, A*I=C*B'
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After that, he needs to calculate C*B`. By finding its corresponding order in the alphabet, He can figure our what she wants to say.
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== Can Eve decrypt the message without finding the inverse of the secret matrix? ==
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No, There is no way to decrypt the message without finding the inverse of the secret matirx.
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== What is the decrypted message corresponding to (2, 23, 3)?
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A*B=C
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<math>A^{-1}*A*B=A*C</math> 
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<math>I*B=A^{-1}*C</math>
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<math>B=A^{-1}*C</math>
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A= <math>\left[ \begin{matrix}2 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 3\end{matrix}
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\right]</math> <br>
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C= <math>\left[ \begin{matrix}1 & 0 & 4 \\ 0 & 1 & 0 \\ 1 & 0 & 1\end{matrix}
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\right]</math> <br>
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B = <math>\left[ \begin{matrix}-2/3 & 0 & 4 \\ 0 & 1 & 0 \\ 2/3 & 0 & -1\end{matrix}
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\right]</math> <br>
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A=<math>\left[ \begin{matrix}2 & 23 & 3 \end{matrix} \right]</math> * <math>B^{-1}</math>
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A=<math>\left[ \begin{matrix}2 & 23 & 5 \end{matrix} \right]</math>
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So, it is "BWE"

Latest revision as of 12:40, 19 September 2008

Application of linearity

How can Bob decrypt the message?

Assuming that Matrix A is what Alice wants to say, and matix B is a 3-by-3 matrix to encrypt Alice's message, and matrix C is the encoded messange.

It can be expressed A*B=C.

In order to find A, Bob needs to find the inverse matrix of B.

A*B*B`= C*B`, A*I=C*B'

After that, he needs to calculate C*B`. By finding its corresponding order in the alphabet, He can figure our what she wants to say.

Can Eve decrypt the message without finding the inverse of the secret matrix?

No, There is no way to decrypt the message without finding the inverse of the secret matirx.

== What is the decrypted message corresponding to (2, 23, 3)?

A*B=C

$ A^{-1}*A*B=A*C $

$ I*B=A^{-1}*C $

$ B=A^{-1}*C $

A= $ \left[ \begin{matrix}2 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 3\end{matrix} \right] $


C= $ \left[ \begin{matrix}1 & 0 & 4 \\ 0 & 1 & 0 \\ 1 & 0 & 1\end{matrix} \right] $


B = $ \left[ \begin{matrix}-2/3 & 0 & 4 \\ 0 & 1 & 0 \\ 2/3 & 0 & -1\end{matrix} \right] $


A=$ \left[ \begin{matrix}2 & 23 & 3 \end{matrix} \right] $ * $ B^{-1} $


A=$ \left[ \begin{matrix}2 & 23 & 5 \end{matrix} \right] $

So, it is "BWE"

Alumni Liaison

Ph.D. 2007, working on developing cool imaging technologies for digital cameras, camera phones, and video surveillance cameras.

Buyue Zhang