$1.$ Given two $2$x$2$ matrices: $(10$ points$)$

$($a$).$Verify multiplication of M x N mod $26=$ N x M mod $26=$ I $($identity matrix$)$

$($b$).$ Use Hill cipher to encrypt the message TESTS

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A$$Z is assigned value $025,$

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a $$b$$ c$$ d$$ e$$ f$$ g$$ h$$ I$$ j$$ k$$ l$$ m$$ n$$ o$$ p$$ q$$ r$$ s$$t $$u$$ v $$w $$x $$y $$z

$0001020304050607080910111213141516171819202122232425$

$$t $19,$ e $--4,$ s $--18,$ t $19,$ s $18$

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Break exams into blocks of two characters with last block SQ $($q is a filler character at your choice$)$ and encrypts one block at a time.