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### Re: Codebusters C

Posted: February 23rd, 2019, 8:30 pm
Anyone know about "ideal" calculators? Basically, the most digits (and with a memory, hopefully) that you can cram into a four-function. RSA is...calculationally demanding, to say the least.

### Re: Codebusters C

Posted: February 23rd, 2019, 9:20 pm
Anyone know about "ideal" calculators? Basically, the most digits (and with a memory, hopefully) that you can cram into a four-function. RSA is...calculationally demanding, to say the least.
I don't do this event but what part of the RSA are you using your calculator most for? It seems like given small primes, it shouldn't be that bad

### Re: Codebusters C

Posted: February 23rd, 2019, 11:42 pm
On a practice test, I had the question "Encode DREW BREES using the keyword VEAR." It displayed VEAR as a 2x2 matrix, so this is clearly a Hill cipher problem. I tried encrypting it as I would a normal Hill cipher but got a different answer than the answer key. I'm pretty sure I did it wrong, so can someone explain to me how to do this problem and the solution you get? Thanks.

### Re: Codebusters C

Posted: February 24th, 2019, 7:43 am
Thank you all for your answers to my questions from before!

### Re: Codebusters C

Posted: February 24th, 2019, 8:04 am
On a practice test, I had the question "Encode DREW BREES using the keyword VEAR." It displayed VEAR as a 2x2 matrix, so this is clearly a Hill cipher problem. I tried encrypting it as I would a normal Hill cipher but got a different answer than the answer key. I'm pretty sure I did it wrong, so can someone explain to me how to do this problem and the solution you get? Thanks.
Which way did you write the DREW BREES matrix? With the letters readable horizontally or vertically?

### Re: Codebusters C

Posted: February 24th, 2019, 9:14 am
Which way did you write the DREW BREES matrix? With the letters readable horizontally or vertically?
Idk how to put a matrix but I did

D R
E W
B R
E E
S

### Re: Codebusters C

Posted: February 24th, 2019, 2:13 pm
Which way did you write the DREW BREES matrix? With the letters readable horizontally or vertically?
Idk how to put a matrix but I did

D R
E W
B R
E E
S
It's supposed to be
D
R
E
W
B
R
E
E
S
(Z)

and then multiply by the 2x2 matrix keyword

### Re: Codebusters C

Posted: February 24th, 2019, 2:48 pm
Which way did you write the DREW BREES matrix? With the letters readable horizontally or vertically?
Idk how to put a matrix but I did

D R
E W
B R
E E
S
It's supposed to be
D
R
E
W
B
R
E
E
S
(Z)

and then multiply by the 2x2 matrix keyword
You can't multiply those two matrices. They don't line up. It's supposed to be
the VEAR matrix multiplied by $\begin{vmatrix}D\\R\end{vmatrix}$
and then the VEAR matrix multiplied by $\begin{vmatrix}E\\W\end{vmatrix}$
etc., etc., I believe.

Although annoyingly, it's not evenly split into chunks of 2 so you'd have to insert an extra letter at the end.

### Re: Codebusters C

Posted: February 24th, 2019, 6:29 pm
Idk how to put a matrix but I did

D R
E W
B R
E E
S
It's supposed to be
D
R
E
W
B
R
E
E
S
(Z)

and then multiply by the 2x2 matrix keyword
You can't multiply those two matrices. They don't line up. It's supposed to be
the VEAR matrix multiplied by $\begin{vmatrix}D\\R\end{vmatrix}$
and then the VEAR matrix multiplied by $\begin{vmatrix}E\\W\end{vmatrix}$
etc., etc., I believe.

Although annoyingly, it's not evenly split into chunks of 2 so you'd have to insert an extra letter at the end.
Yeah, that's what I meant guess I really wasn't clear enough.

### Re: Codebusters C

Posted: February 24th, 2019, 6:33 pm

It's supposed to be
D
R
E
W
B
R
E
E
S
(Z)

and then multiply by the 2x2 matrix keyword
You can't multiply those two matrices. They don't line up. It's supposed to be
the VEAR matrix multiplied by $\begin{vmatrix}D\\R\end{vmatrix}$
and then the VEAR matrix multiplied by $\begin{vmatrix}E\\W\end{vmatrix}$
etc., etc., I believe.

Although annoyingly, it's not evenly split into chunks of 2 so you'd have to insert an extra letter at the end.
Yeah, that's what I meant guess I really wasn't clear enough.
Yeah, UTF is right, it should be $\begin{vmatrix}D\\R\end{vmatrix}$ $\begin{vmatrix}E\\W\end{vmatrix}$ $\begin{vmatrix}B\\R\end{vmatrix}$ $\begin{vmatrix}E\\E\end{vmatrix}$ $\begin{vmatrix}S\\Z\end{vmatrix}$ multiplied by the encryption key, in whichever orientation they gave it to you, to be clear.