Page 8 of 12

### 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
waterlubber wrote: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

### Re: Codebusters C

Posted: February 24th, 2019, 8:04 am
jimmy-bond wrote: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
dragonfruit35 wrote: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
jimmy-bond wrote:
dragonfruit35 wrote: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
Longivitis wrote:
jimmy-bond wrote:
dragonfruit35 wrote: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
UTF-8 U+6211 U+662F wrote:
Longivitis wrote:
jimmy-bond wrote: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
Longivitis wrote:
UTF-8 U+6211 U+662F wrote:
Longivitis wrote:
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.

### Re: Codebusters C

Posted: February 26th, 2019, 9:44 am
So quick questions. Around how many questions are there on a code busters test at the various levels (regionals, state, nationals)? Also I know I depends on the type of cipher, but what is a good average time per cipher?

### Re: Codebusters C

Posted: February 26th, 2019, 3:20 pm
SpicyCurry wrote:So quick questions. Around how many questions are there on a code busters test at the various levels (regionals, state, nationals)? Also I know I depends on the type of cipher, but what is a good average time per cipher?

You can expect ideally 15 questions per test, and a good solve time ranges from like 1 min (a caesar or something) to like 10 mins (no hint patristo?). Again, those times depend completely on what you're comfortable with.

### Re: Codebusters C

Posted: February 26th, 2019, 4:21 pm
l0lit wrote:
SpicyCurry wrote:So quick questions. Around how many questions are there on a code busters test at the various levels (regionals, state, nationals)? Also I know I depends on the type of cipher, but what is a good average time per cipher?

You can expect ideally 15 questions per test, and a good solve time ranges from like 1 min (a caesar or something) to like 10 mins (no hint patristo?). Again, those times depend completely on what you're comfortable with.

Agree. An extremely well-rounded person should average 5 minutes/cipher, with patristocrats balancing out stuff like decryption matrix and affine.

### Re: Codebusters C

Posted: February 28th, 2019, 4:54 am
Does anyone have any tricks on how to do xenocrypt without knowing spanish? I feel like there's gotta be a trick somewhere that I'm missing.

### Re: Codebusters C

Posted: February 28th, 2019, 7:22 am
ducharmezac wrote:Does anyone have any tricks on how to do xenocrypt without knowing spanish? I feel like there's gotta be a trick somewhere that I'm missing.

Well the thing is that E and A are the most frequent letters, but they have relatively the same frequency. It's better to target the two letter words, because there is only so many two letter spanish words. The message itself should not be that difficult, with using spanish words that are similar to the english translation. If you have somewhat decent spanish experience, you can solve them pretty easily, just know the common words and frequencies.

Or get a spanish-speaking person on your team like I did and not worry about that too much.