Codebusters C

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Re: Codebusters C

Postby Umaroth » September 23rd, 2018, 9:51 pm

Since it isn't specified in the rules, does anyone know how test writers unwittingly giving us non invertible Hill cipher matrices will be prevented? This would probably cause a lot of frustration among teams.
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Re: Codebusters C

Postby Name » September 23rd, 2018, 10:07 pm

Umaroth wrote:Since it isn't specified in the rules, does anyone know how test writers unwittingly giving us non invertible Hill cipher matrices will be prevented? This would probably cause a lot of frustration among teams.

For a 2x2 cipher in order to be invertable ad-bc mod 26 has to be coprime to 26
Under the current rules I don't think we have to invert 3x3s?
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Re: Codebusters C

Postby Jacobi » September 26th, 2018, 2:55 pm

Name wrote:
Umaroth wrote:Since it isn't specified in the rules, does anyone know how test writers unwittingly giving us non invertible Hill cipher matrices will be prevented? This would probably cause a lot of frustration among teams.

For a 2x2 cipher in order to be invertable ad-bc mod 26 has to be coprime to 26
Under the current rules I don't think we have to invert 3x3s?



Eh... I would say yes.

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Re: Codebusters C

Postby jlordhe » October 4th, 2018, 4:58 pm

Do you have to be extremely good at math for this event?
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Re: Codebusters C

Postby Unome » October 4th, 2018, 6:04 pm

jlordhe wrote:Do you have to be extremely good at math for this event?

Not for most ciphers. There are a few that require significant math background (e.g. Hill cipher).
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Re: Codebusters C

Postby TheChiScientist » October 4th, 2018, 6:47 pm

Unome wrote:
jlordhe wrote:Do you have to be extremely good at math for this event?

Not for most ciphers. There are a few that require significant math background (e.g. Hill cipher).

Most ciphers just require studying and memorization. Make sure you know your alphabet very well. ;) As Unome said only a few require actual number crunching.
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Re: Codebusters C

Postby cryptoderes » October 5th, 2018, 4:00 pm

Can someone do a quick walkthrough on how to solve an RSA cipher?

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Re: Codebusters C

Postby UTF-8 U+6211 U+662F » October 5th, 2018, 4:31 pm

cryptoderes wrote:Can someone do a quick walkthrough on how to solve an RSA cipher?

Does this help?

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Re: Codebusters C

Postby cryptoderes » October 6th, 2018, 12:24 pm

UTF-8 U+6211 U+662F wrote:
cryptoderes wrote:Can someone do a quick walkthrough on how to solve an RSA cipher?

Does this help?


Ah yes, thank you so much!

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Re: Codebusters C

Postby UTF-8 U+6211 U+662F » October 6th, 2018, 1:53 pm

cryptoderes wrote:
UTF-8 U+6211 U+662F wrote:
cryptoderes wrote:Can someone do a quick walkthrough on how to solve an RSA cipher?

Does this help?


Ah yes, thank you so much!

Just make sure you know encryption and decryption :)

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Re: Codebusters C

Postby Jacobi » October 16th, 2018, 8:36 am

Any tips on solving monoalphabetic ciphers?

Also, can you get a good score without a team member who knows Spanish?

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Re: Codebusters C

Postby Name » October 16th, 2018, 9:23 am

Jacobi wrote:Any tips on solving monoalphabetic ciphers?

Also, can you get a good score without a team member who knows Spanish?



I still need to work on monoalphabetic, but as far as I can tell word patterns are really useful. For example being able to recognize something like xaxybcdxyx as everywhere forms a good basis to work off of.
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Re: Codebusters C

Postby gneissisnice » October 16th, 2018, 11:56 am

Jacobi wrote:Any tips on solving monoalphabetic ciphers?

Also, can you get a good score without a team member who knows Spanish?


Keep an eye out for common words. Frequently appearing three-letter words are commonly "the" or "and", so trying to figure those out can be a good starting point. Single-letter words are really nice since they're almost always "a" or "I" (could technically be "O' I guess if it's a poem or something, but that's rare).

Also keep in mind what the most frequent letters in the alphabet are. If you see a letter appearing frequently, it's likely to be E T A O I N or S, which are some of the most common letters. It's probably not Q X J or Z, haha.

According to the rules, "no more than one" puzzle can be in Spanish for Regionals or Invitationals, so that's likely a pretty small portion of your score, if it appears at all. For States, I think it's "at least one" so that becomes much more important, but I would imagine that the question itself is a bit easier to compensate for the fact that it's in a Spanish. I guess if you really practice, you could probably do reasonably well even without knowing Spanish as long as you know the rules of the language. In the end, I doubt it's going to be a killer, though I suppose that might be what separates the very top teams at States and Nationals.
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Re: Codebusters C

Postby MacintoshJosh » October 18th, 2018, 1:16 pm

Letters can't replace themselves in the key for substitutions right? For example, E -> E.

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Re: Codebusters C

Postby Anomaly » October 18th, 2018, 1:35 pm

MacintoshJosh wrote:Letters can't replace themselves in the key for substitutions right? For example, E -> E.

The rules say that in the aristocrats, patristocrats, and xenocrypts, letters can not encrypt to themselves, so yes that can not happen in the ciphers mentioned earlier.
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