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Re: Codebusters C

Posted: September 23rd, 2018, 9:51 pm
by Umaroth
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.

Re: Codebusters C

Posted: September 23rd, 2018, 10:07 pm
by Name
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?

Re: Codebusters C

Posted: September 26th, 2018, 2:55 pm
by Jacobi
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.

As someone said, "Prepare for everything so you're ready for everything."
If no one said that, someone should have.

Re: Codebusters C

Posted: October 4th, 2018, 4:58 pm
by jlordhe
Do you have to be extremely good at math for this event?

Re: Codebusters C

Posted: October 4th, 2018, 6:04 pm
by Unome
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).

Re: Codebusters C

Posted: October 4th, 2018, 6:47 pm
by TheChiScientist
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.

Re: Codebusters C

Posted: October 5th, 2018, 4:00 pm
by cryptoderes
Can someone do a quick walkthrough on how to solve an RSA cipher?

Re: Codebusters C

Posted: October 5th, 2018, 4:31 pm
by UTF-8 U+6211 U+662F
Can someone do a quick walkthrough on how to solve an RSA cipher?
Does this help?

Re: Codebusters C

Posted: October 6th, 2018, 12:24 pm
by cryptoderes
Can someone do a quick walkthrough on how to solve an RSA cipher?
Does this help?
Ah yes, thank you so much!

Re: Codebusters C

Posted: October 6th, 2018, 1:53 pm
by UTF-8 U+6211 U+662F
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 :)