Cryptanalysis of Bifid

[Anonymous]

I have been looking through several websites, however, I can not understand how to decrypt it or even find the period of a given cipher! Please can someone explain it to me / point me in the direction of good website that will explain it.

[Anonymous]

Hi, {snip} is a very useful website that should help you solve the bifid cipher. ‘Variance’ is just some kind of mathematical statistical term kind of thing, I don’t really understand what it means but it really helps.

Once you’ve found the period, cracking the cipher is still a little difficult but if you can implement simulated annealling then it can be solved very quickly.

[Anonymous]

Wait, are you sure it is Bifid cipher though?

[Anonymous]

A Bifid cipher includes numbers and this challenge doesn’t include 1 number

[Anonymous]

True – but in the general interest of cryptanalysis, is there an easy way to determine the period for a Bifid?

[Anonymous]

The final stage of an encypted bifid contains no numbers, and i’m not referring to the current challenge. I merely wish to try to implement a python program to decrypt a Bifid, so that I am prepared if it comes up. Thanks for trying to help with the snipped website, A, I think I know the one you mean, and I’ve been reading it more closely and It’sstarting to make sense now.

[Anonymous]

Ciphertext from Bifid-enciphered text should just be letters, but it does use the polybius square so there should be no Js in the ciphertext (though if it does contain Js, they could just be nulls intended to make cryptanalysis difficult). This is probably a general question being asked by someone who is preparing for challenge 7 and 8.

Anyway, a quick Google search yielded the first result with a page explaining how to find the period and then finish solving it. Try looking a bit more. Coming here asking for help doesn’t seem much use as the admins will often block posts that explain how to decipher things, or posts that have links to sites that explain cryptanalysis too.

[Anonymous]

Bifid ciphers don’t necessarily need numbers, you can convert.

[Anonymous]

Sorry for snipping the website. Unfortunately most websites which explain ciphers, also include the option to decode the cipher, and we can’t be advertising those (for obvious reasons).

[Author]

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