Use this tag for questions about cryptographic algorithms which were invented (and used) before the computer age.
12
votes
4answers
547 views
Can an Enigma-style cipher of sufficient complexity be considered secure in today's world?
Regarding the German Enigma machines, if I recall correctly, the reason they were defeated was because the Allies were able to generate a massive database of possible rotor settings, and because the ...
12
votes
2answers
809 views
What are the main weaknesses, if any, of a Playfair cipher?
What are the main weaknesses, if any, of a Playfair cipher?
I know that they depend on none of the letters missing, but that is an easy fix if a letter gets dropped. Besides that, are there any other ...
7
votes
1answer
3k views
How does the index of coincidence work in the Kasiki test?
I'm starting to learn about cryptanalysis and I am having a bit of difficulty understanding the Kasiski test's index of coincidence. I have a book (Cryptography Theory And Practice by Douglas Stinson) ...
7
votes
4answers
486 views
Cracking WWII-era codes - code found on a pigeon's leg in Surrey
A recent BBC article entitled WWII code 'may never be cracked' posted a code:
AOAKN HVPKD FNFJW YIDDC
RQXSR DJHFP GOVFN MIAPX
PABUZ WYYNP CMPNW HJRZH
NLXKG MEMKK ONOIB AKEEQ
WAOTA RBQRH DJOFM TPZEH
...
6
votes
1answer
378 views
How to deduce enigma settings given a partial plaintext?
Assuming some large block of text is encrypted with an enigma machine and I only know a small subset of letters before and after encryption, how do I go about figuring out the enigma settings from ...
5
votes
2answers
902 views
How to attack a classical cipher using known partial plaintext?
I have a ciphertext generated by a classical cipher. I do not know what was cipher used to generate it. I do however have the beginning of the plaintext.
What are the cryptanalysis approaches for ...
5
votes
2answers
385 views
Using a mono-alphabetic substitution cipher with a different language per word
How much harder is it to determine the secret key for a mono-alphabetic substitution cipher, if each word is translated into a different language before the cipher is applied?
EDIT
If somehow ...
5
votes
1answer
101 views
+50
How to build an electro-mechanical public key cipher machine?
It is generally assumed that asymmetric encryption schemes were invented in 1973 at GCHQ in Britain and, independently, in 1976 at the MIT.
Imagine, if the abstract idea of having a public key and a ...
3
votes
3answers
378 views
Alphabetic Substitution with Symbols
I was reading on a site about the Zodiac Killer and how he used a basic substitution cipher, but instead of substituting english letters and characters he substituted symbols.
I was wondering, if you ...
3
votes
1answer
233 views
What is the best method to determine the language used in a monoalphabetic substitution cipher?
Working on a cipher (which I assume to be a mono-alphabetic substitution cipher due to the letter frequency) I struggle with the fact that I don't know which language the plain text is written in. ...
2
votes
2answers
314 views
How to get the keyword from a keyword cipher?
I was given a ciphertext and now I am trying to break it via looking for the keyword.
This is a keyword cipher. So:
PlainEnglish: ABCDEFGHIJKLMNOPQRSTUVWXYZ
If ...
1
vote
2answers
196 views
Kryptos : K1. What is the origin of the “palimpsest” keyword?
I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4.
I understand that the keyword "palimpsest" was reverse-engineered using the tableau (and brute-force computer processing), ...
0
votes
0answers
12 views
Can two cipher letters per plaintext letter easily defeat character frequency analysis?
For a class 5 years ago I wrote a paper about defeating character frequency analysis by using two cipher letters per plaintext letter. I didn't get much feedback from the professor so I wonder if ...
