Ciphers invented before the era of computers and modern cryptographic theory. Classical ciphers typically operate on letters instead of bits and are usually designed to be implemented by hand or using simple mechanical devices.

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Correct way to read a given permutation cipher?

In some literature I am reading – where they are explaining the permutation cipher – they have two examples, which encrypt a small block of text. But they seem to contradict each other: First ...
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471 views

What are requirements for this grille?

I'm trying to program a Cardan grille, but I can't find requirements for grille. In my case, grille is square matrix A with $N$ x $N$ size, and elements are $0$ or $1$ (where $1$ means that it is ...
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1answer
144 views

How hard to break a cipher if it has a different key for each word?

Recently I watched the movie 'The Prestige' again but this time the cipher diary impressed me very well. I like to create my own cipher for my diary because I have some time to kill everyday after ...
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1answer
114 views

Number of different substitution alphabet ciphers possible with given conditions?

If you consider a 26 letter alphabet, and a cipher where 24 of the letters are sent to themselves, and only 2 letters switch, how many different substitution alphabet ciphers are there, and what ...
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1answer
342 views

What is total key space in transposition algorithms

How we can measure key space in transposition algorithms? Should we specify the method, like rail fence?
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1answer
205 views

How to solve custom made ciphers? [closed]

How would you go about solving basic custom made ciphers - e.g. one generated from this website http://www.wikihow.com/Write-a-Custom-Cipher-Carefully? This is solving it without knowing the method ...
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1answer
502 views

Brute forcing Cardan grille

Having a "rotating" square Cardan Grill with sides long n cells, how could i determinate the cost of a brute-force attack? How many configurations should be considered to perform an exhaustive ...
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1answer
201 views

Monoalphabetic cipher key

I'm new to cryptography and have just completed homework on Monoalphabetic cipher. I managed to decrypt the cipher text successfully but I cannot identify the key from my plaintext to ciphertext ...
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1answer
168 views

For calculating the index of coincidence for each sequence

I was learning about the finding the key length reading the following web site... http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-vigenere-cipher/ and I really don't ...
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1answer
250 views

Decrypting an Affine Cipher with known characters

I am trying to cryptanalyse multiple cipher–texts that I know are encrypted by different Affine ciphers. I have already analysed the frequency that each character occurs, and compared it to a ...
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1answer
393 views

Four-Square cipher and its keyspace

Am I thinking about this correctly? Consider that the keyspace of the Playfair cipher is equivalent to all permutations of the alphabet, e.g. the number of distinct permutations of 25 objects, and ...
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1answer
613 views

Cryptanalysing Affine cipher

I am trying to cryptanalyse a cipher–text encrypted by Affine cipher. The encryption formula is: $c = f(x) = (ax+b)\bmod m$, where $a$ and $b$ are unknown constants; $x$ is a plain-text symbol, and ...
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0answers
382 views

Hill cipher key space

Key space is the set of all possible keys that can be used to generate a key. We using the number of valid key to describe it. I've given a hill cipher of block size $k$ over alphabet of size $p$, ...
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2answers
225 views

Strategy to crack a presumed substitution cipher

The ciphertext given is: ejitp spawa qleji taiul rtwll rflrl laoat wsqqj atgac kthls iraoa twlpl qjatw jufrh lhuts qataq itats aittk stqfj cae I've done ...
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1answer
58 views

How secure is this modified Bazeries Cylinder?

This device is a modification of the Bazeries cylinder, it has two stacks of 5 rotors which each bear two alphabets plus numbers 0-9, one in correct order and one in random order ( 36 characters in ...
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1answer
95 views

Which algorithm can be performed by humans?

Suppose I want my grandmother to perform encryption without any help from a computer, and she must encrypt the word 'HELLO' for me. I could ask her to instead of typing the real keys, that she always ...
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1answer
87 views

Different patterns of different paterns, wildcard [closed]

I'm not realy experienced with programming and such but I am wondering if the following could be implemented in, lets say, python we have the following ciphertext sequence ...
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2answers
461 views

What are some approaches to attack an triple key polyalphabetic cipher when the IV key and PT key are known?

The cipher is an triple key polyalphabetic cipher also known as an Quagmire IV by the ACA. An example would be here: Quagmire IV example and info (pardon the ads) I posses the IV key and the PT key. ...
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1answer
47 views

Affine cipher: calculate the key from a known plaintext/ciphertext pair

Suppose I have a ciphertext that I know is encrypted using an affine cipher in $\mathbb{Z}_{26}$. The plaintext begins with es and the corresponding ciphertext is ...
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1answer
171 views

Calculation of time needed to crack DES with my CPU

I have a laptop that has the CPU and the RAMs shown below in the images. My question is that, using this CPU and the RAMs, how much time would it take for me to crack an old school DES algorithm ...
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2answers
130 views

Is the complexity of Caesar (shift) ciphers “n * n!”?

Can we say that any shift cipher to be decrypted needs an algorithm of complexity “n * n!”? (where n is number of possible ...
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1answer
119 views

Help deciphering caesar cipher [closed]

I have to to find the shift value and the message for the following caesar cipher. OC_VAWDGPM_VHWTVX_VXJOCVZ_GDX_MWO_VWIZVYGWIZ_NODI_ I have already tried it and with the shift value of 21 i get the ...
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1answer
80 views

Is the Vigenère Cryptosystem malleable? [closed]

Is the Vigenère Cryptosystem malleable, and how can we prove that it is (or it is not) malleable?
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3answers
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How secure is the Vigenère cipher in file encryption if you encrypt the password first?

I created a basic file encryption method, that seems pretty secure to me (based on an answer below, it seems to be an implementation of the Vigenère cipher) , but one of my colleagues claims that it ...
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2answers
408 views

How weak/strong is this hand cipher? (updated) [closed]

In simple steps here the system: first write text. hand cipher then divide into groups of three letters: han dci phe r then choose a key consisting of three letters, for example ...