1
vote
1answer
115 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 ...
3
votes
2answers
133 views

Is there a name for this 'enhanced' caeser shift and if so, is it trivial to break?

This cipher shifts the letter that it will shift to, after each shift... I used to play with this when I was a kid. I was thinking about it recently and realized that it wasn't as simple as I ...
4
votes
1answer
98 views

Question about the definition of a perfect cipher

I need to prove that the following encryption scheme is a perfect cipher: Let $p$ be a prime. The secret key is a pair $(a,b)$ sampled uniformly at random from $\mathbb{Z}_p^* \times \mathbb{Z}_p$. ...
2
votes
2answers
155 views

What is the limit of plaintext required to break the Vigenère encryption?

A theoretical question about the Vigenère cipher: Without any knowledge about the key (not even it's length) can we tell how much known or chosen plaintext is needed for the adversary to completely ...
3
votes
1answer
447 views

Hill-cipher, disordered alphabet

I am going to apply a simple substitution cipher to my input, then encrypt the result with a Hill cipher. How can this be broken, in a chosen-plaintext threat model? In other words, instead of the ...
3
votes
1answer
167 views

Any historical accounts of cryptanalysis of Jefferson's wheel cipher?

David Kahn in his book "The Codebreakers" wrote about Jefferson's wheel cipher, saying that To this day the Navy uses it… (the book was first published in 1967) Are there any historical accounts ...
2
votes
1answer
329 views

Using Chi-Square for Vigenère Cipher

I am writing a program which will use Chi-Square to determine which is the correct keyword for a ciphertext via Vigenère cipher. I came across a website that describes the Chi-Square statistics in a ...
3
votes
2answers
827 views

How can I break a Vigenère cipher with partial plain text?

I have an exercise to do regarding Vigenère encryption. I've got the cipher text: WNZTNVIEEGTJYKRRWYUELWNZTNV and a partial plain text: ...
1
vote
1answer
482 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 ...
4
votes
4answers
1k views

Assistance Cracking Classical Cipher

Below is the cipher text I am trying to break and as you can see its rather short which is why I am having so much trouble. ...
3
votes
1answer
236 views

Has there been any cryptanalysis of RC4-52?

Several websites ( such as Is there a secure cryptosystem that can be performed mentally? ) briefly mention RC4-52 as a modification of standard RC4. RC4-52 has only with 52 instead of 256 elements ...
6
votes
3answers
2k views

Encryption/ciphers/codes in Chinese

I am quite curious as to how you can perform simple encryption for the Chinese language. Saw a similar question related to encryption/Chinese here: About cryptography in a character language, ...
5
votes
1answer
827 views

Example of CHI Square test on Caesar Cipher?

I am trying to get my head round the chi square test, when used with the Caesar cipher. I started off using this formula, $$ X = \sum_{i = 1}^k \frac{f_i · f'_i}{n · n'} $$ Where ...
4
votes
2answers
380 views

How can one break a monoalphbetic substitution chipher at pseudorandom text?

Does anybody know how to break monoalphbetic substitution cipher, if it is applied to some pseudorandom text (for example to some surrogate key filed in a database)? Let us assume that we have only ...
6
votes
3answers
2k 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 ...