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Questions tagged [ciphertext-only-attack]

A cyphertext-only attack is a form of cryptographic attack in which the attacker possesses only the encrypted message, with no corresponding plain text or segment of the key to work with.

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Is it a cryptographic risk to share the same encrypted data over and over again?

Regular scenario Let's say I have secret files which I will encrypt. The resulting container will be shared and might be intercepted. Not good, but that's okay - that's why I encrypted the data in ...
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Basic Vigenere Cipher

I'm taking my first cryptography course and having trouble deciphering some Vigenere encrypted text. I was able to crack the first one: I'm having difficulty with the other two. I think the ...
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Are ciphertext-only attacks on LFSRs possible?

Reading about LFSR, I know that breaking an LFSR by knowing it's design and having enough (plaintext, ciphertext) pairs is an relatively easy task but let's assume we know the design of LFSR and a ...
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What's the difference between a known-plaintext attack and a ciphertext-only attack in terms of performance?

I know that in the KPA the attacker has access to both the plaintext and the ciphertext, but in the end it all comes down to performing an exhaustive key search. I'm not sure if having the ...
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How to solve encryption with ASCII output

There are lots of text files which have unknown data packets with ASCII output (no available plaintext exists with regard to any ciphertext, I have only encrypted outputs). The input data is known to ...
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Textbook RSA Attacks

Given textbook RSA encryption, if an attacker obtains the ciphertext and has the public key that was used, can he or she decrypt said ciphertext without calculating the private key?
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Why is a known-plaintext attack considered a complete break?

I read somewhere that if a cipher has a known-plaintext attack, then it is considered completely broken. Say there is a cipher that someone uses where the algorithm is understood and a known-...
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How to glean info from a message that simply has the letters shuffled?

Suppose someone had published a several hundred page (sensitive) book, but had randomized all of the letters in an order known only to them (e.g. with a vector of random numbers of the same length as ...
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Any benefit to writing a message as a mix of 2 languages before encryption?

For example, imagine a message that is a mix of Japanese and English words; Japanese in unicode, English in ASCII. Japanese doesn't use spaces between words. The sentence structures, anything ...
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Reversing a known encryption algorithm (4-byte repeating key XOR)

I've been practicing for an upcoming CTF competition, and I've finally reached the cryptography stage. I'm a complete newbie in this field (my knowledge is essentially that bcrypt is awesome and md5 ...
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How to attack polyalphabetic affine cipher with only ciphertext?

How to attack polyalphabetic affine cipher with only the ciphertext? A polyalphabetic affine cipher can be seen as the composition of an affine cipher ($p \mapsto c \equiv a \times p + b \pmod{26})$ ...
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Are the following schemes based on a pseudo-random permutation secure?

I am currently working on the following task: Let F be a pseudorandom permutation. Consider the encryption scheme for the message space $\{0, 1\}^n$ defined as follows: $Gen(1^n)$ chooses ...
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Given a pseudorandom function F, is $(F_k(r) \; | \; F_k(r + 1))$ also a PRF?

Given: F is a pseudorandom function, G is a pseudorandom generator with $l(n) = n+1$. The following schemes should be classified as being insecure, IND-COA secure, IND-CPA secure. To encrypt $m \in \{...
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What do you mean by Ciphertext indistinguishability [duplicate]

Wiki definition : A cryptosystem is considered secure in terms of indistinguishability if no adversary, given an encryption of a message randomly chosen from a two-element message space ...
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Are parts of a pseudorandom string also a pseudorandom string?

I am working on an exercise that encrypts a message using only the first $n$ bits of a pseudorandom generator's output $G(k)$, i.e. $F_k(m) := G(k)_{0...n−1} \oplus m$. $k$ is chosen uniformly at ...
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Deciphering “easy” ciphers without hints

I've been keen on IT Security for a long time now and I've learned a lot about networking & security. However trying a "decryption challenge" I'm lacking what I think is basic encryption/...
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Shared modulus attack on RSA

Consider a scenario in which a group of people use a common modulus $n$ in the textbook RSA crypto system, where $n=pq$, $p$ and $q$ are large distinct prime numbers. Is there any chance for an ...
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cipher text only attacks on deterministic homomorphic encryption schemes

If we consider a set of numbers say a set $s=\{a,b,c,d\}$ , where $a,b,c,d>1$ and the numbers $a, b, c, d$ do not share any relation between them , i.e. for any two numbers, $n_1,n_2\in s$ the ...
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AES key from encrypted text and IV

So I'm trying to figure out if it's possible to extract the private key if you have the ciphertext and the IV corresponding to that ciphertext. It's for some kind of a challenge, and can't really ...
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How does cryptanalysis of the Playfair cipher work?

I have a set of Playfair-enciphered data that I'm trying to crack without the key. I know I need to analyse bigrams; I've currently worked out what decrypts to th, <...
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Known vs. Chosen (plaintext and ciphertext) and RSA

I want to know whether I can break RSA (textbook) with known plaintext/ciphertext attacks. Known plain-text Let $c$ be the ciphertext and $m$ the plaintext. $$c = m^a \mod n$$ Since all I have is ...
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Is knowing the distribution of input domain only way to do cipher text only attacks?

Imagine there is a $n$ bit block cipher. The attacker has harvested some how all possible $2^n$ cipher texts for some given key. Without the knowledge of the distribution of input domain as in ...
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Is it possible to translate a piece of language into your own without knowing the language? [closed]

I understand the the texts within the Voynich Manuscript are of an unknown language, and yet cryptographers are still working on it and still trying to decipher it. Does that mean that it is possible ...
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Attacking historical ciphers methodology

It's more a theoretical question of how would you approach it. All you know about the ciphertext it's was generated with a historical cipher. The ciphertext appears to be random, BUT it's divided into ...
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Ciphertext-only attack on Simplified DES

Is it possible to deduce the plaintext block or the key, given only a Simplified-DES ciphertext block (e.g. c=01110110)? I'm reading Cryptography And Network Security, by William Stallings and I'm bit ...
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How to attack a “many-time pad” based on what happens when an ASCII space is XORed with a letter?

I've already sent my correct solution to a homework exercise from Dan Boneh's Introduction to Cryptography class on Coursera: "Let us see what goes wrong when a stream cipher key is used more than ...
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For public-key encryption, why does COA resistance imply CPA resistance?

My professor told me: If a public-key crypto-system is secure against ciphertext-only attacks, then it is also secure against a chosen-plaintext attack. Why is this true? Is there a proof that ...
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Measuring entropy for a ciphertext only attack

When bruteforcing a password (e.g. the common attacks on DES), where you have ciphertext only, you need a way to assess whether a decrypted plaintext is the right one. I believe the EFF DES machine ...
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Is this “layered” XOR cipher secure?

I am aware of the vulnerabilities of simple xor ciphers and recently I came across a block cipher that claims to solve those vulnerabilities. The cipher goes as follows with both the block and key ...