Questions tagged [chosen-plaintext-attack]

The attacker can specify his own plain text and encrypt or sign it.

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How do you prove an encryption scheme is IND-CPA or IND-CCA?

I know for proving a scheme is not IND-CPA or not IND-CCA you can construct an Adversary which has an unfair advantage in an experiment/game, but how would you prove a scheme is IND-CPA or IND-CCA?
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How to crack unknown 8-bit encryption algorithm?

Can anyone tell me how to crack the encryption of 8 bit algorithm, when you have some clue that CBC mode is used, but the algorithm is secret. You also have some encrypted data (chosen plain text), ...
464 views

Differences between OWP and OWF and their IND-CPA security

I am learning about one way permutations and one way functions and am not sure of the differences if there are any. Also in the random oracle model are they both IND-CPA secure?
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Is there any IND-CPA secure stream cipher with a “standard” hardness assumption?

I've read our recent question: "One-time pad using RSA and Diffie-Hellman functions" which asks about the security of a particular way to convert RSA and discrete exponentiation into a stream cipher. ...
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Breaking One Time Pad with CCA

I was taught that: although OTP is CPA secure, it is not the case with CCA. I'm trying to figure how to break OTP with CCA by showing how it fails the IND test. ...
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Recover secret $x$ when $c\equiv m^x \pmod p$ with public $p$ (modified)

Given an encryption system where $c\equiv m^x \pmod p$, $p$ is a known prime, 1. Is it possible to recover $x$ with a known plaintext attack? Given $(p,\text{factorization of }\varphi(p),m,c)$ 2. Is ...
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Is EFS vulnerable to chosen plaintext attack?

I have some backup files encrypted with EFS, but I lost the EFS certificate--thus I am unable to decrypt the files. I understand that EFS uses the user certificate public key to encrypt the symmetric ...
2k views

Construct IND-CPA secure encryption scheme by combining two given schemes

I have two encryption schemes $\Pi_0, \Pi_1$, at least one of them is IND-CPA secure but I don't know which one. The task is to construct a scheme $\Pi$ that is guaranteed to be CPA secure and to ...
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Why is only one oracle + challenge-response phase sufficient for IND-CPA security?

The CRYPTUTOR wiki from UIUC uses the following definition of the IND-CPA game: We (privately) choose a key K according to the key generation algorithm: K $\gets \mathsf{KeyGen}$. We (...
6k views

Finding key of AES in ECB mode

How many plaintext-ciphertext pairs would be needed to guess with probability, say $p=0.5$, the key $k$ of AES under ECB mode? Most of the articles that I found tried attacks on single plaintext-...
671 views

Security game oracle queries

Concerning private key (symmetric) IND-CPA game definition: Attacker $A$ queries the encryption oracle polynomial number of times. $A$ sends the challenger $C$ a message pair $m_0$ and $m_1$. $C$ ...
748 views

Creating own ciphertext after a padding oracle attack?

I've written a script that breaks a cipher text based on a padding oracle for an assignment, but was wondering how I would continue on to create my own cipher text with any plain text I desired? ...
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How can IND-CPA encryption be identity revealing?

This is problem 10 of Chapter 4 "Symmetric Encryption" (pdf) from Lecture notes by Bellare and Rogaway: An IND-CPA secure encryption scheme might not conceal identities, in the following sense: ...
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What is the difference between CPA and IND-CPA?

I am writing a paper and I got comments from the reviewer that I don’t really understand. Is there any difference between a CPA (Chosen Plaintext Attack) and IND-CPA (Indistinguishability under ...
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Challenge-Response Phases in IND-CPA

The IND-CPA game has two challenge-response phases A key is generated by running $Gen(1^n)$ and challenger selects a bit b {0,1} uniformly at random. Adversary gets input $1^n$. Can query the oracle ...
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CPA and pseudorandom generator

Just started learning about Cryptography and Network Security in general, and I can't seem to grasp the understanding of the following question. Please correct me if I am misunderstanding anything. ...
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Modified version of a CPA-secure encryption scheme

The following encryption scheme: choose a random string $r \leftarrow \{0,1\}^n$ and compute the ciphertext $c= \thinspace <c_0, c_1>= \thinspace <r, F_k(r) \oplus m>$, assuming $F$ a PRF; ...
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How to prove that the Permutation cipher is not CPA secure?

Encryption scheme is called a permutation cipher if every plaintext string with letters $a_1,\ldots, a_n$ is encrypted as $a_{\pi(1)}, \ldots, a_{\pi(n)}$ for some (not necessarily uniform) ...
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Chosen plain text and chosen ciphertext definitions clarification

I am trying to understand a concept of CPA and CCA attack and I cannot get one thing from the definition. If an attacker can execute a CPA attack for something like Send 100 dollars to attacker that ...
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CPA-security proof of “l-padded RSA” encryption scheme

The 10.9 exercise from the Katz-Lindell textbook creates a lot of confusion, let me state it here. Consider the following experiment for an algorithm $A$ and a function $l$ with $l(n) \leq 2n-2$ for ...