Questions tagged [chosen-ciphertext-attack]

A chosen-ciphertext attack (CCA) is an attack model for cryptanalysis in which the cryptanalyst gathers information, at least in part, by choosing a ciphertext and obtaining its decryption under an unknown key.

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Trying to understand this Solution related to CCA security

4.25) Let F be a strong pseudorandom permutation, and define the following fixed-length encryption scheme: On input a message $m ∈ \{0,1\}^{n/2}$ and key $k ∈ \{0,1\}^n$, algorithm $Enc$ chooses a ...
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Is Cramer-Shoup Lite IND-CCA secure?

Recently, I studied about Cramer-Shoup encryption scheme. Then, I read a book which mentioned a simpler version of this scheme, the Cramer-Shoup Lite encryption scheme. I was wondering if there is ...
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QR-PKE not CCA secure

Due to a comment stating "... QR-PKE is secure (CPA)..." I've been thinking of how to prove that it's not CCA secure, and would like to understand whether my proof is correct. Here's the QR-...
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Clarification for CCA security (or - why is the following not a Rabin CCA attack?)

In three different, highly reputable sources (e.g. "Introduction to Modern Cryptography" by Katz and Lindell, 2007), the definition of CCA attack doesn't allow the adversary to decrypt the ...
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Analysis of the Vigenere cipher

Im just starting out learning some cryptoanalysis techniques. I came across an idea which analyzes the vigenere cipher. Essentially the video explains that there is a standard english probability ...
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Proving that RSA CCA is possible

I'm reading from William Stalling's Cryptography & Network Security - 7th Edition To me the first line suggests $$(M^e\bmod n)\times(2^e\bmod n)=((2M)^e\bmod n)$$ which means that if we want to ...
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How can we measure the security levels of post-quantum cryptographic algorithms? Is there a standard way of this measurement?

How do we measure the security levels of Post Quantum Cryptographic algorithms such as: NTRU Prime, Saber, Kyber,...that are submited to NIST PQC Standardization Process(Competition) in general? I ...
2 votes
1 answer
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The essential differences between IND-CCA1 and IND-CCA2?

For some encryption scheme $(\mathcal{E}, \mathcal{D})$: In the definition of IND-CCA, the adversary $\mathcal{A}$ can access the decryption oracle $\mathcal{D}$. The deep reason of this setting is to ...
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Do attackers need to know what ciphers are being used when conducting ciphertext-only, known plaintext, chosen plaintext, and chosen ciphertext attack

I am trying to understand the basic ingredients needed to conduct various types of cryptanalytical attacks. For instance, I understand that for Ciphertext-Only Attacks (COA) an attacker only has ...
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Indistinguishability of symmetric encryption under CCA

I am learning about symmetric encryption and its security properties. One of the security notion is security against chosen cipher-text attacks (CCA), particularly IND-CCA notion. Under this notion, ...
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Easy explanation of "IND-" security notions?

There are many schemes that can advertise themselves with certain security notions, usually IND-CPA or IND-CCA2, for example plain ElGamal has IND-CPA security but doesn't provide IND-CCA security. ...
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Building an adversary for a OW-CCA game

Let K_rsa be a RSA genertor with associated security parameter k >= 1024. Let game OW-CCA_Krsa be as follows: How can I build a O(k^3)-time adversary A making at most 2 queries to Invert and ...
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INT-CTXT game adversary

I am trying to answer this question. But I think I got it wrong. I am not sure why and how I can improve it. This is the adversary I came up with. Is this correct? ...
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Rabin Cryptosystem: Chosen-Ciphertext Attack

I read in literature that Rabin Cryptosystem can be broken using chosen-ciphertext attack. It is described that after chosen ciphertext is decrypted attacker can factorize public key $n$ by using ...
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Encrypt-and-mac IND-CCA security

I have been stuck all day trying to understand how to show that an Encrypt-and-Mac ($SE_{EaM}$) scheme is not IND-CCA secure. I have seen this similar post, however it is slightly different and the ...
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Finding RSA private exponent with a chosen ciphertext attack?

Let's say there's this blackbox app that has a known modulus $N$, private exponent $e$, and takes ciphertext $C$ encrypted against $N$ and $e$ input and outputs plaintext $M$. The encryption is done ...
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CCA security in QROM for symmetric schemes

Assume that we have a symmetric encryption scheme $\Pi_s$ that is IND-CCA secure in the standard model. Does this imply that $\Pi_s$ is IND-CCA in QROM?
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CPA + one-time strong signature --> CCA?

Does combining a CPA PKE (public key encryption) scheme with a one-time strong signature construct a CCA PKE scheme? More specifically, let $(Enc,Dec)$ be a CPA PKE scheme, and $(V,S)$ be a one-time ...
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Can CPA secure scheme be converted to CCA secure?

I would like to know if there are some methods or techniques that can convert a public key encryption scheme from CPA secure to CCA secure?
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Bleichenbacher attack test vectors

I was trying to understand the Bleichenbacher attack. I went through the paper of Bleichenbacher to understand it a bit more. However, I tried to get some test vectors to simulate this attack locally ...
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CCA-Security Proof of a Particular Scheme

Suppose we have a scheme that works so: $\mathcal{P}_k =:\{P_k\colon \{0,1\}^{2n} \to \{0,1\}^{2n} \}$ is a strong PRP family. Encryption: $\operatorname{Enc}(k,m)=P_k(m\mathbin\Vert r)$, where $\Vert$...
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Symmetric Key Encryption is not Authentication?

Is there any way to show CCA-secure symmetric-key encryption does not have to be an authenticated encryption? I know you can create a set up that isn't authenticated, but how will you go about it?
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When is a PQ key-exchange algorithm suitable for use with long-term static keys?

I took a look at Cloudflare Circl because I'm curious which Post-Quantum algorithms are implemented in Go, which could be used to exchange a key. I read this comment that SIDH is only good for ...
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Proving the CCA-insecurity of El Gamal encryption scheme

I am trying to prove that El Gamal Encryption is not CCA-Secure. If an adversary queried the encryption oracle for the encryption of $m=1$, he'll get a pair $(c_1,c_2)=(g^y,g^{xy}\cdot m)=(g^y,g^{xy}\...
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Strong pseudo random permutation implies CCA-security

Let $F$ be a strong pseudo random permutation and define a fixed-length encryption scheme $(\operatorname{Enc,Dec})$ as follows: On input $m \in \{0,1\}^{\frac{n}{2}}$ and key $k\in \{0,1\}^{n}$, ...
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AES GCM : is it acceptable to return the wrong plaintext if the tag is incorrect?

Let's start by saying I'm no cryptography expert, I'm just a developer, so feel free to correct me (using words, not downvotes) if what I'm saying is non-sense. Context: I'm doing some crypto as a ...
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Proofs that NM-CPA implies IND-Cpa and $\text{IND-CCA} \leftrightarrow \text{NM-CCA}$

I am looking for a proof for the following two claims from "Serious Cryptography" by Aumasson. NM-CPA implies IND-CPA. [...] IND-CCA and NM-CCA are equivalent notions that imply the presence of the ...
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getting key $k_{2}$ somehow definitely compromise authentication scheme and attacker can see cipher text now...so not secure

I was going through this question of nested encryption: Given $\Pi$ = $({Gen}, {Enc}, {Dec})$ is authentication encryption we have designed new scheme $\Pi^{'}$ = $({Gen^{'}}, {Enc{'}}, {Dec{'}})$ ...
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Not getting idea how to formally chose chosen cipher attack so adversay wins with non-negligible probability

I was going through this question and intuition came that same message can be used to break security but I an not able formalize it well...can someone help how to create chosen ciphertext attack ...
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IND-CCA insecurity of modified CBC encrypt + MAC scheme

I've been puzzling over the following proof for the past couple of days. Since a block cipher in CBC mode can be used to build both an IND-CPA secure encryption scheme and a EUF-CMA secure block, a ...
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Question on the disprove of CCA security

I have a question on the disprove of the CCA-security given in Katz & Lindell's textbook (2nd edition) in chapter 3.7 on page 97. It works like this: Consider our construction based on PRFs: $\...
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IND-CCA game proof of Encrypt-then-Mac

In [BN07, Subsection 4.3], the authors show that if a symmetric scheme $\mathcal{SE}$ is IND-CPA and a MAC $\mathcal{MA}$ is EUF-CMA (though they use the SUF-CMA notation, but I think it refers to the ...
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Guarding against vulnerabilities for a digital signature service (RSA )

Lets's say I have a cipher-module / cryptography-service that signs a hash of some unknown payload. What are the possible attacks that I would need to guard against in this context (primarily assuming ...
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What do NM-CPA and NM-CCA mean?

When I've been researching authenticated encryption, the following terms keep showing up: NM-CPA NM-CCA ....without any definition as to what they mean. I've tried searching the web for their ...
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Question about IND-CCA security

We are given the following securitygame $G^{\text{LOSTNAME}}$: Generate $k \leftarrow \{0,1\}^{\kappa}$ uniformly at random Choose $h \leftarrow \{0,1\}$ uniformly random Create decryption oracle $\...
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Does Elliptic Curve Integrated Encryption Scheme (ECIES) provide IND-CCA2 security?

I am looking for a faster alternative to RSA with OAEP as a IND-CCA2 public key scheme. Elliptic Curve Integrated Encryption Scheme might be a candidate, but I am not sure if it provides IND-CCA2 ...
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Trapdoors for Lattices: CCA-secure encryption

In Trapdoors for Lattices:Simpler, Tighter, Faster, Smaller, Micciancio and Peikert proposed a CCA-secure encryption. However, I am confused about the step in decryption algorithm (p.36 Lemma 6.2.). ...
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Semantic Security Active or Passive attacks?

I'm reading A Practical Public Key Cryptosystem Provably Secure against Adaptive Chosen Ciphertext Attack and here define Semantic Security ... Semantic security, dened by Goldwasser and Micali [14]...
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Security of Paillier against chosen ciphertext attack

Is there a proof by now that Paillier is secure against chosen-ciphertext attack? The original Paillier paper mentions that it is not.
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Is there a relation between passive/active attacks and IND-CPA/IND-CCA?

I've seen some papers drawing a connection between IND-CPA and passive attacks and IND-CCA and active attacks. Can someone explain how IND-CPA relates to passive attacks and IND-CCA relates to active ...
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CCA secure vs AE scheme

We already know that every authenticated encryption scheme is CCA secure, I was wondering about the converse. I believe it is not true, and I am finding trouble to construct a scheme which is only CCA ...
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Can a CCA-secure cryptosystem be used as a CMA-secure MAC?

Can every CCA-secure cryptosystem be used as a CMA-secure MAC? I know that every CCA-secure system is CPA-secure, but I'm not sure about CMA. From what I understand: for a system to be CCA-secure, it ...
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IND-CCA secure symmetric encryption

Although this question maybe looks silly, I have searched similar questions in this forum and googled it but got no desired answers. IND-CCA security has already been deeply studied in public ...
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Why do we encrypt-then mac but sign-then-encrypt?

This question was asked in comments on my answer to should we sign then encrypt or encrypt then sign. I think posing the question as a separate entity is best, so: The general advice for applying ...
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Secure CCA Encryption under Partial Key Exposure

I'm currently learning about chosen ciphertext attack and stumbled across a problem on CCA security. If I have an encryption scheme $(Gen,Enc,Dec)$, which is CCA-secure with $Enc:\{0,1\}^n\times \{0,1\...
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Chosen Cipher Text Security for Double Encryption

If $E_k$ is a CCA secure encryption scheme then why is $E′_{(k_1,k_2)}(M)=E_{k_2}(E_{k_1}(M))$, $D′_{(k_1,k_2)}(C)=D_{k_1}(D_{k_2}(C))$ not CCA secure when $k_2$ is known. Is there a way I can make a ...
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Which attacker model is weaker? IND-CPA or OW-CCA?

I know that IND-CPA is a security goal, which is defined as the inability of an attacker to distinguish two ciphertext of some arbitrary chosen plaintexts. Unfortunately i havent found a good ...
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Indistinguishability versus semantic security?

I found some foundations of crypto course notes that mention that these two are equivalent statements of their own degrees of security and was given the following definitions: I was always under the ...
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How the message is decrypted in an RSA chosen ciphertext attack when it's a modulo?

During the last stage of decryption of a chosen ciphertext attack we are left off with this equation $$c = m \cdot t \pmod n$$ Removing all exponents like $d$ and $e$ where $c$ is the decrypted ...
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IND-CCA1 RSA padding?

I've found a way to complete a task which I'd solve with passwords or by sending keys over the wire (otherwise) by using RSA's homomorphic property. I'm restricted to RSA (any padding; for hardware ...