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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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7 votes
2 answers
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Is a chosen ciphertext attack on PGP still possible?

In a paper from 2002 (pdf), Jallad et al describe a chosen ciphertext attack on PGP by taking advantage of the CFB mode that the block ciphers use under PGP. It's quite a devastating attack. Is this ...
1 vote
0 answers
35 views

crack AES CBC with chosen Ciphertext, IV and known plaintext [closed]

I am currently tackling a challenge involving AES CBC encryption where i have the ability to choose both the IV and the ciphertext, and then provide it to a service. The service decrypts with an ...
4 votes
1 answer
2k views

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 ciphertexts of some arbitrary chosen plaintexts. Unfortunately, I haven't found a good ...
3 votes
1 answer
3k views

How to prove an encryption scheme is not CCA secure

Given the following context below, how does one show or prove the encryption scheme is NOT IND-CCA secure The IND-CPA secure private-key encryption scheme for n-bit messages can be constructed from a ...
0 votes
1 answer
753 views

IND-CCA Security of a encryption scheme which is combination of two schemes

I have two public key encryption scheme $\Pi_0$ and $\Pi_1$ and one of them is IND-CCA secure, another one is IND-CPA secure. Let $\Pi$ be a public key encryption scheme, which is a combination of $\...
13 votes
1 answer
5k views

Why do we encrypt-then-mac but sign-then-encrypt?

This question was asked in comments on my answer to Should we MAC-then-encrypt or encrypt-then-MAC? I think posing the question as a separate entity is best, so: The general advice for applying MACs ...
0 votes
0 answers
68 views

Is the One-Time-Pad IND-CCA2 Secure?

I know that the OTP is considered to have perfect secrecy, but I haven't seen anything about its security against chosen ciphertext attacks, and I was wondering about its secrecy in this regard. My ...
1 vote
1 answer
105 views

CCA security problem

Let $(\mathsf{Gen}, E, D)$ be a CCA-secure public key encryption system with a message space $\{0,1\}^{128}$. Is the following derived cipher $(\mathsf{Gen}, E', D')$ also CCA-secure? Justify your ...
1 vote
1 answer
73 views

Question about the notation $H\leftarrow\mathcal{H}_{\mathcal{K}}$ in an IND-CCA security experiment

In the paper "Hybrid Key Encapsulation Mechanisms and Authenticated Key Exchange" by Bindel et al., I looked at the IND-CCA security experiment (figure 3). In the first line of the game, ...
73 votes
1 answer
35k views

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. ...
2 votes
1 answer
135 views

Why is the adversary in IND-CCA allowed to make encryption queries?

IND-CCA is an abbreviation of "Indistinguishability under chosen ciphertext attack" and generally, an adversary carrying out the chosen ciphertext attack is given a decryption oracle only. ...
14 votes
5 answers
10k views

Does Grover's algorithm really threaten symmetric security proofs?

By Shannon's theorem of perfect security, if I give you a ciphertext 'LOUPL', you can do a brute-force attack and then you would find plaintexts like 'HELLO', 'APPLE', 'SPOON', but you can't ...
0 votes
0 answers
50 views

Chosen plaintext attack on Blum–Goldwasser cryptosystem

As I was reading on some encryption schemes the other day, I stumbled upon the Blum–Goldwasser cryptosystem and read that it is vulnerable to adaptive chosen ciphertext attack. I searched for some ...
3 votes
1 answer
241 views

Kyber-CCA-KEM - Deterministic implicit rejection

In Kyber-CCA-KEM, there's a step in the Fujisaki-Okamoto transformation, where decryption failure results in a random shared secret returned from the decapsulation call. I have a C language project ...
3 votes
1 answer
136 views

Does CCA security require rejection?

It seems like every CCA-secure KEM1 has some sort of check that the decapsulator performs. Sometimes failure will result in rejection ("explicit rejection") or the decapsulator will simply ...
1 vote
1 answer
837 views

CBC not CCA secure

I always get stuck at those kind of exercises in my Cryptography class. I just don't understand how should I build these scenarios of "sending m1 and m2 and then somehow telling if it was m1 or ...
3 votes
1 answer
305 views

KYBER.CPAPKE: IND-CCA Security of Lyubashevsky, Peikert, Regev (LPR) Encryption

The NIST Kyber KEM spec. defines an encryption scheme, KYBER.CPAPKE, that's a variant of the so called Lyubashevsky, Peikert, Regev ("LPR") encryption scheme [1]. While LPR encryption is ...
1 vote
1 answer
429 views

Does CCA security imply perfect secrecy?

Can any encryption scheme that is CCA (Chosen Ciphertext Attack) secure be considered to achieve perfect secrecy?
1 vote
1 answer
92 views

Are RSA-KEM key exchange material cyphertexts indistinguishable from random noise?

First of all, I know that I should not be using RSA in 2023, and that I'm better off with Elligator2 + ECIES for a variety of reasons. However, I am thinking about whether RSA-KEM can be used for PURB-...
2 votes
1 answer
435 views

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 ...
1 vote
0 answers
137 views

Which encryption method support 256 bytes block size?

I am looking at some secret encryption method that apparently uses CBC and a block size of 256 bytes. I can do a chosen-ciphertext-attack. When I modify a single byte in the ciphertext a complete ...
3 votes
0 answers
59 views

Variant of CCA security for Paillier with blinded decryption oracle

Consider a variant of the Paillier encryption scheme where the message space is restricted to $\mathbb{Z}_q$ such that the RSA modulus $N$ of the Paillier cryptosystem satisfies $N > q + q^2$. I am ...
1 vote
1 answer
191 views

How is Crystal Kyber CPA-secure algorithms converted into a CCA-secure algorithm

In Crystal Kyber specification, page no10, there are 3 algorithms namely KYBER.CCAKEM for making the CPA-secure Kyber into CCA-secure one. Q1: How is the shared key K being generated in KYBER.CCAKEM....
1 vote
0 answers
102 views

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 ...
1 vote
1 answer
99 views

Is AES distinguishable if the attacker has an decryption oracle?

Let the following game be given: G^IND-CCA': Prepare a key k <- KeyGen(1^Kappa) Choose a hidden bit h <- {0, 1} uniformly random Prepare a decryption oracle O_Dec. Given a cipher text c, it ...
0 votes
1 answer
122 views

Curious about CCA attack for RSA, and Kerckhoffs's principle in general

I'm a student studying cybersecurity for the first time, and the part where our textbook explains using CCA attacks for RSAs seemed really unclear for me, so I am here seeking for clarification. Our ...
1 vote
0 answers
70 views

Construction of a SKE scheme based on a PRF family and on a MAC with UF-CMA security. Is the scheme secure?

Consider the following construction of a SKE scheme $\Pi^*=(Enc^*,Dec^*)$ based on a PRF family $F=\{F_k:\{0,1\}^n\rightarrow \{0,1\}^n\}_{k\in\{0,1\}^\lambda}$ and on a MAC $ Tag:\{0,1\}^\lambda \...
1 vote
0 answers
54 views

What are the possible CCA attacks on RSA with r||m+G(r) as the padding?

I was trying to come up with simple padding functions for the RSA, then trying to break them just to have a better understanding of why we need all the pieces used in the RSA OAEP... So, I am ...
0 votes
0 answers
102 views

CCA-Attacks in the real (and digital) world

Is any concrete and real examples of CCA-attacks in recent history. I'm aware about examples of WW2, but I'm more interested to modern examples in a digital context (for example against OFB, CBC).
1 vote
0 answers
142 views

Bleichenbacher 1998 "Million message attack" CCA

After implementing and playing around with famous "Chosen Ciphertext Attacks Against Protocols Based on the RSA Encryption Standard PKCS #1" there couple of questions which I can't really ...
0 votes
1 answer
117 views

Is the following scheme CCA secure? I purposed a scheme and I am not sure if it is CCA secure, if not, how can it be CCA secure?

Here is my idea: Under the symmetric key encryption. Alice and Bob share the symmetric key K. Let HASH be a secure hash function and ...
2 votes
1 answer
485 views

CPA secure to CCA secure encryption

Can we use a MAC to transform a CPA secure encryption scheme into CCA secure one?
4 votes
1 answer
149 views

Can we achieve IND-CCA without a MAC?

In modern cryptography, IND-CPA is the lowest security we want. We want at least IND-CCAx security from encryption mode. Their relation can be found in 2007 Authenticated Encryption: Relations among ...
1 vote
0 answers
161 views

Essential requirement for IND-CCA1 and IND-CCA2

I am learning about the concept of two security notions called IND-, which include IND-CPA, IND-CCA1 and IND-CCA2. While I got some grasp understanding about the scenarios between the challenger & ...
0 votes
1 answer
272 views

Can we force a chosen ciphertext to be decrypted to a chosen plaintext while controlling only $e(=3)$ in RSA? [duplicate]

I have bumped into this challenge from a well known CTF site. I don't want to make a reference to it because I don't want this to be a hint for anyone. And also to avoid giving out the source code of ...
1 vote
0 answers
171 views

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 ...
0 votes
1 answer
56 views

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-...
1 vote
1 answer
243 views

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 ...
0 votes
1 answer
139 views

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 ...
1 vote
2 answers
492 views

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 ...
5 votes
1 answer
2k views

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 ...
0 votes
1 answer
125 views

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 ...
5 votes
1 answer
803 views

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, ...
0 votes
1 answer
843 views

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 ...
4 votes
1 answer
2k views

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 ...
1 vote
1 answer
402 views

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 ...
3 votes
0 answers
54 views

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?
3 votes
1 answer
207 views

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 ...
4 votes
1 answer
370 views

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?
3 votes
2 answers
279 views

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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