An adversary model formally defines the power of the adversary. It includes specifics whether the adversary is deterministic/randomized, uniform/non-uniform, interactive/non-interactive and how he interacts with the security game.

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### Relation between attack and attack model for signatures

I would like to know: What is the relationship between an attack and an attack model. For example, let $\Pi$ be the Lamport signature scheme. This signature has its security based on any one-way ...
814 views

### Automated security protocol verification tool for eCK model

I want a tool that (runs on Win7 and) can perform automated verification of a protocol in the eCK security model as described in Microsoft Research's paper "Stronger Security of Authenticated Key ...
155 views

### How to build a security model

What are the minimal components to build a security model proof for a protocol? This question might seem trivial, but having read many papers-- from the IEEE, ACM, etc., that talk about a KMP-- I ...
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### How to rigorously prove that $Enc_{\Pi'(k)}(M) = Enc_{\Pi(k)}(M) || LSB(k)$ is CPA secure assuming $\Pi$ is?

Assume $\Pi$ is a CPA secure scheme. Let $\Pi'$ be a derived scheme, such that the encryption of a message $M$ is as follows: $Enc_{\Pi'(k)}(M) = Enc_{\Pi(k)}(M) || LSB(k)$, where $LSB(k)$ is the ...
140 views

### Parameterizing adversaries with security parameters

In many cryptographic games, the adversary doesn't seem to be parameterized by the security parameter.‡ Are such games equivalent to variants in which the adversary is parameterized by the security ...
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### What is adversary's advantage in cryptography and why we use it?

The definition of adversary's advantage seems a bit odd for me and I am wondering why do we use it to measure the power of an adversary rather than just use the probability of a PPT adversary ...
241 views

### Homomorphic & Functional encryption: Mapping unencrypted outputs to encrypted outputs using existing data

Let's assume I have datapiece A which, after being put through a model or neural network, has a known output X in the unencrypted space. When I move datapiece A into an encrypted space, and put it ...
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### Explanation of the term “view” for algorithm or adversary

What is the view of an algorithm/adversary? Is view just a term used to describe the output over a set of inputs for a probabilistic algorithm? For example: Consider experiment Mac-forgeA,Π (n). ...
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I am a newbie of this topic. I have trouble understanding what exactly are the capabilities of passive adversary/active adversary in real world and ideal world.
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### Idiomatic description for an adversary in possesion of a quantum computer?

I was wondering what the "accepted" way is to describe an adversary who: is in possession of a quantum computer with which they can efficiently run quantum algorithms such as Grover's or Shor's ...
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In the ideal/real proof paradigm we sometimes find simulators with the capacity of set adversary random tape. My question: when do we have to consider the necessity of simulators set adversary random-...
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### Correctness of ideal protocol of MPC in presence of malicious adversary

In presence of malicious adversaries in ideal protocol of Multi Party Computation, how can honest parties get the correct output? i.e., corrupted parties modify their inputs and give to the trusted ...
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### How does Kerckhoffs's principle apply to Adversarial Neural Cryptography?

Martın Abadi and David G. Andersen recently published a paper on arxiv titled: "LEARNING TO PROTECT COMMUNICATIONS WITH ADVERSARIAL NEURAL CRYPTOGRAPHY" (https://arxiv.org/pdf/1610.06918v1.pdf). I ...
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### Question about proof of pseudo-random random generators being one way functions

I've been looking over this proposition and proof in the book "Introduction to modern cryptography" and am a little confused. Picture is attached at the bottom). Why is it that we do not multiply the ...
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### Why is it allowed to Generate Keys inside the game?

I am studying reductions to prove security of crypto systems. Generally "games" are used for the proofs. For example, the next image was extracted from the page 91 of the book Post-Quantum ...
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### How do adversary models and security types relate [from InfoSec SE]

I have been told to move the question to this forum in order to get a better insight, so here we go: Reading some questions in this forum I encountered this answer mentioning IND-CPA as a requirement ...
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### Are covert and rational adversaries same?

Aumann and Lindell defined covert adversaries in 2009 which is informally adversaries which have a epsilon-deterrence to cheat. Some authors (for ex. John R. Wallrabenstein) have defined similar ...
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### Security proof. Adversary source of random coins.

Consider the game-based security proofs, i.e. a game played between the challenger and a PPT adversary. My question is... what is the source of random coins for the adversary? Is is valid to say ...
882 views

### Definition of cryptographic advantage vs. probability of success

In game-based security definitions, like for example the one defining IND-CPA security, a given cryptosystem is said to be secure if any probabilistic polynomial time adversary has only a negligible ...
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Hey crypto SE, i'm having a bit of trouble with this question. Can anyone help me to understand how to go about solving this problem? Any help is appreciated :) Show G is insecure against adaptive ...
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### MAC security and adversaries with memory

The usual definition of MAC security is (roughly) that there is no "efficient" adversary that has non-negligible advantage in the "MAC game" where the MAC game is as follows: the challenger chooses a ...
75 views

### Attacks on code misusing RSA_public_decrypt

I've encountered some code that I'm reviewing that is misusing RSA_public_decrypt to "authenticate" a variable-length response without using any hash. The code ...
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Hello all, I'm new to crypto, I'm not sure if my thought process is correct ? any assistance will be helpful. How useful is the partial info that A gets from (a), (b), and (c) ; in (c) A can ...
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### Times of nested algorithms in proofs of security

Proofs of security may be constructed such that an adversary $A$ is used to construct an adversary $A'$. The reduction/algorithm which uses $A$ has to perform a number of computations in order to ...
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### Proof by reduction clarification

If I execute a proof by reduction using a given adversary A as a subroutine to A'. How do I know that using adversary A which can solve a given hard subproblem, is the most efficient subroutine to use ...
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### Indistinguishable encryptions in the presence of an eavesdropper

I'm trying to understand how the messages $m_0$ and $m_1$ can be distinguished here. I understand the adversary game, so in short: Adv chooses $m_0$ and $m_1$, one them is encrypted and Adv is able to ...
284 views

### What kind of adversary is a compromised party?

Imagine multiple parties executing a secure multiparty computation protocol to evaluate a function securely. Let Alice be one of the parties who is intended to get all the partial results and combine ...
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### Is the simulation-based proof difficult and needed? [closed]

What is the role for simulation-based proof under the semi-honest model without considering malicious adversaries? I agree with that a view of a some party is important to prove that a protocol is ...
83 views

### What does this advantage statement signify?

In many Attribute Based Encryption papers I see this line... The advantage of an adversary A in this game is defined as Pr[b' = b] − 1/2. Can someone explain what it means to me? I assume it means ...
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### RSA-FDH Signature Scheme EUF-CMA

I am aware of attacks whereby an attacker is able to forge a message IF the hash of the original message is the same hash as their current message. The question is, is it still possible for RSA-FDH to ...
469 views

### Comparing stronger vs. weaker assumptions

If I have to argue that an assumption A is stronger than B, should I argue this way:- An adversary breaking the security of A does not translate to breaking the security of B. But, if an adversary ...
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### What does non-collusion assumption mean in server-aided protocol based on secret sharing?

Suppose $m$ clients split their own input into $n$ shares using additive secret sharing scheme (mod something). Then, each of the clients sends each share to each of $n$ external servers. After ...
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### How to provide security against malicious adversary in Ring LWE homomorphic encryption scheme?

I was reading Ring LWE homomorphic encryption scheme referred in http://www.wisdom.weizmann.ac.il/~zvikab/localpapers/IdealHom.pdf But this encryption scheme provides security mostly in the semi-...
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### Given the block cipher compute max PRF advantage

Hey all I'm having a bit of problem with this question. Not sure how to approach it. Any help will be appreciated :)
306 views

### what is PFS game?

when i reading about this paper, in the Setup of SIM section 5.2, it says that "According to the definition of PFS game", i wonder what the definition of PFS game ...
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### Build a scheme that is CCA secure but not authenticated

Trying to understand a solution from this paper: Summary: $E'_K=0||E_K(m)$ and $D'_K(0||c)=D_K(c)$ and $D'_K(1||c)=1$ IND-CCA secure (how?) as $1||c$ and $0||c$ are are easily decryptable Not ...
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### The differences between the attackers in the definitions of IND-ATK and NM-ATK

I read the definitions of IND-ATK and NM-ATK in a paper. Let $\Pi = \left( Gen, Enc, Dec \right)$ be a public key scheme. And let $A = \left( A_{1}, A_{2} \right)$ be an adversary attacking $\Pi$ in ...