Cryptography Stack Exchange
Cryptography Stack Exchange

Questions tagged [game]

20 questions
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Hiding/Obscuring position information in a board game

There has been a question on the BoardGameGeek forums that basically boils down to this: There is a player character on a regular rectangle map at position (px,py). There is one "AI" character that moves across this map according to some function…
fho
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Origin of "abort" in cryptography proofs

It's a very standard move in a game-based security proof to have a transition in which we "abort" on some event such as a hash collision; the two games are identical apart from the abort step, and we add the probability of the abort to the advantage…
Paul Crowley
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"Simulator Based" vs "Game Based" security proof for a two-party computation protocol

I am trying to find out how to write a security proof for a two-party computation problem. I have read some examples to write simulators like $x_1 ∧ x_2$ problem and the example in Goldreich's book. I have also read some parts of Lindell's toturial…
m123
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sUF-CMA security of Lyubashevsky's ID and signature protocol

I have been working on the post-quantum safe ID/signature-schemes of Vadim Lyubashevsky (https://www.iacr.org/archive/asiacrypt2009/59120596/59120596.pdf). I am in particular studying the security proof, and wanting to structure this in a game based…
Rory
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How to bound the advantage of the following pair of games?

I'm reading a paper Code-Based Game-Playing Proofs and the Security of Triple Encryption, and I encounter a question in section 4.3, which designs the following games: Lets just focus on the medium two pairs of games, $R_1/C_1$ and $R_2/C_T$. $R_1$…
Ji Li
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Hiding/Obscuring position information in a board game (Part 2)

This is basically a follow-up question to Hiding/Obscuring position information in a board game which technically answered the question, but raised some well deserved critique. To quickly summarize the question: Consider a board game with a…
fho
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Does the PRG game allow for bad randomness picks?

In the game-based definition, we say that $G: \{ 0, 1 \}^n \rightarrow \{ 0, 1 \}^{\ell(n)}$ is a pseudorandom generator if For all ppt distinguishers $D$, there exists a negligible function $\nu$ such that: $$Pr[D( r) = 1] - Pr[D(G(s)) = 1 ] \leq…
eternalmothra
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Proving semantic security implies security from key-recovery attack

I am working on problem 2.11 from the book: A Graduate Course in Applied Cryptography by Dan Boneh and Victor Shoup. The problem reads as follows: Problem 2.11: Let $\mathcal{E} = (E, D)$ be a cipher defined over $(\mathcal{K}, \mathcal{M},…
Tom Finet
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What exactly is a game, challenger, and adversary?

Here is my understanding of the concept of security games. I bolded some parts that I am not sure about. A cryptographic object is formally defined by its algorithms and what security notions it achieves. Such notions capture an adversary’s power…
eternalmothra
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Building an Adversary for a PRF game

Here is the game: How can I make an $\mathcal{O}(k^2)$-time adversary making only one query to its Fn oracle and achieving advantage $= 1 - 1/(p-1)$ Here is my idea so far: query $2^{-1}$, which when it goes through the Encryption algorithm, will…
Diego Starr
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How are probabilities combined in the game hopping proof technique?

I'm currently studying a paper (Sequences of Games: A Tool for Taming Complexity in Security Proofs) on proving semantic security using the Game Hopping technique by Victor Shoup. On pages 9-11, he is using a sequence of three games, $Game 1$, $Game…
tur11ng
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Algorithmic game theory and protocol design for communication

There is a field of exchanging information that combines cryptography and game theory. I am interested in understanding this field, but it's a little complex for me. To begin with there is a paper of Barany which shows that instead of having a…
Hunger Learn
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An upper bound for advantage in a security game

Suppose I have defined a security game in a private-key (symmetric) encryption scheme. Remark: Note that encryption algorithm is probabilistic, so for a specific message m, $Enc_k(m)$ might output a different ciphertext when runs multiple times,…
EddyLiu
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Proof that semantic security implies key-recovery security

I'm trying to prove that semantic security implies key-recovery security. There is already a question that addresses this, but it doesn't explain the setup of the security reduction, which is what I'm interested in. My idea is as follows: Given an…
cmplx96
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Proving 2-way nesting security

I recently came across the theorem about $n$-way nesting. It states that if $\mathcal{E}=(E, D)$ is semantically secure, then $\mathcal{E}$ is secure for $n$-way nesting. I'm trying to prove the specific case of $n=2$. For the encryption…
libre
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