Questions tagged [security-definition]

Questions about formal definitions of "security" for various cryptographic schemes (e.g. perfect secrecy, semantic security, ciphertext indistinguishability, etc.)

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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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515 views

Can a secure MAC break if the adversary is given oracle access to Verify?

In the Mac-forge experiment, the adversary is given access to a tag-generation oracle, which generates a tag for each message given by the adversary. The adversary's task is to generate a valid tag on ...
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1k views

What is the difference between mutual authentication and unilateral authentication both ways?

I am currently reading Engineering Security by Peter Gutmann, on page 7 he states: proper mutual authentication is quite different from unilateral authentication in both directions He references ...
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133 views

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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318 views

On the Definition of a PRG and a CSPRG

I've been looking at the definition of a PRG, here. This is a broader notion than a cryptographically secure PRG ("CSPRG"), which is described here. I am realizing that I am very confused by this ...
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36 views

decrypting a one-time-pad that outputs 0,1 in preknown probabilities

assuming a two users want to use a one time pad ciphersystem, and they are using a program that was developed by a third party that was supposed to create random undependable bits, but for some reason ...
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38 views

Can ideal functionalities share variables

I am trying to define an ideal world for a protocol that requires two functionalities to interact with each other. Lets call them $\mathcal{F}_1$ and $\mathcal{F}_2$. Now $\mathcal{F}_1$ maintains a ...
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60 views

Security aspects of a splitted Pohlig-Hellman system

Given a Polig-Hellman (is that really the name for that?) system with $$C = M^k \bmod p$$ where $M$ is the message, $C$ is the ciphertext, $k$ is a (secret) key (any integer relatively prime to $p-1$...
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58 views

Quantifying bit security for smart-vercauteren encryption scheme

I am working on project that requires to compare in terms of security between two encryption schemes, one of them is the SV scheme. However, I dont know what are the steps exactly towards quantifying ...
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690 views

Ideal system for an encryption scheme

What is the ideal system for an encryption scheme? For a pseudorandom permutation the ideal one is a random permutation, for a pseudorandom function the ideal one is a random function. For an ...
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47 views

Game-based proofs and semantic security

After reading this question, I understood that "game-based" and "simulation-based" have to do with the way that security properties are postulated. In particular, IND-CPA is a canonical example of ...
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36 views

Precise Definition of 1-out-of-2 Oblivious Transfer

What's the precise definition for 1-out-of-2 OT? and what's the best way to show that it can't be achieved under unconditionally secure setting? I am reading about it and just couldn't get my head ...
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127 views

Reduction to security of proof system for proving knowledge

I want to prove security of my system by reduction to the security of an underlying non-interactive proof system for proving knowledge. I know a game that captures the desired security property of my ...
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51 views

How does the offline authentication work?

In these slides, offline and online PUF-based authentication protocols are explained in minute 16:30 and 17:30, respectively. I understand the way the online protocol works. Basically, the server ...
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74 views

Non-Repudiation vs Identity-Binding

There are 3 properties offered by a cryptographic digital signature scheme: Integrity guarantee of the message signed. Authenticity guarantee of the message signed. Non-repudiation of the message ...
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131 views

Indistinguishable encryptions and CPA-secure example

Let $ F $ be a PRF and $ G$ be a PRG with expansion factor $n \to n +1 $ For the following encryption scheme, decide whether it has indistinguishable encryptions and whether it is CPA-secure. ...
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95 views

Mersenne Twister's vulnerabilty with small-size distributions

C++ rookie here, trying to wrap his head around (CS)PRNGs. I (assume that I) already understand the concept of the Mersenne Twister being "broken" (i.e. not cryptographically secure) due to its ...
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44 views

Proofs of security for anonymity in a multi-party setting

I'm looking for material that proves the anonymity of parties in a non-interactive setting. I would like to know if there are simulation based proofs (UC) and property based proofs (game based) for ...
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37 views

A qusetion about the security game of Certificateless signatures

Recently I read Certificateless Public Auditing for Data Integrity in the Cloud , I have a question about the security of proposed HOMOMORPHIC AUTHENTICABLE CLS. (Sec. IV). For the Type-I Adversary, ...
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206 views

Design flaw in IND-CKA definition of Searchable Symmetric Encryption?

I am a graduate student interested in searchable encryption research. I carefully read the Secure Indexes paper published in 2004, and I was confused about the IND-CKA, the game-based security ...
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63 views

RIsk mitigation: block cypher vs xor

It sort of looks like to me that there is a kind of risk mitigation in the architecture of block cyphers vs the xor cypher. In XOR, the risk is entirely in the random number generator. The XOR ...
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48 views

Homomorphic encryption and approximated GCD 2

This is a further question to the one reached here Homomorphic encryption and approximated GCD. I am now thinking about a symmetric cipher in which the plaintext set is integers, illustrated as ...
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44 views

Are there any security definitions for DNS?

Given a recent post on the Tor blog and the corresponding discussion on HN I was wondering if there are any security definitions for DNS or similar name systems. So something similar to ACCE for TLS ...
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481 views

Relationship between “Entropy” and “Security” in crypto functions

There is a lot of confusion between "entropy" and "security" of a cryptographic function. I like to visualize it as the entropy being the water, and the crypto function being a glass. So for ...
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203 views

Privacy-Preserving Protocols and Proofs of Security

While dabbling in privacy-preserving protocols (mainly using Semi-Homomorphic Encryption) and coming up with miscellaneous ideas for comparison tests or other similar primitives, based on obfuscation ...
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37 views

Understanding a security proof

I am reading the paper "RingCT 3.0 for Blockchain Confidential Transaction: Shorter Size and Stronger Security" (https://eprint.iacr.org/2019/508.pdf), an improvement to Ring Confidential Transactions....
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30 views

Importance of Backward and forward secrecy

Which security feature is more important in security protocols being used in different applications? Forward Secrecy or Backward Secrecy
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36 views

Every encryption scheme that is perfectly secret it holds that for every distribution over the message space $M$, every $m, m' ∈ M$, and every $c ∈ C$

Prove or refute: For every encryption scheme that is perfectly secret it holds that for every distribution over the message space $M$, every $m, m'∈ M$, and every $c ∈ C$: $$Pr[M = m | C = c] = Pr[M = ...
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36 views

Is this simple proposed scheme semantically secure?

Suppose we have two parties, including $P_1$ and $P_2$ using a type of symmetric encryption algorithm, say, AES256. Let's assume the shared key is: $K$. Encryption: Each party generate a key such ...
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57 views

DLP instances for given number of congruences

Let $S$ be the set of $k$ congruences of the type $g_{i}^{x_i} \equiv h_i \pmod{n_i}, \quad \forall i,1\leq i \leq k$ What would be the best way to describe such set $S$ with a term in literature. ...
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56 views

1-out-of-2 Oblivious Transfer Security

Just started reading Oblivious Transfer. I am searching for a proof of security based on RSA implementation but I can't find anything simple to understand. Can someone direct/show me to an easy to ...
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21 views

What is the difference between these pairings classifications?

I know the basic definitions of bilinear groups. For example, there is a bilinear pairing that uses elliptic curves and has the following properties: For $G_1$, and $G_2$ are cyclic groups of prime ...
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33 views

Simulator in the ideal world computes the proof for parties for $F_{NIZK}$

In the definition of $F_{NIZK}$ in [GOS06b], on receiving prove from a party, the functionality forwards the statement to the ideal world adversary $S$. This ideal world adversary then creates a ...
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111 views

Formal security-definition reference

Is there a reference where all common formal security-definitions are summarized (such as OW-CPA, IND-CPA, IND-CCA1, IND-CCA2, EUF-CMA and so on)? I need a PUBLISHED reference (paper, book) which ...
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87 views

Interpretation of message space distribution in the definition of perfect secrecy of encryption schemes

I am a beginner to cryptography, and have started reading Katz and Lindell's book titled "Introduction to Modern Cryptography". I'm unable to understand what the probability distribution over the ...
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26 views

Value of security through amiguity?

Let's say that you have a symmetric cipher which takes in an 8 bit plain text value and a key, and generates cipher text which can be decoded using the key to get the original plain text value. Since ...
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43 views

Outsourced Multiparty computation proof in Ideal world

I need to know in an outsourced two party computation where honst $A$ and $B$ outsource their private and secure data to a malicious server, why we need to design a simulator that interacts with an ...
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61 views

Role of trusted party in the Ideal model in Malicious case

Imagine there is a protocol supporting outosurced multi party computation. There are three parties involved in the protocol: client $A$, client $B$ and a server. Client $A$ and $B$ send their private ...