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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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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94 views

Does an information-theoretically secure hash function exist?

Does an information theoretically secure hash function exist? (By exist I mean is discovered/invented and implemented, not whether it could exist.)
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Collision resistant functions - definition

Let $f$ be a collision resistant function i.e. it is computationally impossible to find $x_0, x_1$ such that $f(x_0) = f(x_1)$. If a computationally bounded adversary demonstrates that he knows some $...
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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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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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1answer
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Security of this PRF [closed]

Given $F$ a secure PRF with input size $\lambda$. Define $F'$ as $F'(k,x||x') = F(k, 0||x)\oplus F(k, 1||x')$ with $x$ and $x'$ of $\lambda-1$ bits. Is $F'$ a secure PRF?
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Looking for a formula for “Given $x_1$, $\ldots$, $x_{n-1}$, the output $F(x_1,\ldots,x_n)$ is dependent of $x_n$ and is of $l$-bits security”

Suppose I have a function $F(x_1,\ldots,x_n)$, where each $x_i$ is of $l$-bits security (suppose each $x_i$ is a binary string of length $l$). At the same time, suppose there are $n$ persons, each one ...
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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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1answer
99 views

On the security definitions [duplicate]

What are the differences between: perfect security information-theoretic security semantic security indistinguishability Are there any other definitions which are closely related? Do these security ...
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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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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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2answers
79 views

What is the Knowledge Of Secret Key Assumption (KOSK)

From what I've read it seems to be where an entity must prove that they own the secret key. Which is done by signing a message M using said secret key. Is this ...
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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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2answers
146 views

What is the security concept in printer cartridge?

Based on this datasheet or this patent, one of the usage of PUF is printer cartridge identification and authentication. I was wondering why printer cartridge needs identification and authentication. ...
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32 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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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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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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457 views

What is the difference between information-theoretic and perfect types of security?

I'm having a hard time pinning down an exact definition of the difference between information-theoretic and perfect types of security. A rigorous definition seems elusive... A. Wikipedia puts the ...
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2answers
556 views

Why the definition in $\epsilon$-differential privacy is multiplicative rather than additive?

According to its mathematical definition, a random algorithm $M: D\rightarrow R$ satisfies $\epsilon$-differential privacy if the adjacent datasets $x, y \in D$ where $D$ is a whole dataset and ...
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1answer
157 views

Comparison of security definitions for signatures

The two main security definitions for signatures are EUF-CMA and the strong version of it sEUF-CMA. What I see that their difference is that in EUF-CMA experiment, the adversary needs to produce a ...
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1answer
155 views

Codes of “SAS und Chiffrierdienst”

The german site "SAS und Chiffrierdienst der DDR" http://scz.bplaced.net has some interesting content under point 11.3 in the category "manuelle Verfahren" I found ciphers named from A to D. But I ...
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1answer
191 views

Formal definition of collision resistance for hash function

In my cryptography class, the professor said that collision resistance for a fixed hash function is not a "precise" definition. The reason is since a fixed hash function is a single instance of a ...
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1answer
70 views

Why is the security level defined by $\log _{2} \inf \{ t_{i}/\varepsilon_{i} \mid i \in I \}$

In public-key cryptography, the security level indicates the strength of an adversary in breaking a scheme or solving a problem, which can be seen as the time cost of breaking a scheme or solving a ...
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1answer
74 views

What is the security model of the FHE system introduced in Fully Homomorphic Encryption Using Ideal Lattices?

How would one construct a security model to play against the adversary, and define the security of the overall scheme? This is in reference to the scheme introduced in "Fully Homomorphic Encryption ...
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1answer
99 views

Definition of symmetric cipher and definition of asymmetric cipher

So I'm currently taking a cryptography class right now and my professor has told the class that she can't even define symmetric cipher for us without getting into asymmetric ciphers and the textbook ...
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3answers
290 views

Is there a cryptographic approach to availability

Background Cryptography can be said to provide the tools used to fulfill the goals of information security. The three pillars of information security are confidentiality, integrity, and ...
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467 views

Does GCM (or GHASH) only provide 64-bit security against forgeries?

In a recent comment a doubt was voiced about my answer, which claims GCM to requires $2^{128}$ for a successful forgery. The doubt was that the square root needs to be taken meaning the security would ...
3
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1answer
297 views

What's the difference between perfect security and unconditional security?

This paper refers to two distinct security models: perfect security and unconditional security. Until now, I knew of them as the same thing and equivalent to information-theoretic security. From the ...
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58 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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107 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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2answers
116 views

How is n-bit security calculated with nested encryption?

What will the total $n$-bit security be if I encrypt a message with a 128-bit XOR cipher and then take that ciphertext and encrypt it with a 128-bit key. Is the total security level now 256? One ...
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2answers
123 views

Does encryption using PRP mean indistinguishable encryption against an eavesdropper?

I am a student studying cryptography by reading "Introduction to Modern Cryptography". I have some confusion about encryption using PRP (e.g., AES). Briefly speaking, a keyed deterministic ...
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1answer
609 views

Difference between eavesdropping and traffic analysis

I was wondering what is the conceptual difference between these two passive attacks on a network. I was reading about them on Wikipedia and they seem quite similar to me. Is there a difference?
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1answer
145 views

Adaptive vs. Static security model in ABE

From Lewko, I understand the difference between an adaptive and selective model: Adaptive model: the attacker can adaptively query the challenger for private keys. Selective model: the attacker has ...
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2answers
349 views

Identifying negligible functions

I am having a hard time understanding and applying the formulas that are used to identify a function is negligible or not? One text defines it as; a function $f$ from the natural numbers to the non-...
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1answer
131 views

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 ...
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3answers
374 views

Is it possible to exactly reverse engineer an unknown cipher inside a black box?

Consider the following arrangement:- There is an unknown cipher algorithm operating inside the black box. You can enter infinite key /plain text pairs, and observe all of the outputs. The box might ...
4
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1answer
325 views

Is the practice of “security through obscurity” violating Kerckhoffs's second principle?

Security through obscurity is the reliance on the secrecy of the design or implementation as the main method of providing security for a system or component of a system. Kerckhoffs's second principle:...
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1answer
97 views

What does $1^n$ mean? [duplicate]

I often see the notation of powers of 1 in cryptography papers. For example, let $n$ be security parameter, then what does $1^n$ mean?? From high school student perspective, powers of one is always ...
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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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1answer
102 views

How well is it understood mathematically why encryption schemes are hard to crack?

I have read some intro material into cryptography. It mainly goes into the current encryption schemes like AES, but not very deeply into the mathematics of why they are secure. I know that encryption ...
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0answers
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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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1answer
50 views

Fairness and guaranteed output delivery

Why for achieving the fairness and guaranteed output delivery, less than a half of the parties should be corrupted? ($t < m/2$, where $t$ is the number of corrupted parties and $m$ is the total ...
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1answer
76 views

Any Arbitrary Function

According to the attached reference, does it mean that the adversary computes $PPT(initial~input)$, $PPT(z)$ and $PPT(f_i(x',y'))$? For example, suppose the corrupted party, in the malicious model, ...
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1answer
54 views

Which of these deductions are true about the simulator and the adversary?

Which of these deductions make sense? The simulator is actually being run by the adversary. It makes sense that the adversary initializes the simulator (which is just a program) with the input that ...
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1answer
68 views

Is function Deterministic or Probabilistic in the malicious security definition?

As you see, according to the attached definitions from "Efficient Secure Two-Party Protocols", the definition of the security in the semi-honest world has two cases for $f=(f_1,f_2)$.(deterministic ...
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1answer
370 views

Strong One-Way Function

In the book "Foundations of cryptography-Oded Goldreich-Page 33", if we use the deterministic polynomial-time algorithm instead of the probabilistic polynomial-time algorithm for case 2 (Hard to ...
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1answer
73 views

A problem exists with the security proof in the secure AND example in the malicious model [closed]

Imagine that the malicious adversary in the real world uses $Y = 0$ as its input, therefore he computes the output as ($X$ && $y=0$) = $0$. We can conclude that the real view in the real world ...
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1answer
106 views

The interaction between the malicious Adversary and the Simulator and Real-Ideal' views

This example is from “Efficient Secure Two-Party Protocols-Carmit Hazay-Yehuda Lindell”. And the security proof of the above example is this: I have drawn a picture that is deduced from the above ...
3
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1answer
103 views

Security proof in the Malicious Model

According to the above protocol(Efficient Secure Two-Pary Protocols-Hazay-Lindell-page 27), the authors proved the security of this protocol according to the two paragraphs below: We separately ...