1
vote
0answers
301 views

Is there any analysis of freebsd's “geli” encrypted geometry provider?

I've done a few obvious searches on google and google scholar and not turned up any security analysis of FreeBSD's geli. Is there some out there, or has it gone unanalyzed since its introduction ...
0
votes
2answers
248 views

Why are these techniques not feasible to crack RSA?

For $d = e^{-1} \mod \phi(n)$ $$d\cdot e \operatorname{mod} \phi(n)=1$$ $$d = (e^{-1} \operatorname{mod} \phi(n))$$ With having $e$ and $n$, we can calculate the value of $d$ , the private key for ...
1
vote
2answers
955 views

How do I calculate the private key in RSA?

Given $n=pq$ for $p,q$ known, I can calculate $\phi(n)$. $e$ is selected such that $\gcd (e,\phi(n)) = 1$. Using this, how do I calculate the RSA private key? Example: I have $n = 35$, with ...
2
votes
2answers
220 views

Need 32-bit mixing function that has perfect avalanche between octets

for my hobby tinkering project, I need a mixing function that takes 32-bit input and has 32-bit output (and will, most likely, run in a 32-bit C environment) and the following property (independent of ...
0
votes
0answers
38 views

Correlated or biased coin protocols?

There are a number of papers in the literature describing secure/fair coin flipping protocols. Unfortunately in my case, I am looking for coins that are epsilon-biased or epsilon-correlated. I am ...
-2
votes
1answer
92 views

counting points not on elliptic curve [closed]

Given an curve with equation $y^2=x^3+ax+b$, I want to find the number of pairs $(a,b)\in \mathbb{F}_p \times \mathbb{F_p}$ NOT on the curve. How do I do it? I have an intuition that it is $p$, but ...
1
vote
1answer
124 views

Does it make sense to stretch non-keys?

I was thinking about stretching salt. Key-stretching is good against brute force guessing and assumes your system isn't compromised. Salting a one-way makes it so you have to compute * n for each ...
0
votes
0answers
182 views

If H(m) = 0 for some m, how can a DSA signature be forged?

If we know for some message $m$ that $H(m) = 0$, how can we forge a DSA signature with only the public key? I got that $g^s*r = (g^x)^r$ where $x$ is the private key, but that's one equation with 2 ...
0
votes
1answer
103 views

Is an elliptic curve over $\mathbb{F}_p$ order preserving for the points $(x,y) \in \mathbb{Z}_p$?

Let $E\colon y^2=x^3+ax+b$ be an elliptic curve, and consider its realisation over the finite field of prime order $p$: $E(\mathbb{F}_{p})$. Then if $0<a,b$ is the following true? $$\forall ...
0
votes
1answer
86 views

Enhance CSPRNG output [duplicate]

If I XOR the output from 2 CSPRNG will the result be better (more random) than the output from either one? Assume one of the PRNG is biased.
3
votes
1answer
210 views

counting points on elliptic curve

Given an elliptic curve with equation $y^2=x^3+ax+b$, and i want to find the number of points $(a,b)\in E(\mathbb{F}_p)$ where the polynomial has repeated roots, how do i do it? I have an intuition it ...
0
votes
2answers
294 views

Regex searchable word list for space-less monoalphabetic substitution [closed]

I am working on teaching myself basic cryptography, in the process I created a simple substitution cipher based on a single alphabet, and a statically defined offset (no key for now). Now that ...
4
votes
3answers
246 views

Can insecure algorithms be combined to form a secure algorithm?

This is hypothetical as I can't think of any reason to do this, but out of curiosity... Could I, for example, take the MD5 digest of a message and concatenate it with the SHA-1 digest (not quite ...
4
votes
2answers
149 views

Is a simple stream cipher “partially homomorphic” if no integrity check is applied?

My understanding is that, simply put, a stream cipher is just a CSPRNG such that $R(i,k)$ will produce a deterministic but statistically random sequence, where $i$ is an IV, and $k$ is the session ...
0
votes
1answer
68 views

The real-life meaning of proving over a group that doesn't support the oracle?

If I proved a scheme's security under GDH assumption, in real-life, if this DDH oracle does exist, then it's good, but what about other side ? In real-life, if this DDH oracle doesn't exist, then ...
0
votes
0answers
46 views

Why doesn't this authentication protocol work? [duplicate]

I am a student taking a cryptography course so forgive me if this comes off as a silly question. This is an assignment question: Alice ------R--------> Bob Alice <-----[R]B------ Bob Alice ...
3
votes
2answers
190 views

Why doesn't this dummy mutual authentication protocol provide mutual authentication?

I am a student taking a cryptography course so forgive me if this comes off as a silly question. This is an assignment question: $Alice \rightarrow R \rightarrow Bob$ $Alice \leftarrow [R]B ...
4
votes
3answers
191 views

Why can an RSA signature be authenticated ONLY with the signer's public key?

I'm an undergraduate Math student currently taking a cryptology course. I have a question about the RSA signature authentication mechanism. An RSA signature can be authenticated with the public key ...
4
votes
1answer
187 views

Keyed digest function with odds of collision below the birthday bound?

I wonder if it is possible to devise a function $F(K,S,R_S)\mapsto D$ where: $K$ is some key (I have freedom on $K$, it could even be generated by a trusted party); $S$ is in $\{0,1\}^s$, say ...
1
vote
2answers
420 views

RSA performance

I was wondering what is the performance bottleneck in RSA algorithm? Is it the size of message, calculating the modular inverse, exponentiation? Say I have a fixed value of n to encrypt and decrypt ...
0
votes
2answers
151 views

Is the composition of collision resistant hash with non collision resistant hash a collision resistant hash?

Suppose $h_1$ is collision resistant, and $h_2$ isn't. Will $h(x)=h_2(h_1(x))$ always be collision resistant? [Edited:] the output of h2 must be uniformly distributed
2
votes
2answers
477 views

Graphically representing points on Elliptic Curve over finite field

I have taken elliptic curve $E\colon y^2=x^3-4x+20$, defined over $\mathbb{F}_{29}$. The number of points on the curve, $\left|E(\mathbb{F}_{29})\right|=37$. I took base point $P=(1,5)$, and got ...
7
votes
2answers
2k views

Using the same RSA keypair to sign and encrypt

The RSA signature operation is basically the same as encrypting with the private key. In particular, both operations use the same kind of keys. Is it safe to use the same RSA keypair both for ...
1
vote
0answers
415 views

What is the chance of a collision when using SHA-3?

I currently am writing a web app and am using two random hashes that are before and after the string and are both 50 char long (alphabet, numbers, and special chars). ...
1
vote
0answers
106 views

$\phi$ function in Dual_EC_DRBG

I am trying to understand the operation of the Dual_EC_DRBG. I'm reading the formal specification (SP 800-90) and can't seem to find a definition of the $\phi$ function used throughout the definition ...
1
vote
2answers
389 views

How does Google's “authenticator number generator” work?

I have two-factor authentication enabled on my Google account, and I have this app on my phone which generates a number I have to type when I'm logging in to Google-Mail. But I don't understand how ...
9
votes
3answers
257 views

How hard is to invert the function that computes the middle-bits of (x^2)?

I'm designing a function f that should be moderately hard to invert and very fast to evaluate in a modern CPU. The function will be used in a proof-of-work function. I've read that the middle-bits of ...
-4
votes
3answers
463 views

IV's from Crypto++ AutoSeededRNG always ends the same: Problem with the PRNG? [closed]

I am using a AutoSeededRNG from Crypto++ to generate IVs for use in CBC encryption. I am encoding the IVs using Base64 for future use (decryption). I notice that ...
2
votes
1answer
152 views

What does this step in this protocol for the Yao's Millionaire Problem mean?

I was reading “An Efficient Protocol for Yao’s Millionaires’ Problem” (Ioannidis and Grama 2003). In the proposed protocol in section three, it is written: (Step 4) For every $i$, $1 \le i \le d$, ...
3
votes
2answers
148 views

What is the function of the secret key “r” in Poly1305?

Poly1305-AES uses two per-connection keys $k$ (for AES) and $r$ (for Poly1305's compression function) and a per-message nonce n to execute. I've read the original paper on the implementation, and I ...
8
votes
1answer
367 views

Did NIST verify “post-quantum” claims in the SHA3 proposal papers?

I have been reading Bernstein’s “Quantum attacks against Blue Midnight Wish, ECHO, Fugue, Grøstl, Hamsi, JH, Keccak, Shabal, SHAvite-3, SIMD, and Skein” paper from 2010… This document disproves ...
0
votes
0answers
247 views

Blum-Blum-Shub Cryptosystem

I am given $N$, which is Bob's encryption key. I was able to successfully factor $N$ into $N=p*q$. Alice encrypts a messages for bob and sends $a = [1,1,1,0,0,0,1,0,1,1,0,...]$ $b = 1545164156...$ ...
0
votes
2answers
131 views

Why use two affine transformations in Multivariate Cryptography?

I'm reading Multivariate Cryptography and would like to know why we use two affine transformations to scramble the central map? Why not use only one?
1
vote
1answer
411 views

Can AES decrypt with a wrong key?

The title is asking the question in layman terms, but what I really mean to ask is this: Let $x \in \lbrace 0,1 \rbrace^{128}$ (an arbitrary input block) and let $K \in \lbrace 0, 1 \rbrace^{128}$ ...
3
votes
1answer
333 views

Purpose of leading zero in PKCS1-v1_5 padding

According to this document the padded message has the following structure: $EM \;= \; 0x00 \; || \; 0x02 \; || \; PS \; || \; 0x00 \; || \; M$ What is the purpose of this null byte at the beginning ...
1
vote
1answer
138 views

Weak Stream Cipher cryptanalysis

Hi I have a stream cipher which uses a keystream of: F(r) || F(r+1) || F(r+2) || ... Suppose F(r) is the RSA encryption algorithm: ...
2
votes
2answers
155 views

Publicly exposed hash of private key

Would exposing a cryptographic hash function's digest (e.g. SHA-3) of RSA private key data compromise the key? If so, what are the possible (cryptanalysis-) vectors for attacking the key if an ...
1
vote
0answers
51 views

Can you clarify the proof that secure LR-two party protocols do not exist?

In the paper “Multiparty Computation Secure Against Continual Memory Leakage” on pg. 1237, the footnote #1 discuss why it is not possible to construct a leakage resilient two-party protocol. But I'm ...
3
votes
1answer
122 views

Why is Lamport-Diffie secure?

Why is Lamport-Diffie secure? I note that there is a demonstration based on onewayness (in the book postquantum cryptography). But a one way function is not sufficient to ensure that it can not infer ...
5
votes
1answer
253 views

Can you help me understand hash-preserving encryption?

I have rather simplistic understanding of cryptography, so I have to beg a pardon in advance if the question has internal contradictions. Imagine data $A$ with a hash $hashA$. This data is encrypted ...
3
votes
1answer
248 views

Can minimum encrypted message length be used to identify public key algorithm or derived some of its features?

Encrypting a very small message using public key cryptography always result in larger encrypted messages. Is it possible to deduce the algorithm used, key length, etc just by looking at the minimum ...
0
votes
1answer
401 views

Is this encryption scheme perfectly secure?

Let $m = 6$, and let $\mathbb{Z}_m$ denote the set $\{0,…,m-1\}$. Let $X \mod m$ denote the remainder obtained when dividing $X$ by $m$. (a) Consider the symmetric encryption scheme in ...
0
votes
1answer
334 views

Security of SecRandomCopyBytes on OSX and iOS

How secure is SecRandomCopyBytes() (Apple's RNG)? Has anyone ever reviewed it?
1
vote
0answers
76 views

How can user privacy be preserved in certificateless cryptography?

In certificateless cryptography, how can a user preserve his privacy from Key Generation Center? If the KGC becomes malicious, how can the user's privacy be preserved? I read "Privacy-Preserving ...
4
votes
1answer
139 views

Are ideal hashes possible to create?

In a hash function, you map an input of arbitrary length to an output of finite length such that the relationship is one-to-one (or at least that's what you are trying to achieve). Hence, isn't it ...
1
vote
0answers
186 views

What would make it impossible to deny that decryption of a package has taken place?

I'm part of a team designing a system where a user have to be able to read a certain package, if he has preformed an action or series of actions that makes it legal for him to do so. The tricky part ...
6
votes
2answers
713 views

Can the XOR of two non-collision-resistant hashes be collision resistant?

Suppose I have two hash functions, of which neither (or only one) is collision resistant, and I want to create a new hash function by taking the bitwise exclusive or (XOR) of the results of those two ...
1
vote
0answers
60 views

TCR hash functions from MD5

I'm reading Collision-Resistant Hashing: Towards Making UOWHFs Practical (pag. 10 and 11) and here say The most direct way to construct a TCR hash function is to key a function like MD5 or SHA-1. ...
6
votes
1answer
190 views

Can homomorphic encryption filter?

Often in articles homomorphic encryption is praised as the holy grail of encryption for cloud storage. This is done by suggesting that it can do any computation, and as such could be used for ...
4
votes
1answer
222 views

Homomorphic Encryption and Semantic Security using Lattices?

I've been reading Brakerski and Vaikuntanathan's "Efficient Fully Homomorphic Encryption from (Standard) LWE" and I'm still digesting pieces at a time. Under section 1.1, "Re-Linearization: Somewhat ...

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