3
votes
1answer
330 views

Is $q(n)=1/n$ a negligible function?

By definition - $q(n)$ is a negligible function if for every positive integer $c>0$ there exist an integer $N_c$ such that for all $x>N_c$ : $q(n)<1/x^c$ So for the function $1/x$, if we ...
3
votes
1answer
349 views

Generating a valid signature on El-Gamal without knowing the private key

Suppose we are given $p$, the large prime, $g$ which is the primitive root for $p$, $b$ which is calculated as $b=g^x$ mod $p$ where $x$ is the private key and $0<x<p-1$. Also suppose we know ...
3
votes
1answer
189 views

Derive a public EC key from two public EC keys

Alice has two EC key pairs: $a_1$, $a_2$ are private keys (integers), $A_1$, $A_2$ are the corresponding public keys (points). Alice and Bob want to create a new public key $C$. Alice must prove that ...
3
votes
1answer
139 views

What security differences are there between E(p',“well-known-plaintext”) vs. hash(p') where p'=KDF(p)

I am using a KDF to derive a key, p' from a password p. I would like to know if the password is correct before using the derived ...
3
votes
1answer
131 views

md5sum collision question

I've been reading the wikipedia page, trying to get a better understanding of how to produce a collision. http://en.wikipedia.org/wiki/MD5#Collision_vulnerabilities The wikipedia page above states: ...
3
votes
1answer
397 views

Should new applications still use RSA? Is it worth going down the ECDH route for protocols?

I am currently designing an application for communication between two and more users. At the moment I am trying to figure out what methods to use for the asymmetric cryptology. With the recent ...
3
votes
1answer
333 views

iOS Data Protection: What is the Input of the LFSR?

Every time a file on the data partition is created, Data Protection creates a new 256-bit key (the “per-file” key) and gives it to the hardware AES engine, which uses the key to encrypt the ...
3
votes
1answer
476 views

Explain the 'Breaking 104 bit WEP in less than 60 seconds' paper

Could you explain the 'Breaking 104 bit WEP in less than 60 seconds' paper, without skipping too much technical details. Could you an answer questions, like: how is '1.24/256' a significant ...
3
votes
2answers
182 views

Why do fully homo-morphic constructions use 'ring' or 'lattice' structures?

Is there a significantly advantage to these data structures, or is it simply the status-quo and the easiest to use for describing constructions?
3
votes
1answer
76 views

Modes for encrypting small binary blobs?

Suppose I am building an encrypted document storage system. Suppose each user has a "user key": a symmetric key. Suppose each document is encrypted with a "document key". So, in order to give a ...
3
votes
1answer
72 views

Applications of 3-collisions

I recently read Improved Generic Algorithms for 3-Collisions by Joux and Lucks (Asiacrypt 2009), available as http://eprint.iacr.org/2009/305.pdf. I was wondering about applications of this technique ...
3
votes
1answer
4k views

Generating a secure random number in javascript

What I am trying to do is generate a large (4096bit) random number in JavaScript that is cryptographically safe to use. My approach is the following: I am creating a ...
3
votes
1answer
407 views

Elliptic curve parameter generation

I am curious of the details of how one would go about generating elliptic curve parameters. (I know standardized parameters exist, but I'm trying to understand both how they were generated and the ...
3
votes
1answer
471 views

Clipper chip (SKIPJACK) key exchange protocol

According to the Wikipedia page for NSA (emphasis mine): However, NSA's Fortezza hardware-based encryption cards, created for the Clipper project, are still used within government, and NSA ...
3
votes
1answer
46 views

Distributing blocks with validation and non-dependant list generation

Problem Suppose I have a system of nodes that can communicate with a parent node, but not among each other. Suppose then a file on the parent node is split up into blocks and divided among the ...
3
votes
2answers
891 views

one-time pad key related attack [duplicate]

In one-time pads we always say do not use same key twice to encrypt ASCII messages, but if we use a random key to XOR a random ...
3
votes
1answer
270 views

Any historical accounts of cryptanalysis of Jefferson's wheel cipher?

David Kahn in his book "The Codebreakers" wrote about Jefferson's wheel cipher, saying that To this day the Navy uses it… (the book was first published in 1967) Are there any historical accounts ...
3
votes
1answer
290 views

Is there a field guide to ECC for the IT Security layman?

I'm trying to understand ECC from an IT layman's perspective and am trying to separate the theory from the standards, and understand why certain features are implemented or not implemented in the ...
3
votes
1answer
314 views

Sigma-protocol for 3SAT problem

I have some questions from previous years exams, I hope you could help me with them. :) Let $g,h$ denote generators of a group $G$ of large prime order $n$ such that $\log_g h$ is unknown to anyone. ...
3
votes
2answers
131 views

Distinguish messages

Since i cannot comment on questions, I give my own: If a secret key encrypt algorithm can encrypt messages of arbitrary length and the encrypt algorithm is probabilistic then: suppose the adversary ...
3
votes
1answer
96 views

Data-validating protocol

I have to implement protocol of secure data transfer that can be described as Alice selects data to send from finite set $m\in M$ (e.g. $M$ could be a column of values in database table) Alice ...
3
votes
1answer
377 views

Chaum undeniable signature - justification for probability of misleading the verifier?

Can anyone explain me in details why does the following statement hold true in Chaum and van Antwerpen scheme for undeniable signature? The probability that a dishonest signer is able to ...
3
votes
1answer
236 views

Attack vectors introduced by compilers

I have a question about attacks on the implementation of cryptographic code that are enabled by compilation and compiler-optimisations. I am aware of this. Would anyone be able to point me to other ...
3
votes
1answer
455 views

DGK Cryptosystem Key Generation and Decryption Issues

I detailed here the DGK (Ivan Damgård, Martin Geisler and Mikkel Krøigaard) cryptosystem, and I managed to get it to work, most of the time... The BIG problem that I am facing at the moment is that ...
3
votes
1answer
271 views

Elgamal test vectors

I know that Elgamal algorithms have fallen out of fashion, and they are not included in any widespread cryptographic standard nowadays. However, they are still present in several popular crypto ...
3
votes
1answer
403 views

Security analysis of a matrix multiplication protocol

Suppose Alice would like to obtain the product of two mXm matrices i.e. A and B. Alice has A, whereas Bob has B. Since Alice does not want to reveal A to Bob, she chooses a mXm random invertable ...
3
votes
1answer
169 views

uniquely identify a symmetric key

Is there a safe way to uniquely identify a symmetric key? I know with asymmetric keys you typically use a hash of the public key, but I assume that using a hash of a symmetric key would reveal too ...
3
votes
1answer
323 views

ElGamal signature - exploiting fallacious implementation

This question is related to ElGamal signature scheme as defined here ElGamal signature without calculating the inverse Show how one could exploit an implementation ElGamal signature scheme in which ...
3
votes
1answer
391 views

Are there reference implementations of ECQV implicit certificates?

I am interested in exploring ECC implicit certificates, specifically using the ECQV protocol. While the actual implementation would not difficult to perform using building blocks provided by most ECC ...
3
votes
0answers
54 views

How to generate an RSASSA-PSS signature with MGF1-SHA256?

As part of rooting a device, I need to generate a 256-byte RSASSA-PSS signature using SHA256 as the hash and MGF1-SHA256 as the mask function, for an update file I created. I can choose any 32-byte ...
3
votes
0answers
68 views

XTS and 256-bit data blocks

I am developer of an application that uses XTS with ciphers which use 128-bit blocks (AES, Serpent and Twofish). I now want to use XTS with a cipher which uses 256-bit blocks (Shacal-2). AFAIK, I ...
3
votes
0answers
39 views

Can the attack in https://eprint.iacr.org/2008/469.pdf be parallelized?

Can this attack be parallelized? It is a $2^{57}$ complexity collision attack on SHA-1 based on disturbance vectors. If it is practical it is easy on a GPU ($\approx1.1$ GPU-days). If it is ...
3
votes
0answers
41 views

Election communication protocol

I'm not a cryptography expert, but this seems like it falls into this area. Imagine I want to design an election system (senate race for example) where I send the exact same ballot of 100 candidates ...
3
votes
0answers
118 views

Yaos Millionaire Problem: Why distance >= 2?

I'm currently reading about Yao' Millionaire Problem: http://research.cs.wisc.edu/areas/sec/yao1982-ocr.pdf Alice and Bob want to know which of them is richer. Let $j \in \{1, \cdots 10\}$ be Bobs ...
3
votes
1answer
38 views

How are the IVs of SHA512/256 and SHA512/224 calculated?

This seems odd to me, because there are a lot of resources out there saying that the initializer values of SHA512 and SHA384 are the first 64 bits of the fractional parts of the square roots of prime ...
3
votes
0answers
83 views

Elgamal with secret key equal to zero possible?

From various sources (e.g. this paper, page 3), the key generation algorithm of Elgamal samples the secret key $x$ from $\mathbb{Z}_q$, which is identifiable to $\{0, 1, 2, \dots, q-1\}$. My ...
3
votes
0answers
37 views

EC Schnorr signature: multiple standard?

I 'm working on some EC-Schnorr signature code. Reading various papers on that, it's seems EC-Schnorr is not standardized as well as ECDSA. For example, I found two main differences in two main ...
3
votes
0answers
25 views

About BGV Scheme Batching Technique

I am reading BGV12 about BGV homomorphic scheme right now.But I am being stuck to understand Batching technique in this paper. In Pack function (page 32),this paper feeds ciphertext $c_i$ and sk ...
3
votes
0answers
56 views

When to chose hardware accelerated crypto for Big Data

if you were to recommend a cipher/mode configuration that emphasizes performance for your customers, would you recommend a hardware based accelerated solution over one that isn't? For big data at ...
3
votes
0answers
35 views

Benchmarks for second round CAESAR competitors

I'm interested in how the second round CAESAR competitors stack up in terms of software performance against each other and against chacha20-poly1305 with both small and large messages. Sadly the only ...
3
votes
0answers
29 views

is accessing elements of an array in secret order vulnerable to timing attack?

Suppose there is an array containing bytes 0...255. Suppose this array is shuffled using a key for random data. Since this is indexing the elements of a table using secret data, is it vulnerable to ...
3
votes
0answers
43 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 ...
3
votes
0answers
74 views

How to attack polyalphabetic affine cipher with only ciphertext?

How to attack polyalphabetic affine cipher with only the ciphertext? A polyalphabetic affine cipher can be seen as the composition of an affine cipher ($p \mapsto c \equiv a \times p + b \pmod{26})$ ...
3
votes
0answers
63 views

Majority encryption algorithm?

Assume that I want to leave an encrypted message to a group of $n$ people in a way that they can only decrypt it if they work together in the following sense: For some fixed $k < n$ every ...
3
votes
0answers
39 views

Committing to a secret shared value

Suppose I run a multiparty protocol. At the output stage, I have the function output in a secret shared manner among all parties. Now I want all the parties to commit to their value of the secret ...
3
votes
0answers
63 views

Is OCB the state of the art in authenticated encryption modes of operation for block ciphers?

OCB mode seems to represent the state of the art in authenticated encryption modes, largely due to its speed – it is faster than GCM even when GCM has hardware support. Its only drawbacks seem ...
3
votes
0answers
27 views

Does length prepending fix the key reuse problems with CBC and CBC-MAC?

As I hope everybody is well-aware, re-using the key for CBC-MAC and CBC is a really bad idea. Now, there's also the paradigm to prepend the message length to the CBC-MAC (as "associated data") to ...
3
votes
0answers
33 views

Is an instruction similar to PCLMULQDQ valuable in post quantum key exchange?

This paper describes a Quantum Key Exchange based on the Ring Learning With Errors problem. When used with ECC, there is only a slight performance impact. Assuming this is the popularized approach ...
3
votes
0answers
100 views

How secure is $\operatorname{AES256}_{\operatorname{ECB}}(\operatorname{ChaCha20}(\text{plaintext}))$?

Suppose I encrypt a bytestream using ChaCha20, and then encrypt the resulting ciphertext using AES in ECB mode. How secure is the combination?
3
votes
0answers
40 views

Can you give me a summary of cryptographic hardness assumptions?

Until recently, I had a link to a website which summarizes up-to-date cryptographic hardness assumptions. But, unfortunately I cannot find it. The webpage is categorized well problems such as, DL ...

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