# All Questions

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### A rudimentary challenge–response authentication based on dot products in $\mathrm{GF}(2)^k$

We are building a rudimentary challenge–response authentication protocol based on dot products in $\mathrm{GF}(2)^k$. Assume a user has a password $\mathbf{p} \in \mathrm{GF}(2)^k$. When logging in, ...
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### Change of axis positions in Vigenere Square

Is there any history of codes in which there have been changes in the normal axis positions of the Vigenere Square? Have been working on a code which has two non-normal positions -- one with the ...
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### java.util.Random and Dice Rolls

For this question, a dice roll will be considered two 6 six sided dice, to give a possible output of 2-12. Given a java.util.Random instance r, the output of one roll would be: ...
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### Designing hash function in space-efficient identity based encryption

Let $n$ be an RSA-prime and we know prime factorization of $n(=pq)$. The hash function is the current context maps from a given user identity(id) to a positive integer less than $n$, whose jacobi ...
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### Cryptographic Operations and Security

sign((M’, TAlice, sign(( encrypt(( encrypt(M, KpbBob), M’), K), TBob), KsBob)), KsAlice) Can you tell me six security-related facts ...
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### Is there an “additive” proof-of-work?

I'm trying to find a proof-of-work algorithm with the following properties: If A(1) is a proof of work with Difficulty(A(1))=n (requires n basic operations on average), then one can find a proof of ...
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### if using cbc+hmac dealing with small size of data(less than 128bit) , will it cause any problem?

if use AES-cbc,HMAC-SHA256, and there is some txt needed to be enc, and I divide this txt into small packages with variable length, then enc them. some of these package can be less than 128bit. Is ...
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### Elliptic curve trapdoor function without modular arithmetic?

From what I understand, an elliptic contains a set points satisfying the equation $y^2=x^3 + ax + b$ together with the point at infity. It seems clear how multiplication with a scalar and a point ...
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### How many characters per block in an El Gamal ECC cryptosystem?

While I look for how many characters that can be encrypted using the The elliptic curve ElGamal cryptosystem. of each block found for these lines. But I can not understand Actually in our case we ...
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### CP-ABE: structure of the secret key SK

I am working on Ciphertext-Policy Attribute based Encryption (CP-ABE) and I need to understand how a secret key looks like. For example, assume that the universe of attributes is defined to be ...
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### proving the security of 1 out of 2 oblivious transfer using AND function

Hello ladies & gentlemen, I need to improve the security of 1-out of 2 oblivious transfer using AND function method with a given info. use one-out-of-two oblivious transfer as building block, ...
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### Key generation in Digital Signature Algorithm

In DSA, one needs to generate two primes $p$ and $q$ such that $q$ is $256$-bit and $p$ is $3072$-bit and $p-1$ is a multiple of $q$. Question: How to generate such $p$ and $q$. Attempt: First, use ...
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### Importance of ShiftRows in AES

If ShiftRows is excluded from AES, then an attacker can attack the modified AES by simply treating $128$-bit input as $4$ $32$-bits blocks. The attacker can attack these $4$ blocks separately. ...
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### Secure symmetric encryption algorithm for any-size base62 data

I am searching for a secure algorithm to encrypt base62 (or any other base) data for ids in urls. It should feature: No blocksize etc, limiting the length of the message to a factor of n If you ...
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### Decrypting A Cipher Text without knowing the key or plaintext

i'm new to cryptography and i am doing a research based on cryptanalysis of vigenere cipher. If i have a ciphertext which is encrypted using vigenere cipher, is it possible for me to decrypt the ...
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### How does chosen ciphertext attack on Elgamal work?

Can it be proven that attacker can obtain the full message if he knows some plain-ciphertext pairs?
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### Complexity to find an preimage of a hash function

Suppose a hash function based on Merkle-Damguard construction. Its compression function is given as $H_i=E_{m_i}(H_{i-1})$, where $E_{m_i}()$ denotes the encryption of an ideal block cipher with ...
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### CCA security of a system that splits messages and encrypts each packet

Propose a symmetric key based crypto-system for implementing a secure email system. This system is based on AES and CCA secure. Suppose that you have to encrypt a large message and that this message ...
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### The Inhomogeneous Short Integer Solution (ISIS) problem with a clue

The Inhomogeneous Short Integer Solution (ISIS) problem is as follows: given an integer $q$, a matrix $A \in \mathbb Z^{n\times m}_q$, a vector $b\in \mathbb Z^n_q$, and a real $\beta$, find an ...
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### Hokkaido (proof-of-Work system) and pseudo-random permutation table

This question is regarding a proof-of-work system suggested in this article "Cryptology ePrint Archive: Report 2005/356". The outset goal of the Hokkaido algorithm is to provide a task to somebody's ...
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### Permutation parity after cycle-walking

Let $E$ be a random even permutation of the set $\{0\dots n-1\}$. We construct a permutation $P$ of the set $\{0\dots m-1\}$, for some $m\le n$, using cycle-walking; that is, computing $P(x)$ is as ...
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### openssl - Recommended way to encrypt and sign S/MIME messages using openssl

OpenSSL has two command line tools, cms and smime, that can encrypt and sign S/MIME messages. Both can specify ciphers and ...
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I'm trying to solve excersise 7.6 from Hoffstein - Introduction to Mathematical Cryptography page 459 (http://goo.gl/oRyInT) Let $p$ be a prime and let $i$ and $j$ be integers with $gcd(j, p − 1) = ... 0answers 41 views ### Test framework for hash functions for collision resistance? I have two questions about the assessment of collision resistance in hash functions. Given a hash-function what would be the next step to inquiry about it's collision resistance / probability of ... 0answers 51 views ### How can I calculate the size of an encryption key? I have encryption algorithm that has two variables are used as encryption key. How can I calculate the size of the encryption key. I will show an example of what the variables can be: ... 0answers 89 views ### How can I prove CPA secure by using a new scheme gen,enc,dec from GEN,ENC,DEC? Given public key encryption scheme$(gen; enc; dec)$, we now construct a new scheme$(Gen; Enc; Dec)$as follows: The key generation algorithm$Gen$is the same as$gen$. Each ciphertext for a ... 0answers 27 views ### Do OpenPGP SmartCards have the same or better security than an air-gapped machine? Are OpenPGP SmartCards, such as the OpenPGP SmartCard V2, suitable enough to have secure communications? Meaning, if I connect my smart card to my Mac which is connected to the internet and always ... 0answers 19 views ### The number of surviving key after “Meet in the middle stage” in 3-subset MITM attack In 3-subset Meet in the middle attack, how can we calculate the number of surviving key after meet in the middle stage? and how can we calculate the complexity of Key testing stage? I have read about ... 0answers 78 views ### recommendation to see documentaries about history of cryptography Can anybody recommend any good documentaries which go into some history about cryptography and state of cryptography as of date ? I am not asking for favorites or subjective good documentaries but ... 0answers 90 views ### Franklin-Reiter related message attack m2 = a(m1)+b As shown in their paper, https://www.cs.unc.edu/~reiter/papers/1996/Eurocrypt.pdf, if one is given an equation relating the two messages m1 and m2 as well as other information one can crack both the ... 0answers 60 views ### Is it possible to add OpenSSL engine for a block algorithm with different input and output block size? I need to add a new symmetric cryptography algorithm to OpenSSL, and I thought that the best way to do it is via its engine API. This algorithm will later be used by an application via the OpenSSL ... 0answers 31 views ### How good is middle cube method with jumbled digits? I had to make my own prng for a stream cipher for an inter school science project (I am mentioning that a lot). So I thought of cubing the seed instead of squaring it (like in the middle square ... 0answers 43 views ### Is Paillier cryptosystem commutative? Is Paillier cryptosystem commutative? If not, how can we construct an oblivious decryption protocol based on Paillier? 0answers 42 views ### NRPAD and FPAD padding schemes (Korean Seed?) I've got an API spec that specifies NRPAD and FPAD as possible padding schemes. I see these being used together with the Korean SEED algorithm. The SEED specification however is void of any padding ... 0answers 39 views ### symmetric encryption A5/1 and A5/2 algorithms where does the key (Kc) used to generate the keystream comes from and also where does the 22bits counter comes from 0answers 18 views ### Fast root finding algorithm for Binary Goppa codes decoding using linearised and affine polynomials I am trying to implement the root finding algorithm from the following paper - Finding roots of polynomials over finite fields by Sergei V. Fedorenko, Peter V. Trifonov link : ... 0answers 69 views ### The Short Integer Solution (SIS) problem for square matrices The short (or small) integer solution (SIS) problem is as follows: given an integer$q$, a matrix$A \in \mathbb Z^{n\times m}_q$, and a real$\beta$, find a nonzero integer vector$e\in \mathbb Z^m$... 0answers 21 views ### A5/1 and LFSR incrementation I am working on A5/1 and I'm not sure to all understand about it. We consider that we receive a burst(228 bits-sequence) to encrypt every 4.615 milliseconds. So when we have initialized our LFSR's ... 0answers 25 views ### signed message susceptible to block re-ordering , block deletion , block replication We would implement a Public Key Cryptography (PKC) based digital signature by breaking the message into blocks and signing each block independently. One of the issues associated with digital ... 0answers 51 views ### Low exponent attack against RSA According to this: http://www.cims.nyu.edu/~regev/teaching/lattices_fall_2004/ln/rsa.pdf One can calculate the message m, if there was no padding scheme involved. My question: is it possible to find ... 0answers 23 views ### Help in uderstanding NIZKPoK notation (and how to code it) needed Hello fellow cryptographers I have a rather silly question for you; I am aware of how Schnorrs NIZKPoK / SoK works when someone must prove knowledge about DL: y = g^x; (and how to code it) RFC ... 0answers 136 views ### Serpent 256bit Non bit sliced version (Table Sbox/IP/FP/LT/ILT) (Non-bitslice notation rules) Good afternoon! I got some mismatches while counting Round Keys at non bitsliced version of Serpent. I have used official AES submission outputs (file ecb_iv.txt). AES submission package test vector: ... 0answers 61 views ### Public key encryption without ciphertext expansion Say I have a database column that is defined as VARCHAR(255) that stores names. I can assume that names can be up to 255 chars. I need a public key encryption so that I can replace names with their ... 0answers 41 views ### Password generation/storage scheme How bad is the following strategy for a password manager on a local machine? The user wants to sign up for somesite.com where he needs a password. The user has previously generated a secret key ... 0answers 26 views ### Elliptic Curves Readdition I found the term re-addition in https://www.hyperelliptic.org/EFD/g1p/auto-shortw-projective.html and I cannot figure out what it is. It has actually same complexity of addition and I dont see the ... 0answers 20 views ### Computing the redundancy of language for a Vigenère cipher with m=5 Redundancy of L = 1- Entropy of L/ log base 2 {P} The Redundancy of L is given by 1 minus the Entropy of L divided by log base 2 of the Cardinality of the Plaintext space. Could someone advise me how ... 0answers 67 views ### initiate the elliptic curve when we consider a curve in a prime field for example Weierstrass form and want to initiate it in Miracl,we should give these inputs for initiate curve: ebrick_init(&binst,x,y,a,b,n,window,nb) ... 0answers 121 views ### Existential Unforgeability of signature scheme against Adaptive Chosen Message Attack While reading a literature on signature schemes, I came across the concept of Existential Unforgeability of signature scheme against Adaptive Chosen Message Attack. Can anyone point me to the paper ... 0answers 72 views ### Need help solving a shift cipher problem? A three letter alphabet {a, b, c} has probabilities p(a) = .5 and p(b) = p(c) = .25. A shift cipher is applied to pairs of letters. More precisely: plaintexts consist of two-letter sequences of ... 0answers 50 views ### Forward Secrecy with pseudorandom functions Let$H_1$,$H_2$be keyed hash functions (e.g.$H_i(x) = SHA_{256}(s_i||x)$for pseudorandom$s_1$,$s_2$). Let$s_n = H_1^k(s_0)$,$k_n = H_2(s_n)$, where$s_0\$ is a secret (pseudorandomly chosen ...

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