0
votes
0answers
86 views

Is a RSA 2048 bits public key secure [duplicate]

I realize servers such as Google, Yahoo, which use RSA has 2048 bits public key. After comparing those keys, I realize that the public keys share a common property, that is first 9 bytes and last 5 ...
1
vote
1answer
85 views

Why do we need password in a server which uses TLS?

Suppose a server uses TLS to protect communication between us and the server. I observe that in the TLS handshake protocol, password is not mentioned anywhere. Then why do we need to have a ...
1
vote
1answer
255 views

Crypto libary with Commutative Encryption

I want to implement Mental Poker in JavaScript as a toy program and lead in to a larger serious project so I did my research and found Massey-Omura cryptosystem and the Shamir three-pass protocol ...
2
votes
1answer
406 views

Can public key be recovered from ciphertext & encrypted private key?

I'd like to implement something like a write-once public/private encrypted shared secret (no better quick description for the lack of terminology knowledge). I guess, I'm trying to implement HSM. The ...
3
votes
1answer
209 views

Security of RSA with $\gcd(pq, (p-1)(q-1))\ne 1$

The Congress of ThéOùÇa enacted that civilian use of any public-key encryption system is authorized on the territory of ThéOùÇa, subject to meeting certain security requirements published by the ...
0
votes
1answer
57 views

When homomorphic encryption goes wrong?

Consider I have two ciphertext $c_1$ and $c_2$ encrypted using RSA encryption. By definition if I multiply them I'd get $c_1.c_2 \ modN$. My question is what would happen if $c_1.c_2 >N$. Can we ...
0
votes
1answer
176 views

Show that the equal difference property exits for a modified DES encryption system

My cryptology professor gave us this problem on a past homework assignment and I only managed to get one of the 3 parts correct. Needless to say, I want to know how to do the other two parts as well. ...
3
votes
2answers
212 views

What, cryptographically speaking, is a “long message”?

I have read about long message attacks on some cryptographic hash functions. However, I don't quite understand what is being referred to as a "long message". Also, do long message attacks only apply ...
1
vote
2answers
333 views

CRC32 vs. low 32 bits of cryptographic hash

I was having a discussion with a colleague yesterday whose education and experience exceeded mine. He said something yesterday that sounded incorrect to me intuitively, but I don't have the knowledge ...
0
votes
2answers
96 views

what is contained in a public key certificate

Public key certificate is a digitally signed document which verifies the sender is indeed the person. May I know how can the receiver tell the sender is indeed the person solely based on information ...
-1
votes
1answer
447 views

Simplest code for 64-bit block RSA-like encryption/decryption and key generation

Looking for the simplest code in C. Need a set of functions that will first generate a public/private 64-bit key pair, and then the function to code/decode a given 64-bit block, no built-in checksum ...
1
vote
0answers
158 views

Type of cipher used where ciphertext has no discernible pattern, spaces. Type?

What type of cipher could give ciphertext where for example random ASCII chars between say F-z (symbols and numerals inclusive), but with only a few spaces? Frequency of chars shows some similarities ...
1
vote
2answers
419 views

RSA Decryption given n, e, and phi(n)

my cryptography professor gave us this problem for extra credit a while back and I attempted it but I didn't get it correct. I have gone back to it, but I'm even more lost now than I was the first ...
1
vote
1answer
349 views

AES— Brute force attack versus Known plain text attack

I am taking a codes and cryptology course and the following is a questions on a past exam that I could not and still can't solve: ...
1
vote
0answers
79 views

Why is it hard to calculate Logarithm on Diffie Hellman?

i read something about Diffie Hellman. What i don't understand: Alice selects a randomly generated Number, calculates X = g^x mod p and sends X to Bob. If she calculates g^x, she needs to calcluate ...
0
votes
1answer
53 views

RSA signature scheme

In RSA signature scheme, it is a common practice to 'sign' the hash value of the message so that the length can be fit. Question: If we have $s=m^d \bmod n$ where $d$ satisfies $ed \equiv 1 ...
5
votes
2answers
474 views

Are there any digital signature algorithms in common use that result in 32-byte signatures?

I don't consider myself to be an expert in this field, so forgive me if there is an obvious answer. I am having a tough time finding an algorithm that can sign data and output a 32-byte signature, ...
0
votes
0answers
82 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 ...
0
votes
1answer
120 views

Symmetric vs non-symmetric pairing based crypto

I am trying to find a comparison of how different pairing-friendly elliptic curves perform (in terms of security) in real world applications; I am using PBC library, and it has type A curves and type ...
3
votes
1answer
88 views

Why develop new stream ciphers when block ciphers can be trivally made into streams?

I've just been reading about a new drop-in replacement for the RC4 stream cipher, but why develop new stream ciphers when AES can be made into a stream with a little XORing?
1
vote
1answer
81 views

Is equal length of primes in Paillier cryptosystem is mandate for security reasons?

In continuation to this question about length of primes , I am in doubt about the restriction on length of primes itself . In Paillier cryptosystem , equal length of primes are used . My doubt is ...
1
vote
0answers
61 views

DLOG in $\mathbb{F}_{p^n}^*$?

Assume that we are given an element $g\in \mathbb{F}_{p^n}^*$ and $g$ does not belong to any of the smaller subfields contained in $\mathbb{F}_{p^n}$. If the degree of $g$ is some number $q$, how much ...
0
votes
0answers
189 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: ...
0
votes
0answers
92 views

Public key encryption without ciphertext expansion [duplicate]

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 ...
0
votes
0answers
53 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 ...
0
votes
1answer
102 views

Direct sum of Binary numbers In Mixcolumns

I have just started learning cryptography and I am trying to make sense of the direct sum on some binary numbers. I am trying to find a column of a state space after a Mixcolumns operation has been ...
1
vote
2answers
217 views

Encrypting twice with same key gives back plain text

I read in the answer here that when encrypting twice the plain text with same key could result in plain text as shown below $encrypt_{key}((encrypt_{key}(plain)) = plain $ Which block-cipher ...
10
votes
1answer
2k views

What are SNARKs?

What does it mean and what is it used for, I have been hearing this term a lot lately. From the context I've heard it talked about it seems to be connected with zero knowledge?
3
votes
1answer
210 views

How can a good pseudo-random number generator be made?

I am trying to make a pseudo-random number generator so that I can use it in a synchronous stream cipher for encrypting plain text. I want it to generate numbers which are as random as possible. What ...
2
votes
1answer
397 views

What are these twist attacks with cost $2^{58.4}$ on NIST P-224 curve, and when do they apply?

This page on Twist security mentions a combined attack and a twist rho attack, applicable in particular to NIST P-224 curve with cost $2^{58.4}$ something, with no mention precise definition of ...
6
votes
1answer
459 views

Understanding Twist Security with respect to short Weierstrass curves

I'm trying to understand the "Invalid-curve attacks against ladders" section of SafeCurves Twist Security page and I have difficulties to apply it to short Weierstrass curves. That section claims ...
2
votes
1answer
919 views

Why does openssl use SHA1 in ECC when I use secp384r1 curve

I need a small clarification that why openssl using SHA1 in ECC when I am using secp384r1 curve, but in rfc they are saying we should use SHA2. Thing here is am using nanoECC in my DTLS, nanoECC ...
-1
votes
2answers
211 views

Encryption algorithm designed to be easy to decrypt by machine but impractical to decrypt by hand

I am looking for - or considering the design of a new - encryption algorithm that does not use variable keys, such that it is easy for a computer to encrypt and decrypt any message regardless of its ...
1
vote
0answers
223 views

About the Algebraic Normal Form (ANF) of S-Box in DES

I've thought up a way to represent the transformation of S-Box in DES by ANF. Let $x_i\;(1\le i\le 6)$ be the input of an S-Box, $y_i\;(1\le i\le 4)$ be the output, for example, then $$y_1= 1\oplus ...
1
vote
1answer
538 views

A simple attack on DESX in time $2^{120}$ [duplicate]

Let $\mathcal{M}$ be our message space and $\mathcal{K}$ our key space. Now, let $\mathrm{E} : \mathcal{K} \times \mathcal{M} \to \mathcal{M}$ be a block cipher. Define the block cipher ...
5
votes
1answer
243 views

Why does NTRUEncrypt lack a formal security proof?

Is there any particular reason why NTRUEncrypt lacks a formal security proof? That is, a demonstration that it achieves certain security notion (e.g. IND-CPA). I know there is a provable-secure ...
0
votes
2answers
79 views

public key certificate on TLS/SSL

Currently I am working on a public key certificate. I got a question: Why is a public key certificate needed for TLS/SSL? Wouldn't TLS/SSL itself is enough? What is the role of the certificate?
1
vote
1answer
458 views

rsa public and private keys

I have a question about RSA key generation. This is a simple RSA algorithm: Choose p = 3 and q = 11 Compute n = p * q = 3 * 11 = 33 Compute ?(n) = (p - 1) * (q - 1) = 2 * 10 = 20 Choose e such that ...
1
vote
2answers
110 views

RSA prove $a^{\varphi(n)/g} \equiv 1 \pmod{n}$

I should prove that $a^{\varphi(n)/g} \equiv 1 \pmod{n}$, so I thought I would prove it with primitive roots but I got stuck. Here is the assignment: Let $p, q$ be primes such that $p \ne q$. ...
0
votes
1answer
144 views

RSA CRT modulo reduction

I am working on RSA CRT and there is a point that I don't understand : So we have $n=pq$ and $c = m^e \bmod n$ an encrypted message. To decrypt $c$ with RSA CRT, we have to compute : $d_p = d \bmod ...
1
vote
1answer
79 views

Are there any many to one encryption frameworks available?

I am reasonably new to the cryptography. For my use-case I need a method where in I would need a receiver to accept encrypted messages from a range of senders (each having their own, say, public key). ...
2
votes
1answer
455 views

The Boneh-DeMillo-Lipton fault attack (RSA CRT)

I am trying to understand the Boneh-DeMillo-Lipton fault attack on RSA CRT signature. Suppose that we sign a message $m$ with RSA-CRT : $d_p = d \bmod (p-1)$ and $d_q = d \bmod (q-1)$ $s_p = ...
2
votes
2answers
287 views

What is a q-type assumption?

I've seen the term "$q$-type assumption" used in a few papers without a definition. A google search doesn't seem to come up with anything useful either (except the same papers without a definition). ...
0
votes
1answer
71 views

Client-server communication

The base scenario goes as follows: A program stores some user's confidential data encrypted on their disk. The user is most probably clueless and the disk might get stolen, but these are the classical ...
-2
votes
1answer
100 views

Isn't Groth-Sahai proof system applicable beyond Bilinear groups?

Classical paper by Groth-Sahai on NIZK proof system is titled as "Efficient Non-interactive Proof Systems for Bilinear Groups". To my understanding, only (Pairing Product Equation) PPE are defined ...
2
votes
1answer
422 views

Frequency analysis of Vigenere Cipher

For Vigenere cipher, I understand Find period first (say we have p = 6) Find highest frequency of letter in each group (from 1 to 6) and assume it is "e" in plaintext What if we have more than ...
1
vote
1answer
389 views

Monoalphabetic cipher key

I'm new to cryptography and have just completed homework on Monoalphabetic cipher. I managed to decrypt the cipher text successfully but I cannot identify the key from my plaintext to ciphertext ...
1
vote
0answers
56 views

Infer encoding mechanism from $n$-grams distance?

I have a series of obfuscated strings which across the set of strings have regions of high variance and regions of low variance – implying some encoding mechanism as opposed to an encryption procedure ...
0
votes
1answer
100 views

A one way Function provably reversible at N applications with the same seed?

I'm looking for a function that is generally one way from some secret $F(s, A) \rightarrow Y$, where $A$ is known, $Y$ is produced (also known), and $s$ is kept secret. But whose repeated application ...
2
votes
2answers
134 views

Is it safe to salt a MAC?

Say that I define a scheme where the salt is public and is MAC-ed with the message: $k = KDF(password, salt)$ $tag = MAC_k(salt || message)$ Is it safe to salt the MAC this way? Assume that the salt ...

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