# All Questions

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### 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 ...
2k views

### Is HTTPS secure if someone snoops the initial handshake?

Let's say I'm on an open wireless network that's being actively sniffed and I connect to an HTTPS site. Even though my subsequent traffic is encrypted, couldn't the sniffer use the data from the ...
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### To what extent is WhatsApp's statement on secure messaging realistic?

As those of you who use WhatsApp Messenger probably know, with their recent update chats and calls are now encrypted. Here's what WhatsApp claims: Messages you send to this chat and calls are now ...
827 views

### Additive ElGamal cryptosystem using a finite field

I'm trying to implement a modified version of the ElGamal cryptosystem as specified by Cramer et al. in "A secure and optimally efficient multi-authority election scheme", which possesses additive ...
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### What would happen to AES if we replaced MixColumns with ShiftColumns?

I have this as a question in an assignment and I guess I don't fully understand the steps. I understand that if we omit MixColumns, then every byte of the ...
134 views

### Polynomials and efficient computability

In public key crypto, the popular definitions of security (CPA, CCA1,2) depend on PPT adversaries. I'm trying to understand why adversaries should be PPT. It's clear that adversaries should be at ...
116 views

### The difficulty of computing discrete logs

I understand that in Diffie-Hellman it should be hard to compute $a$ given $g$ and $g^a$. In computational Diffie-Hellman, it appears to be hard to compute $(g^{ab})$ from $g^a$ and $g^b$. As for ...
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### What happens if no final subtraction is done in Montgomery multiplication?

I'm doing Montgomery arithmetic modulo $N = 2^{255}-19$ for the Curve25519, picking $R = 2^{256}$ for Montgomery. After multiplying two numbers $0 \leq A,B < N$ in the Montgomery representation ...
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### What happens if someone implements tree-base signature scheme incorrectly?

I'm learning about signature schemes and read about Merkele's tree-base signature scheme. There are paragraphs about how the key and signings are generated. Using so-called tree structure and pseudo ...
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### Unknown Hash or Cipher [on hold]

I'm trying to identify what method was used to hash or encrypt a string of text, I have the plain text and the output, however, I have been unable to identify the method used to produce the output. ...
219 views

### Zero knowledge-proof for discrete log that is not honest-verifier

Take a cyclic group of prime order. The Schnorr-protocol for proving knowledge of the discrete logarithm of some group element is honest-verifier zero-knowledge, meaning that if the verifier chooses ...
35 views

### Can we do modulus switching for number theoretic encryption?

Can we do modulus switching for number theoretic encryption such as Paillier or ElGamal?
20 views

### How to find the time complexity of modular multiplication? [duplicate]

There are two number of length m bits. How do I prove that the complexity of modular multiplication of these two numbers is $O(m^2)$.
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### What is the private key in RSA?

I'm new to cryptography and I have a doubt: I read some pages a bit different definition for the RSA private key: In 1 - (n, d) In 2 - ...
108 views

### Authentication protocol which detects client impersonation from another machine

Consider following authentication protocol. Client ClientA knows some initial secret KeyA shared with server. Client also knows IP of legitimate server. Now when client wants to establish connection ...
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### improve of cryptography algorithm [on hold]

This is my algorithm.. ...
32 views

### Boolean functions in cryptography

I recently started becoming interested in Boolean functions. Because they are defined as $f: \{0, 1\}^n \rightarrow \{0, 1\}$, or in other words only over $\{0, 1\}$, I guessed they can somehow be ...
21 views

### How do attacks on WEP work?

There is an abundance of tools and tutorials on how to break WEP encryption. However, I fail to find a nice resource that gives a clear break-down of why the attacks are possible. For example, I know ...
609 views

### RSA encryption using multiplication

Generally in RSA we encrypt as $m^e \pmod n$. Will RSA work if we replace the power by normal multiplication? $E = (m \times e) \mod n$ and decryption as $c \times d \mod n$. What will be $d$ ...
62 views

### Is correlation in vector distributions “dangerous”?

Consider the two vector distributions $\xi,\chi$ described below, each one outputting integer vectors of length $n$ with coefficients in $\{0,\dots,n\}$. Distribution $\xi$ samples each coefficient ...
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### Symmetric cipher speed (AES vs Camellia vs Twofish)

If I have understand correct, Twofish is more secure (harder to break) than AES and Camellia, but Twofish is slower than AES and Camellia. But how can I mesure the speed difference between AES vs ...
18 views

### Currently Best Integer not bit FHE [on hold]

HElib encrypts and evaluates on bits. Are there any FHE that evaluates on encrypted integers? If there are more than one, which one to choose?
603 views

### Generation of a cyclic group of prime order

I am trying to implement a cyclic group generator in Java, but I am running into some issues. In many cryptosystems, the following phrase is expressed during the key generation stage. Let G be ...
53 views

### Understanding the Hidden Subgroup Problem specific to Integer Factorization

I've been reading about the Hidden Subgroup Problem (HSP), specifically trying to understand how it is related to the integer factorization problem. I've read What exactly is the impact of the hidden ...
184 views

### Formal verification in cryptography

I have seen in some places that people use formal verification and/or computer-aided verification for cryptography (tools like ProVerif, CryptoVerif, etc.). How do these approaches work?
29 views

### Modelling crypto protocols using Formal methods

How to start working with SPIN/Promela for modelling cryptographic protocols using formal method such as LTL?
73 views

### How to choose the reduction function in rainbow tables?

I have a question regarding Reduction Functions in Rainbow Tables. If the hashing function is MD5 or SHA-1 etc then should the reduction functions also be MD5 or SHA-1? That is, should the Reduction ...
44 views

### How secure is the OTR protocol?

I am using Adium and wondering how secure it is. I believe it uses AES-256 (I do not understand what that means) by default. It also requests that users exchange fingerprints with each other before ...
52 views

### Is the use of a 4-round Blake2b permutation in OPP justified?

The MEM-AEAD construction uses a 4-round Blake2b permutation in masked Even-Mansour mode as a (tweakable) block cipher. 4 rounds of the Blake2b permutation are already broken to my knowledge. Why ...
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### Why are hash functions like SpookyHash and MurmurHash so highly collision resistant?

Why are hash functions like SpookyHash and MurmurHash so highly collision resistant? I tried to test these hash functions using a few billion input messages and I found that there is no hash value ...
64 views

### Is this cascading encryption, and is my security weakened as a result?

I'm trying to understand what is, and what is not, considered cascading encryption. All of the posts and conversations I've read over the past few days discourage the practice, including this article. ...
326 views

### mode of operation in cryptography

We need to choose a mode of operation for a Telnet like application where the average message size is between 7 and 1024 bytes. What is the best mode of operation in this case? a. CBC b. CFB c. ...
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### Are there any free to use video and audio chat programs that offer end-to-end encryption that do not let the service know of the content? [migrated]

Skype is compromised, FaceTime is compromised, and I believe Ovoo is compromised. Does anyone know of any genuinely free (not free-to-try or in-app purchase-type applications) that offer end-to-end ...
77 views

### What does the TLS 1.2 client finished message contain?

I am implementing TLS 1.2 and I'm stuck on the client finished message. My question is: what is the size and structure of a clients finished message in TLS 1.2 when using the ...
2k views

### Why should I make my cipher public?

As I understand it, the less people know about the internals of my protocol or cipher, the more secure the protocol is. However Kerckhoffs's principle states that A cryptosystem should be secure ...
69 views

### Practical differences between circuits and turing machines for cryptography

In formal cryptography, we model algorithms (mostly our adversaries) as (Probabilistic) Turing Machines or as boolean circuits. In our lecture on formal cryptography, we learned that circuits are more ...
40 views

### How is decryption done in AES CTR mode?

Since AES CTR mode uses a unique IV and counter to produce the key to XOR with the plain text to get the ciphertext, the question is so as to how decryption is done. Since AES CTR produces a ...
61 views

### Extracting key bits from linear cryptanalysis equation for SDES

From the linear cryptanalysis of SDES, we get a linear equation consisting the K[1, 3] of the round key 1 and 2. From this how will I retrieve the key bit? How do we solve the linear equation we get ...
31 views

### How robust is my coded output?

I create codes and ciphers and as a hobby and I was wondering if there was any outfit that would 'test' your output to see how resilient it is. Is there a group anywhere that will accept code, try to ...
66 views

### Backdoor in NIST elliptic curves

Let $E$ be an elliptic curve defined over a finite field $F_q$ with prime order $n$ and $P,Q \in E$ and $k$ be private key such that $kP=Q$. Since $n$ is prime, $E$ is isomorphic to $Z_n$. Suppose ...
12 views

### Shamir secret sharing and homomorphism [on hold]

Problem: Implement Shamir’s (k, n) Secret Sharing (SSS) scheme, with $k = 3, n = 5$, to (a) Find shares of a given set of numbers. (b) Compute average from shares (c) Choose any three averages ...
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### One time Key Encapsulation Mechanism?

For KEM's, do you only exchange a private key once via the public key encryption and then do all further encryption with this private key, or is a fresh private key sent out with each message? The ...
44 views

### How solid is this method of encryption? [on hold]

Let's say your message is "This is a message." Now translate it into numbers. a=1 b=2 c=3 so on and so forth. Now take those numbers and turn them into three digits based on a randomly generated ...
763 views

### How can mega store my login details and still be secure?

I understand how Mega's encryption works. For a quick summary of all those in the future looking for an answer on this... here is how it works: Upon first signing up for an account you make a ...
433 views

### Security of tokenization of plain text conversations - cryptanalysis

I came across a marketing video here. They claim to perform AES encryption and tokenization of sensitive data, at the corporate gateway, before it leaves the company firewall destined for the public ...
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### Best known attack

I always have listened the term best known attack but I have doubts respect to this term, becase there are several kinds of attacks for example structural attacks, inversion attacks. It is possible to ...
11 views

### Can someone please decrypt “NUZGIEJX” using Vigenére [on hold]

The key is "FUN". I just want to make sure I am doing it correctly.