# All Questions

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9 views

### How to extract key parameters from an RSA key? [closed]

I have generated a private-public keypair using the GnuPG utility. The following lists the public key. I want use this public key for my signature verification routine that I'm trying to build using ...
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### Prove E is not perfectly secure for any integer L > 1

Let 𝒨 = {0, 1}^𝐿 − {1^𝐿} be the set all 𝐿-bit strings except the string of 𝐿 1s. Let 𝒦 = 𝒨 and let E be the one-time pad encryption scheme with 𝒦 for the key space and 𝒨 for the message space....
11 views

### Does keeping IV secret increase security of CTR mode?

Let's suppose I encrypt something with CTR mode and keep the key and IV secret. Does keeping the IV secret together with the key increase strength of encryption?
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### Salsa20 Expansion function

I am a beginner in Cryptography and I just started coming across Salsa20 cipher and I was wondering if it has a key expansion just as AES does and if it´s possible to calculate it from its own key. ...
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### Why are there different versions of the Pohlig-Hellman attack?

I think I have an understanding of the Pohlig-Hellman attack on elliptic curves. From page 31 of Pairings for Beginners: Find the group order $\#E(\mathbb{F}_q)$, call it $n$, and factor it. Example: ...
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### Breaking RSA with knowledge of the secret key $(n, d)$

I am following the discussion in Koblitz in the second paragraph in the RSA section (page 94 on my edition).The goal is to show that knowledge of an integer $d$ such that $$m^{ed}\equiv m \mod n$$ for ...
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### What curves can be used with what algorithms?

I've been trying to improve my understanding of elliptic-curve cryptography; I'm currently trying to understand the extent to which curves are interchangeable. Examples of curves: P-256, Curve25519 ...
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### Proving to a 3rd party an email received in a@domain2.com was truly sent from a@domain1.com

Example: I send an email from address@domain1.com to address@domain2.com Using only the email I received in address@domain2.com, I'd like to prove to a 3rd party that I also own address@domain1.com ...
33 views

### Who is the inventor of the OFB block cipher mode of operation

Handbook Applied Cryptography gives two resources for the OFB mode 1980 FIPS 81. This doesn't give any references, unlike NIST. 1983 ANSI X3.106, unfortunately pay-walled. The question is simple, ...
47 views

### Why is this code working

I was doing some introductory challenges at CryptoHack and one of the challenges, more precisely it was Favourite Byte, XOR with a single byte. I did my solution with XORing given string and single ...
35 views

### Trimming uniformly random input for elliptic curve private keys

Imagine there is 256-bit uniform input from CSPRNG. Suppose there is a curve like secp256r1 whose curve order is slightly less than 256 bits. We cannot just ...
33 views

### What settings could've been used to make the following AES-256 encryption? [closed]

Okay, so i have a friend, which are currently attending a basic cryptography class at college, gets so excited about this newly learned encryption method, more specific, AES-256. He wanted to test his ...
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### What exactly is a game, challenger, and adversary?

Here is my understanding of the concept of security games. I bolded some parts that I am not sure about. A cryptographic object is formally defined by its algorithms and what security notions it ...
118 views

### Two untrusting people want to come up with a random number

Two people want to come up with a random number. They don't trust each other nor any third party. What are the known solutions to this problem? I am a quantum cryptography student and am currently ...
44 views

### Is OFB-mode a stream-cipher?

I've seen that OFB is considered as a block cipher mode. But could we consider it also as a family of stream cipher?
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### Modulo p in Elliptic Curve Cryptography

To carry out Elliptic Curve Cryptography between parties, are all elliptic curve equations considered to be in the form $\bmod p$? For example, the $secp256k1$ Bitcoin curve of the equation $y^2=x^3+7$...
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### Coefficent alteration in elliptic curve equation for Elliptic Curve Cryptography [duplicate]

Something caught my attention while reading about the mathematics behind Elliptic Curve Cryptography. When setting up the elliptic curve equation for communicating between parties, why are only the $a$...
39 views

### Which application protocols use elliptic curve key recovery?

Section 4.1.6 of https://www.secg.org/sec1-v2.pdf describes a technique for recovering public keys from ECDSA signatures. I guess Ethereum uses this. Like if you want to validate a particular ...
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### Alternative to physical aspect of security

To answer my question, imagine a device that has some sort of secret(s) (stored on a crypto coprocessor), that is encrypted with some sort of symmetric encryption (like AES). If to make this device ...
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Masking is the process of replacing operations (internally to some cryptographic algorithm) on intermediate values with operations on secret shared values. Then, even if some number of these secret-...
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### Can two different hash function create two unlinkable ed25519 keys from the same randomness?

Assume the following scenario: Alice has access to 32 bytes of true randomness $s$. Alice hashes $s$ with SHA-512, and uses the resulting hash as the secret $d_{A}$ for ...
102 views

### Help breaking ECDSA with biased nonces

I am currently trying to do the cryptopals challenge 62, breaking ECDSA with biased nonces, with the help of those two links (1 2) that describe accurately the attack. However, after around 15 hours, ...
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### Hash verification by key

I want to implement the following algorithm, but don't know what tools to use. D - data I generate some universal value for D - Y I generate some random key - K, get a hash of D by this key - H I ...
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### Is CBC mode of encryption still safe as long as it's not use to send messages over a network?

I'm still reading about the Padding Oracle attack and Side Channel attack that can be performed to decrypt cipher text encrypted with CBC though it's still not clear to me. But base on my little ...
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### EC implementation on Edward curves : what modulo is used in implementation?

I'm trying to implement EC scalar multiplication in the fastest way possible (but still with a good curve) on a GPU. I'm specifically looking to implement it based on https://github.com/Chair-for-...
50 views

### Possible to directly calculate the Recovery ID from a msg, signature and public key in ECDSA/secp256k1?

Problem Let's say I receive a signature $(r,s)$, the corresponding public key and the message that was signed. I don't have access to the private key. I need to know what the ...
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### Is possible to break the encryption on a password by this encryption?

I wonder if it is possible to break the encryption on a password by such encryption: Where E is the encryption function that uses a known public key of the server.
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### Hiding/Obscuring position information in a board game (Part 2)

This is basically a follow-up question to Hiding/Obscuring position information in a board game which technically answered the question, but raised some well deserved critique. To quickly summarize ...
329 views

### Can Fixed–Diffie–Hellman be attacked?

Recently I'm studying Diffie-Hellman key exchange protocol and I've noticed that the basic Diffie-Hellman can be attacked by Man-In-The-Middle attack. I've also read about the Fixed Diffie-Hellman ...
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### Is it reasonable to use DRBG and PBKDF together?

I want to generate a random number using DRBG with below follow: Entropy source -> DRBG -> PBKDF adding PBKDF is redundant ?
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### While Such Algorithm Option Is Possible, How Can Vernam Be The Only Unbreakable Cryptography?

Suppose Alice and Bob choose a number face to face. Let's call it "97" Alice's original message is "Where did you study?" Suppose we have an artificial intelligence. Let this ...
118 views

### Solving system of linear equtions over binary field with error

I have system of linear equations $f_1, \ldots, f_m$ over binary variables $x_1,\ldots,x_n$ where $m$ is much larger than $n$. We know if all equations are correct, we can find solution easily using ...
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### Decrypting a polyalphabetic cipher

I'm currently trying to crack a ciphertext with three rotating substitution ciphers. I've tried dividing the cipher up into three parts and do text frequency analysis since I know the language but no ...
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### Perp notation question

What does the symbol $\perp$ mean? I saw this on a paper where some entity outputs $\perp$.
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### Why is the output size exactly half the capacity for sha-3?

For the SHA-3 family of hash functions, the output size $d$ is always chosen as $d=c/2$, i.e. exactly half the capcity. What is the rational for this? Naively, I think that $d=c$ would make more sense ...
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### RLWE with invertible elements

Let $R = \mathcal{O}_K$ be the ring of ingtegers of $K$, where $K$ is an algebraic number field, and $q$ a modulus. Let $\chi$ be some error distribution used to sample an element $e$. A primal RLWE ...
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### Is it possible to create an algorithm for identification and key exchange using the diffie hellman algorithm with exactly three messages?

Suppose I want to create a new protocol for communication between two sides, I want to use the Diffie hellman protocol for exchanging keys & also want to do a few more steps later so that the ...
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### What does j9T mean in yescrypt (from /etc/shadow)?

For example I have a shadow string $y$j9T$PaFEMV0mbpeadmHDv0Lp31$G/LliR3MqgdjEBcFC1E.s/3vlRofsZ0Wn5JyZHXAol5 There are 4 parts id : y (yescrypt) param : j9T salt :...