# All Questions

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39 views

### Validating JWT works with small changes to public key, why?

I was trying to verify the following JWT on JWT.io with the following public key: ...
64 views

### “Dave Check” for a tweakable P-256 ECDH KDF

I have two devices with hardware tokens that contain P-256 private keys, and which allow me to compute ECDH shared secrets with arbitrary public keys. I need to build a tweakable key derivation ...
187 views

### Is this toy RSA demonstration flawed?

I want to present the basics of how RSA works to an audience of beginners in cryptography. The problem is that I am lightyears from being an expert. After reading about how RSA works in wikipedia, ...
44 views

### Is it safe to use shared secret as a symmetric key in one way communication?

I have a one way communication from one device to another, which needs to be secure and there cannot be any feedback in the other direction. Now both sides happen to have ECC P-256 key pairs and they ...
39 views

### Breaking zero knowledge protocol for graph hamiltonicity

The FLS zero knowledge protocol for graph hamiltonicity proceeds as follows. The prover (proving graph hamiltonicity of graph G) picks a random cycle graph C, and sends its commitment to verifier. ...
25 views

### Problem with Fiat-shamir on poly-round interactive protocol?

I have read in many places that Fiat Shamir technique is used to convert constant round interactive protocols to non-interactive arguments. What would be the problem in applying Fiat Shamir to poly-...
49 views

### Is there a zero knowledge proof to show an encrypted blob is the key for a given public key?

Let's say I have a private key x with a corresponding public key y. If I encrypt x as ...
102 views

### Could public-key crypto be performed long ago if the idea had been discovered?

Public-key cryptography was not invented until the 1970's. Apart from the idea not existing earlier (as talked about here), is there any reason it could not have been used earlier? For example, are ...
33 views

### Erasure Coding: How does it function?

Following article explains a simplified version of Erasure Coding: Link to the article here is the recipe: Take a file of size M. Split the file into k chunks, each of the same size M/k. ...
29 views

### Guess the number of characteristics in differential cryptanalysis

I am doing some research on differential cryptanalysis for my master thesis. I analyzed some toy ciphers like the one in the popular tutorial about differential and linear cryptanalysis from heys Link....
54 views

### Generating nicer diceware passwords without losing entropy

Yes, another one of those "I have found a great password-generation strategy" waiting to be shot down! It seems that although diceware aims to be a secure and user-friendly password generation ...
39 views

### Output a pad (un-keyed, variable length) from an input seed (fixed value for same seed)

I want a function $y = f(x, len)$: $x$ is the seed. $y$ is the output. $len \in \mathbb{Z^+}$ is the length (bytes) of $y$ Select a seed string $x$ to generate a string $y$. For each same pair of $x$ ...
56 views

I have an application that stores data on the devices. Currently AES/CBC/PKCS5Padding from javax.crypto.Cipher(see reference) is ...
45 views

### Carmichael's function (in RSA) big O notation

What are some ways in which we can compute Carmichael's function and what are the corresponding time complexities in big O notation?? Edit: What are some different Java algorithms that we can use to ...
42 views

### Understanding need for PKI

For simplicity let's say I only have RSA and AES on my hands and I want Alice to talk with Bob over a secure channel. With secure I am implying no MITM and Alice and Bob know they are talking to each ...
53 views

### Is it safe to reuse the salt for generating symmetric keys for a chat application?

I'm writing a program that allows two users to communicate over E2E encrypted chat with a secret they have agreed upon in the past. The process works as follows: A key is derived from the secret ...
46 views

### How to perform the lfsr scrambling used in PCIe for 2 byte input?

In PCIe Gen 3 on-wards there is 128b/130b encoding used which scrambles incoming bit using a LFSR with polynomial: $$G(X) = X^{23} + X^ {21} + X^{16} + X^{8} + X^5 + X^2 + 1.$$ Is there any way to ...
42 views

### How are certificate status obtained on browsers?

There are two ways of checking the status of a digital certificate:- Offline Authentication (CRL) Online Authentication (OCSP, SCVP) Several browsers (like Mozilla Firefox) have given up the use of ...
37 views

### How are CRL implemented?

The source from where I learn states:- CRL (Certificate Revocation List) is the primary means of checking status of certificates offline. But I can't seem to understand how is it possible for a ...
36 views

### MuSig/Schnorr key aggregation: How get the combined private key

Given all parties' private keys in MuSig, is it possible to get a combined private key corresponding to the combined public key? I know it's possible to sign a message, but how to get the combined ...
89 views

### If an algorithm can not produce a true random stream, then an algorithm can not alter its entropy [closed]

Can a transform lower the Kolmogorov entropy of a true random stream and then restore that stream with out loss. If no true then then a transform can not raise or lower the entropy.
14 views

### Sign and encrypt or just sign? [duplicate]

When signing a file or message we can encrypt it with our private key. Is there really any good reason to do this (other than preventing the lazy from reading our message in transit)? Since this ...
33 views

### Tuning the signature size of Sphincs+

If I only need a small number of signatures (perhaps $2^{10}$) for the lifetime of my key pair, how would I calculate the consequent signature size? Unfortunately managing state for an LMS or XMSS ...
129 views

### When to use Argon2i vs Argon2d vs Argon2id?

I've read the manual, and multiple articles / StackExchange posts about this topic, but still can't decide which implementation of Argon2 is best for my use case. I want to securely encrypt passwords ...
83 views

### Discrete logarithms on elliptic curves

In many examples of attacks on public key cryptography, examples of the form $a ^ x = b$ are used, but I can not understand the correlation between this and the multiplication of the generator point ...
658 views

### Does XOR'ing a random number with its inverse reduce its security if the result is a palindrome?

[And four related questions/examples below:] 2) If a random 256-bit number is XOR'ed with its reverse (i.e. the big-endian version XOR'ed with the little-endian version), does this reduce the ...
51 views

### Security of RSA public key depending on how it's computed [duplicate]

I understand that the public key in RSA encryption may be computed using Euler's totient function or Carmichael's totient function. I'm now trying to figure out how the choice of totient function ...
28 views

### How does concatenating diverse hash functions affect collision resistance?

Let's suppose I take 3 different types of hash functions and concatenate them for future safety so that: digest = Hash3( Hash2( Hash1( text ))) Does the birthday attack mean in this case that I must ...
33 views

### Why do I want to use PGP subkeys?

I understand the general notion in play: if my laptop/computer is stolen or compromised I can revoke that particular subkey so (as long as people have updated their keys) they can't impersonate me. ...
20 views

### aspnet_regiis private key storage

I am using aspnet_regiis.exe to Encrypt a connectionStrings on an ASP.Net application. The application in productions runs on a <...
34 views

### Why does the NIST CTR DRBG apparently output the internal state when no additional input is given?

After reading through the specification of the FIPS CTR_DRBG in SP 800-90A (see Section 10.2.1), I got the impression that the output of the DRBG coincides with its internal state as long as no ...
27 views

### How to solve inverse modulo? [migrated]

Inverse modulo can be solved easily by Euclidean algorithm but 3 to the power minus 13 mod 2 can not be easy, I appreciate if anybody can give a solution. For example: $3^{-13} \bmod 2 = ?$
61 views

### P256 Key size and validation [duplicate]

Given a public key on the P-256 Curve is it correct to say that the public key is 64 bytes long ie. (x,y)? Secondly is the private key 32 bytes long? if so, how is the private key generated and why ...
76 views

### Strongest collision resistance test?

An administrator is testing the collision resistance of different hashing algorithms. Which of the following is the strongest collision resistance test? A. Find two identical messages with different ...
35 views

### What is the difference between an anonymous-encryption scheme and an authenticated-encryption scheme?

I was going through Indy-SDK when these two schemes were referenced. I want to know the precise differences between the two. Indy-SDK links for reference to: authenticated-encryption scheme ...
59 views

### How to prove which complexity class a problem belongs?

How to prove that a problem is computationally hard? For example, how to proved that the problem of integer factoring into two prime numbers is difficult? How to prove that the decoding problem of a ...
6k views

### How to check a file was encrypted (really & correctly)

I would like to audit how an implementation of an encryption algorithm is really performed with the following given data of the problem: the encryption mechanism is reversible (this isn’t a signature)...
31 views

### Is there an O(1) in space complexity k-of-n signature scheme?

I was looking in depth into Schnorr signatures recently, and while they are very attractive for their ability to be aggregated, this only works for n-of-n ...
254 views

### AES-CBC streaming configuration IV usage

I am interested in the implications of using AES-CBC in a streaming configuration. Reading the specifications of a few protocols I notice that when using AES-CBC they include IV + ciphertext + HMAC ...
21 views

### key recovery in the ideal cipher model

I'm reading up on the ideal cipher model and can't wrap my head around some basic calculation. Let $E$ is an ideal cipher with $n$-bit key and $n$-bit block. For each key $K$, $E_K$ is random ...
89 views

### Diffie-Hellman algorithm and MITM attack

How does the Diffie-Hellman algorithm prevent MITM attack? I have tried to search about it but i couldn't find any understandable reasons.
48 views

### Understanding the Definition of Most Significant Bits in the Hidden Number Problem

Boneh's and Venkatesan's "Hardness of computing the most significant bits of secret keys in Diffie-Hellman and related schemes" defines the Hidden Number Problem (HNP). The HNP shows that computing ...
38 views

### SDES algorithm purpose

What is the purpose of SDES algorithm? (Session Description Protocol Security Descriptions) What are the problems in the way it exchanges keys? I have tried to search about these quastions but i ...
83 views

### Are there any practical differences between running a PRNG on a subset of bits from an RNG compared to running the RNG?

Given an RNG and a PRNG. We define RNG(k) to mean that the RNG produces k random bits. We define PRNG(k, seed) to mean that the PRNG uses seed to produce k pseudo-...
112 views

### Basic CPA walkthrough

My professor put this on the slides but gave us very little context. It is meant to be an overview of how it works at a high level. I have a programming background and I get the general idea of ...
54 views

### How to go about distributed private/public key pair generation?

I'm trying to implement a protocol in which two parties generate a private/public keypair, where both know the public key, but each party has only one part of the private key and cannot derive the ...
33 views

### How to execute Brute Force Attack and Differential Cryptanalysis on DES [duplicate]

Please explain me the steps of attack implementation
67 views

### Simple commitment scheme using secure hash function

Can I create a simple commitment scheme using a secure hash function? If so, is concatenation with a random secret enough to preserve hiding? (i.e. $C = H( random\_string || message)$) Thank you
I want to know how to be sure that each prime number can be written in the form $6k±1$. How I can find the prime number that exists after a composite number with this property of prime or other ...