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1answer
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: ...
1
vote
2answers
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 ...
3
votes
2answers
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, ...
0
votes
1answer
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 ...
0
votes
1answer
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. ...
1
vote
1answer
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-...
1
vote
1answer
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 ...
1
vote
1answer
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 ...
0
votes
0answers
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. ...
1
vote
0answers
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....
0
votes
1answer
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 ...
0
votes
1answer
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 $x$ ...
1
vote
1answer
56 views

Is the Java function AES/CBC/PKCS5Padding vulnerable to padding oracle?

I have an application that stores data on the devices. Currently AES/CBC/PKCS5Padding from javax.crypto.Cipher(see reference) is ...
-4
votes
0answers
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 ...
2
votes
1answer
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 ...
2
votes
1answer
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 ...
2
votes
1answer
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 ...
1
vote
1answer
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 ...
0
votes
2answers
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 ...
0
votes
1answer
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 ...
-2
votes
1answer
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.
-1
votes
0answers
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 ...
1
vote
0answers
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 ...
8
votes
1answer
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 ...
0
votes
2answers
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 ...
2
votes
1answer
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 ...
0
votes
1answer
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 ...
0
votes
1answer
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 ...
1
vote
1answer
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. ...
0
votes
0answers
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 <...
2
votes
1answer
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 ...
0
votes
0answers
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: $3^{-13} \bmod 2 = ?$
-1
votes
1answer
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 ...
0
votes
1answer
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 ...
1
vote
1answer
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 ...
-1
votes
0answers
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 ...
16
votes
7answers
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)...
0
votes
0answers
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 ...
3
votes
1answer
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 ...
2
votes
1answer
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 ...
0
votes
2answers
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.
2
votes
0answers
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 ...
1
vote
0answers
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 ...
3
votes
2answers
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-...
1
vote
1answer
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 ...
1
vote
0answers
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 ...
-3
votes
0answers
33 views

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

Please explain me the steps of attack implementation
2
votes
1answer
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
4
votes
0answers
48 views

Does the bias in RC4 drop asymptotically further in the keystream?

It's well-known that the RC4 keystream has significant biases that become less prominent later in the keystream. The most severe bias is in the second byte, which has a 128-1 bias towards zero. Other ...
-2
votes
1answer
104 views

Why can every prime number be written as 6k±1? [closed]

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 ...

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