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Im looking to learn about forging CBC-Macs.
Given the CBC-Mac for a Message M and the Key used to encrypt the message K.
Can I create a new message M' which would have the same CBC-MAC?
Original Unknown Message: M
CBC-Mac of Original Unknown Message: X
Key used in CBC Block cipher: K
New message with CBC-Mac = X: M'
|
I am reading a networking book by Mike Meyers, and it says that a certificate is a file that contains
A public key, and
A signature (cryptographic hash of the public key, encrypted with the private key).
I can understand that the signature helps ensure that the public key was not tampered with. If I make a request to... |
I'm somewhat new to cryptography and I've been looking at knowledge extractors in proofs of knowledge and I am a little confused by the use of somewhat different definitions.
In textbooks or early papers, (as an example see Definition 4.7.2 in Goldreich's textbook [G]), I've seen the knowledge property defined roughly ... |
I am trying to determine how to apply ZK proofs to the asymmetric scenario below.
Say there is a list of 5000 secret elements on a centralized web server.
Users are trying to guess what those 5000 elements are.
However, users don't want to reveal their incorrect guesses to the central server.
Users submits proofs of t... |
Does anyone know where to find bigram frequencies for English alphaber with space?
|
Suppose I first define some function f(x) where x is some unsigned 256-bit integer, and the function's output is a set of distinct strings of any length so that output set would be 2^256 unique strings, i.e. a bijection for the specified domain of x.
Example f(x) = 0xAA || x || 0xBB (|| indicates byte concatenation), b... |
I am trying to learn about basic hashing using the modulo operator and am a bit confused. In the text that I am reading, it says that the modulo operator can be used to accept an input of any length and return a fixed-size output. However, take 1mod11 = 1 and 21mod11 = 10. The first equation yields a one-digit number a... |
I have read that perdersen commitment can be used to hide the messages such as transactions by participants. The verifier will just have to make sure that the difference of the commitments is zero. But I don’t quite understand how is this verification valid.
For eg, for the input messages, 10, 5, 2, Alice could choose ... |
I am learning to utilize flush+reload method to get private key of CRT-RSA.
CRT-RSA calculates two parts separately: mp = c^dp mod p and mq = c^dq mod q
x = b^e mod m is calculated by the code below.
[![enter image description here][1]][1]
There is a loophole in this method, that is, the execution of Square-Reduce-Mul... |
Moderator note: this question has moved there at reverseengineering-SE.
I'm trying to reverse the save game of an old game. It use text codes to save the games (anyone remember this?). When decoded the data contains game info like level, checkpoint, objects in inventory, etc.
I ported the code of the decoding function... |
In the "On the Non-malleability of the Fiat-Shamir Transform" article by Faust et.al., there is a definition for unbounded NIZK. What unbounded means in this context? It does not look like perfect ZK because the distinguisher is PPT and not unbounded as required here.
|
In Whatsapp, are the same private keys used in all my devices? Is the sharing of the keys from scanning the QR code on the web browser to link to my device? Thank you!
|
Suppose in a network, the identity of users is their public key, which is generated based on the ECDSA algorithm. That is, to create a valid identity, a user must generate an ECDSA public key and then send it to the network administrator for validation. Then, the network administrator needs to know if the user followed... |
Assuming that I want to encrypt a 1 GB file with e.g. AES in GCM mode or ChaCha20Poly1305.
[I'm specifically referring to the cryptography module for Python: https://cryptography.io/en/latest/hazmat/primitives/aead/ but I can't find anything in the documentation]
For "non-AEAD" ciphers, the syntax is basically
cipher =... |
this is a school challenge.
I have a cipher file which is the audio file, and no key of course, encrypted with AES ECB mode. The size is around 550 Kb. I know the key size used is 16 bytes, and I have the plain file of 20 Kb that is part of the whole original plain file, but I do know the offset of it.
I guess attackin... |
I want to share the secret key of the BFV scheme among N users using the additive secret-sharing protocol (n-out-of-n threshold secret-sharing). Can anyone please help me to adapt the two algorithms correctly?
Note that the secret key of BFV is generated as a random ternary polynomial from
R
2
(
R
2
is the key d... |
Not sure if this falls into crypto from contextual point of view but it is about hashing algorithms. I have two directories -- assets/ and cache/. Anytime there is a file added, deleted, or changed in the assets/ directory, a corresponding, application specific file will be generated in the cache/ directory. On top of ... |
I know exactly how a generated BitLocker recovery key works and I can write a code to brute-force it.
How is the recovery key generated though?
I could think of some answers:
it is generated using an algorithm which generates a random number using a specific seed;
it is generated using some information extracted from... |
I've recently become quite interested in lattice based cryptosystems, and I wish to understand them more deeply. I have only a rudimentary understanding of the shortest vector problem (SVP), and its brother the closest vector problem (CVP), which are central to this form of cryptography, though I understand lattices, v... |
I want to implement Camenisch-Lysyanskaya Signatures based on the strong RSA (SRSA) assumption using python. However, I have a question.
Here public key of the signature PK=(n,a,b,c) and private key SK=p
But while signing the message, only the parameters from public key is used. Am I missing something because for signi... |
In Regev's Paper "On Lattices, Learning with Errors, Random Linear Codes, and Cryptography" he considers in the introduction of the paper the "learning from parity with error". Where we have an unknown $s \in \mathbb{Z}_2^n$ our goal is to find this $s$, given a list of equations with errors e.g. $\langle s,a_i \rangle... |
What kind of attack of image encryption that exist out there, especially if the cipherimage was created using secure stream-cipher like Salsa20 (256 key) or ChaCha20 (256 key)?
From https://cr.yp.to/streamciphers/attacks.html#chacha20 page, i know that the algorithm itself can be attack using Brute force attack to find... |
I am implementing pollard kangaroo to compute the discrete logarithm of a group element $G$ of generator $g$. $G$ is a$\mod p$ multiplicative group ($p$ a prime number). So, I want to solve $g^a=h$ knowing $a\in[[0,w]]$.
What I am basically doing:
Define $w=2^{58}$
I define $k$.
Split $G$ into $k$ subset $S_i$.
I defi... |
I am looking at the description of Weil MOV Attack from the Vanstone, Menezes Book (Guide to Elliptic Curve Cryptograpy)
Suppose now that the prime order $n$ of $P \in E(F_q)$ satisfies
$gcd(n,q) = 1$. Let $k$ be the smallest positive integer such that
$q^k \equiv 1 \pmod n$, the integer $k$ is the multiplicative orde... |
Let's say you downloaded a file from a certain website, and later the website claims that it didn't made that file available, is there any way to prove that the website is lying?
Example 1: You download a youtube video and the channel later delete the video and claim that the video was never there.
Example 2: A website... |
I saw some recent papers(e.g Encrypted DNS --> Privacy? A Traffic Analysis Perspective) about adopting ML technology to overcome cryptography implemented to ensure network security. Network packets have a fixed form and limited possibilities for each section which could be used as side-channels. I'm wondering what are ... |
CMAC is defined for AES for authentication. My question is pretty simple: is it possible to extend CMAC for ChaCha? Does it even make sense? I cannot find anything related and I am wondering if I am missing something trivial.
When compared to AES, there are algorithms for AEAD with AES, in addition to CMAC for AES. CMA... |
In the TLS 1.2 handshake, after checking the certificate, the public key from the certificate was used to encrypt the data to create a symmetric encryption key, hence the authentication took place on the factor of knowing the private key, as it is needed to decrypt that data.
In TLS 1.3, the public key cannot be used t... |
I need to send sensitive information from frontend to backend and from backend to frontend. Which is best to do this by encrypting all the communication between the parts? Should I use symmetric/asymmetric in encryption? What is the best approach?
|
I want to share the secret key of the BFV scheme among N users using the additive secret-sharing protocol (n-out-of-n threshold secret-sharing). Can anyone please help me to adapt the two algorithms correctly?
Note that the secret key of BFV is generated as a random ternary polynomial from R 2 ( R 2 is the key distribu... |
The famous names of mathematicians at Bletchley Park are now a matter of public record and include eminent figures such as Max Newman, JWS Cassels, Philip Hall and Sandy Green as well as the more cryptanalytically celebrated Alan Turing, Jack Good and Bill Tutte.
Other countries also began making use of mathematicians ... |
I'm doing a small code that performs a simple SSL/TLS analysis and I'm stuck on determining the size of the key exchange in the case of DH / DHE.
If I take the following example (wireshark capture) :
p Length: 128
p: acb31[...]
g Length: 1
g: 02
Pubkey Length: 128
Pubkey: 1935[...]
I just thought I could get the neces... |
The NIST publication for AES defines $Nb$ as:
Number of columns (32-bit words) comprising the State. For this
standard, Nb = 4.
In Section 5.2: Key Expansion, $Nb$ has been used to calculate the number of round keys to be generated.
Section 6.3 states:
This standard explicitly defines the allowed values for the key ... |
I need a way to make the signatures shorter, currently with a ring size of 1000 members I get a signature size of 34000 bytes, this is too big for me I need a way to make it smaller.
I tried compressing the signature with gzip but it only makes it bigger, the only other solution I can think of is to use other linkable ... |
I've been messing around with lattice based cryptography and came across the SWIFFT algorithm, a provably secure cryptographic hash function which has a security proof stating that finding collisions is as hard as reducing a lattice, a provably difficult problem, infeasibly difficult.
I could understand basically using... |
I am having difficulty visualizing the stepping process.
The permutation of Wheel I of Enigma I is as follows:
ABCDEFGHIJKLMNOPQRSTUVWXYZ
EKMFLGDQVZNTOWYHXUSPAIBRCJ
For this rotor, the stepping notch is at Y. The literature states that the letter Q is visible when the notch is positioned, and after the step, R is... |
I'm trying to verify a time stamp token embedded into a PDF using the PDF 2.0 feature of the "Document Time-stamp Dictionary". The embedded time stamp token is exactly the token of a time stamp response from a time stamp authority server.
Since the OpenSSL library of Ruby doesn't seem to provide the necessary interface... |
Imagine an MPC protocol where both multiplications and additions come for free (2 round). The protocol works over arithmetic circuits, and the security setup is as relaxed as possible:
Semi-Honest.
Honest Majorities.
Does such a protocol exist?
If so, what would be the most restrictive security model, and maintain t... |
I am wondering if there might be a scheme for the following scenario: Let's suppose a government wants a truly democratic intelligence agency. For this the government publishes all intelligence reports in an encrypted format to the public and allows people to do a majority vote to declassify its contents.
A naive solut... |
I have a pair of coordinates of which all values belong to $Z_{p}$ where $p$ is a prime. I want to construct a straight line that goes through those two coordinates. Then I want to generate two more random points on that line. I also need a function that returns the value of y given any x on that line. For that I can t... |
Given a random 256bit key used for data encryption with Streaming AES GCM
I would like to wrap it for backup with AES GCM.
Is it safe to use
HKDF(
km = new random 256bit key
salt = Argon2(weak password) 256bit
algo = HMACSHA512
outputkey = 256bit )
in theory the km parameter has to be stored safely off... |
I'm trying to understand CKKS (non bootstrappable) and I'm struggling with the encoding part. Particularly with to questions.
I'm using the original paper , "Homomorphic Encryption for Arithmetic of Approximate Numbers
", also this notes "Lattices, Homomorphic Encryption, and CKKS"
and this blog.
Given a vector $z\in \... |
I have some troubles with this proof from Foundations of Cryptography by Oded Goldreich p.52.
Why exactly does the parsing of x to x'x'' take quadratic time in length x'x''? If I have |x'x''|=p(|x'|), and a x of this length. I will try step by step all prefix lengths |x'| in {1, 2, ..., |x|}, till I have p(|x'|)=|x|. S... |
How many timestamps are issued when someone signs a PDF with timestamp Long Term Archive (LTA)? Why is it necessary to issue more than one timestamp?
|
TL:DR I'm learning RSA. I've made it to the decryption stage but I don't know how to handle huge exponents. These are my values:
p = 17
q = 31
e = 7
m = 2
n = 527
(n) = 480
de = 7(343) = 2401
d = 343
PU = {7, 527}
PK = {343, 527}
C = 128
So I'm unable to handle the processing of the decryption of Cipher text 128, wi... |
I am trying to solve this problem from https://toc.cryptobook.us/book.pdf.
I am having trouble with this question :
(Baby Bleichenbacher attack). Consider an RSA public key (n, e), where n is an RSA
modulus, and e is an encryption exponent. For x ∈ Zn, consider the predicate Px : Zn → {0, 1}
defined as:
Show that by q... |
I've been reading lately some contradicting messages with regards to the quantum-safe resistance of AES128. First, there are blog posts by Ericsson people like these ones:
Can quantum attackers break AES-128?
No. NIST estimates that a quantum computer breaking RSA-2048 in a
matter of hours could be built by 2030 for a... |
When I'm convincing non-believers that crypto is secure, I have a hard time with hash functions and the associated block ciphers.
It is easy to show why RSA is hard to crack: I multiply two small primes and ask people to factorize the product. They find it difficult compared to the multiplication step.
It is easy to sh... |
Yesterday IBM announced that they have a 433 bit quantum computer, called Osprey. There is nothing in the press releases I can find that says whether it can or cannot run Shor's Algorithm.
They also say they are on track to release "Condor", an 1121 bit processor next year.
Shor's algorithm, as far as I know, requires ... |
I'm working on this past exam paper and found this question about pre-image resistance and its relation to data integrity:
Displaying the hash of a file on a website in order to provide data integrity relies only
on the preimage-resistance property of the underlying hash function. Is this true or false?
I answered fals... |
I'm creating a mobile chat application using python (django) as backend, and I'd like to implement an end-to-end (E2E) cryptographic system for protecting messages.
Now, as I understood so far, when one of the user create the chat, the server will go to generate 2 couples of public and private key, and the next step is... |
So I'm currently working through this cryptography question and so far I have the answer of an increase of hackers due to increase in computational power. But apart from that I don't know what else. Number spoofing? Weaker security mechanisms in organisations? Not really sure apart from the computational power increase... |
I am currently studying the Kyber Paper. I have a question about section 2.2 Compression and Decompression, but first I would like to quote the statement:
Compression and Decompression. We now define a function
$\text{Compress}_q (x, d)$ that takes an element $x ∈ \mathbb{Z}_q$
and outputs an integer in $\{0,..., 2^d ... |
I have a CBC-MAC scheme using AES as the block cipher (T=H_K1(M)), which gives me a tag and a stream cipher using another key and a nonce, which gives me a cryptotext (C=E_K2(N,M)). So my question is based on a known-plaintext attack to create a valid (ciphertext, nonce, tag)-tuple.
I already figured out how I can crea... |
Suppose you have two files encrypted with AES-256. One of the two files is 5MB, the other one is over 1GB. Their passwords are reasonably strong: >12 characters, letters, numbers, upper and lower case characters. If you tried to brute-force them, would it take a shorter time to try the same number of passwords on the s... |
Here is my idea:
Under the symmetric key encryption. Alice and Bob share the symmetric key K. Let HASH be a secure hash function and Enc_k(message) be the encryption message m by AES in the CBC mode with a random IV
First, Alice compute c = Enc_k(message)
Second, Alice compute t = Hash(m)
Third, Alice sends (c, t) to B... |
I am reading the paper A Concrete Security Treatment of Symmetric Encryption and am confused by the reduction from ROR to LOR on page 11. Specifically, when it says:
When $\mathcal{O}_2(\cdot)=\mathcal{E}_K(\mathcal{RR}(\cdot,0))$, we have that $\mathcal{O}_1(\mathcal{LR}(\cdot,\cdot,0))$ and $\mathcal{O}_1(\mathcal{... |
I am having a university assignment that requires me to study on the threats that quantum computer poses to modern cryptography.
At the moment, I know that modern symmetric encryption will reduce their key size strength in half through Grover's algorithm. It can also break existing standardized RSA, Curve448 and Curve2... |
As far as I know, key exchanging algorithms are vulnerable to an active MITM attack.
Let A (Alice) and B (Bob) be parties with no secret information. An adversary C
playing man-in-the-middle interacts with A pretending to be B, and
interacts with B pretending to be A. At the end, C establishes a
separate channel with ... |
Suppose Alice has a verifiable (message, signature) pair from Cedric, who would not cooperate and routinely uses an algo (ecdsa, eddsa, rsa, or insert yours here) to sign messages.
Alice wants to interactively prove to Bob she has that (message, signature) pair with the valid signature, obviously. It doesn't have to be... |
I've recently become interested in homomorphic encryption, specifically how boolean gates are constructed to do arbitrary circuit arithmatic on the encrypted data without decrypting it.
I have heard that all you need are arbitrary addition and multiplication operations to arbitrarily construct boolean gates that can op... |
Given the following code, extracted from a Bip39 implementation for Android by Zcash
PBKDF2SHA512(
passphrase = veryHighEntropy secret bytearray,
salt = pontentiallyLowEntropy secret bytearray,
iterations = 2024,
)
What happen if the passphrase gets leaked? is the total entropy of the hash reduced to the e... |
Problem example
Let's say I have a plaintext with length of 50 bytes. I want to encrypt it using a stream encryption algorithm ChaCha20-Poly1305.
Poly1305 generate a 128 bit hash (16 bytes), so encrypted message will be of length 50 + 16 = 66... If I append nonce to it (12 bytes), it'll be 78 bytes.
But... When I add f... |
Suppose there is a ciphertext $C_1$ that hides message $m_1$ using a distributed additively homomorphic public key. I would like the holders of the key to run a protocol where if $m_1 = 0$, then it will return a ciphertext of $0$, but if $m_1 \neq 0$, then it will return a ciphertext of $1$. However, I would like thi... |
I am trying to understand digital signatures and digital certificates. I know that digital certificates verify a server's public verification key but what does the website's (client) private verification key sign?
|
I was reading the SPHINCS+ paper and got confused in the signing with FORS (forest of random subsets) part.
I understand how we can sign a message using FORS but I couldn't understand how we choose the corresponding WOTS+ key to sign the FORS root node with.
If we are going to choose only one of the XMSS trees in the b... |
Compute $n = pq$ where p and q are prime. Fix $e$ to be coprime to $\phi(n)$. Compute $d = e^{-1} \pmod n$ and verify $ed \equiv \phi(n) \pmod n$. We sign the (hash of) a message with $s = h^{d}$. A verifier computes $s^e = h \pmod n$. Why can't an attacker fix $h'$ and solve ${s'}^e = h' \pmod n$ to forge a signature ... |
I need an encryption scheme where a single source/location can encrypt using their private key and while anyone with access to the corresponding public key can decrypt it. It has to be asymmetric to avoid any one else deriving that private key and pretending to become that source. For example, government issues an encr... |
I am currently trying to follow the proof of correctness in the CRYSTALS-Kyber paper. The following is an excerpt of the proof:
On the one hand, I am interested in how exactly one justifies/argues that $\mathbf{y}$ is pseudorandom, based on the MLWE assumption. About the difference $(\mathbf{y} - \text{Decompress}_q(... |
Suppose I have some plaintext $M$, and I want to have some process $f$ to make ciphertext $M':=f(M,s)$, where $s$ is some secret. The ciphertext $M'$ can be decrypted by using some decryption process $M=g(M',k_1,k_2)$, where $k_1$ and $k_2$ are two keys, and $k_1$ is a random key (cannot be controlled, such as the curr... |
I have a course work for university.
The question is:
My solution to the question is:
P||R = D(K,C)
However, in the question it doesn't say we are given R so I'm not sure how to get P from P||R.
This could be because my understanding of concatenation is incorrect as I see it as simply adding the nonce to the plai... |
Is it possible to generate a new valid signature for some arbitrary message using DSA if we know existing signatures for the same message? We are an adversary, therefore we do not hold the private key, but we have access to a couple of signatures for the same message, say $(r_1, s_1)$, $(r_2, s_2)$.
|
I am trying to understand the post quantum based signature scheme Dilithium. I know what the hard problems are in the scheme, but I am having trouble in understanding the utilization of short integer solution in the scheme. Specifically speaking, I can't understand exactly where this problem is used in the scheme. Also... |
Recently, I started looking up for details about implementing a blind signature on ed25519 cryptographic. I saw this article https://stan.bar/blindsig/ by Stanislaw Baranski about it.
In the first point, it says that Bob generates random number (nonce) $k$ in range $(1, q-1)$, computes
$r=k \times G (\mod p)$
$r=k×G(\m... |
I know that the security of both are the same (only nonce size is different). But which one is faster and better to use, when encrypting a lot of files (500+, from 1MB to 200MB)?
|
Given a RSA modulus $n$, which is the product of two safe primes:
\begin{align*}
P &= 2p + 1 \quad\quad\quad
Q = 2q + 1 \\
n &= P \cdot Q = 4p q + 2 p + 2 q + 1
\end{align*}
The hidden group order is then
\begin{align*}
\Phi(n) &= (P-1)(Q-1) = 4p q
\end{align*}
Choosing some random element $z \in \mat... |
In this paper I'm reading (specifically section 3.1), the authors say that the BFV encryption scheme supports plaintext multiplication, which basically means that given a ciphertext, $c$ that is an encryption of a plaintext $p_1$ and a plaintext, $p_2$, one can easily compute an encryption of $p_1 \cdot p_2$. What's mo... |
Considering that P1 has value x, P2 has value y and they want to compute x+y without telling the other what he has,So P1 and P2 secret-share their values to each other.
Now P1 gets x1 and y1, P2 gets x2 and y2 and they locally compute xi+yi. If P1 want to compute x+y = (x1+y1)+(x2+y2), P2 need to send x2+y2 to P1, but ... |
In the SPHINCS+ paper(https://sphincs.org/data/sphincs+-paper.pdf) part 3.2, it explains that they are not using l-trees as a direct consequence of the use of tweakable hash functions.
I have read the tweakable hash function part, but the math made me so confused. Can you explain to me the difference between the usual ... |
Let $(E:y^2=x^3+ax+b) $ on $\mathbb F_q$, with $ q \mod 2=1$.
If $\gcd(3,q-1)=1$ and $a=0$, then it's easy to find the cardinality of the curve $E$ : $|E|=q$.
Are there an another conditions on $(q, a, b)$, where it's easy to find $|E|$?
|
Let $n = pq$, $p,q$ are two large primes, then $\mathbb{Z}_n^*\cong \mathbb{Z}_p^* \times \mathbb{Z}_q^*$. We disclose $n$ and keep $p, q$ secret. Is it secure if we disclose a random element $a$:
$a\in \mathbb{Z}_n^*$, $a = 1 \mod p$
That is, to disclose a random chosen element in $\langle 1\rangle \times \mathbb{Z}_q... |
Web Crypto API allows creating ECC keys with some known curves: https://developer.mozilla.org/en-US/docs/Web/API/EcKeyGenParams
Those are P-256, P-384, P-521.
However as answered at this answer https://crypto.stackexchange.com/a/30273/99862
There are secp256k1, and secp256r1, and maybe more?
Which is the exact P-256 im... |
I am confused about whether/how ZKP based entity/message authentication scheme can achieve identity privacy, especially unlinkability. The security properties I'm looking for in the scheme is authentication (identity proof), such that the prover can prove it has some kind of identity so that it is allowed to be in the ... |
$ G \space is \space an \space elliptic \space curve \space group \space G \space with \space order \space q$
and three hash functions are defined as this:
$$
H_1: \{0,1\}^*\times G \rightarrow Z^*_q
$$
$$
H_2: \{0,1\}^*\times G \times G \rightarrow Z^*_q
$$
$$
H_3: \{0,1\}^*\times Z^*_q \times G \times G \rightarrow ... |
I'm trying to understand the complexity of computing the Merkle root for stateful hash based signature schemes. Section 4.1 of the chapter on hash based signatures in "Post Quantum Cryptography" – by Bernstein, Buchmann and Dahmen (Springer Berlin Heidelberg states) -
($H$ in the following excerpt is the height of the ... |
I am trying to understand how adding padding like the PKCS1.5 RSA signature scheme can prevent the existential forgery attack in RSA. Is it just by changing the structure of the message?
|
In The Algorithmic Foundations of Differential Privacy (Dwork, C; Roth, A), the formal definition of differential privacy is given as:
"
The randomized algorithm $\mathcal{M}$ with domain $\mathbb{N}^{|\mathcal{X}|}$ is $(\epsilon, \delta)-$differentially private if for all $\mathcal{S} \subseteq Range(\mathcal{M})$ an... |
I was reading this post https://senderek.com/SDLH/ about Shamir's hash function, which is defined as follows:
Let $p,q$ be positive prime integers and let $n=p\times q$. Let $\ell = \mathrm{lcm}(p-1, q-1)$. Find $g \in (\mathbb{Z}/n\mathbb{Z})^*$ such that $\ell$ is the smallest positive integer for which $g^\ell \equi... |
What kinds of properties does a KDF need to have in order to be considered secure? What steps should be taken during analysis to test for flaws?
In particular, I mean a KDF that is going to be used as a one-time pad. If the plaintext is 1 MB, then the KDF will produce a 1 MB key. And xor them together tp produce the ci... |
I'm deriving a shared secret using ECDH with Ed25519 keys. According to the specification (page 5), the shared secret then can be any valid Curve25519 public key, i.e. any valid 32 bytes. My environment is such that I need to map this shared secret to being only 31 bytes long. A simple solution to this would be to just... |
In Zero-Knowledge (ZK) proofs/arguments of knowledge, the ZK knowledge property informally says that it is possible to simulate the output of a (malicious) verifier interacting with a prover knowing a witness $w$ without using $w$ at all:
$$\{OUT_{V^*_\lambda} \langle P(w,x) , V^*_\lambda(s_\lambda, x) \rangle\}_{\lamb... |
So I'm currently working on a past exam paper related to cryptography, this question essentially asks the reader why digital signature schemes are not used today.
Yet, when I did my research on this topic online, I found out that most technologies do in fact use digital signature schemes. In fact I'm even confused by w... |
I have a course work for university, the question is:
Consider a symmetric encryption scheme with its encryption operation written as
$$C = E(K, R||P)$$
where $E$ is a block cipher encryption algorithm, $K$ is an encryption key, $R$ is a random nonce (i.e., it is randomly generated for each encryption), $P$ is a plain... |
We call two ensembles $X$ and $Y$ indistinguishable in polynomial time if for every probabilistic polynomial-time algorithm $D$ and for every positive polynomial $p(\cdot)$, and all sufficiently large n's we have $$|Pr[D(X_n,1^n)=1]-Pr[D(Y_n,1^n)=1]| < \frac{1}{p(n)}$$.
One question I didn't confront with at the beginn... |
In the zero-knowledge cryptography nomenclature, we have multiple representations of arbitrary computation suitable for submission to various proof backends (e.g. Groth16). Two specific examples spring to mind: rank-1 constraint systems (R1CS) and Algebraic Intermediate Representations (AIR).
What are these called?
|
If a password p is selected from a space of 2^64 passwords, and the server stores this as a hash, h = SHA-256(p||s) where s is a random 128-bit salt. How many maximum hashes would an attacker need to perform to recover "p" given (h,s)?
I was thinking that this is a pre-image attack so the attacker needs to find the sam... |
I`m solving one crypto problem on rsa.
p^e - q^e = C1 (mod n)
(p-q)^e = C2 (mod n)
n = p*q*r; p,q,r are prime numbers
e = 2 * 65537
We have e, n, C1, C2.
It's impossible to find p, q, r from this system of equations, since there are 3 unknowns in the system of 2 equations. But is there any way to reduce the possibl... |
OU cryptosystem: $N = p^2q$, the secret key is the factorization of $N$, the public key is $g\leftarrow \mathbb{Z}_N$, $g^{p-1} \neq 1\mod p^2$, to encrypt an element $m $ $\in$ $\mathbb{Z}_p$, choose $r\leftarrow \mathbb{Z}_N$, then $Enc(m)= g^m\cdot h^r$, where $h = g^n$
In paper: Paillier's Cryptosystem Revisited [... |
Let $a_n$, and $b_n$ two sequences generated by two LFSR with connection polynomials $P$, and $Q$.
How to show the sequence $(a_n \cdot b_n)$ can be generated by a LFSR wit connection polynomial of degree upper bounded by $\deg(P)\cdot \deg(Q)$?
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As we know, the Schnorr signature enjoys the linearity property, which does not exist in ECDSA. It seems the Schnorr signature is more efficient and can bring more features than ECDSA. What is the advantage of ECDSA over the Schnorr signature? Will ECDSA gradually be replaced by the Schnorr signature (especially after ... |
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