Questions tagged [attack]

A cryptographic attack tries to theoretically and/or practically attack the security properties of a cipher and/or algorithm.

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Security of a scheme to prevent MitM in multi-AES

$$c_i'= AES_{128}(c_i,[i,k_i,0]) $$ $$k_i' = k_i \oplus c_i' \bmod 2^{60} $$ $$K_{i} = k_i' \cdot (c_i \oplus c_i') $$ $$c_{i+1} = AES_{256}(c_i',[i, k_i', K_{i}])$$ Those two AES operate each in ECB ...
J. Doe's user avatar
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Different public keys $(e_i,N_i)$ but same decryption exponent $d$

We are given a number of distinct RSA public keys $(e_i,N_i)$ sharing the same unknown decryption exponent $d$. The $e_i$ were computed from $d$ drawn first, so we have different public keys. Can we ...
Pyp's user avatar
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What does it mean the "Distinguisher" in LWE decision version?

As we know in block ciphers, the distinguisher means that despite thousands ciphertexts (and plaintexts), allows an attacker to distinguish the encrypted data from random data. This attack is ...
R. Jalaei Salahi's user avatar
3 votes
2 answers
73 views

Breaking a 'Many' - Time Pad [closed]

I'm working on a problem, where given 12 ciphertexts, I'm trying to decode the 12th and find out the key. I've implemented a crib dragging attack, where the crib is a purely guessed word (not known/...
k0redump's user avatar
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Algorithm attack on an hash attack (Python)

Here is an attempt at a Python implementation of what is described in the paper I attached as an image. The algorithm is too slow or there is something wrong with the code. Any ideas! ...
surimaji's user avatar
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153 views

How to achieve $d-$privacy considering some secrets?

We have a set of secrets $S = \{x_1, x_2, \dots, x_n\}$ known to an adversary. Each $x_i \in S$ belongs to user $u_i$ who needs to obfuscate his secret using the notion of $d-$privacy defined in the ...
Amirhossein Adavoudi's user avatar
1 vote
1 answer
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Help with HMAC Known plaintext / mac puzzle

Finally caving and asking for help...I'm not in the field, just doing random CTF challenges to learn more and I've really been enjoying it in general. However, I'm totally stuck on this puzzle at the ...
Heath's user avatar
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Time-memory tradeoffs in RSA Meet-in-the-Middle attack

We assume a standard secure RSA public key $(n,e)$, e.g. 3072-bit $n$ and $e=65537$. The Meet-in-the-Middle attack (not to be confused with Man-in-the-Middle attack) on textbook RSA recovers $m$ from $...
fgrieu's user avatar
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"crandall" - unsolved CTF challenge - ASIS-quals-2023

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akonzu's user avatar
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4 votes
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Is this new bound for Wiener Attack well accepted?

I found this recent paper The Wiener Attack on RSA Revisited: A Quest for the Exact Bound, which reported a new bound $d\le \frac 1 {\sqrt[4]{18}} N^\frac 1 4$. Is this well accepted in the ...
Zixi Sean's user avatar
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Primal attack On Kyber algorithm specifications

In the Kyber Algorithm specifications document, chapter 5.1.2 primal attack, it says that: Given the matrix LWE instance $(A,b=As+e)$, one builds the lattice $\Lambda = \{x\in \mathbb{Z}^{m+kn+1}:(A\...
qiuxicj's user avatar
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Nonce reuse in GMAC without ciphertext (only AAD)

As we all know, nonce reuse in AES/GCM can easily be catastrophic. However, I'm wondering if the same risks are present if an adversary has access to: Ciphertext and corresponding MAC of one message ...
Julian Durchholz's user avatar
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RSA - Twin Primes across two messages

This was a CTF challenge I was unable to solve, but I thought I may had come close. We were given two $N$'s $N_1$ and $N_2$ each calculated with $P_1 \times Q_1$ and $P_2 \times Q_2$; however, $P_1 = ...
Nasica's user avatar
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A question about "attacks on MAC key space"

At page 336 in "Handbook of Applied Cryptography - Menezes", I see the sentence For $n$-bit MAC with $t$-bit key space this requires $2^t$ MAC operations, after which one expects $1+2^{(t-n)...
hellobc's user avatar
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A RSA crypto CTF chanllenge with known private key ,cipher text and modules factor n

Here is a CTF chanllege about RSA(The competition has ended for serval hours),and here is the critical encryption code: ...
Ayumi80s's user avatar
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How by changing ciphertext can the attacker know the length of the padding in POODLE attack

I try to understand the POODLE attack. I read that the attacker try to change one byte of the last block of the ciphertext. Becasue the last block is only have padding and the last byte is the padding ...
eitan's user avatar
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Can an attacker impersonate any party in a modified Needham-Schroeder protocol?

We are doing symmetric Needham-Schroeder protocol in university. We were provided a modified protocol and needed to answer the following questions. Original protocol: Modified protocol: Task a) An ...
PCFX's user avatar
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3 votes
1 answer
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how 0/n split prevent BEAST attack against TLS?

I read that to mitigrate BEAST attack openSSL tried to inject empty TLS record before each real TLS record. and by doing that there is no opportunity to execute an attack but i dont understand way? ...
eitan's user avatar
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RSA Oracle - CTF

I am trying to solve a challenge regarding a RSA oracle which allows me to encrypt/decrypt any plaintext/ciphertext I want, but there are a few checks that I have to bypass, and my goal is to decrypt ...
Shark44's user avatar
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2 votes
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CTF - AES Padding Oracle [closed]

I am trying to solve another CTF challenge. The challenge consists in trying to exploit an oracle that decrypts any hex text we send (see code below). I am kind of stuck on this one as this is not a ...
Shark44's user avatar
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2 votes
1 answer
599 views

CTF - DES Challenge

I am trying to solve a CTF challenge based on DES. I attached the code of the challenge to the question. So far I have noticed that the otp used for the encryption is the same for the entire session, ...
Shark44's user avatar
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AES CBC - Find IV (CTF)

I am currently trying to solve a training challenge based on AES with CBC. This is the infos I'm given: ...
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The specific nature of a 51% attack - in relation to a multiple choice question that I was marked as incorrect on

In a course I'm taking the following question came up: ...
phoenixestant's user avatar
1 vote
1 answer
111 views

Use of PRNG's vulnerability for attacking a cryptographic system

I am investigating a PRNG which fails some of NIST tests (FFT, ApproximateEntropy and Serial). If such a generator is used in cryptography for any purpose, what consequences can it has? How this ...
user110019's user avatar
2 votes
1 answer
84 views

Bit flipping attack in hash function for message authentication

In this picture we have a use of a hash function for message authentication. M is plaintext message. H is hash function. E is encryption block with K symmetric key. || is concatenation of plaintext M ...
Allexj's user avatar
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5 votes
1 answer
441 views

Leaking key when adding small order point

I was (trying to) read the following paper: https://eprint.iacr.org/2015/673.pdf Page 2 says: A related attack is to replace a point P with P + T, where T lies in a small subgroup. If the user ...
Enthusiast's user avatar
1 vote
1 answer
322 views

Solve congruent equation likes N = p*q c1 = (2*p + 3*q)**e1 mod N c2 = (5*p + 7*q)**e2 mod N

Here is a CTF crypto challenge likes(its write up is public on https://ctftime.org/writeup/15438): $$N = p*q\\ c1 = (2*p + 3*q)^{e_{1}} mod N\\ c2 = (5*p + 7*q)^{e_{2}} mod N$$ After i transform these:...
Ayumi80s's user avatar
1 vote
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Predicting compromised OpenSSL 3.0 DRBG

The OpenSSL 3.0 rand function's DRBG uses the getrandom() system call to get 48 bytes of secure entropy from the kernel. It also ...
Wesley Jones's user avatar
2 votes
1 answer
245 views

Best practices on implementing a password manager

I'm a dev new to security and cryptography. I'm writing a password manager and Time-based OTP combo in dart/flutter to use in multiple devices and platform for fun and use it personally for real. I ...
anthonychwong's user avatar
2 votes
1 answer
76 views

The second moment and fourth moment of $\mathcal{P}(V)$?

Backgroud: I am reading the paper "Learning a Parallelepiped: Cryptanalysis of GGH and NTRU Signatures". (here is the link). And I got stuck in understanding the computation of moment. ...
zbo's user avatar
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2 votes
1 answer
166 views

Double Ratchet Algorithm: Active Man in the Middle Attack without Root-Key or Ratchet-Key

I am currently studying the Double Ratchet Algorithm from Signal (link to the documentation). I stepped over a security issue which I was not able to find that it was mentioned anywhere. I assume that ...
p_1092131280's user avatar
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92 views

Are Veracrypt, XTS and flash memory attacks feasible?

Some time ago I had a question here about WinRAR security and probably the most common recommendation I came across was to use Veracrypt. Veracrypt uses XTS, but according to others, XTS encryption is ...
Hasbo's user avatar
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2 votes
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118 views

How can I extend the RSA LSB Oracle attack, to n-LSBs?

Suppose we have an RSA-Oracle that can encrypt and decrypt our input. The the decryption output is equal to: $ (C^d \mod N) \mod 2^n $. How can I extend the LSB oracle attack, using the using ...
Jamal's user avatar
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3 votes
1 answer
63 views

Cost of attacking textbook RSA signature of $b$-bit hash of the message

A signature system applies textbook RSA to a $b$-bit hash of the message. What's the cost (preferably, as CPU time on common hardware) of existential forgery assuming known signature of $r$ random ...
fgrieu's user avatar
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2 votes
1 answer
682 views

Crack RSA with $e$ and $d$?

Is it possible to decipher a ciphertext, in RSA with small primes (two 128-bit factors) when we only have ciphertext $c$, private exponent $d$ and public exponent $e=65537$ to crack it? I try hard on ...
Siyanew's user avatar
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1 vote
2 answers
478 views

Stuck on a cryptanalytical research project [closed]

This is not a technical question, but rather it seeks advice on what to do if cryptanalytical research goes wrong. I've discovered a new attack that works great in theory, but in practice, it fails. I ...
MayDen's user avatar
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5 votes
1 answer
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Is it insecure to sign the value 0 with ElGamal?

Is it insecure to sign the plaintext 0 with ElGamal signature algorithm? Can this leak the private key, give the possibility to forge other signatures or does provide any other attack vector?
PCFX's user avatar
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1 vote
1 answer
222 views

Decentralized identity, how to prevent duplicate uses of the same identity

In a system that relies on decentralized identity, is it possible to prevent duplicate uses of the same real-life identity, i.e. same real-life person creates more than one user entity (each is ...
rapt's user avatar
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3 votes
1 answer
272 views

Breaking Ed25519 Discrete Logarithm with Degenerate Curve Attack

Following this question ed25519 attacks and also this paper on degenerate curve attacks https://eprint.iacr.org/2015/1233.pdf, I tried to implement my own attack: Given a point (0, y) and a scalar (k),...
J Medeiros's user avatar
2 votes
1 answer
78 views

Significance of theoretical weaknesses?

What is the significance of theoretical weaknesses? Any real life incident where a theoretical weakness was ignored and later it compromised the system? Whats the dividing line between theoretical and ...
crypt's user avatar
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1 vote
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How does the security of AES change if we allow multiple uses in a row? How does it change if we limit the key space? And introduce a filter function?

$$f_0 = A$$ $$f_{n+1}=AES(f_n,k_n)$$ $$f_i = B$$ For given 128-bit values $A, B$ we want to find a chain of suitable 128-bit keys $k_1$ to $k_i$. The total length $i$ is undetermined. Every valid key ...
J. Doe's user avatar
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1 vote
0 answers
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Does privacy-preserving linear (logistic ) regression necessary?

The linear regression is simply $y=Wx+b$, where the server holds $W$ and $b$ and the client holds $x$. The private linear regression means the client sends encrypted $x$ to the server, and receives ...
Zhengyi Li's user avatar
1 vote
0 answers
69 views

Non-uniform plaintext distribution -- AES attack

Are their any attacks on AES (any mode) in which before the attack is mounted, the adversary is aware that the input distribution is non-uniform? Most of the work assume that the plaintext is ...
nivedita's user avatar
3 votes
1 answer
185 views

Can the BB'06 attack to PKCS padding be generalized?

As Bleichenbacher states, a wrong implementation of the parsing function of the padding could lead to a signature forgery attack when using a low exponent. In the provided example he assumes the ...
supergiox's user avatar
2 votes
1 answer
200 views

Trying to understand the 2nd subgroup in the Weil Pairing used for the MOV attack

EDIT: The bounty is actually to draw more attention. I accidentally chose the wrong reason. $E$ – Elliptic Curve over finite field $\mathbb F_p$. Let $k$ be the embedding degree of the Curve with ...
user93353's user avatar
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2 votes
1 answer
250 views

Generic attack on Hmac sha256

Is there any generic attack on HMAC SHA 256 ? I am currently reading up on attacks on Hmac sha-256. However most of the papers I've found are about side channel attacks such as Differential power ...
Donnie's user avatar
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How to solve a system of modular equations with exponential difference

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 ...
Roman's user avatar
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2 votes
1 answer
248 views

Do we always choose a generator of prime order for ECDH? If yes, then why?

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 $gcd(n,q) = 1$...
user93353's user avatar
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0 votes
1 answer
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Various attacks on cipher-images & tools, especially stream-cipher?

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/...
akez's user avatar
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1 vote
0 answers
838 views

CTF AES attack (ECB, CBC, CFB, OFB, CTR) [closed]

Hi I'm trying to understand the logic behind a CTF challenge basically we are given a program which encrypt some data, we have the following options: Select encryption mode (EBC, CBC, CTR, OFB, CFB) ...
Daniele Linguaglossa's user avatar

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