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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Cracking a PRNG by observing ranks within groups of its output

Suppose that I am generating random numbers with Python's random module, so that there is a known random number generator (Mersenne Twister in this case). I've ...
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256 views

Bleichenbacher RSA1024 signature forgery, closed-form solution

Hal Finney's writeup (Bleichenbacher's RSA signature forgery based on implementation error) shows a formula for RSA3072. I tried to replicate the attack for RSA1024 and failed, since the first term of ...
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Statistical saturation attack on block ciphers

I was wondering if anyone around here could give me some explanation on this type of attacks. Pretty much the only thing that I could find is A Statistical Saturation Attack against the Block Cipher ...
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126 views

Implementation Attacks on Hashes

So I am familiar with attacking implementations of block ciphers via side channel attacks, cache-timing attacks, etc. What implementation attacks are there against hashes or hashed based functions (...
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345 views

How hard is a known prefix hash preimage attack on SHA-2?

Suppose the attacker knows $X, Z$ such that $H(X || Y) = Z$ If bit-length(Y) < 60 then a brute force attack is possible. What if ...
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156 views

Is the “Pico” alternative to passwords vulnerable to man-in-the-middle?

Maybe someone has already heard about "Pico" by Frank Stajano. In short: It is a model for an alternative for using passwords for authentication and seems to be very interesting. Regarding the paper, ...
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102 views

Pollard's Rho - Restricting the random function to the exponents

Pollard's Rho is usually constructed using a function $f:G \rightarrow G$ which behaves 'random enough' in order to detect a collision with Floyd's cycle detection trick. It is easy enough to observe, ...
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204 views

Timing Attack on OpenSSL by Brumley

I am referring to this paper by David Brumley and Dan Boneh: Remote Timing Attacks are Practical (In proceedings of the 12th Usenix Security Symposium, 2003). In this paper on page 4, Brumley ...
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49 views

Complexity of AES key reconstruction from state 1 output and plaintext

Assuming that I am able to read the plaintext as well as the output of round 1 of an AES-128 encryption: Is it possible (if yes: how?) to obtain the RoundKey with a lower complexity than brute-force ...
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93 views

Non-exact substitution cyphers

Picture a simple substitution cypher of text with length $N$(spaces optional): Plain : ATTACK AT DAWN Encrypted: ELLETI EL HEPG Another way to represent the encrypted text is with an $N \times N$ ...
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310 views

RSA signatures that allow hash to move around in block

I'm looking at a broken RSA signature padding implementation in a real device. It's a very-badly implemented version of PKCS #1-like encoding, but before PKCS added the DER-encoded hash identifier. ...
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91 views

*feasible* pre-image attacks against reduced SHA-1

(tldr: see last paragraph) Although SHA-1 is vulnerable to collision attacks, it is still resistant to pre-image attacks. SHA-1 was designed to be resistant until a brute-force attack of $2^{160}$ is ...
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180 views

Cost of attack on DSA with attack on DLP

Are there any (recent) estimates of cost of attack on DSA by solving the discrete logarithm? I'm especially interested in attacks that use Pollard's rho algorithm. Are there any optimized ...
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34 views

How large a product out of 3 close-by factors need to be to avoid factorization?

For encryption a prime $P = 2 \cdot Q \cdot R \cdot S +1$ was used. An adversary want to solve the discrete log problem $m \equiv g^i \bmod P$. For this he want to use the Pholig-Hellmann algorithm. ...
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19 views

attacks and defenses on multi party Diffie-Hellman protocol

I tried to create a 4 partied Diffie-Hellman implementation for 4 people using its cyclic group property. However, I am not sure regarding those 2 issues, and would appreciate if you could elaborate ...
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Why is this attack complexity equal that exact number of bit operations?

in the this paper,section 3,autors attack hamsi-256. Im trying to make a parametrized version, so i need to understand how do they estimate the complexity of attack in bit operations,that reads as ...
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44 views

What if an AES Whitebox 1024-bit (or larger key) is created? Does it increase complexity consistently?

Following the Chow et al paper and Muir's tutorial, I was able to implement the AES algorithm using tables embedding keys of 128, 192 and 256-bit sizes, later extended to 1024, 2048 and 4096-bit sizes....
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60 views

How to solve a simple case of a RLWE problem

I've been reading up on the Ring Learning with Errors problem and the proposed attacks, in relation to homomorphic encryption. Some of the literature has been quite difficult to understand - what I ...
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Why, in general, are proofs of possession (POPs) “clearly” not sufficient for substantiating the knowledge of secret key (KOSK) assumption?

In Ristenpart, Yilek - The Power of Proofs-of-Possession: Securing Multiparty Signatures against Rogue-Key Attacks they have the statement: In general, such proofs of possession (POPs) are clearly ...
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347 views

RSA encryption extremely large public exponent

I'm trying to do learn a bit about RSA by doing CTF's and now I am doing one problem probably more than 7 hours so I would really appreciate a hint here from an expert. I have an encrypted message $c$...
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188 views

show that G' is not a secure PRG even if G is

Hello I'm trying to show that the function G'(s) = G(s) || G(G(s)) is not a secure PRG even if G is. My first question is that in this case, how do I know what G ...
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168 views

Need tips on how to break Fiat-Shamir sigma-protocol (programming challenge)

I'm completely stuck on an university programming challenge and I need some tips to get me out of the valley I'm in, you don't need to give the full answer if you do not wish to. What we have: Fiat ...
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161 views

Boneh and Durfee attack on RSA

I am a maths teacher and I'm trying to understand the Boneh and Durfee attack on RSA. I am not very familiar with cryptography. I found a dutch scripting about it. I know that: $ e*d\equiv1+k*\phi(...
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19 views

Can we protect PRESENT from the Statistical Saturation Attack if we change the permutation layer to a random permutation layer?

This is continuation-question based on: If PRESENT had different permutations s would that protect it against Statistical Saturation Attack? Can we protect PRESENT from Statistical Saturation Attacks ...
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51 views

How can I match each encrypted message with the public key used to encrypt them for a common encryption attack RSA

I have five encryption mods ($n_1$ through $n_5$) with the same encryption exponent ($e$) and the same message encrypted using the five public keys giving $E_1$ through $E_5$ that were not given in a ...
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185 views

How to generate an El Gamal signature without knowing the private key x?

Let $x$ be the private key. Let $k$ be a random generated number $< p-1$, with $p$ the large prime. Let $g$ be the generator of $p$ the large prime. Let $r$ be the equality $r=g^k$ Let $m_e$ be an ...
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51 views

Voting protocol - How many dishonest tallying centres can the protocol cope with?

We have the voting protocol that is described here. I am looking at the following exercise: Determine how many dishonest tallying centres the protocol can cope with before the following properties ...
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101 views

Correlation attack on Lagged Fibonacci Generator

Say that one uses a known LFG (2 known lags $a$ & $b$, known inner state length $N$, known modulo $m$) to hide some text with a basic à la Vigenère cipher: $C_i=(P_i + {PRNG}_i) \bmod 26$. Say ...
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1answer
209 views

Recovering plaintext from AES-128 given round key 10 and ciphertext

I'm working on an old CTF challenge where AES-128 was used on a 16 byte block. I have the round 10 key and the ciphertext. What techniques exist for obtaining the plaintext?
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54 views

Unique numbers with $P^aQ^bR^c \mod N$ for each combination of $a,b,c$ possible? Would it be safer than separate form (like $T^a \mod P$ for each)?

Main question: Is the computation of $a,b,c$ in $P^aQ^bR^c \mod N$ (much) harder than in $T_p^a \mod P$, $T_q^b \mod Q$, $T_r^c \mod R$ ? (assuming the first form exists) $P^aQ^bR^c \mod N$ With $P^...
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Prove that a given signature scheme is secure under random message attacks

This is a follow up to my previous question. Consider the following signature scheme: $\operatorname{KeyGen} (1^k$) : On input of a security parameter $k$, choose a symmetric bilinear group with $...
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54 views

Prove that a signature scheme is RUF-NMA and not EUF-CMA

I am working on the following exercise: Now, assume the following signature scheme: $\operatorname{KeyGen} (1^k$) : On input of a security parameter $k$, choose a symmetric bilinear group with ...
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44 views

(Side channel) attack on a PIC18 micro controller

I'm trying to get some practical experience on (side channel) attacks. First I want to note all possible vulnerabilities. I thought about: Preset I have physical access and I own/wrote the software, ...
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44 views

Non CPA on custom MAC

While preparing for a crypto exam there is a task we don't really understand: task Let $E_K$ be a permutation $\{0,1\}^b \rightarrow \{0,1\}^b$ defined by a blockcipher with the key $K$. Let $M = (...
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1answer
92 views

Question about key establishment protocol and key exchange attack

If an adversary $M$ observes a session of the protocol between $A$ and $B$ and learns the session key $k_{AB}$.How Can the adversary mount a successful impersonation attack and communicate with $B$ on ...