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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The difference between these 4 breaking Cipher techniques?

I'm trying to understand the difference between the following and what they actually mean : Known plaintext attack Known ciphertext attack Chosen ciphertext attack Chosen plaintext attack Any ...
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2k views

What does a “real” quantum computer need for cryptanalysis and/or cryptographic attack purposes?

The cryptographic world has been buzzing the word "quantum" for a while now (even the NSA is currently preparing itself for a post-quantum crypto world) and quantum-related hardware engineering is ...
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469 views

Relationship between a key stream having a high entropy and whether it is cryptically secure in a stream cipher

Hi i am trying to build a key stream generator for my homemade stream cipher.The key stream output has a close to maximum entropy value and a large periodicity. What does it take for this generator to ...
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Is it possible to find the key for AES ECB if I have a list of plaintext and corresponding ciphertext?

Assume I have a list of plaintext text and its corresponding ciphertext which was created using a specific key with AES in ECB mode. Can I recover that key? If, how big does the list of plaintext ...
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196 views

How safe is a prime with $P=2 \cdot Q \cdot R \cdot S \cdot t+1$ for discrete logarithm? How to enhance/compare?

To get some certain properties for my use case I need a prime $P$ which has the form: $P=2\cdot Q \cdot R \cdot S \cdot t+1$ with $Q,R,S,t$ primes as well. Why that form - Use case Together with ...
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419 views

Are there any long term RC4 bias based exploits?

The RC4 cipher possibly exhibits low level bias in it's long run PRNG keystream. I'm specifically excluding short term bias attacks which I'm defining as outputs < 1024 bytes. Are there any real ...
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SHA-1 collisions - what about practical attacks?

I understand the theoretical problem with hash collision but when it comes to practice, I get very confused. Suppose a attacker would like to forge a certificate (or any kind of structured piece of ...
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3k views

Is MD5 second-preimage resistant when used only on FIXED length messages?

I fully realize that MD5 should not be used in any new project, but in my particular situation I have severe CPU performance issues, so MD5 is convenient. I have read a lot about MD5 security for this ...
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1answer
508 views

ECDSA key recovery - floating point values

I'm currently attempting to recover an ECDSA key. I have $m$, $m'$ and signatures $(r, s)$, $(r', s')$, and I know that $k$ is constant, the curve is NIST P-192 and the hash function of the. As such,...
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305 views

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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1answer
132 views

Could a strong round function be immune to slide attacks

An excerpt from the wikipedia article on slide attacks states: ...The only requirements for a slide attack to work on a cipher is that it can be broken down into multiple rounds of an identical F ...
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418 views

If PRESENT had different permutations s would that protect it against Statistical Saturation Attack?

The block cipher PRESENT is vulnerable to the Statistical Saturation Attack for up to 15 rounds (PDF) and a simple example is here. So my questions are, if some (or all) of the permutations were ...
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When is a cipher considered broken?

We've all read how some people claim AES is broken because there was supposedly a way to get the plain text from a cipher text faster than brute-force. But is this the definition? Is a cipher broken ...
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1answer
284 views

Is the RSA signature attack from Desmedt and Odlyzko practical?

I would like to understand how the attack from the Desmedt and Odlyzko on RSA signatures (and subsequents works) can be made practical. This attack describes a way to forge the signature on a new ...
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1answer
149 views

Attacks on schemes based on elliptic curves when the transmitted points are not on the curve

Some elliptic curve schemes require to send a curve point during the normal execution of the protocol. For example, ElGamal encryption and ElGamal signature require this. On the other hand, ECDSA does ...
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1answer
127 views

Determine RSA modulus from encryption oracle

Suppose we have an RSA encryption oracle $E(m)$ which basically just calculates $m^e \mod n$ for a given message $m$. Here $e=65537$ is known but $n$ is not. Can we determine the value of $n$ without ...
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How is encryption broken today?

There are often articles in the news that state that a certain country or hacker has been able to decrypt/hack highly protected systems: Some examples are the Lockheed Martin RQ-170 Sentinel that was ...
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1k views

How can I implement the elliptic curve MOV attack myself?

I understand and have implemented elliptic curve signatures in Python without the use of libraries like Sage, and would like to implement the MOV attack against certain weak types of elliptic curves. ...
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1k views

Understanding Twist Security with respect to short Weierstrass curves

I'm trying to understand the "Invalid-curve attacks against ladders" section of SafeCurves Twist Security page and I have difficulties to apply it to short Weierstrass curves. That section claims ...
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1k views

How can I attack a Triple-Block cipher with 2 keys (like 3DES) with a cost of ≤ 2⁵⁶

I am trying to solve something and I have but I have no idea anymore. Maybe anyone of you has an idea/solution/hint. Given is a block cipher $F$ with key length $n$. It looks like this: $$c = ENC_{k1}...
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2k views

Is there a generic attack on encrypted CRC32 when used as a MAC?

I am examining a protocol that uses CRC32 as a MAC (see note 1) the weaknesses of this method but I would nevertheless like to see if it is just weak or actually relatively easily to break. The ...
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94 views

How does the CBC Padding Oracle Attack work in General?

Right now we don't have a single generalized question asking how the CBC padding oracle attack works. We have e.g. this one and this one but the former is distracted by the concrete values being ...
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872 views

What are the implications of a birthday attack on a HMAC?

After collecting approximately $2^{n/2}$ message-tag pairs a collision can be observed. So two different messages (m1 and m2) will have the same tag. This paper states: Then, for any string x, (...
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290 views

Which attacks are possible against raw/textbook NTRU encryption?

In the same fashion that these questions about attacks to textbook RSA and ECC, I was wondering what are the immediate drawbacks of applying NTRU Encryption directly, without any padding scheme, such ...
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4answers
2k views

What is the malicious potential of a key-substitution-attack?

What is the idea behind a key-substitution-attack? We start from a given pair of message $m$ and signature $s(m)$. The signature can be verified by anybody in possess of the public key $y$: $v(m, s, ...
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643 views

Generate 64 bit HMAC

Given $plaintext$ and its respective authentication $tag$ which is generated from HMAC-MD5 so that $|tag| = 128$ bits. If the application is constrained and can send only $64$ bits. Is it ok, if we ...
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330 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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1answer
479 views

RSA 1024 bit forge a new matching signature from a chosen message

I have an RSA signature scheme with 1024-bit key where I know the following: Public modulus $N$ Public exponent $e=3$ A lot of signatures Summary: To compute a signature, an MD5 hash is calculated ...
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3answers
702 views

One Time Pads and reuse of the decrypted message?

How is it insecure when Alice encrypts a message with a One-Time-Pad to Bob, and Bob then uses the decrypted message from Alice as the next One-Time-Pad? For example: Alice sends Bob a message ...
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1answer
77 views

Deriving user keys from ID

The "normal idea" is to generate a key per user, send them to the users (securely, of course), and store them in a database. But what if I use a keyed hash (like Blake2b) with a server key and then ...
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3answers
764 views

How much processing power should you assume an attacker has?

The answer to this question says that you should assume an attacker can do one billion operations per second: Key Size for Symmetric Homomorphic Encryption Over the Integers Is that a single attacker ...
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113 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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81 views

TLS-conformant ciphertexts and SSLv2-conformant ciphertexts for Blechenbacher attack for DROWN attack

This is regarding the published paper on the DROWN attack (https://drownattack.com/drown-attack-original-report.pdf) It was mentioned in the paper that for TLS, RSA PKCS#1 v1.5 is used to encapsulate ...
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1answer
3k views

Can you help me understand the RSA Broadcast Attack?

I am currently working on a broadcast attack on RSA. This is what I have: 17 ciphertexts $C_i$ and corresponding moduli $N_i$ for a single common message $m$. Public key $e = 17$ The first part (of ...
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1answer
90 views

Is it Possible to Generate a Duplicate DH Session Key from 2 Pairs of DH Keys?

This might sound pointless at first, but I want to know if it's computationally feasible to generate the same resulting session key in 2 different DH key exchanges. The purpose would be for a man-in-...
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1answer
1k views

Shared modulus attack on RSA

Consider a scenario in which a group of people use a common modulus $n$ in the textbook RSA crypto system, where $n=pq$, $p$ and $q$ are large distinct prime numbers. Is there any chance for an ...
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1answer
918 views

Algorithm for factoring knowing RSA private key

According to this and this paper from Alexander May is possible to factor given the knowledge of the RSA private key. This is possible via Coppersmith and LLL reduction. Now I am trying to implement ...
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1answer
170 views

Attacks on MICKEY 2.0 Stream Cipher

I would like to know if there are any known attacks, besides from side-channel attacks (differential fault attack, correlation power analysis, template attack), against MICKEY 2.0 or MICKEY-128 2.0. ...
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1answer
113 views

Password-Managers: what is the IND-CDBA attack logic?

In the work of Paolo Gasti and Kasper B. Rasmussen On The Security of Password Manager Database Formats, they describe two attack forms: IND-CDBA and MAL-CDBA. While I understand the MAL-CDBA attack ...
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0answers
34 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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2answers
2k views

Is it possible to break AES-128 ECB if you are given a ciphertext and a small portion of the key?

If you are given the ciphertext and the first half bytes (8 bytes) of the encryption key (key is 16 bytes in total), can you use this to break AES-128 ECB encryption and determine the last 8 bytes of ...
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1answer
167 views

RSA: How effective is this keypair-trash attack [duplicate]

A question that could very well be part of xkcd's "what if?": Let's say Monica made a piece of software that sends all RSA keypairs to a central database after they're not used anymore. Something ...
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1answer
3k views

RSA Attack, known public key and ciphertext. Can decrypt the message m?

I'm stuck with this problem: Assume Alice and Bob are using RSA to communicate each other. Given Bob's public key $(217,7)$, Alice send the ciphertext $c=53$ to Bob through RSA encryption. Now, Eve ...