# 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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### 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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### Known Plaintext Attack against 3-round SPECK48/96

I am attempting to break 3-round SPECK48/96 using a known-plaintext attack, provided with 10 PT-CT pairs. Here is a diagram: I have seemed to almost figure this out, but I cannot figure out how the ...
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### What is the strength and attack vectors of this simple scheme?

Let's say that Alice wants to communicate some secret value $S$ to Bob through a public channel in a way that other people don't know what the value was. To do this, Alice publishes that secret value ...
133 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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### Reversing a hash of known hashing algorithm

I am sure this is a very easy thing to do but I am not sure how to go about solving a problem like this, So there is this hash function which operates on a message which is in the form of a byte array ...
168 views

### Anonymity problem after voting with blind signatures

In a distributed voting system (all the messages are public, but signed and maybe encrypted/blinded), having: $d$, $e$, $N$ — registrar key params $m$ — msg $r$ — random blinding factor $m'$ — ...
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### 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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### Many time pad attack (XOR) [duplicate]

The question is quite similar to Many time pad attack and I was trying to rely on the top answer, but still am a bit confused, so any explanation and help will be much appreciated. Assume I have a ...
562 views

### Collusion Attack CP-ABE

Suppose that there are Alice with attributes $A$ and $C$ and Bob with attributes $B$ and $D$. I have a ciphertext with this policy: $A\ \operatorname{AND}\ B$. Why don't users collude ? If Alice ...
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### Decrypting messages crypted with one time pad (used more than once)

I have a stream cipher with a key (that is unknown to me) that is used more than once. Messages are ciphered in this way: ciphered_message = message XOR key Let'...
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### 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. ...
535 views

### RSA private key finding method

Bob uses RSA with $p=83$ and $q=103$. His public key is $e=445$. Alice claims that she can calculate Bob's private key without using the definition $d=e^{−1}\bmod φ(n)$? But how?
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### What are possible caveats when generating a group for use as parameters for Diffie-Hellman key exchange?

As reusing a widely used group for Diffie-Hellman key exchanges might lead to far easier third-party key discovery through precomputation for that specific group, I would like to know what can ...
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### Best attack on double DES followed by XOR with third key

What is the best attack here? $E_k(m)=DES_{k1}(DES_{k2}(m)) \oplus k3$
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### How does the Flickr length extension attack work?

I am currently reading about the length extension attack on Flickr (pdf) but not understanding what's going on there. ...
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### Cycling hashing in PBKDF's and their limitations in strength?

I hope this question isn't too similar to one that's already been asked. I also want to point out I know part the answer already, AFAIK: I just want some expert input on this. Let's model a hash that ...
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### Practical attack on an impractical implementation of Rijndael (AES?)

My understanding of the cryptanalysis of AES, is based on what I've read on Wikipedia and my intuition, I have nothing but self-taught education on the subject. So I want you to imagine: I have only ...
1k views

### Does frequent key change weaken encryption?

Following scenario: We are using OTR for communication between Alice and Bob which means after each successfull message exchange a re-keying happens for both parties leading to new AES-keys for the ...
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### Do we have anyway of knowing if avoiding self-permutation in RC4 makes it any stronger?

OK, so lots of questions get asked about RC4 but I want to make mine specific and hopefully answerable. RC4 Design as I'm sure anyone reading this knows, uses self permutation in stage 1 of the KSA. ...
4k 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 ...
165 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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### Attack on textbook RSA with small messages

We learned in class that if Alice wants to send a small message $m$, such that $m < N^{\frac{1}{e}}$, so we can break the system using $e$-th square of $m^e$. But what if Alice knows this flaw and ...
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### What happens when domain parameter $q$ in DSA is not prime number

Suppose that attacker creates domain parameters $(p,q,g)$ where $q$ is not prime number (but $q$ still divides $p-1$) and that signer generates new key pair using these domain parameters. How exactly ...
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### 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 ...
1k views

### How long does it take to decrypt an RSA/ECB encrypted message?

I am working on assignment where I have specific scenarios and I am little bit struggling with this one. Alice sends and email to Bob.For this e-mail, she uses the following method of encryption: ...
714 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 ...
493 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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### ephemeral-ephemeral ECDH and MITM attack [duplicate]

ephemeral-ephemeral ECDH is it susceptible to MITM attack ? if yes, can you please give me a detailed answer ( Workflow that can be followed by the attacker) and how we can prevent this attack (static-...
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### 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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### Are there any practical attacks that create a printable chosen prefix MD5 collision?

I would like to create two ASCII text messages with the same MD5. Is this possible? If not, is there a similar but less strict attack that could work? Or to rephrase my last question: what are the ...
345 views

### ElGamal scheme attack when one message is known and ciphertexts are intercepted

Let $G$ be a finite cyclic group of order $p$ and let $pk = (g, h=g^a)$ and $sk=(g,a)$ be Bob's ElGamal public/secret key pair in $G$. To encrypt a message $m$, a random number $r$ is selected and a ...
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### 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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### 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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### security in format preserving encryption

In format preserving encryption an attacker knows the format and data type of the plain text. The format of the plain text and cipher text are same. usually cipher text are unreadable form. then how ...
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### How multiplicative property of RSA can be exploited

It is known that RSA has the multiplicative property $E(m_1) \cdot E(m_2) = E(m_1 \cdot m_2)$ because $m_1^e \cdot m_2^e = (m_1 \cdot m_2)^e \pmod n$ But how can this property be used to break ...
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### Identification by RSA

Suppose we have identification scheme as such: Bob takes random $r$, and encrypts it with Alices public RSA key $(n,e)$, sends $r^e$ to Alice. Alice decrypts $r$ and sends it back to Bob, becomes ...
Okay this is how I understood it according to this: Alice $A$ establishes a connection to $KDC$ and prepares for session key Exchange $k_{ses}$ $A$ encrypts the request with her key $k_A(A, B)$ ...