Tagged Questions

analysing cryptographic algorithms, potentially uncovering weaknesses in them (e.g. "breaking" them or casting doubts on their actual security)

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0
votes
1answer
104 views

Prime factors of non-random keys

I have been working on a challenge i found on the internet. It is as follows: You've stumbled onto a significant vulnerability in a commonly used cryptographic library. It turns out that the ...
2
votes
3answers
140 views

Frequency of letters change by the length of the texts?

In terms of the frequency of letters, how is it possible to have different frequent letters when the length of the text I'm analyzing is shorter? At the moment, I'm comparing the frequencies of a ...
4
votes
0answers
73 views

How has the “power” of cryptography evolved from its beginnings till today? [closed]

I'm looking for a historical overview for the change in cryptographic power, which I hereby define as How far state-of-the-art cryptography is ahead of state-of-the-art cryptanalysis. In other ...
3
votes
0answers
89 views

What informal indicators exist for estimating the computational infeasibility of cryptographic problems?

When assuming a block cipher primitive is secure, or a number theoretic problem is hard, this assumption is usually based on how far we are from breaking the primitive or solving the problem using ...
0
votes
1answer
162 views

Partially-known-plaintext attack of a stream cipher based on modular arithmetic

I have a function called $F$, using modular arithmetic as does RSA, defined as $$x\mapsto F(x) = g^x\bmod p$$ where $p$ is a 1024-bit prime and $g$ is a generator of $\mathbb Z_p^*$. A secret key $r$ ...
5
votes
2answers
121 views

ML/NN Cryptanalysis

Is it computationally plausible to use NN/ML to do any of the following tasks? "Real" cryptanalysis. Cyclic neural networks for extended computation, but break the hash all the way through. ...
1
vote
0answers
225 views

Example of second preimage attack [closed]

Please, I'm trying to understand second-preimage attacks on cryptographic hash functions. I understand the definition well: given a message and it's hash, an attacker finds another message which ...
1
vote
1answer
128 views

Can a properly implemented ed25519 private key with public underlying data be cracked?

If the underlying data is public albeit hashed with SHA-512, does that make a difference on the strength of ed25519? Please quantify the extent. Can ed25519 be cracked after a certain amount of ...
2
votes
2answers
85 views

Should tweak be unique per message?

Since tweaks are like IV,Salt for block cipher inputs . Should they be unique for each message ? If they are to be unique per message then what is the advantage of giving tweak directly into the ...
-1
votes
1answer
122 views

How to determine which type of crypto is used in a text file? [closed]

is there a tool or a way to determine which type of crypto is used in this type of text: ...
0
votes
1answer
57 views

Bicliques for permutations

So I'm trying to understand the complexity of the biclique attack on Grostl and I have some questions: 1) The paper introduces sliced bicliques where on Grostl one constructs a biclique of dimension ...
11
votes
3answers
2k views

Is 80 bits of key size considered safe against brute force attacks?

I came across KATAN Family of Ciphers for small domain input blocks . They cipher arbitrary block lengths 32,48,64 but their key size 80 bits only. Is 80 bits of key size considered safe with ...
1
vote
1answer
93 views

Cracking Stream Cipher

I need to crack a stream cipher. I have a set of plain text and encrypted text pairs. The hint to the question asks me to use entropy analysis and look at the hex dump of the encrypted text. However, ...
5
votes
5answers
478 views

Is there a technique to confirm that a given large integer value is a product of two primes?

Given a list of 2048 bit integer values in which one or few 2048 bit integer values may be product of two prime numbers and other values may be just 2048 bit odd integers numbers. My question is - ...
1
vote
1answer
84 views

Is knowing the distribution of input domain only way to do cipher text only attacks?

Imagine there is a $n$ bit block cipher. The attacker has harvested some how all possible $2^n$ cipher texts for some given key. Without the knowledge of the distribution of input domain as in ...
2
votes
1answer
209 views

Predicting Java's PRNG using partial output

I have a program (a game) that uses Java's nextInt function with parameter 0x10000 to get a random 16-bit number. Java's ...
1
vote
2answers
126 views

Cryptanalysis of an certain algorithm

Is an attacker of an cryptographic algorithm allowed to change order of sub-keys but not changing their number in attack? Would it be called an attack on broken algorithm of cipher?
1
vote
1answer
70 views

Secret key model for a compression function cryptanalysis?

How do we analyze the security of a compression function in the secret key model? More formally, let $H$ be a hash function and $F(IV,M)$ its compression function. Suppose we generate a MAC as ...
-2
votes
3answers
1k views

How can I find the prime numbers used in RSA?

I got this question in a local hacking event, but I couldn't solve it. Problem Statement ---- Continuing their snooping habit, NSA kept bugging Alice's communication. Resorting to the age old ...
2
votes
2answers
155 views

Impact of distinguishing between random text and cipher text?

In theory, distinguishing cipher text from random text is considered insecure for any PRP algorithm. Say for example - due to Patarin's proof with about six rounds of Feistel Network - the attacker ...
1
vote
1answer
945 views

How can i predict the next number of a long sequence of seemingly random numbers? [closed]

How can I accurately predict the next random number between 1 and 999, given past results. I have no knowledge of the PRNG or algorithm used. How can I predict the next number of a long sequence of ...
5
votes
1answer
186 views

How can I break this encryption scheme?

Let $p$ be a large public prime. Alice holds a private key $(e_1,d_1) \in Z_{p-1}^*$ such that $e_1 d_1 = 1 \mod {p-1}$. Bob also holds a different private key $(e_2,d_2)$ with the same property. ...
2
votes
2answers
135 views

implication of tweak on bruteforcing a block cipher

Consider a KPA attack, where the attacker gets known plain text and the corresponding cipher text. Since the encryption algorithm is known, he can brute force all possibilities of key bits. What is ...
1
vote
1answer
76 views

Why is the security of block cipher not a function of key and tweak?

The proofs and security of block ciphers constructed especially of Luby Rackoff Constructions and Feistel Networks is based on the number of queries and round functions. The security measure is always ...
3
votes
2answers
110 views

What's the alternative should PKI collapse?

Premises - please check it and critique if necessary: If factoring the products of large numbers suddenly becomes simple, PKI goes up in smoke. Is this correct? If it is correct, it seems to me ...
9
votes
3answers
526 views

Can we ensure the security of a crypto-algorithm and -implementaton against acoustic cryptanalysis?

Like people always say: “Attacks only get worse…” — which is why I'm asking early. I have been reading the paper “RSA Key Extraction via Low-Bandwidth Acoustic Cryptanalysis” published December 18, ...
1
vote
1answer
88 views

Can I use the cipher text ouput of only one DES rotation as plaintext to check validity?

I have made a python code for one DES rotation. Can I use the resulting cipher text as a plain text for the same rotation with the same key? I think the answer is no, I can't do so. But I need to be ...
5
votes
1answer
241 views

RSA exhibits symmetrical properties — is it possible to form a cryptanalytic attack?

This question is broken into two sections really: Symmetry in RSA I have been analyzing raw RSA and I have noticed some interesting symmetrical properties of the algorithm. Assume that $M$ is a ...
3
votes
1answer
117 views

How would using only one s-box affect security of Blowfish?

Schneier says: Fewer and smaller S-boxes. It may be possible to reduce the number of S-boxes from four to one. Additionally, it may be possible to overlap entries in a single S-box: entry 0 ...
4
votes
1answer
138 views

Cryptanalysis of AES on SSD with TRIM enabled

Attack scenario: SSD physically retrieved from a computer that is turned off. The entire disk is encrypted with AES 256-bit (GNU/Linux, LUKS). The SSD has had TRIM enabled for several years and the ...
3
votes
2answers
326 views

DES — Can I recover the key when I have both ciphertext and the plaintext?

Given a message and DES encrypted form of said message, is it possible to efficiently compute the key used to encrypt the data?
5
votes
1answer
1k views

Can you explain “weak keys” for DES?

A weak key for DES is a key $K$ such that $DES_{k_1}(DES_{k_2}(x))=x$ for all $x$. I don't get why are the 4 keys $k_1||k_2$: $1^{112}$, $0^{112}$, $0^{56}||1^{56}$, $1^{56}||0^{56}$ considered as ...
2
votes
1answer
147 views

Can you help me with this DES variant analysis?

I'm struggling with some DES variant that I got as an exercise (exercise taken from Katz-Lindell Ex5.14). The variant is as follows: The left half of the master key is used to derive all the ...
1
vote
1answer
91 views

How do we arrive to the equation for solving D in RSA?

We have been shown that DE is congruent to 1 mod phi(n). How do we arrive to the real equation for figuring out d that is d = e^-1 mod phi(n). I want to know the entire process. I am just curious, ...
1
vote
0answers
187 views

Is there any analysis of freebsd's “geli” encrypted geometry provider?

I've done a few obvious searches on google and google scholar and not turned up any security analysis of FreeBSD's geli. Is there some out there, or has it gone unanalyzed since its introduction ...
0
votes
2answers
224 views

Why are these techniques not feasible to crack RSA?

For $d = e^{-1} \mod \phi(n)$ $$d\cdot e \operatorname{mod} \phi(n)=1$$ $$d = (e^{-1} \operatorname{mod} \phi(n))$$ With having $e$ and $n$, we can calculate the value of $d$ , the private key for ...
0
votes
0answers
226 views

Blum-Blum-Shub Cryptosystem

I am given $N$, which is Bob's encryption key. I was able to successfully factor $N$ into $N=p*q$. Alice encrypts a messages for bob and sends $a = [1,1,1,0,0,0,1,0,1,1,0,...]$ $b = 1545164156...$ ...
1
vote
1answer
131 views

Weak Stream Cipher cryptanalysis

Hi I have a stream cipher which uses a keystream of: F(r) || F(r+1) || F(r+2) || ... Suppose F(r) is the RSA encryption algorithm: ...
2
votes
2answers
145 views

Publicly exposed hash of private key

Would exposing a cryptographic hash function's digest (e.g. SHA-3) of RSA private key data compromise the key? If so, what are the possible (cryptanalysis-) vectors for attacking the key if an ...
3
votes
1answer
117 views

Why is Lamport-Diffie secure?

Why is Lamport-Diffie secure? I note that there is a demonstration based on onewayness (in the book postquantum cryptography). But a one way function is not sufficient to ensure that it can not infer ...
0
votes
1answer
334 views

Is this encryption scheme perfectly secure?

Let $m = 6$, and let $\mathbb{Z}_m$ denote the set $\{0,…,m-1\}$. Let $X \mod m$ denote the remainder obtained when dividing $X$ by $m$. (a) Consider the symmetric encryption scheme in ...
0
votes
0answers
232 views

How good is the RandomPool generator in Crypto++ library?

How good is the RandomPool generator in Crypto++ library? I never heard of it before… I wonder if there is a Fortuna C implementation that I could use in an Objective-C project. Also: How secure is ...
2
votes
3answers
286 views

Is it possible to attack RSA with a WalkSat derivative?

We consider a large $n$-bit number $N$. We want to find a factor, if it admits any. For $m$ taking values from $1$ to $n$, perform the following three steps (actually, for each $m$, perform many ...
1
vote
0answers
49 views

AES and Known-plaintext attack [duplicate]

Can you help me to finding some papers that shows AES is secure against known-plaintext attack?
2
votes
3answers
145 views

Help me about Advanced Encryption Standard (AES)

Suppose $E_k$$(a, b, c)$ is encryption of values $a, b$ and $c$ with key $k$ through encryption algorithm AES (AES-128) and each $a, b$ and $c$ are 300 bits integer values. Also Suppose this ...
0
votes
0answers
43 views

Merkle-Damgard transform: necessity of the Length block [duplicate]

The Merkel-Damgard transform append the message length (in blocks) to the message itself and then computing the 'chained hash' algorithm. Does the last block (which contains the length of the ...
4
votes
1answer
510 views

Can cryptocurrency mining devices be used for cryptanalysis?

In the past year or so we have seen production of ASIC devices designed for mining of cryptocurrencies. These devices can perform SHA256 hashing at rates much higher than was seen in the past and are ...
1
vote
1answer
126 views

Is encrypting a public key with a symmetric key safe?

Assume the sender wants to share their ephemeral/long-term public key with intended receiver only and both share symmetric key. Is it secure to encrypt the (full/partial) public key (of RSA, ECC) ...
1
vote
0answers
37 views

Computing A, B given A+K and B+K [duplicate]

In his writeup of the Solitaire keystream generator algorithm, Bruce Schneier warns not to use the same key for two different messages: The first rule of an output-feedback mode stream cipher, any ...
1
vote
1answer
94 views

Applying differential cryptanalysis to ciphers with addition mod $2^{32}$

I am studying differential analysis and have a question. Consider the following simple cipher: $$c_1 = S(m_1 \oplus k_1) \oplus k_2$$ (Plaintext $m_1$ xor with key $K_1$, then result goes into an ...