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

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139 views

SIMONs Cryptoanalysis

I'm reading Cryptanalysis of the SIMON Family of Block Ciphers. In Section 3.1, it says: For SIMON, consider an n-bit input difference $\alpha= x\oplus x'$ to $F$ of Hamming weight one. As the ...
7
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1answer
271 views

Is TEA considered secure?

Wikipedia claims that the best attack on the surprisingly simple TEA block cipher, that isn't a related-key attack, has a time complexity of $2^{121.5}$. So despite how unsophisticated the cipher ...
2
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3answers
263 views

Problems with using AES Key as IV in CBC-Mode

I'm a pentester and currently analysing a web application which are using some strange encryption scheme. The point is: They encrypt using AES-128, generate a (not cryptographic secure) key and use ...
4
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1answer
214 views

How to solve cipher encrypted with Vigenère + Columnar Transposition?

Vigenère's weakness is Kasiski's test and index of coincidence. However, if you put columnar transposition on top of Vigenère, that weakness is gone. The text is now shuffled and you can't search for ...
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0answers
70 views

How to decrypt a text which is ciphered same length key? [duplicate]

I have ten piece of ciphered texts. I know that they ciphered with a same-length key. Any idea how I can decrypt the ciphertexts? What kind of algorithms should I use? What are the points of taking ...
3
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1answer
95 views

Is ISAAC Cipher Cryptographically Secure?

http://en.wikipedia.org/wiki/ISAAC_(cipher) This question was asked before but the answers seem vague, and I want to know about ISAAC specifically, not ISAAC+. It seems some cryptanalysis was ...
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1answer
55 views

find $x$, given $\{c_ix = k_i + y_i\}_{i=[1,n]} $

Given $$c_1x = k_1 + y_1 $$ $$c_2x = k_2 + y_2 $$ $$\vdots $$ $$c_nx = k_n + y_n $$ where the values of $\{c_1 \ldots c_n \}$ and $\{ k_1 \ldots k_n \}$ are known, and $x, \{y_1 \ldots y_n \}$ are ...
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1answer
88 views

How do you test the security of your cipher? [closed]

I got asked this question and I didn't know what to answer. How do you test the security of your cipher? What comes to my mind now would be to test it with famous attacks: padding attacks, ...
2
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1answer
138 views

Can I make a PRNG that is secure even when state can be modified by user?

I am interested in making a PRNG which, after being initially seeded, can accept and incorporate client data as the only ongoing source of "entropy". It is not directly for a cryptographic purpose, ...
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1answer
56 views

Why does knowing the number of points on a curve help solve ECCDLP?

Perhaps, this is a really obvious question, but I am still having trouble understanding how this all fits together. Why is knowing the number of points on an Elliptic Curve helpful in cracking it? ...
2
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2answers
183 views

DES with actual 7 byte key

Do we have any library or any mechanism where we can use true 7 byte key for DES instead of 8 byte key. I need it for keys analysis in DES and 8 byte key requirement for associated library is creating ...
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18 views

Cryptography — with a semi-priveleged user in the middle — to prevent request-tampering with another server

I'm working on a chat server for a mobile app I am writing. I would like to use a different application server for non-chat related operations and another application for chat operations. I would ...
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2answers
787 views

Are AES-256's related-key weaknesses exploitable if it is used to build a hash?

Assume it is made a hash based on AES-256 encryption (perhaps because this is hardware-accelerated, but no standard hash is); and it is used the Merkle–Damgård structure, that is padding of the ...
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1answer
160 views

cryptography and use of python programming language [closed]

why is it recommended to write cryptography programs ,for example crypt-analysis projects with python programming language? what is the advantages of python? why not use c or any other language?
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0answers
147 views

An example of Knapsack Cryptosystem cracks/attacks?

I have been studying papers on various ways to crack the knapsack cryptosystem, unfortunately the mathematics in these papers involves lattices and LLL which is over my head. The paper "New Attacks ...
4
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1answer
133 views

Is Chaocipher a secure cipher under ciphertext-only attack?

Chaocipher was invented by John F. Byrne in 1919. The algorithm was recently revealed – see Moshe Rubin's Chaocipher Revealed, the Algorithm (PDF). While a known plaintext attack successfully finds ...
3
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1answer
110 views

XOR with constant key in CBC mode

I have a hypothetical encryption scheme where somebody uses the one-time pad in CBC mode. That is, the block cipher is $E(k, m) :=k⊕m$, and that block cipher is used in CBC mode. Now, I am assuming ...
3
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0answers
137 views

Using the same private key for two ECC key pairs

Let $(d_1,Q_1)$ and $(d_2,Q_2)$ be ECC key pairs over two different elliptic curves (say NIST P-224 and NIST P-256). According to the Elliptic Curve Discrete Logarithm Problem (ECDLP), if the private ...
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1answer
66 views

Perl DES PCBC as protection against decryption/crypt analysis

Is error propagation in DES PCBC a good method to prevent decryption/crypt analysis by third parties? If I had a very large file encrypted with Perl's DES with the PCBC option, and then removed the ...
2
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1answer
122 views

Explanations for the complexity values for second preimage attack on GOST?

I've been reading the article "A (second) preimage attack on the GOST hash function" by F. Mendel et al (link) and I'm having some difficulty to grasp some of the values of complexities/probabilities ...
2
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2answers
176 views

How does compression before encryption leak info about the input?

Apparently current best practices recommend that you do not compress before you encrypt. For example in this blog entry (*): http://sockpuppet.org/blog/2013/07/22/applied-practical-cryptography/ It ...
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1answer
123 views

How to solve custom made ciphers? [closed]

How would you go about solving basic custom made ciphers - e.g. one generated from this website http://www.wikihow.com/Write-a-Custom-Cipher-Carefully? This is solving it without knowing the method ...
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1answer
129 views

Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
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3answers
1k views

Why does SHA-1 have 80 rounds?

Why does SHA-1 algorithm have exactly 80 rounds? Is it to reduce collisions? If yes, then why do SHA-2 and SHA-3 have a lower number of rounds?
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1answer
72 views

How does the key size per data bit influence the security?

The likelihood of breaking, for instance, an AES-128 cipher is 100% after $2^{128}$ tries in brute force, meaning that I've got to try $2^{128}$ keys to certainly break it. What if I (hypothetically) ...
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0answers
47 views

Why the same characteristics cannot be used to recover all FEAL4 keys

I am trying to understand how differential Cryptanalysis works. Here I read how to use differential cryptoanalysis for cracking FEAL4 cipher. The big gotcha with this process is that you cannot ...
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2answers
281 views

Breaking Double Encryption

I am trying to understand how an attacker knows when he has successfully decrypted a ciphertext for an assignment. As such, some pointers/hints for the following questions would be greatly ...
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1answer
98 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
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3answers
120 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
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0answers
72 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 ...
0
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1answer
137 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 $r$ ...
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2answers
119 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. ...
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0answers
189 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 ...
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1answer
120 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 ...
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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 ...
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1answer
113 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
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1answer
56 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 ...
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3answers
1k 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 ...
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1answer
91 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, ...
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5answers
467 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 - ...
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1answer
83 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 ...
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1answer
187 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 ...
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2answers
124 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?
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1answer
69 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 ...
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3answers
830 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
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2answers
147 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 ...
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1answer
617 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 ...
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1answer
180 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
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2answers
128 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 ...
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1answer
70 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 ...