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

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(n,n) Shamir secret sharing [duplicate]

In (n,n) Shamir secret sharing if n shareholders do not have the public values (X values) can they still obtain the secret with only Y values?
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71 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 ...
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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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324 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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235 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 ...
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AES and Known-plaintext attack [duplicate]

Can you help me to finding some papers that shows AES is secure against known-plaintext attack?
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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 ...
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112 views

Partial encryption of a file?

I want to partially encrypt a large block of data using AES. Meaning: given plaintext[0:1100], I would like to encrypt ...
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113 views

Cryptanalysis not based on method used to encrypt? [closed]

When doing cryptanalysis on RSA or something number theory based, there are various attacks that all seem to involve number theory (Wikipedia: RSA_(algorithm) ~ Attacks_against_plain_RSA). Similarly, ...
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Career advice for our readers [closed]

I am a first year math PhD student with work experience and an MS in math. Do you have any advice regarding internships involved with cryptography and other mathematics other than the NSA? Thanks.
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180 views

Differential Cryptanalysis of FEAL-4

I'm currently carrying out a differential attack on the FEAL-4 algorithm, however I have hit a bit of a wall. Basically I attacked the final round first ($K3$) using the differential characteristic ...
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Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate]

Possible Duplicate: Two untrusted party want to exchange data: how to insure each one gets the data it needs? I am trying to come up with what could maybe be a novel algorithm for an ...
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How secure would this code be against cryptanalysis?

Simple version: Create software that takes a database of the dictionary, alphabet, and phrases. Randomly generate a database of random strings of letters/numbers/symbols of varying length. Randomly ...
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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 ...
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386 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 ...
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75 views

Analyzing security flaws of cipher

I know using homebrew encryption can be very dangerous as it is very likely to have many flaws in its design. The following concept is just for learning purpose in case anybody is getting red flags ...
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Text in random image encoder: is it flawed?

I have created a small cryptographic programme: You input your text A random image is generated Random coordinate pairs in number equal to the chars of the message are generated. The red component ...
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349 views

Cryptographic Symmetric Stream Cipher

Let me know a cryptographic symmetric stream cipher system with only two functions say S() and P() and it should satisfy the ...
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554 views

detecting ROT13/base64 encryption

Is there anyway to detect that a cipher is encrypted with ROT13 Or Base64 without decrypting it using the algorithm and check that the result means (works)? I mean does an algorithm exists that test ...
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Counter Mode with a sequence of zeros bits plaintext, is it secure?

I had a quiz last week in computer security course. There was a confusing question that I am still looking for a good and clear answer. First, I know that counter mode with a good block cipher is ...
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66 views

“Kernel attack” on MinRank — why do we guess $\left\lceil \frac k n \right\rceil$ vectors?

The kernel attack on MinRank is described here (page 5). My question refers to this line: Note that if $m = \left\lceil \frac k n \right\rceil$, the system essentially has only one solution ...
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83 views

rotational cryptanalysis on modulo multiplication?

I saw the paper 'Rotational Cryptanalysis of ARX', it is effective against design primitives using XOR, addition, and rotation. http://www.iacr.org/archive/fse2010/61470339/61470339.pdf However ...
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147 views

How does Blowfish avoid successful cryptanalysis? [closed]

I have researched the Blowfish algorithm and am curious as to why there exists no effective cryptanalysis for this algorithm as of yet. What basic principles or features allow Blowfish to achieve ...
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106 views

A variant of Shamir secret sharing

Suppose implement the Shamir secret sharing as following: we select a degree $d$ polynomial $P$ with a zero coefficient of 0, and all other coefficents selected randomly from $Z_p$; and to this ...
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111 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 ...
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193 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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58 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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229 views

modfied man in the middle attack diffie hellman

I have been given a problem in preparation for my cryptography final that I'm not sure how to solve. It asks me to suppose a scenario where instead of where an attacker would intercept some message ...
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393 views

WIN LM Password Hashes (using John the ripper) [closed]

In a problem set, we've been asked to use John The Ripper to crack a list of Win LANMAN passwords. They are of the following form: 953A55E36AB85C0B9DA92C18555E42E1:0169295E0A6A6B35B2DD9932D10C1978 ...
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277 views

What is the complexity of the Square attack against the reduced 4-rounds 128-bit Rijndael variant?

I'm looking at a square attack against a reduced version of AES-128 with only 4 rounds (with block and key size of each 128 bit). I have a set of 256 plaintext-ciphertext block pairs. What is the ...
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35 views

Using Permutation polynomial to compute a MAC

Is the following MAC secure? For a block $y_i$ in a file, we defined a MAC as follows: $Mac_i:PRF(k,i) \cdot g^{y_i \cdot r_i} \bmod p$. Where $p$ is a prime number, $g \in \mathbb{G}$,$PRF(k,i)$ is ...
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83 views

Will current encryption always remain secure? Is there mathematical proof?

Current encryption algorithms, such as AES, RSA, elliptic curve, etc. work based on known mathematical problems. I am specifically interested in the RSA. Will such security always remain secure? One ...
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how to calculate non linearity of AES S-box?

S-box has to satisfy different design criteria. How to calculate non-linearity , propagation criteria for an AES S-box?
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Generating child keys for a hill climb algorithm

As a little pet project I'm writing some code to do a little cryptanalysis. Starting with something simple I have created a hill climbing algorithm for solving a simple substitution cipher. So I ...
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131 views

Roots of polynomial in Shamir secret sharing

I need to know whether one can obtain any roots of the polynomial in Shamir secret sharing if he possesses less than threshold shares. For instance in (t,n) if he has t-1 shares can he obtain any ...
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383 views

RSA decrypting of a huge file by parts [closed]

I need to decrypt a huge file that I own previously encoded by myself with a RSA public key (it's possible for this step using a symmetric algorithm key). Problem is that I can't load it in my ...
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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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286 views

Security of SecRandomCopyBytes on OSX and iOS

How secure is SecRandomCopyBytes() (Apple's RNG)? Has anyone ever reviewed it?
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61 views

Self changeable key [closed]

If key changes itself when it send/receive message what would be could breaking method? So: $E: m×k$ in which $k$ is last generated key $D: c×k$ in which $k$ is last generated key $k{_n} = ...
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Decrypt a message which is encrypted using XOR? [duplicate]

This is a puzzle asked in a contest. Given that encryption , decryption happens as per following rule/code: ...
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Is ASCON cipher broken?

http://eprint.iacr.org/2015/030 present several attacks of ASCON but does not have a conclusion section. I'm having troubles estimating what are the consequences on the use of ASCON. What's your ...
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139 views

Brute force against computational security

One-time pad is secure under brute force with respect to either of the definitions \begin{align} \Pr[M = m] &= \Pr[M = m | C = c]\\ \Pr[C = c | M = m_0] &= \Pr[C = c | M = m_1] \end{align} ...
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Memory requirement in light weight block ciphers cryptanalysis

If we have a light weight block cipher where the block length is different than the key length. Let's say the block has a length of 64 bits while the key is 80 bits. For an attack to be successful, ...
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113 views

Base64 with shuffled alphabet

I have a base64 'cipher' text, I know that in clear text is a hidden xml document (I do not know nothing about its structure), but the base64 aplhabet was somehow shuffled. Is there any smart way, how ...
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32 views

Linear Code - Hamming - Finding nearest vector

I am studying for my finals and I have a review problem I can't solve. For purpose of doing this problem by myself, I'll leave out certain details. So this is concerning Hamming distance I suppose. ...
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55 views

Polynomial Inversion over Galois Field

Hello guys I am looking to calculate the Inverse of a given polynomial in Galois field I have found the little Fermat's algorithm and the Itoh-Tsujii I am getting a bit confused with both algorithm ...
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RSA OAEP: prevention of partial decryption of ciphertexts

I'm trying to understand RSA encryption (as a beginner in cryptography). go on this wiki page http://en.wikipedia.org/wiki/Optimal_asymmetric_encryption_padding scroll down to the 2 numbered points: ...
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172 views

Decrypting A Cipher Text without knowing the key or plaintext

i'm new to cryptography and i am doing a research based on cryptanalysis of vigenere cipher. If i have a ciphertext which is encrypted using vigenere cipher, is it possible for me to decrypt the ...
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How can I calculate the size of an encryption key?

I have encryption algorithm that has two variables are used as encryption key. How can I calculate the size of the encryption key. I will show an example of what the variables can be: ...