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

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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 ...
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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 ...
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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 ...
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533 views

Berlekamp-Massey algorithm: case when sequence length is less than double the length of the LFSR

Suppose that we have a sequence of $N$ digits which is produced by a Linear Feedback Shift Register (LFSR) and the shortest such LFSR is of length $L$. A very important tool in cryptanalysis of stream ...
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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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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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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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318 views

Safety of DSA key parameters sharing

I'm looking for a solution to use in a context where I need to be able to generate new asymmetric key pairs quickly (using a widely recognized algorithm, and EC-DSA is not applicable). It sounds like ...
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344 views

Can I build a secure tweakable block cipher from a normal one by adding key and tweak?

Let (E,D) be a secure block cipher. Consider the following tweakable block cipher: ...
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245 views

What does the linear assumption over bilinear groups mean?

In the abstract of "Cryptography with Tamperable and Leaky Memory", at the end of the 3rd paragraph, the authors say: In both schemes we rely on the linear assumption over bilinear groups. What ...
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84 views

What does “adaptively secure” mean?

In a paper it says "In the generic group model, the PRF is adaptively secure for inputs of $\mathbb{Z}_q^n$". Maybe a stupid question, but what does "adaptively secure" mean exactly?
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998 views

How to get the keyword from a keyword cipher?

I was given a ciphertext and now I am trying to break it via looking for the keyword. This is a keyword cipher. So: PlainEnglish: ABCDEFGHIJKLMNOPQRSTUVWXYZ If ...
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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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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 ...
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327 views

How should we interpret the cryptanalysis results of SIMON and SPECK?

The NSA recently released SIMON and SPECK light weight block ciphers. Although initial spec release did not have much of cryptanalysis details, two works later appeared providing the cryptanalysis for ...
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121 views

Can you explain what the AES paper means by “sharing active S-boxes”?

I am reading the "Biclique cryptanalysis of the full AES" paper. What do they mean by "sharing active S-boxes"? How can this concept can be advantageous to make a bicycle? If there is someone who ...
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247 views

How insecure in practice?

I am in attempt to understand relative insecurity of certain encryption schemes. Particularly of interest is DES and RC2. I know AES is better and should be used to encrypt. But practically, if ...
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162 views

What are the dangers of predictable (repeated) plaintext structures?

When using a "good", modern cipher (specifically one that provides ciphertext indistinguishability), is it a problem at all if there is some well-known structure in all plaintexts? For example, ...
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173 views

How hard is to find the operators of an addition knowing the sum of them?

I want to learn whether or no there is a cryptographic primitive,scheme assumption that is based on the following hard problem if it is hard . By hard we mean that we have a polynomial adversary: The ...
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297 views

How do I demonstrate that a PRNG not designed for cryptography is not suitable for generating passwords?

This is a replication of this question on Stack Overflow. There's class Random in .NET runtime which is designed for use as a cheap fast source of pseudo-random ...
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655 views

Finding CRC collisions for specific divisor

My current textbook (Information Security: Principles and Practice by Mark Stamp) discusses how to determine the CRC of data via long-division, using XOR instead of subtraction to determine the ...
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324 views

Entropy of the key

Suppose a $1000$-bit key used in the one-time pad is not randomly and uniformly generated. Suppose that the values of the first $5$ bits are $0$, and the other $995$ bits are randomly generated and ...
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274 views

Revealing random bit permutation

I am new in cryptography. I want to determine the complexity of revealing a random bit permutation which is used as block cipher for plaintexts (bitstrings of length n). An adversary catches different ...
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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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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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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 ...
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164 views

What is the limit of plaintext required to break the Vigenère encryption?

A theoretical question about the Vigenère cipher: Without any knowledge about the key (not even it's length) can we tell how much known or chosen plaintext is needed for the adversary to completely ...
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188 views

Hypothetical unknown cipher - security in obscurity?

I'm curious what would happen in the following scenario: Suppose an attacker gets a hold of a cipher-text of sufficiently large length. And suppose he has the means to verify a successful decryption. ...
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97 views

Why constrain the message lengths in indistinguishability in the presence of an eavesdropper?

I need your help with a very basic concept in cryptography which I can't understand/prove on my own. I'm trying to prove and understand why, under "indistinguishability in the presence of an ...
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322 views

Break double encryption

Let $E_k$ : {0,1}$^l$ be a block cipher encryption function with block-size $l$ and key-length $n$. In class, we saw that a double encryption with two independent keys $E{}'_{k_1k_2}(x)$ = ...
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136 views

High Power Computing for Crypto Research

Obviously, much of cryptography requires the assumption that adversaries have bounded computing power. So, I was wondering, are there any fields in cryptographic research for which high power ...
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72 views

What's causing the poor randomness in this program: the LCG, or the program logic itself?

(Crypto Gods, I should begin by stressing that I haven't lost my mind: I'm not doing this in real life, I'm just trying to understand the theory behind what's happening. With your help, hopefully I ...
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334 views

Precomputation attacks on RSA

Are precomputation attacks - such as outlined in RFC 3610 chapter 5 - possible on RSA PKCS#1 v1.5 signature generation? If yes, are such attacks taken into account when calculating the cryptographic ...
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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 ...
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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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127 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 ...
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142 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 ...
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259 views

Computing p and q from private key

We are given n (public modulus) where n=pq and e (encryption exponent). Then I was able to crack the private key d, using Wieners attack. So now, I have (n,e,d). My question is, is there a way to ...
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227 views

How much does a successful Distinguishing Attack “break” the attacked stream cipher?

I started reading about the most recent cryptanalysis of RC4 and it's variants. One of the papers I just finished reading ("Two Linear Distinguishing Attacks on VMPC and RC4A and Weakness of RC4 ...
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235 views

How to prove a cipher resistant to differential cryptanalysis?

How do you prove that a cipher is resistant to differential cryptanalysis? It's said that Rijndael has been proven resistance to differential cryptanalysis. How do cryptographers do that?
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65 views

Comprehension question on a signature protocol based on the RSA assumption

We have the following two-party protocol between Alice and Bob. Alice sends messages $m_1, m_2, \ldots \in_R \mathbb{Z}_n^*$ to Bob and Bob signs these values by calculating $v_1, v_2, \ldots \in_R ...
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234 views

Understanding one-way hash functions construction

I understand the needs that lead to the development of cryptography and I am quite familiar with the uses we make of the cryptographic tools. But, as a programmer, I am conditioned to see them as ...
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379 views

Using Chi-Square for Vigenère Cipher

I am writing a program which will use Chi-Square to determine which is the correct keyword for a ciphertext via Vigenère cipher. I came across a website that describes the Chi-Square statistics in a ...
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241 views

Regarding matsui's Paper on Linear Cryptanalysis of DES

I's going throught the the Paper by Matsui on Linear Cryptanalysis of DES . In that he says $NS_{5}(16,15)=12$ And then in the next paragraph he says considering the expansion and permutation phases ...
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572 views

ECC algorithm pollard's $\rho$ complexity

One of the methods to break a ECDLP is Pollard's rho algorithm. When ECDLP is defined over a finite field $F_p$, and given a relation $S=w.T$, where S and T are a member of $F_p$. Then ECDLP is to ...
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643 views

RC4 : Keystream reconstruction?

First up: it's a step in some challenge found on the Internet, where we get an application and a file. The application must be feed with that file and a password (the password is the flag for the ...
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477 views

DES Crack simulation

I wish to simulate an implementation of a DES Cracker using verilog. But every paper I read give only abstract hints but no concrete steps or how really to go about it. How is it usually done? For ...
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55 views

Hill Cipher question

Recently, I was given three ciphers to crack for my cryptography class. At this point, I have guessed that one of them is likely a Hill cipher (probably 3x3, as that is the most complex we have done ...
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62 views

LFSR Output Sampling for Berlekamp-Massey

Looking at the use of Linear Feedback Shift Registers in cryptographic algorithms, I have learned that the Berlekamp-Massey algorithm can be used to find the (shortest) LFSR that generates a given ...
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168 views

Is there a way to compare the 923 bit pairing based key with RSA or AES, etc

I've see many articles, most of them basically the same, praising Fujitsu for cracking what is referred to as a 923 bit pairing based encryption. I understand that in comparing RSA to AES you've got ...