Analysis of individual security aspects of a cipher or algorithm, not the security of a cipher or algorithm in general (which would lean towards “algorithm-design”).

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What does the probability subscript mean in Shannon's secrecy definition?

Shannon's secrecy can be defined as: $$P_M (M=m) = P_{SK,M}(M=m|E(SK,m)=c)$$ What does $P_M$ means? (same question for $P_{SK,M}$) I know that is the probability space M, M being the messages; I do ...
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2answers
32 views

Linear cryptanalysis complete key guessing

In linear crypt analysis, partial sub keys are guessed and verified for its correctness with the help of plaintext and ciphertext. From the partial sub key, how it is possible to guess the complete ...
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1answer
42 views

Ciphertext with uneven letter distribution

I have a ciphertext encrypted with an unknown method. It is part of a challenge (personal quest), so I can not post it. The letter statistics is the following: ...
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0answers
14 views

Breaking Vigenere via Kasiski/Babbage method? (non-programmatic)

I'm really hoping someone can explain to me what is going on in the second major component of this form of analysis. If you wish, for convenience, here's a page that already has some ciphered text ...
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0answers
11 views

Please help me decrypt this Classical Cipher [on hold]

Can any one help me decrypt this message: noohaiisee spyg iOyh h ol ceet pbcuoonnss
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0answers
23 views

Permuted Hash Table

Suppose we have a hash table, $HT$, consisting of $100$ bins.The hash table uses a hash function $H$ that is public. We all know that given value $a$ we can compute the address in the hash by ...
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1answer
24 views

Updating values authenticated by Merkle Tree

Assume we have 4 values: $v_1,v_2,v_3$ and $v_4$. We construct a Merkle tree on top of them such that the values are leaves of the tree. I send the values and the tree to an untrusted server. But I ...
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4answers
90 views

How to break Universal Re-Encryption algorithm?

Let p be a prime, and g be an element of $ℤ^*p$ of prime order q. Let x ∈ ℤq be the private key, and $h = g^x$ (mod p) be the public key. To encrypt a message m ∈ $ℤ^*p$, pick two random ...
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1answer
175 views

Why was the Navajo code not broken by the Japanese in WWII?

In reading about this topic recently, to my understanding, the encryption schemes used on top of the Navajo language were very simple and definitely could have been broken (my research shows they ...
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7answers
29k views

Are there two known strings which have the same MD5 hash value?

Is there an example of two known strings which have the same MD5 hash value (representing a so-called "MD5 collision")?
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1answer
42 views

“Royal Flags Wave Kings Above” [on hold]

I'm a starter to cryptanalysis and in fact to cryptology. Last night I was decrypting a message from a book that I would quite odd. It doesn't make sense. The decrypted message is "Royal Flags Waves ...
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1answer
99 views

How to determine if padding has been used while encrypting a message with RSA?

I am trying to decrypt a RSA encrypted text file. I have a 2048 bit public key. Analyzing the public key with openssl reveals the exponent used is 3. ...
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2answers
4k 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 ...
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3answers
2k views

Webcam random number generator

I have a question about random number generators. I have read from a real random number generator, based on a webcam ("randcam"). My problem is, that I do not really understand how the generation of ...
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1answer
67 views

Secure blinding factor switching at malicious server-side (Switching in One Time pad)

Suppose all the values and operations are defined over a finite field $\mathbb{F}_p$ where $p$ is a large prime number. Assume all values are non-zero. Here $(z)^{-1}$ denotes multiplicative inverse ...
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2answers
154 views

Advantages of making streamcipher stream depend on plaintext?

Most descriptions that explain how streamciphers work (like the one on Wikipedia), tend to describe a model that boils down to a simple “$ciphertext = plaintext \oplus stream$”, where the stream is ...
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1answer
131 views

How to clock a linear feedback shift register?

I have some trouble understanding what happens when a LFSR is clocked. I have tried many examples but I do not get the correct result. Can anyone point out my errors? I have the following polynomial: ...
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0answers
63 views

When we use one time pad TWICE in two different ways

Assumption and Notations: All the values defined over the field $\mathbb{F}_p$, where $p$ is a large prime number. We denote multiplicative inverse of value $v$ by $v^{-1}$. All values are non-zero ...
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1answer
43 views

Difference of full codebook and non full codebook

While reading a paper about Dynamic cube attack, I saw two terms: full-codebook and non-full-codebook attacks. What do they mean? What is the difference? Regards
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1answer
177 views

When all shares of a secret are given to adversary as a permuted matrix

Suppose we have a secret $\sigma$. The secret comes from a universe in which the elements are not necessarily distributed uniformly. We split $\sigma$ into $n$ shares $[\sigma_1,...,\sigma_n]$ ...
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0answers
19 views

Shamir SS: To associate shares to the public values $x_i$, when the shares are permuted [duplicate]

Suppose we use $(t,n)$ Shamir secret sharing as follows: We share the secret $\beta$ as $S=[s_1,..., s_n]$, where $X=[x_1,...,x_n]$ are the public values. For the sake of simplicity, lets assume ...
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3answers
31k views

How does one attack a two-time pad (i.e. one time pad with key reuse)?

My question might appear the same as the question Taking advantage of one-time pad key reuse?, but actually I did read all the answers and none of them helped me with the details I need. I am new to ...
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2answers
49 views

RSA numerical questions

Let $n$ be the modular arithmetic, $p$ and $q$ the two large primes such that $n=p*q$ and $e$ the public exponent. Here they are two "simple" numerical questions: If $p = 13$ and $q = 17$, what is ...
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0answers
38 views

When we use permutation and random long sting to hide a message

This question is modified version of this: Can we use merely permutation to hide a message? I have an English name $m=m_1 || m_2 ||..||m_{30}$. I pick a random string $d=d_1 ||..||d_{70}$ I mix ...
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1answer
79 views

Can we use merely permutation to hide a message?

This question is related to this: When all shares of a secret are given to adversary as a permuted matrix I think the below question is a simplified version of that. Assume we have a 40-bit ...
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1answer
149 views

Why $e>n^{3/2}$ prevents Wiener's attack

Here's the Wiener's attack as I understand it. Suppose $n=pq$ with $q < p < 2q$, and $d < n^{1/4}/3$ where $ed=k\phi(n)+1$ and $e < \phi(n)$. $$\begin{align*} n-\phi(n) ...
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1answer
49 views

Affine cipher and plaintext attacks

Last year, a question concerning plaintext attacks was posted at Mathematics.SE: “Plaintext attacks: affine cipher”. I have no problem to see how to solve it when we are given two ciphertexts and ...
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3answers
1k views

Can I use a one time pad key twice with random plaintext?

I understand the basics of OTP: $|\text{key space}| = |\text{plaintext space}|$ implies perfect security, key reuse destroys this. Cryptanalysis on the $N$-Time Pad for $N > 1$ involves finding ...
3
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2answers
54 views

How to attack RSA-CRT with large public exponent?

Suppose we have $(n,e)$ and the ciphertext $c$ where the public exponent $e$ is of the same length, 1023-bit, as the modulus $n$. It is also assumed that the factors of $n$ are balanced. The message ...
3
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1answer
364 views

Is XOR adequate for encrypting truly random data? [duplicate]

It is well-known that the two-time pad is very insecure. However, it seems unexploitable in the case where the plaintext is indistinguishable from random (ex. symmetric keys). Is this property ...
2
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2answers
231 views

Autocorrelation in Autokey

I know that Vigenère can broken using auto-correlation (as explained at cryptool-online.org). Now my question is: Why does this also work with autokey (tested it using crypttool)? To prove that I ...
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0answers
106 views

Homogenous and heterogeneous Unbalanced Feistel Networks

Unbalanced Feistel networks can be homogenous (F-function identical in each round), or they can be heterogeneous (F-function not always identical in each round). The advantage of heterogeneous UFNs ...
3
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0answers
101 views

help with cryptanalysis of a sponge permutation

I have been studying and researching hash functions. So far my research has led me to the sponge construction. It appears that the permutation used in the sponge to stir the state is more or less ...
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2answers
5k views

Predicting values from a Linear Congruential Generator

I have learnt that Linear Congruential Random Number Generators are not cryptographically secure - my understanding is that given an LCG of the form: ...
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4answers
1k views

How Brittle Are LCG-Cracking Techniques?

There are published techniques for cracking LCGs, but to my eye those techniques seem very brittle — very minor changes can add nonlinearity that renders techniques like the LLL algorithm unusable. ...
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3answers
4k views

Is javascript RSA signing safe?

I'm currently working on a secure open source messaging system (https://github.com/DSMNET/DSMNET). I'm currently using the cryptico.js (https://github.com/wwwtyro/cryptico) library to encrypt all the ...
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1answer
78 views

Using e-ID Number for Encryption and Digital Signing

I want to use e-ID number for performing Encryption/Decryption and Digital Signing - and in order to do so, I've opted a PGP-oriented approach which goes a bit like this. Generating PGP key-pair ...
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1answer
43 views

Understanding the cryptography used in a file [closed]

I use a software that stores a raw binary file with information, and exports it to a text file. I have access to the data in the original binary file. You can find a sample of the contents of the raw ...
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30 views

How to calculate unicity distance of Fleissner grille?

I need to calculate unicity distance of Fleissners grille of $M \times M$ size. All I know is that plaint text redundancy equals $2$. The alphabet is not specified. Is it possible to calculate its ...
5
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2answers
109 views

Name and security of these non-invertible functions?

I would like to learn more about a specific set of non invertible functions: The function should accept 2 inputs: one hidden and the other visible. The output and the function should also be ...
5
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1answer
87 views

Can somebody help me understand RC4 Spritz? (Three Questions)

So ever since I first took a stab at understanding stream Ciphers, not one stood out more than RC4, because it's so fantastically simple. As most people reading this will know, with its fantastic ...
4
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1answer
89 views

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 ...
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0answers
52 views

Encryption technology for DARPA

I'm working on a short story taking place in the near future in which a hacker gains access to the DARPA mainframe and files related to a highly classified DARPA project. Being ignorant about state ...
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4answers
10k views

Found a way to crack AES-128, what now?

Let us assume the following scenario: I have just found a way to crack AES-128 in a reasonable time (1-2 days). How do I publish and prove this? I remember reading about lots of people who cracked ...
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4answers
2k views

Any practical uses of machine learning for cryptography?

I am about to go study for my masters in machine learning, data mining and high performance computing, but have recently become very interested in cryptography after taking Dan Boneh's Cryptography ...
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4answers
473 views

Can machine learning analyze random number generator?

I'm studying for random number generators(RNG) and I saw about machine learning a few days ago. So I searched analysis of RNG using machine learning. But I couldn't find such fields. Are there such ...
6
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1answer
94 views

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 ...
6
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2answers
95 views

RSA: Proving that $p+q-1 < 3 \sqrt{N}$, where N = pq and p,q are prime?

I'm doing some research into attacks on the RSA cryptosystem and have stumbled across Wiener's attack. Within the proof there exists the statement "$p+q-1 < 3\sqrt{N}$". No proof is given for ...
6
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3answers
1k views

A simple block cipher based on the SHA-256 hash function [duplicate]

I've come up with this little routine for doing encryption using the SHA-2 (in this case SHA-256) hash function. As such it is a block cipher with a 256 bit (32 byte) block size and an arbitrary key ...
18
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2answers
3k views

What are the main weaknesses of a Playfair cipher, if any?

What are the main weaknesses of a Playfair cipher, if any? I know that they depend on none of the letters missing, but that is an easy fix if a letter gets dropped. Besides that, are there any other ...