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

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Is One Time Pad considered Chosen-Plaintext Attack Secure?

If we're considering Chosen-Plaintext Attack setting, then the adversary has access to the Encryption Oracle right, and we know that OTP is only considered secure if we use the key only once. How ...
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75 views

Negilible Function $\frac{1}{n!}$

Is $\frac{1}{n!}$ a negligible function where $n$ is a security parameter? Application: I have a vector of n>100 elements. I permute it and give it to an adversary. The adversary can break it if it ...
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46 views

Does the plaintext have to be at least as long as the key in Polyalphabetic substituion cipher

In polyalphabetic substitution cipher, if we have a key $k$ (a string of letters) of length $n$ does the plaintext $m$ (also a string of letters) have to satisfy $|m| \geq n$? Also, side question, ...
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98 views

How do we guarantee plaintext is coprime in RSA?

The specifications for RSA state: $P^{\phi(N)} \equiv 1 ~mod~N$ if and only if $P$ and $N$ are coprime. Here $P$ is the plaintext and $N$ is the product of two suitable primes $x_1, x_2$. My question ...
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121 views

Why cant Public Key Encryption be perfectly secure? [duplicate]

I would be very grateful for any help. I cant figure out why (probabilistic) public key encryption schemes can never provide perfect secrecy? Any Ideas? Excerpt: In contrast to the private-key ...
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84 views

Recovering key length from transposition block cipher ciphertext

First of all I would like to say hello to all StackExchange users. So far I've been stalking the forum for some time, now it's time to leave the shadows. In my master thesis I'm writing about ...
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60 views

Security of a custom non linear hill cipher

Initially let me state that this is an atypical type of cryptographic encoding. First I break up my key into three parts $k = {W,\overrightarrow{b},\alpha}$. the $W$ is simply a $n \times n$ matrix, ...
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67 views

How to make PKCS conformation oracle for trying Bleichenbacher’s RSA attack?

I was trying to understand Bleichenbacher’s CCA attack and thought of work it out in python. Can some one throw some light on the the logic behind the oracle used to check PKCS conformation? Will a ...
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68 views

Is it hard to recover $p$ from $k \phi(p)$?

Given $k\phi(p)$, is it hard to recover $p$? Here, $p$ is a large prime, $\phi(\cdot)$ is Euler's totient function and $k$ is an unknown integer. Or what's the complexity to recover $p$ from $k ...
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Missing public exponent

Using LUC RSA, I have a list of 8 public keys $(R_1,n_1)$ through $(R_8,n_8)$, and a list of $8$ messages $M_1\dots M_8$. The messages have all been double encrypted. However, one of the public key ...
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54 views

Malicious party security model: When one party is corrupted at a time

Consider we have three parties,namely client $A$, client $B$ and a server. Client $B$ and the server can be malicious, but we do not allow the adversary to simultaneously corrupt the server and ...
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64 views

Reducing the keyspace for a brute force attack on a chained 64-bit xor

I have a block of data which I know is encrypted using a chained 64-bit xor (sorry if that makes no sense, I'm not familiar with crypto lingo). I know a little bit about what the plaintext should look ...
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148 views

Are well designed crypographic codes unbreakable? (NOT ciphers)

Codes are not to be confused with ciphers. It is known that all known ciphers are theoretically breakable except the one-time pad and this isn't what the question is about. Some cryptographic codes ...
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146 views

Permuted vectors

Consider we have two vectors $v_1, v_2$ of size $n$, and each vector contains $n$ elements. We permute the vectors as: $\pi (k_1,v_1), \pi (k_2,v_2)$. Where $\pi (k_i,v)$ denotes a permutation of a ...
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115 views

Image sharing without data overhead

The idea is to share $n$ images among $n$ persons so that all images can be reconstructed by someone in possession of all shares. However, there must not be any data overhead (which means the shares ...
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41 views

Determine encryption method with input and output

A website stores username and password in a session cookie. In the cookie the password is "encrypted" or modified in some way. Given that the "encrypted" version is always the same, I do not believe ...
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97 views

Known plaintext attack on 3 round SIMON block cipher

I am attempting to write a program to perform a linear approximation attack on a reduced round version of the SIMON block cipher, but I am stuck on how to actually apply the linear approximation to ...
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63 views

Words in “index of coincidence” in relation to the Vigenère cipher

I am trying to interpret the formula for index of coincidence from here… I am not understanding $f_i$. How can I calculate $f_i$ in this context? Is this the appearance of single word like ...
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109 views

Vigenère, auto-correlation vs Kasiski examination

What are the differences between 'Kasiski examination' and 'auto-correlation' ? In Cryptool site, they state that autocorrelation analysis is more efficient and clearer than the Friedman or Kasiski ...
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94 views

Finding Vigenère cipher key(s) [closed]

How can we find the key used with a Vigenère cipher in small number of steps? If we have text like: Peit Wokm! Mhfa fepatgb ets bvvrvxmea ebte bae twkd qiqi ...
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174 views

Is chaotic encryption secure?

I know this sounds too broad. But I noticed that there was a chapter on chaotic crypto in the recent Handbook of Information and Communication Security Editors: Stavroulakis, Peter, Stamp, Mark (Eds.) ...
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96 views

RFID Protocol Cryptanalysis

Assume we have the following scheme for RFID: TAG & READER both have initially k keys. Every session the TAG computes $k_i$=F($k_{i-1})$ where F is a function which computes XOR of previous key ...
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Looking for C++/Python Open Source code library for cryptanalysis of classical ciphers [closed]

I've done a significant amount of coding over the years working on classical ciphers (e.g., Chaocipher, D'Agapeyeff). My main programming languages today are C++ and Python, although there was a time ...
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103 views

(Simple) Tool for analysing performance (speed in particular) of cryptographic hash function?

I am doing some research for which I intend to insert some (external) function in different cryptographic hash functions and I would like to analyse how the insertion of this extra code in the hash ...
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80 views

How much of Probability do I need to know to study Cryptography?

I have just started MSc in Computer Security. I didn't study probability before. Now, I have some short time to complete my MSc semester. What are the minimum topics from 'Probability' do I need to ...
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60 views

Algebraic cryptanalysis on public-key schemes

The book Algebraic Cryptanalysis (Bard, G.V.; Springer, 2009) speaks about transforming a symmetric scheme into a system of polynomial equations and solving these equations to break the scheme. But ...
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129 views

What use is the signature without the message under RSA?

Using RSA for signing & verification, is there a way to take a valid signature for an unknown message, and for someone else to generate a valid signature using a different key against the valid ...
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187 views

Crack linear congruential generator knowing every other word in sequence

I need to crack one of the example of linear congruential generator. I have $X_{n+1} = (a \cdot X_n + b) \bmod m$ and I know every other word in the output sequence: ..., 3158, ..., 1888, ..., ...
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93 views

What makes this mixer function resistant to differential cryptanalysis?

I recently learned how differential cryptanalysis works, and decided to have a play around with testing various designs for resistance against attack. My testing algorithm is essentially to loop ...
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41 views

Vigenère + columnar transposition

I'm trying to decode a text which is encoded by Vigenère followed by a columnar transposition. The method I want to use is trying random columnar transpositions and then rating how much the text that ...
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43 views

Recover keys using statistical saturation attack

I am having trouble here performing this attack on a block cipher. This is my block cipher, it is a toy with really bad diffusion just for the sake of performing a successful attack ...
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105 views

Stacked LFSR - why not used?

New to cryptographic, weak in math. I have designed a PRG which consist of 33 LFSR's, each 32 bits wide. I use one of the LFSR's as "selector", using the 5 LSB from this register to select one of ...
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225 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 ...
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407 views

Purpose of expanding then shrinking in SHA-1

What is the purpose of expanding then shrinking in SHA-1? Does it serves any security purposes?
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103 views

How do you implement a cipher as one lookup table?

I am reading up on whitebox cryptography and have trouble understanding how are ciphers implemented as one lookup table? assuming my plaintext is just 4 bits so the size of my lookup table should be ...
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Practical strength of non-2^n RSA key lengths [duplicate]

It has for many years been popular to use RSA keys that have lengths that are powers of two. E.g. 1024-bit, 2048-bit and 4096-bit key lengths are all popular for use with OpenPGP implementations such ...
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26 views

How to check if a sequence is generated by a linear congruential generator? [duplicate]

Assume a linear congruential generator is defined by $x_i=(x_{i-1}\cdot a+c)\bmod m$ and I am given the values $a$, $c$, $m$ and a sequence of numbers starting at the $n$th bit. Can I tell whether ...
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54 views

Statistical saturation attack on block ciphers

I was wondering if anyone around here could give me some explanation on this type of attacks. Pretty much the only thing that I could find is this What I really need is basic explanation of the ...
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64 views

Statistical saturation attack on block ciphers

I was wondering if anyone around here could give me some explanation on this type of attacks. Pretty much the only thing that I could find is this What I really need is basic explanation of the ...
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1answer
64 views

Why are modes of operation used, what attacks do they prevent?

I know you always need to use a mode of operation when using a block cipher, AES for example, and Wikipedia has a good explanation for what modes of operation are Now I know if i do not use a mode of ...
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235 views

When is a cipher considered broken?

We've all read how some people claim AES is broken because there was supposedly a way to get the plain text from a cipher text faster than brute-force. But is this the definition? Is a cipher broken ...
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191 views

Known plaintext, unknown 128 bit block cipher

I have an encrypted configuration file from an embedded device which I'm trying to decrypt. The file seems to be encrypted in 128bit blocks, as changing a single option causes a 16 byte block to ...
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1answer
125 views

Differences between Work Factor and Time Complexity

I am interested to know if work factor means the same thing as time complexity. Quoting Work Factor : Uncovering keys in cryptosystems The Work Factor of a cryptosystem is related to its ...
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105 views

Vigenere ciphers : Need help for math analysis

I've been learning about Vigenere ciphers and then thought of another method to Encrypt and decrypt that. This's my method to encrypt : ...
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1answer
89 views

Complexity of attacks on affine cipher

I am interested in the complexity of attacking affine ciphers under the following two scenarios during a Ciphertext only attack during a Chosen Plaintext attack For an alphabet of size $m$, how ...
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266 views

Is cryptanalysis of CTB-Locker really impossible?

It seems that CTB-Locker make a lot of victims nowadays, and yet, the full encryption scheme of it is now publicly known [1,2]. Would any of you could find a weakness to exploit in this encryption ...
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298 views

How to accurately calculate Unicity Distance for English?

The Unicity Distance for the DES cipher is around $8.6$ characters, and can be calculated using the $U=H(k)/D$ formula, where $D = R - r$, and where $R = 8$ is the number of bits in a byte (ASCII is 7 ...
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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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71 views

How to construct the blind factors in practice?

I'm Implementing a protocol that uses masking techniques (or blinding factors), so we can mask a value $y_0$ as $m_0=y_0 \cdot r_0$ where $y_0 \in \mathbb{Z}_p$ and $r_0 \stackrel {R}\leftarrow ...