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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If you have a file and XOR every bit with a random bit, can you extract any information?

Say you have a file that is not random, and you XOR every bit with a random bit (not pseudo, but really random). Can someone who sees only the result extract any information from it? Obviously, it ...
2
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3answers
277 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
105 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 ...
6
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2answers
918 views

How does cryptanalysis of the Playfair cipher work?

I have a set of Playfair-enciphered data that I'm trying to crack without the key. I know I need to analyse bigrams; I've currently worked out what decrypts to th, ...
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1answer
132 views

Unbreakable code and mathematical impossibility

Is an unbreakable code mathematically possible , considering a code with finite number of characters but has infinite combinations , using brute force is it not compulsory that the correct code be ...
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1answer
129 views

security in format preserving encryption

In format preserving encryption an attacker knows the format and data type of the plain text. The format of the plain text and cipher text are same. usually cipher text are unreadable form. then how ...
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0answers
44 views

Cryptanalysis and Copying encrypted volumes

I just recently concerned myself with cryptography due to Snowden's revelations and there are a few things I cannot really wrap my head around but maybe you can help me with that. I am not a ...
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0answers
46 views

How to find an impossible differential?

Given an arbitrary SPN-based cipher with X rounds. How to find an impossible differential for this cipher? What are strategies to find one?
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1answer
77 views

What is meant by - computational complexity $2^x$?

Recently Bi-clique Cryptanalysis allowed to obtain following results on full AES ES that claim to have The first key recovery attack on the full AES-128 with computational complexity $2^{126.1}$ The ...
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1answer
82 views

What is the difference between H(M) and H3(M, s, IDA)? [closed]

What is the difference between H(M) and H3(M, s, IDA)? I am aware of Hash function with a Message and a Key, but there are three parameters in: H3(M, s, IDA). Here M is the message, s is the key, ...
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3answers
3k views

How to attack a classical cipher using known partial plaintext?

I have a ciphertext generated by a classical cipher. I do not know what was cipher used to generate it. I do however have the beginning of the plaintext. What are the cryptanalysis approaches for ...
4
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0answers
339 views

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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2answers
648 views

Cryptanalysis of S-DES - Equations

I am trying to derive equations for s and t in the cryptanalysis of a Simple DES algorithm, but I haven't been able to deduce ...
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0answers
204 views

Finding Patterns in Encrypted Data

I am looking for an application (Windows) or code example that might help me find patterns in an encrypted file. I have a ciphertext for which I want to see when a key is repeated. I am not trying ...
2
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2answers
543 views

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 ...
2
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1answer
44 views

Does failure of indistinguishability of encryptions imply lack of CPA-security?

Suppose we have an encryption scheme that fails the indistinguishability of encryptions test. That is, given messages $m_0, m_1$ and a ciphertext $c_b = Enc_k(m_b)$, where $b \in \{0, 1\}$, the ...
2
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1answer
72 views

On composition of encryption schemes

If we composed (as in function composition) multiple CPA-secure encryption schemes would the result also be CPA-secure?
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2answers
88 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 ...
2
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1answer
74 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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1answer
149 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 ...
13
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1answer
2k views

Duration for attacking Two-Key Triple-DES Encryption using all RAM ever built?

I am considering attacks on Two-Key Triple-DES Encryption assuming $2^{32}$ known plaintext/ciphertext pairs (that's a mere 32MiB of ciphertext) by the method devised by Paul C. van Oorschot and ...
0
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1answer
600 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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0answers
65 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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2answers
818 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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0answers
75 views

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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2answers
90 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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1answer
93 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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1answer
222 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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1answer
111 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 ...
1
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1answer
150 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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0answers
54 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 ...
2
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1answer
145 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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0answers
250 views

Is chaotic encryption secure? [closed]

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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1answer
300 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 ...
2
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1answer
106 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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1answer
165 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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1answer
86 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 ...
2
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1answer
81 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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1answer
169 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 ...
2
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1answer
2k views

What is the probability of breaking the AES algorithm?

I am doing a project which requires the encryption to be done using AES. Is it really possible (technically) to crack AES? If yes, please tell me: What is the probability of breaking AES? How ...
6
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1answer
471 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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1answer
112 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 ...
2
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1answer
113 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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1answer
195 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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1answer
428 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?
10
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1answer
855 views

How would one crack a weak but unknown encryption protocol?

I asked a question on security.stackexchange, but was told it would be a better fit here: http://security.stackexchange.com/questions/32779/how-would-one-crack-a-weak-but-unknown-encryption-protocol ...
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0answers
33 views

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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63 views

Statistical saturation attack on block ciphers [duplicate]

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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3answers
407 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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1answer
102 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 ...