analysing cryptographic algorithms, potentially uncovering weaknesses in them (e.g. "breaking" them or casting doubts on their actual security)
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148 views
How are constructs with data-dependent swaps and rotations cryptanalyzed?
Linear and differential cryptanalysis seem well suited for constructs with a (relatively) simple fixed structure of boolean expressions. But some ciphers incorporate swaps of array elements where the ...
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3answers
164 views
Is it possible to work out the hash algorithm from a list of known message-hash pairs?
For example, in my situation I know hash(20) = 486e9638177faf1f34e49910491b77af.
I also know the hashes for all values from 0 to 20.
Is it possible to work out the ...
2
votes
2answers
703 views
How can I do a brute force (ciphertext only) attack on an CBC-encrypted message?
Given a CBC ciphertext and IV, how can I find the encryption key?
We are limited with an 8 chars key, each char in the range of [a..h], so I can generate every possible key (these are only $8^8 = ...
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2answers
598 views
How can I break REDSHIRT / REDSHIRT2 encryption?
Recently, a user on Gaming.SE asked a question about whether the user password in the video game Uplink could be modified after being initially set. The game does not contain an option to change the ...
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2answers
952 views
How much computing resource is required to brute-force RSA?
It's been over 30 years since Rivest, Shamir and Adleman first publicly described their algorithm for public-key cryptography; and the intelligence community is thought to have known about it for ...
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2answers
123 views
Can you help with that definition for a CCA?
The following is a definition taken from Introduction to Modern Cryptography by Katz and Lindell.
I'm having a hard time understanding some basic concepts! Can you please help me?
...
2
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2answers
153 views
Getting the encryption method and key from the encrypted data and the raw data
I have some pairs of plaintext and ciphertext data, from which I need to be able to decrypt the other passwords stored in the database.
The password field typically contains something like
...
2
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2answers
254 views
AES-CTR vulnerability to cryptographic oracle
I am new to cryptographic issues and from what I googled so far I could not retrieve the information I need.
Consider the use of AES-128 in CTR mode.
Let M be the set of possible plaintexts, for ...
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3answers
134 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 ...
2
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2answers
246 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:
...
2
votes
2answers
296 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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2answers
168 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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2answers
423 views
Cryptanalysis of Linear Feedback Shift Registers
It is well known that simple m-sequence linear feedback shift registers have a linear algebraic structure and therefore the generator seed can easily be deduced using the Berlekamp-Massey algorithm. ...
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1answer
109 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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2answers
2k views
How does a chosen plaintext attack on RSA work?
How can one run a chosen plaintext attack on RSA?
If I can send some plaintexts and get the ciphertexts, how can I find a relation between them which helps me to crack another ciphertext?
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1answer
53 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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2answers
132 views
Source for examples with broken cryptography
I've heard again and again that many crypto systems have been broken in the past for one reason or another and that it is best to use one that has been peer reviewed, etc etc. However, I've yet to see ...
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2answers
112 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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1answer
92 views
Hill-cipher, disordered alphabet
I am going to apply a simple substitution cipher to my input, then encrypt the result with a Hill cipher. How can this be broken, in a chosen-plaintext threat model?
In other words, instead of the ...
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votes
1answer
154 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 ...
2
votes
1answer
181 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 ...
2
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2answers
335 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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1answer
309 views
Example Rainbow Table Generation
I have read up on rainbow tables and think I understand the idea behind them. However, I find that it would be better for me to actually attempt to implement a (very basic) rainbow table generator in ...
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2answers
136 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 ...
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1answer
559 views
Cryptanalysis Affine Cipher: Brute-Force Search Vs. Meet-in-the-middle
Affine Cipher:
$Enc(x) = (ax + b) \mod m$
$Dec(x) = a^{-1}(x-b) \mod m$
For a brute-force key search, we need to do $a \cdot b$ encryptions in the worst case.
For a meet-in-the-middle attack, how ...
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1answer
175 views
ElGamal message signatures retrieving the secret value x
If the GCD(r, p-1) is small and the value k is used to sign a message using ElGamal is also small. Then the secret value of x can be determined.
Why is this true? How would one retrieve x?
...
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2answers
254 views
How can one break a monoalphbetic substitution chipher at pseudorandom text?
Does anybody know how to break monoalphbetic substitution cipher, if it is applied to some pseudorandom text (for example to some surrogate key filed in a database)?
Let us assume that we have only ...
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votes
1answer
291 views
The use of cribs
I'm looking to incorporate more crib usage in breaking ciphers in unknown enciphering schemes, or at least to gleam what information I may. This seems to be a big hurdle to me, and I'm looking for ...
2
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1answer
101 views
How to design a practical and secure MAC scheme?
I am sorry, but I need to introduce some concepts which are not directly related to cryptography to make myself clear, I hope I won't stun you with this ... (I'd rather explain it here than redirect ...
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0answers
61 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 of ...
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vote
1answer
118 views
Do practical key-less cryptosystems exist?
Hopefully the question isn't too broad or off.
Basically, are there any practical, and by practical I mean secure enough that a ciphertext only attack is infeasible, key-less cryptosystems? For ...
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2answers
120 views
Help me describe/identify this challenge-response protocol/algorithm?
My area of expertise is reverse engineering, specifically embedded systems. I do attack cryptographic systems, but this largely involves key recovery or exploiting the implementation.
I was asked to ...
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1answer
72 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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3answers
217 views
How to encrypt data and know it will be secure for at least a few decades?
I want to encrypt a small amount (few kilobytes) of data and be fairly confident it will be secure against brute force decryption and advances in cryptanalysis for at least a a few decades (or more). ...
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vote
2answers
157 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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1answer
328 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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1answer
78 views
Security of Salsa20 with some known plaintext?
Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known?
Assume that a different IV and Key are generated before each file is ...
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2answers
160 views
Brute force a ciphered message?
I wrote my own cipher to encrypt messages. I would like to test a sample ciphered message to see how strong it is. Are there any tools for such task either in Windows or Linux ?
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2answers
165 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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2answers
354 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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1answer
51 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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1answer
55 views
What is total key space in transposition algorithms
How we can measure key space in transposition algorithms? Should we specify the method, like rail fence ?
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1answer
89 views
Using Chi-Square for Vigenere Cipher
I am writing a program which will use Chi-Square to determine which is the correct keyword for a ciphertext via Vigenere Cipher.
I came across a website that describes the Chi-Square statistics in a ...
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1answer
64 views
How does this Cesar Cipher work?
Suppose I have this cryptogram: http://pastebin.com/QpfRMBg1
Clearly it's a Ceasar Cipher which decrypts to: http://pastebin.com/r50heZuU
with a simple shift of 10... OKay, no big deal. Let's take a ...
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1answer
158 views
Is there a security analysis of CryptDB?
Its interesting to see critical thinking being applied to cryptDB in contrast to all the hoopla around it here . cryptDB is not a major theoretical breakthrough but potpourri of technologies to make ...
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1answer
294 views
AES encryption for images [closed]
Why AES based encryption is not recommended for encrypting images with high redundancy in their content? for example, the encryption of an image which shows a bird in the blue sky. Most of the pixels ...
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1answer
492 views
Deciphering a key from XOR encrypted cypher using boolean logic
Assume there's an unencrypted message A, and an encrypted message B. You know that message B was encrypted using a simple XOR method of A with a private key K, resulting in message B. Thus,
B = A ⊕ K
...
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1answer
204 views
Security analysis of a “one-time pad” type hill cipher
Suppose the Hill cipher were modified to something like a one-time pad cipher, where Alice wants to send a message to Bob, and she chooses a key matrix randomly everytime a new message is sent (and ...
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1answer
108 views
Are there any hand ciphers not obsoleted by computer cryptanalysis?
Computerized cryptanalysis has obviously made formerly "secure" hand ciphers like Playfair, Four Square, and the Hill Cipher obsolete because they can be defeated in seconds. But is there a hand ...
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1answer
88 views
Measuring Shannon's diffusion
Shannon's idea of diffusion is fundamental to cryptography.
Besides being a descriptive idea, is there any work on measuring or expressing it? Saying something like "System A has more diffusion than ...
