analysing cryptographic algorithms, potentially uncovering weaknesses in them (e.g. "breaking" them or casting doubts on their actual security)
8
votes
1answer
557 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 32 Giga Bytes of ciphertext) by the method devised by Paul C. van Oorschot ...
3
votes
3answers
173 views
Are asymptotic lower bounds relevant to cryptography?
An asymptotic lower bound such as exponential-hardness is generally thought to imply that a problem is "inherently difficult". Encryption that is "inherently difficult" to break is thought to be ...
3
votes
1answer
323 views
Does the Biclique attack on AES pose a credible risk to its security?
I have heard a lot about the biclique cryptanalysis research on AES, which as far as I know is the closest anyone has got to breaking AES.
Exactly how close did they get? Does this attack propose a ...
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 = ...
1
vote
0answers
101 views
Security of stream cipher based on Matrix multiplication GF(256) with randomized padding
The actual question is stated at the end of the text. Suppose you have a (grossly inefficient) confidentiality stream cipher with the following components:
The keyed function ...
2
votes
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?
0
votes
2answers
134 views
CPA distinguisher for matrix multiplication in GF(256) with randomized padding
What is the best CPA distinguisher for the function $F_k:\{0,1\}^{8n}\to\{0,1\}^{16n}$ described below?
Let $E_k$ be a $2n\times2n$ matrix with elements in $GF(2^8)$, selected by generating bit ...
4
votes
2answers
244 views
Predicting PRNG given some of its previous output
I a have a question about PRNGs and this is my very first experience with them. I have the following generator that takes a 56-bit seed 'p' during initialization and then chooses both X and Y randomly ...
8
votes
3answers
456 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 ...
2
votes
2answers
334 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 ...
8
votes
2answers
6k 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 ...
6
votes
4answers
486 views
Is compressing data prior to encryption necessary to reduce plaintext redundancy?
As explained in William Stallings' Book, in PGP encryption is done after compression, since it reduces redundancy.
I couldn't relate encryption strength with redundancy. Could anyone explain more on ...
3
votes
2answers
225 views
Is it generally possible to employ brute force methods when the encryption scheme is not known? Why or why not?
Lets say you are presented with an encrypted string of bits or text, and no other information. What would be necessary before you could apply brute force methods to decrypting the string? How would a ...
4
votes
1answer
192 views
S-box Cryptanalytic Resistance
In DES, different S-boxes were tested for cryptanalytic resistance and the most secure one was chosen for the algorithm itself.
How do different S-boxes offer different levels of security against ...
0
votes
0answers
46 views
Elliptic curve Cryptography [duplicate]
Possible Duplicate:
Can we use elliptic curve cryptography in wireless sensors?
How to map message character to point lies on Elliptic Curve? how to ecc used in wireless sensor networks? ...
6
votes
2answers
1k 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:
...
1
vote
0answers
178 views
Deciphering a Message [closed]
I have this message to decipher:
UYDVKUYEHJNRFRLYZIPVSUQYGAFFBXKAJLVRIETJIUOTSVKXHQZUWYLIOQHQEJR
I have tried using methods such as:
Ceaser cipher, Atbash cipher, Railfence etc.
I also tried ...
5
votes
0answers
400 views
What are the popular crypt analysis tools? [closed]
What are the popular crypt analysis tools out there ? for something like Cipher Text only attacks or any attacks in general which does frequency analysis et all
3
votes
1answer
173 views
Security analysis of a matrix multiplication protocol
Suppose Alice would like to obtain the product of two mXm matrices i.e. A and B. Alice has A, whereas Bob has B.
Since Alice does not want to reveal A to Bob, she chooses a mXm random invertable ...
1
vote
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 ...
1
vote
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 ...
8
votes
3answers
446 views
What is the best way to put a backdoor in an encryption system?
How can you put a backdoor into an encryption algorithm? Are there any techniques that can be used to reduce the time it takes to break a key?
I am looking for practical examples encryption schemes ...
6
votes
1answer
300 views
Exposing RSA private-key data… bad?
We know that exposing $p$, or $q$ or $\phi(n)$ results in trivial attacks on RSA since they allow us to factor $n$ and to compute the private exponent $d$.
In OpenSSL (and most RSA implementations) ...
5
votes
2answers
2k views
Rijndael vs. Serpent vs. Twofish: General comparison
Can anyone explain (or give a link to document about) why Rijndaal won the AES, especially comparing it to other finalists (Serpent and Twofish)? What criteria were used to make decision?
Or is there ...
0
votes
0answers
109 views
What will be the way to go about deciphering this kind of cipher? [closed]
I've come across this cipher and have tried unsuccesfully to decipher it.
http://codepad.org/aea7Wuyl
The only 'hint' that I have gotten so far as to how I am supposed to crack it is the word ...
7
votes
2answers
407 views
How does the MOV attack work?
What exactly is the MOV attack, how does it actually work, and what is it used for?
It's explained briefly here and I'd like to know what it is more / what is it fully used for.
-4
votes
2answers
147 views
Any techniques for evading frequency based crypt analysis without encrypting?
Are there any general techniques for evading frequency based crypt analysis without using any encrypting techniques
6
votes
3answers
2k views
Encryption/ciphers/codes in Chinese
I am quite curious as to how you can perform simple encryption for the Chinese language.
Saw a similar question related to encryption/Chinese here: About cryptography in a character language, ...
3
votes
1answer
267 views
Differential cryptanalysis - breaking the last round of FEAL4?
I've been trying to learn cryptanalysis. I've come across this resource which proved very helpful:
http://theamazingking.com/crypto-feal.php
So far I've been almost successful in breaking FEAL4 ...
3
votes
3answers
595 views
A simple block cipher based on the SHA-256 hash function
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 ...
4
votes
1answer
484 views
Known Plaintext attack against XTEA?
I'm looking for information on known-plaintext attacks against XTEA. I'm most interested in the worst case scenario: if an attacker has all 8 bytes of input and all 8 bytes of output, how much ...
1
vote
0answers
76 views
Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate]
Possible Duplicate:
Two untrusted party want to exchange data: how to insure each one gets the data it needs?
I am trying to come up with what could maybe be a novel algorithm for an ...
1
vote
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 ...
5
votes
2answers
546 views
Cycle attack on RSA
I originally posted this question in the mathematics section, you can see it here.
Let $p$ and $q$ be large primes, $n=pq$ and $e : 0<e<\phi(n), \space gcd(e, \phi(n))=1$ the public encyption ...
2
votes
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 ...
2
votes
1answer
558 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 ...
6
votes
2answers
1k views
Definition of Textbook RSA
What is the definition of Textbook RSA?
What are some of the properties of textbook RSA?
How does it differ from other RSAs?
2
votes
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?
...
1
vote
1answer
451 views
Verilog simulation of Data Encryption Standard
I interested in developing DES(in verilog) for my college project.Can i get help in understanding the simulation results of DES encryption and decryption ?
thanks in advance .
6
votes
1answer
124 views
Message space in security definitions
What is the message space in the following example and how does a message space relate to a security definition?
I mean, what difference does it make to such a definition if your message space is ...
4
votes
1answer
548 views
Example of CHI Square test on Caesar Cipher?
I am trying to get my head round the chi square test, when used with the Caesar cipher.
I started off using this formula,
$$ X = \sum_{i = 1}^k \frac{f_i · f'_i}{n · n'} $$
Where ...
2
votes
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?
...
4
votes
1answer
125 views
What are the consequences of a MAC tag collision?
I've seen some proofs of MAC security that are based on the extremely-unlikely event that two MAC tags collide (ie, they are equal for distinct messages). Suppose that this extremely unlikely event ...
6
votes
2answers
2k views
How does a chosen ciphertext attack work, with a simple example?
Can someone please explain - using a simple example - how a chosen ciphertext attack works?
6
votes
2answers
299 views
For public-key encryption, why does COA resistance imply CPA resistance?
My professor told me:
If a public-key crypto-system is secure against ciphertext-only attacks,
then it is also secure against a chosen-plaintext attack.
Why is this true? Is there a proof that ...
4
votes
1answer
405 views
Linear Cryptanalysis
What is the principle of linear cryptanalysis, as applied to a block cipher ? For instance, this page gives the rough outline of differential cryptanalysis.
3
votes
2answers
654 views
Decrypting DES with decrypted and encrypted data
I got two 8 bytestrings
One which is decrypted is:
FF FF FF FF FF FF FF FF
and one which is encrypted is:
16 05 78 B0 0A C2 78 7F
Encryption mode is CipherMode.ECB
I need the key used in DES ...
5
votes
1answer
261 views
If the PSK is known, is it possible to decrypt traffic from other clients in a WPA2 wlan network?
If in a public WLAN WPA2-PSK is used, but the PSK is more or less publicly available, does this mean that an attacker with that PSK can easily decrypt wlan traffic from/to other clients of that WLAN?
...
6
votes
1answer
368 views
How to deduce enigma settings given a partial plaintext?
Assuming some large block of text is encrypted with an enigma machine and I only know a small subset of letters before and after encryption, how do I go about figuring out the enigma settings from ...
2
votes
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
...
