analysing cryptographic algorithms, potentially uncovering weaknesses in them (e.g. "breaking" them or casting doubts on their actual security)
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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?
...
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 ...
5
votes
2answers
260 views
Analysis of Repeatedly Enciphered Plaintext using Same Algorithm / Key
Please forgive the impracticality of this question, but I'm curious about the behaviors of encryption algorithms applied to their own output.
Suppose I have an encryption algorithm E and (using the ...
5
votes
2answers
127 views
Security of tokenization of plain text conversations - cryptanalysis
I came across a marketing video here. They claim to perform AES encryption and tokenization of sensitive data, at the corporate gateway, before it leaves the company firewall destined for the public ...
5
votes
2answers
565 views
Assistance Cracking Classical Cipher
Below is the cipher text I am trying to break and as you can see its rather short which is why I am having so much trouble.
...
5
votes
0answers
58 views
MD4 First preimage - state of the art
What's the state of the attack to get the first preimage on MD4?
Is it still this http://www.di.ens.fr/~leurent/files/MD4_FSE08.pdf in 2^102 ?
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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
4
votes
2answers
1k views
How does a padding oracle attack work?
I am unsure of how a padding oracle attack works.
What I am not getting is how changing one bit at one time allows one to exploit(get keys) ASP.NET machines.
Can anyone explain this?
4
votes
1answer
101 views
What is 'security margin'?
I have been academic papers about Rijndael, Serpent, and Twofish, and there is this term that is vague to me. I cannot find a tangible definition in google. Can someone briefly define, describe, ...
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.
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 ...
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 ...
4
votes
1answer
205 views
repeating-key xor and hamming distance
I read that to break repeating-key xor you can do the following: try a keysize $n$ and compute the hamming distance between the first $n$ bits of the encrypted string and the bits $n+1$ to $2n$ of the ...
4
votes
1answer
297 views
How was the complexity of the Biclique Attack calculated?
The abstract of the Biclique Attack paper claims:
The first key recovery attack on the full AES-128 with computational complexity $2^{126.1}$.
What does $2^{126.1}$ mean in this context? And ...
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 ...
4
votes
1answer
143 views
Where can i find relative software for differential cryptanalysis?
Is there any publicly known software for differential cryptanalysis over some cryptographic building blocks as blocks ciphers or cryptographic hash functions
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 ...
4
votes
1answer
136 views
Question about why RSA is hard to attack
I think I understand why RSA is hard to attack but I'd like to get clarification if I actually do.
Assume there are two people, Alice and Bob, who are attempting to communicate privately but that we ...
4
votes
1answer
153 views
Can a nested block cipher avoid the meet in the middle attack by using a secret initialization vector for the inner encryption?
It seems to be believed that encrypting twice with a block cipher using an independent key each time is not as secure as you might expect because of the "meet in the middle" attack.
This is an attack ...
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 ...
4
votes
1answer
226 views
If a cryptanalytic breakthrough is made, what process should be followed?
If a researcher manages to make a cryptanalytic breakthrough on a cryptographic algorithm or protocol that is in use, what should they do?
Has this ever happened before? What are the implications for ...
4
votes
3answers
206 views
Comparison: complexity measures vs. security
Assume that you want to compare several cryptographic primitives (say, encryption schemes), and choose one. You need to consider several complexity measures, such as the key length, encryption time, ...
4
votes
2answers
203 views
Tunnels used in md5
I'm reading a paper about finding collisions for the MD5 hash algorithm involving the concept of tunnels.
But I couldn't understand about the difference between point of verification and point of ...
3
votes
2answers
230 views
If Bob steals Alice's private key, how exactly would he read her encrypted documents?
So Bob grabs Alice's secret key when she isn't looking and her encrypted files, doesn't he need to know her passphrase to read her files?
What I am reading is that no he does not need it but as far ...
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 ...
3
votes
2answers
500 views
What is the smallest plaintext/ciphertext size for an algorithm like?
When I read about a choosen plaintext attack, for example on AES the block size is always 128 bits, does it mean the attacker will only supply 128 bits data words as "plain text" ?
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votes
6answers
306 views
Where can I begin to study the math behind modern cryptography?
I've been studying (more like breathing and eating) crypto for almost a year now, implementing algorithms, reading books, studying code, etc. The deeper I go in, the more I realize there is; I feel ...
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 ...
3
votes
2answers
464 views
Difficulty of breaking RSA for a given key size
Is it true that breaking a 1024-bit RSA key is as difficult as breaking a 128 bit symmetric key (e.g. AES)? I know that breaking a RSA key is equivalent to factoring the modulus $N$. To factor it, you ...
3
votes
2answers
840 views
Brute forcing CRC-32
I'm working on a cryptosystem which uses IDEA. The designer made the mistake of including a CRC-32B hash of the password unencrypted in the header, so that the system can quickly reject bad ...
3
votes
3answers
252 views
Where can I find useful data for cryptography/coding theory?
When implementing cryptographic/coding theory algorithms one need to use data like big prime numbers, numbers in Z_n and their inverses, irreducible polynomials in Z_n[x] and so on... While sometimes ...
3
votes
2answers
653 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 ...
3
votes
1answer
127 views
Using an MD5 hash as a password
Suppose Alice is using a password prompt that only accepts up to 32 characters for any particular password.
Memorization of long strings of random characters is not one of Alice's strengths, so she ...
3
votes
1answer
105 views
How can we determine if two discrete logarithms are equal?
Let $p$ be a prime number, and let $g_{1},g_{2},...,g_{n}$ be $n$ generator of $Z^{*}_{p}$. We have a list $y_{1},y_{2},\dotsc,y_{n}$ of elements in $Z^{*}_{p}$ such that for every $i\in ...
3
votes
1answer
89 views
Why doesn't this replay attack work on ECDSA?
I've just started working with elliptic curves and ECSDA in particular, so my understanding of the underlying math isn't great. The thing I'm currently stuck on is trying to understand why replay ...
3
votes
2answers
204 views
How can I break a Vigenère cipher with partial plain text?
I have an exercise to do regarding Vigenère encryption.
I've got the cipher text: WNZTNVIEEGTJYKRRWYUELWNZTNV
and a partial plain text: ...
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 ...
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
1answer
162 views
Is the last step of an iterated cryptographic hash still as resistant to preimage attacks as the original hash?
Considering a cryptographic hash, such as MD5 or SHA2, denoted by the function $H(m)$ where $m$ is an arbitrary binary string, there is a lot of material available that deals with potential weakness ...
3
votes
1answer
213 views
Is XOR in a CBC-like mode secure?
Assuming that $K_{n}$, $P_{n}$, and $C_{n}$ are individual bytes of the key, plaintext, and ciphertext respectively.
The first byte of ciphertext is computed like this:
$C_{1} = K_{1} \oplus P_{1}$
...
3
votes
1answer
248 views
Get RSA PlainText without Knowing Private Key
If I have an algorithm,RSA-Crack(), that, for a given RSA public key (n,e), is able to decrypt 1% of the messages encrypted with that key (without knowledge of the corresponding private key).Can there ...
3
votes
1answer
123 views
Proof that Alternating Step Generator and modifed ASG' have equivalent security?
The Alternating Step Generator (ASG) is a PRNG combining 3 LFSRs. Output of the ASG is the XOR of the output of two clock-gated LFSRs. At each step, a single one of these LFSRs is clocked, according ...
3
votes
1answer
117 views
Understanding a Blowfish cryptanalysis
I'm reading a cryptanalysis on Blowfish, and I've come across something that I don't quite get. Let's denote
$$\delta = a \oplus a'$$
where a and a' are bytes that cause a collision in some S-box ...
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
229 views
What is the best method to determine the language used in a monoalphabetic substitution cipher?
Working on a cipher (which I assume to be a mono-alphabetic substitution cipher due to the letter frequency) I struggle with the fact that I don't know which language the plain text is written in. ...
3
votes
1answer
212 views
Hill cipher, unknown letter value
I've been struggling on this problem for a while now : the Hill cipher is well-known to be vulnerable to known-plaintext attack due to its linearity. Given a key matrix $K$ of size $n\times n$, one ...
3
votes
1answer
166 views
Has there been any cryptanalysis of RC4-52?
Several websites ( such as Is there a secure cryptosystem that can be performed mentally? ) briefly mention RC4-52 as a modification of standard RC4.
RC4-52 has only with 52 instead of 256 elements ...
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 ...
3
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0answers
101 views
Questions on rank-attacks in Multivariate Cryptography
While reading this article on rank attacks on STS (a public-key scheme based on Multivariate Quadratic (MQ) equations), I stumbled upon some claims that I've also seen in other presentations on ...
2
votes
2answers
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 ...
