analysing cryptographic algorithms, potentially uncovering weaknesses in them (e.g. "breaking" them or casting doubts on their actual security)
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0answers
26 views
Can two cipher letters per plaintext letter easily defeat character frequency analysis?
For a class 5 years ago I wrote a paper about defeating character frequency analysis by using two cipher letters per plaintext letter. I didn't get much feedback from the professor so I wonder if ...
3
votes
2answers
240 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 ...
1
vote
1answer
360 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 ...
4
votes
1answer
114 views
Security strength of RSA in relation with the modulus size
NIST SP 800-57 §5.6.1 p.62–64 specifies a correspondence between RSA modulus size $n$ and expected security strength $s$ in bits:
...
3
votes
1answer
43 views
differential and linear cryptanalysis
I have been reading about differential and linear cryptanalysis. They were mainly introduced by Adi Shamir and Biham to show weakness of DES. However, many of articles state that they have been ...
4
votes
1answer
160 views
What do recent announcements about solving the DLP in $GF(2^{6120})$ mean for RSA
After just reading the post Do recent announcements about solving the DLP in $GF(2^{6120})$ apply to schemes proposed for cryptographic use?
I was a bit confused. DSA, ElGamal and others are based on ...
7
votes
2answers
348 views
Why are bitwise rotations used in cryptography?
Any understanding I have of cryptography stops right around the cipher level. As such, I'm just curious as to why bit shifts and moreover circular bit shift are so prevalent in cryptography.
1
vote
1answer
88 views
How insecure in practice?
I am in attempt to understand relative insecurity of certain encryption schemes. Particularly of interest is DES and RC2. I know AES is better and should be used to encrypt. But practically, if ...
8
votes
1answer
188 views
Do recent announcements about solving the DLP in $GF(2^{6120})$ apply to schemes proposed for cryptographic use?
A recent paper by Göloğlu, Granger, McGuire, and Zumbrägel: Solving a 6120-bit DLP on a Desktop Computer seems to "demonstrate a practical DLP break in the finite field of $2^{6120}$ elements, using ...
5
votes
3answers
624 views
Recommended skills for a job in cryptology
First let me apologize if this is an ill posed question. Let me also note that I do not in any way seek a comprehensive answer, simply your thoughts on what makes for a valuable asset to a company ...
2
votes
1answer
136 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 ...
1
vote
1answer
131 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 ...
1
vote
2answers
145 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 ...
3
votes
1answer
175 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 ...
20
votes
10answers
2k views
Now that quantum computers have been out for a while, has RSA been cracked?
D-wave systems has released a commercially viable quantum computer. This means; in theory, that all asymmetric encryption algorithms, such as RSA are now useless, due to the speed at which quantum ...
1
vote
1answer
89 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 ...
2
votes
3answers
179 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 ...
6
votes
1answer
452 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 ...
10
votes
8answers
901 views
RSA with small exponents?
Just to establish notation with respect to the RSA protocol, let $n = pq$ be the product of two large primes and let $e$ and $d$ be the public and private exponents, respectively ($e$ is the inverse ...
5
votes
2answers
137 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 ...
0
votes
1answer
102 views
decryption many time pad
I have eleven ciphertexts that were encrypted with the same key (which I don't know). I want to decrypt the last ciphertext. I read similar question like Many time pad attack but I can't solve my ...
1
vote
1answer
54 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 ...
1
vote
1answer
73 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?
5
votes
0answers
61 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 ?
2
votes
1answer
164 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
58 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 ...
10
votes
3answers
584 views
How practical are side-channel attacks and how much of a concern are they?
I see a lot of research in very sophisticated side-channel attacks on crypto systems. Most (but definitely not all) seem to follow a trend, namely, the crypto system does something very dumb like ...
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 ...
16
votes
5answers
8k views
Taking advantage of one-time pad key reuse?
Suppose Alice wants to send encryptions (under a one-time pad) of $m_1$ and $m_2$ to Bob over a public channel. Alice and Bob have a shared key $k$; however, both messages are the same length as the ...
2
votes
1answer
104 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 ...
0
votes
1answer
180 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 ...
3
votes
6answers
336 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 ...
4
votes
3answers
212 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, ...
6
votes
1answer
165 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
...
0
votes
1answer
63 views
Efficient algorithm for remainder calculation over prime field for ECC implementation?
I am working on 224-bit elliptic curve cryptography. In this 224-bit * 224-bit multiplication results 448-bit output. I am reducing 448-bit into prime field range( prime number $2^{224}-2^{96}+1$) ...
3
votes
1answer
126 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 ...
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vote
1answer
57 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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votes
1answer
329 views
Is a steganographic technique which has a universal decoder novel/secure? [closed]
I've come up with an approach to steganography which needs review of both its cryptography and its math. There's a complete working implementation at https://github.com/bramcohen/DissidentX and the ...
0
votes
0answers
54 views
Strength of Combining Hash functions [duplicate]
If I combine two hash functions, what will the impact on the strength of the resulting function.
If I combine in following way:
H1*H2 (multiply)
H1 + H2 (concat)
H1 Xor H2
H1 (H2)
EDIT:
Lets say H1 ...
0
votes
1answer
140 views
Possibility of factorisation of rsa modulus due to vulnerability in java implementation code
Below is my implementation of the RSA algorithm. Actually I'm choosing the private key (d) instead of public key (e) and computing the public key.It is working fine but
I want to know if this is a ...
0
votes
1answer
108 views
How to solve the reverse of an equation that uses MOD?
I've been tasked with reverse engineering an unknown crypto function. The function uses the following constants:
$a=380951$:
I noticed that this is a prime number
$b=3182$:
I noted that this is a ...
4
votes
1answer
148 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 ...
-1
votes
1answer
106 views
Chosen Plaintext Attacks
Assuming the ability to launch Chosen Plaintext Attacks (CPA), how many oracle calls an attacker
needs to break the affine cipher? and how
2
votes
2answers
190 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 ...
2
votes
2answers
460 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. ...
-2
votes
1answer
101 views
ASCII Message in TV show? [closed]
So I was watching a popular series tonight (Person Of Interest) when suddenly during a frame change I noticed a very quick blue screen with writing.
At the time I never thought anything of it as it ...
1
vote
1answer
97 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 ...
4
votes
1answer
103 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, ...
2
votes
2answers
291 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 ...
2
votes
2answers
141 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 ...
