analysing cryptographic algorithms, potentially uncovering weaknesses in them (e.g. "breaking" them or casting doubts on their actual security)

learn more… | top users | synonyms

7
votes
1answer
657 views

Implementation of Tao Xie and Denguo Feng's MD5 attack

It is well known that MD5 is completely broken today - however, to understand the theory behind the attacks I am looking for an implementation of the collision attacks described in the 2009 paper A ...
6
votes
4answers
321 views

How to forge Schnorr signatures if you can guess the challenge

Underlying the Schnorr signature is an identification protocol: let $G$ be a cyclic group where discrete log is "hard" and choose $g$ as a generator of $G$. Now have Alice pick a random (secret) ...
7
votes
3answers
1k views

Understanding CRC

There are zillions of articles describing CRC. What can I read to (more deeply) understand what's really going on? Both from an algebraic perspective and a bit-manipulation perspective, I'd like to ...
4
votes
2answers
1k 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 ...
6
votes
2answers
326 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 ...
6
votes
1answer
428 views

Would RSA-encrypting a private key for itself constitute a vulnerability?

I'm planning to encrypt some individual files for storage, using the GnuPG implementation of RSA. If I happened to encrypt the private key corresponding to the public key used for encrypting -- either ...
27
votes
5answers
4k views

How can we reason about the cryptographic capabilities of code-breaking agencies like the NSA or GCHQ?

I have read in Applied Cryptography that the NSA is the largest hardware buyer and the largest mathematician employer in the world. How can we reason about the symmetric ciphers cryptanalysis ...
4
votes
2answers
648 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" ?
5
votes
1answer
268 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
2answers
194 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 ...
20
votes
2answers
4k views

Why does nobody use (or break) the Camellia Cipher?

If Camellia is of equivalent security and speed to AES, concerns arise. First of all, assuming the above, why is Camellia so rarely used in practice? Why aren't there any breaks in Camellia? Does ...
14
votes
2answers
554 views

How long would the 100 Year Cryptography Project have secured its data had it been started 100 years ago?

The goal of the Tahoe-LAFS 100 Year Cryptography project is to "enhance Tahoe-LAFS's cryptographic system so that Tahoe shipped today/next year might remain safe from cryptographic attacks for a 100 ...
5
votes
1answer
140 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 ...
8
votes
3answers
274 views

Is there an algorithm to find the number of intersections of two sets?

Suppose both I and my friend have a set of integer numbers. We want to know the number of common elements in our two sets but without knowing elements of the sets of each other. So I don't want my ...
10
votes
3answers
464 views

Are these emerging threats against AES affecting your designs?

Recentally, an attack on AES was discovered which reduces its computationally complexity, by a very slight amount. The first key recovery attack on the full AES-128 with computational complexity ...
29
votes
10answers
5k 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 ...
3
votes
3answers
322 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 ...
1
vote
1answer
668 views

The use of cribs [closed]

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 ...
9
votes
1answer
5k views

How does the index of coincidence work in the Kasiki test?

I'm starting to learn about cryptanalysis and I am having a bit of difficulty understanding the Kasiski test's index of coincidence. I have a book (Cryptography Theory And Practice by Douglas Stinson) ...
15
votes
3answers
2k views

Reverse engineering a hash?

I understand this may not be the best place to ask a question like this, but I believe that this community may be the best/only place I can ask such a question. I have inputs and outputs from an ...
10
votes
1answer
606 views

Security of N bit HMAC

Lets say that I am using 128 bit HMAC. How many operations are needed to find a "non secure" message. Is a birthday attack possible?
10
votes
5answers
337 views

Tactics available to help prove security of a new system?

I believe that the accepted tactic to "prove" a system as secure is to allow the crypto-community to review it and if no vulnerabilities are found over a long period of time (5 or 6 years), then a new ...
6
votes
1answer
149 views

Are there any tools for expressing the cipher operations as a system of equations?

The first step In Algebraic-attack is expressing the cipher operations as a system of equations. Is there an automated tool to do this?
13
votes
8answers
2k 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 ...
28
votes
7answers
17k 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 ...
22
votes
2answers
1k views

How do I apply differential cryptanalysis to a block cipher?

I've read a lot of summaries of block ciphers particularly with regards to the NIST competitions stating that reduced-round block ciphers are, for example, vulnerable to differential cryptanalysis. I ...
14
votes
2answers
492 views

What is the general justification for the hardness of finding preimages for cryptographic hash functions?

Since most cryptographic hash functions are simple, compact constructions does this simplicity impose a limit on the complexity and the size of a function that can generate preimages? That is, given a ...
15
votes
4answers
1k views

Is Wiener's attack on RSA extendable to larger keys with low hamming weight?

Using small private exponents with RSA improves performance. However, it has been shown (Wiener, 1990) that if $\log d \leq \frac14 \log N$, the private exponent $d$ can be reconstructed from the ...