All Questions
8
votes
1answer
326 views
Why did NIST remove The Lempel-Ziv Compression test from the Statistical Test Suite?
NIST removed "The Lempel-Ziv Compression" test from the Statistical Test Suite in revision 2008 and above and has not incorporated it since – see revision 2010.
Why was it removed? Does it no longer ...
4
votes
1answer
244 views
Sites to find crypto intermediate values
Does anyone know of any sites where intermediate values of multiple crypto algorithms (not just the famous ones), including hashes, can be found? I don't just mean intermediate values of encrypting. ...
6
votes
1answer
119 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?
15
votes
3answers
672 views
Is using slow password hashing on the client side easier attackable than on the server side?
As we know, one should use a slow password hashing algorithm instead of a fast one for storing passwords, to hinder brute force attacks when the database is compromised. The problem with this is that ...
10
votes
8answers
848 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 ...
7
votes
3answers
505 views
Modern integer factorization software
What are the modern software packages that can be used to factoring large numbers into primes. By modern I mean developed and made public within the last 5 years. I'm interested in things that are ...
7
votes
1answer
449 views
Replacing the Rijndael S-Box?
The Rijndael S-Box design generates a permutation cycle of type $2+27+59+81+87$. What effect would replacing that permutation with a cycle of type $256$ have on the security of AES?
15
votes
6answers
239 views
advances in usability for cryptography/authentication
I'm wondering if there have been any recent advances (say, the past 5-10 years) in human usability for cryptography and/or authentication?
By that I mean something that makes it easier for an ...
8
votes
4answers
294 views
Should DES be avoided when developing new systems?
According to wikipedia "DES is now considered to be insecure for many applications".
However, since it can be broken relativily simply, should it not just be avoided for all applications?
21
votes
4answers
6k views
How can I generate large prime numbers for RSA?
What is the currently industry-standard algorithm used to generate large prime numbers to be used in RSA encryption?
I'm aware that I can find any number of articles on the Internet that explain how ...
2
votes
2answers
145 views
Protocol to generate Client Certificates at the start of a SSL session automatically?
A more secure form of 'cookie' could be created for SSL communications through the following method.
The client generates and requests the server to sign a certificate.
Then the client authenticates ...
4
votes
1answer
1k views
What are the details of the DES weakness of reusing the same IV in CBC mode with the same key?
I think I once faced the recommendation, that the initialization vector should always be random and never be used twice with the same key.
How serious is this weakness?
Also, is AES less effected ...
16
votes
5answers
7k 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 ...
10
votes
3answers
896 views
Known methods for constant time (table-free) AES implementation using 'standard' operations?
There are several known methods for implementing AES in constant time using SIMD operations, mostly based around fast byte shuffling (for instance Hamburg and Kasper/Schwabe). Are there any similar ...
4
votes
3answers
542 views
Is it feasible to build a stream cipher from a cryptographic hash function?
A few years ago I devised a symmetric-key system that worked like so:
...
12
votes
4answers
688 views
With sufficient randomness, is XOR an acceptable mechanism for encrypting?
I have heard criticism of various cryptosystems saying that "at their heart, they were just XOR."
Is this just ignorance, or is there something inherently wrong with XOR based ciphers?
8
votes
2answers
508 views
Salting when encrypting?
I was attending a database encryption session at a developers conference. The presenter (who was a published author on the subject) said that MS SQL Server did not support salted hashes in the ...
12
votes
2answers
790 views
What are the main weaknesses, if any, of a Playfair cipher?
What are the main weaknesses, if any, of a Playfair cipher?
I know that they depend on none of the letters missing, but that is an easy fix if a letter gets dropped. Besides that, are there any other ...
18
votes
4answers
433 views
Necessity of Randomness of Salts?
Given the desire to have unique salts for each user of your system, is it actually necessary to create a cryptographically-random salt for each user? If your system already has some other unique user ...
15
votes
7answers
1k views
How can SSL secure a two-way communication with only one key-pair?
As I understand it, SSL involved the use of a public-private key pair. How does this enable two-way communication?
Suppose I have some server with which I wish to communicate securely. I connect to ...
16
votes
5answers
1k views
Current mathematics theory used in cryptography/coding theory
What are the mainstream techniques borrowed from algebraic geometry (or some other branch of mathematics) which are currently used in cryptography/coding theory? I've only heard about a small subset ...
20
votes
2answers
956 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 ...
26
votes
2answers
1k views
What makes a hash function good for password hashing?
Using a cryptographic hash to store e.g. passwords in a database is considered good practice (as opposed to storing them plaintext), but is subject to attacks on said cryptographic hash, assuming the ...
27
votes
4answers
5k views
What are the practical difference between 256-bit, 192-bit, and 128-bit AES encryption?
AES has several different variants (AES-128, AES-192, AES-256), but why would I use one over another?
8
votes
3answers
1k views
How can a random salt for a hash function work in practice?
I understand the theory behind the use salts in hash functions, but when I see it implemented, the implementations always generate the salt on the fly and the salt appears to be different for every ...
11
votes
1answer
380 views
How to provide secure “vanity” bitcoin address service?
Bitcoin addresses are RIPEMD-160 hashes of the public portion of a public/private ECDSA keypair (along with an abbreviated hash of the hash to provide a check code, as @pulpspy notes in a comment). ...
15
votes
2answers
1k views
How were the DES S-box values determined?
It seems like the S-boxes in DES have essentially random values.
How were these chosen?
20
votes
3answers
3k views
How can I use asymmetric encryption, such as RSA, to encrypt an arbitrary length of plaintext?
RSA is not designed to be used on long blocks of plaintext like a block cipher, but I need to use it to send a large message.
How can I do this?
12
votes
2answers
329 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 ...
10
votes
2answers
439 views
Why do we append the length of the message in SHA-1 pre-processing?
As we know, SHA-1 is irreversible, so why do we append the length of the message to the preimage?
10
votes
2answers
250 views
Why use a 1-2 Oblivious Transfer instead of a 1 out of n Oblivious Transfer?
When initiating an oblivious transfer, why would someone use a 1-2 oblivious transfer rather than going for an 1 out of n oblivious transfer? Perhaps a slight time overhead for the extra message ...
24
votes
3answers
3k views
What are the benefits of the two permutation tables in DES?
Why do we use a permutation table in the first step of DES algorithm and one at the end of algorithm?
45
votes
14answers
3k views
Time Capsule cryptography?
Does there exist any cryptographic algorithm which encrypts data in such a way that it can only be decrypted after a certain period of time?
The only idea that I can think of, is something like this: ...
20
votes
1answer
1k views
Does the generator size matter in Diffie-Hellman?
For the Diffie-Hellman protocol I've heard that the generator 3 is as safe as any other generator. Yet, 32-bit or 256-bit exponents are sometimes used as generators. What is the benefit of using ...
13
votes
4answers
545 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 ...
5
votes
1answer
135 views
Can a proof be constructed to show there is no distinguisher?
Let's assume a simple algorithm like the Skein hash function.
Is it possible, given the algorithm, to construct a proof that it does not have a particular distinguisher, something like:
$P(xyz)$ is ...
