All Questions
-1
votes
1answer
116 views
How to bring little changes in DES algorithm
I thought of implementing DES modes of operation as a project...But my guide asked to change or to modify the DES algorithm in such a way to overcome drawbacks of DES...So is there any way to do ...
1
vote
1answer
61 views
What are rounds in the context of ciphers?
Another recent question on security margin included in its answer the discussion of how many rounds are broken so far. What is the definition of a round?
0
votes
1answer
118 views
Request for 1024-bit primes $p$ , subgroup $q$ and subgroup generator $g$
I need to find a prime $p$ of $1024$ bits with a $160$ bit sub group size $q$, such that $q|p-1$ , and $g$ is the generator of the sub group size $q$.
I'm looking for the numeric values of $p$ , $q$ ...
0
votes
1answer
80 views
Secure way to compare two secret numbers without disclosing them?
For example, two people want to know who is the older, without disclosing their age. Is there a secure way to do this without a third party involved?
-3
votes
1answer
100 views
AES implementation in java that allows key of 320-bit length [closed]
I need an implementation of AES(Rijndael) in java that allows use of a 320-bit key.
Please suggest a reliable implementation
1
vote
1answer
89 views
Hashing a password with SHA256 on the client then bcrypt on the server
I'm trying to implement a cryptographically secured storage site (not Mega, or anything similar) and am trying to prevent the user's password from ever touching the server. The password is used to ...
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, ...
0
votes
1answer
87 views
Obtaining a key that's using ice algorithm
I have a text file that has been processed by the SNOW steganography tool that uses ICE encryption. However, I do not know the key that would enable me to decrypt and retrieve the message hidden.
...
2
votes
2answers
253 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 ...
0
votes
1answer
65 views
Tell me about non-MD5/SHA1 key fingerprints
I understand there are specifications for public-key fingerprints that use modern hash algorithms like SHA2. What are they?
5
votes
3answers
276 views
RSA primes vs. largest known primes
In the context of a new largest (mersenne) prime number being found this week -
The largest known prime number is now 2^57,885,161 − 1, and it took 5 years to find ...
-1
votes
2answers
154 views
What are alternatives to the random oracle model for modelling hash functions? [closed]
I was looking for more realistic alternatives to the ROM for describing hash functions in theoretical proofs. I came across the common reference string model (where hash functions can be modeled as ...
0
votes
1answer
130 views
Bitcoin, couldn't a miner steal money? [closed]
What prevents a miner's block from being accepted across the network if the hash checks out when miner forges transactions in the block?
For example, lets say I'm mining and I want to steal money ...
0
votes
0answers
19 views
Kryptos : K3. What is the accepted transposition for a solution?
I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4.
It's understood that K3 is solved via transposition, but I have seen several solutions. Which is the best/accepted one?
0
votes
2answers
150 views
Is such a crypto-system available?
$E(k_1, pt) = c_1, E(k_2, c_1) = c_2, D(k_{new}, c_2) = pt$, where $k_{new} = f(k_1, k_2).$ Sharing $k_{new}$ and $k_2$ should reveal no information about $k_1$.
Clarifications:
Being able to ...
0
votes
3answers
194 views
How to check the strength of an encryption algorithm?
I asking for advice on how to check strength of an encryption algorithm.
0
votes
2answers
64 views
What is RSA key normalization?
How can I understand the term RSA key normalization? What exactly is done in the process??
Please explain.
2
votes
2answers
171 views
Why does the recommended key size between symmetric and assymetric encryption differ greatly?
In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key ...
0
votes
0answers
39 views
Padding in PMAC
How does padding in PMAC work? I have been told two stories: Firstly, I have been told that it works similar to CMAC padding, and secondly, I have been told that it does not need padding.
I find the ...
2
votes
2answers
132 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 ...
0
votes
1answer
58 views
Is there a problem with constructing a CSPRNG using MD5 or SHA1?
Is there any security concerns with building a CSPRNG using a broken hash function like MD5 or SHA1? The design is such that a CRC-like function is used for mixing entropy and MD5 is used as the ...
1
vote
2answers
98 views
What are some approaches to attack an triple key polyalphabetic cipher when the IV key and PT key are known?
The cipher is an triple key polyalphabetic cipher also known as an Quagmire IV by the ACA. An example would be here: Quagmire IV example and info (pardon the ads)
I posses the IV key and the PT key. ...
0
votes
2answers
139 views
Generate random number which should depend on key
i want to generate random number for example from [1..100].
This algorithm which generates random number should work similarly like ("Linear congruential generator").
Here:
c - increment should ...
1
vote
1answer
86 views
Entropy in natural language texts
I have a couple of related questions:
I read about an estimate, ascribed to Turing, of the entropy of English text to be between 0.6 and 1.3 bits per letter. The modern day corpus, including the huge ...
4
votes
1answer
180 views
Why do the elliptic curves recommended by NIST use 521 bits rather than 512?
Wikipedia says in reference to the elliptic curves officially recommended by NIST in FIPS 186-3:
Five prime fields for certain primes p of sizes 192, 224, 256, 384, and 521 bits. For each of the ...
2
votes
1answer
97 views
Crypto puzzle as proof of randomness?
I need an untrusted client to generate a random public/private keypair (in particular, an Ed25519 keypair, which can be generated really fast), but I'm only allowed to see the public key. The ...
2
votes
2answers
68 views
Zero-knowledge identification of the majority commitment
Alice is communicating with $n$ people. We do not assume that the $n$ people don't trust each other or trust Alice. Alice doesn't trust them either, and needs to assume that they will not form a ...
0
votes
1answer
90 views
AES CBC with fixed or predictable IV, what are the risks?
I am making a call with parameters from application "A" to a web application "B".
Parameters are in the query string of the URL. They don't need to be hidden.
But I want to be sure that nobody can ...
0
votes
0answers
32 views
Security of .net AES implementation and security of a hash MAC
Hello I wanted to ask if there is any review about the security of the AES implementation of the .net Framework?
I found nothing concrete to that question, searching the Internet.
And, but this is a ...
0
votes
1answer
133 views
What are some different cryptography methods?
Some of the most effective cryptography methods and algorithms are based of factoring large prime numbers (e.g. RSA). I'm curious whether there are some other cryptography methods. Somethings that is ...
0
votes
1answer
80 views
Trapdoor implementation
Please refer to this secure index paper. On page#6, a trapdoor is defined as
...
1
vote
2answers
106 views
Store hashed email and compare hash values
I have a number of different systems sending me email addresses, but I don't actually need the underlying email, just a hash of the email address. I know I can compare hash values to find matches ...
-1
votes
1answer
222 views
ECDH VS. DH benchmarking in JAVA
So basically my problem is the odd result i get when measuring the time it takes to generate a ECDH key in java vs. the time it takes to generate a DH key.
I compare the time it takes to generate:
...
2
votes
2answers
119 views
Commutativity of keyed hashes
Definition
${H_1}^{K_1}(X)$ means data $X$ hashed by keyed hashing algorithm $H_1$ with key $K_1$.
Short question
Is $H_1^{K_1}(H_2^{K_2}(X))$ equal to $H_2^{K_2}(H_1^{K_1}(X))$?
Is ...
2
votes
0answers
55 views
How do you construct a practical full-domain hash function?
I am looking for practical constructions for Full Domain Hash.
I have read Random Oracles are Practical by M. Bellare and P. Rogaway, the construction suggested on page 8, under "Uniformity: a ...
5
votes
2answers
177 views
Why would this method of discrete logarithm finding not work?
Say we do know $b$ but not $k$, and are given $g$ such that $g\equiv b^k\pmod p$. And say there exist factors $E = e + m'p$ ($e \equiv b^i \bmod p$) and $F = f + m''p$ ($f \equiv b^j \bmod p$) of $g$. ...
2
votes
1answer
142 views
Visualization of cryptography
I think CrypTool is great software. And what I find most useful in it is visualization of algorithms such as Caesar, Vigenere, AES, DES. And my question is: does anyone know other tools which are ...
-1
votes
2answers
127 views
Is (2^333)-1 a prime number? [closed]
How can I see if $2^{333}-1 $ is a prime number?
Does this have to do with Mersenne prime numbers ($2^n-1$) ??
Thank you!
1
vote
1answer
129 views
What is a tweakable block cipher?
Pretty simple question - but I can't seem to find much information about it.
What exactly is a tweakable block cipher?
How do they differ from traditional block ciphers?
What is the 'tweak'? Is it ...
1
vote
0answers
53 views
Prevent/minimize replay attacks in public message board
Assume we have a public message board where anyone can send a message to. If plain messages are used, anyone can impersonate anyone. The goal is to disallow impersonations. We can use public key ...
5
votes
3answers
190 views
How to best obtain bit sequences from throwing normal dice?
Throwing normal dice, one can get sequences of digits in [0,5]. Which is the best procedure
in practice to transform such sequences into bit sequences desired?
1
vote
2answers
123 views
Kryptos : K2. What is the origin of the “abscissa” keyword?
I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4.
Similar to the "palimsest" keyword for K1, the keyword "abscissa" for K2 was determined by brute-force.
To better ...
4
votes
1answer
90 views
Why is feed-forward mechanism used in hash functions?
The compression function of SHA-1 when used in Davies-Meyer mode adds its input to the chaining values at the final step. For the first message block, the IV is used as the input and in the next step, ...
1
vote
1answer
121 views
Decryption a chunk of file with AES
We are having a requirement to store large files (~1GB) encrypted and decrypt them when reading. We are looking to use AES-CTR or AES-GCM mode to encrypt the data. There are scenarios where we want to ...
0
votes
1answer
72 views
Question about use of IV in this cipher
Main cipher objective : Generate a keyed CSPRN stream, that does not expose useful information about the state of the CSPRNG, and xor this with the plaintext. To prevent an attacked who could somehow ...
1
vote
1answer
415 views
How do I derive the time complexity of encryption and decryption based on modular arithmetic?
I want to calculate the time complexity of two encryption and decryption algorithms.
The first one (RSA-like) has the encryption
$$ C := M^e \bmod N $$
and decryption
$$ M_P := C^d \bmod N. $$
...
1
vote
1answer
89 views
Using Chi-Square for Vigenere Cipher
I am writing a program which will use Chi-Square to determine which is the correct keyword for a ciphertext via Vigenere Cipher.
I came across a website that describes the Chi-Square statistics in a ...
3
votes
2answers
100 views
How is the x coordinate of a “point at infinity” encoded in a Secp256k1 signature?
I'm testing an implementation of Bitcoin, which uses the curve Secp256k1 for ECDSA, and I want to see how it handles the point at infinity (0) if present in a signature. For example, r could be the x ...
3
votes
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 ...
1
vote
0answers
40 views
School exercise on untrusted channel comunication [duplicate]
Possible Duplicate:
Why is H(k||x) not a secure MAC construction?
I've the following problem:
two parties, A and B, share a secret key Kab.
M is a plaintext message, H an unkeyed hash ...
