All Questions

5
votes
1answer
112 views

How can I find the order of the group that an elliptic curve is defined over?

I have a Weierstrass elliptic curve ($y^2=x^3+a \times x+b \mod p $) How can I find the order of the group itself? I have seen Mathematica has a GroupOrder[] ...
2
votes
0answers
77 views

How is HMAC(message,key) more secure than Hash(key1+message+key2)

I understand how for hash functions which are vulnerable to length extension attacks (such as SHA1 and SHA2) it is safer to use a HMAC construction. What I don't understand is, how or why is ...
1
vote
0answers
74 views

RSA timing attack

Given an RSA implementation that uses Montgomery multiplications and CIOS exp algo, but NOT CRT. Given a decryption1 oracle that takes chosen cipher text and responds the plain text and the time it ...
0
votes
1answer
94 views

Hash Function to get same value for different messages [duplicate]

I am studying a function where I found the some hash properties. Hash functions: Given a code c is computationally infeasible to find m such that ...
3
votes
2answers
143 views

secure integer comparison

I have been going through a huge amount of papers to find a simple and a practical method to compare integer numbers without revealing their original values. I know that this falls within the area of ...
-1
votes
2answers
735 views

Decrypting Triple-DES using 2 keys in crypto tools

I'm currently working on crypto tools to encrypt/decrypt 4 blocks of messages using Triple-DES with 2 keys. So, I've reached the final cipher text, but now I have to do the reverse and get the ...
1
vote
1answer
88 views

how to use salt to sign a message and how is it effective? [duplicate]

I've had an assignment to sign a file using hash and salt, so I read about salt and I got why it's important when it comes to password, but not to sign messages. How do I sign something using salt? ...
2
votes
2answers
94 views

Soundness idea of basic zero knowledge prood

I am having a hard time figuring out the soundness proof of the bellow zero knowledge protocol. As it is a typical proof, I would love to deeply understand it. zero knowledge argument that $h \in ...
1
vote
1answer
128 views

How to solve custom made ciphers? [closed]

How would you go about solving basic custom made ciphers - e.g. one generated from this website http://www.wikihow.com/Write-a-Custom-Cipher-Carefully? This is solving it without knowing the method ...
-1
votes
1answer
32 views

In Needham Schroeder key distribution what happens if responder's part is not encrypted in step 2 with Kbs but encrypted instead by Kab in step 3

The Needham-Schroeder protocol is: 1 A→S:A,B,Na 2 S→A:{Na,B,Kab,{Kab,A}Kbs}Kas 3 A→B:{Kab,A}Kbs 4 B→A:{Nb}Kab 5 A→B:{Nb−1}Kab Here Na and Nb are nonces. Kab is the key between a and b Kas is ...
1
vote
1answer
644 views

CryptoJS.AES result always has same first few bytes?

When using this very minimal CryptoJS AES example: ...
1
vote
1answer
64 views

What is the idea behind hashing the QueryString in OAuth?

In OAuth 1.0a and 2.0 using MAC Authorization, I need to generate a hash of all the QueryString Parameters, which requires normalization (alphabetical ordering) of them. I'm trying to understand what ...
2
votes
0answers
41 views

McEliece information set decoding attack vulnerability

Wikipedia states that McEliece is open to "information set decoding attack". What is an "information set decoding attack" and how serious is the vulnerability? (is it just a matter of choosing proper ...
1
vote
2answers
81 views

McEliece key size

There's a lot of references about McEliece key size being the barrier for proper usage of the algorithm, exactly (or roughly) how large are the keys?
1
vote
1answer
64 views

Distinguishing Attack on CBC-MACs

I want to ask again about distinguishing attack on CBC MAC, based on the paper published by Ketting Jia, Xiaoyun Wang, Zheng Yuan, and Guangwu Xu: Distinguishing Attack and Second-Preimage Attack on ...
-2
votes
1answer
108 views

Zero Knowledge Proof for Correctness of the product of additive ElGamal Ciphers [duplicate]

Suppose we use Additive ElGamal defined as follows: Let $(K,E,D)$ be a triple. The key-generator $K$ outputs the description of a finite multiplicative group $G$ of prime order $q$, with three ...
-1
votes
1answer
83 views

How to create PSK key? [closed]

I'd like to create a PSK key to use with TLS-RSA-PSK-WITH-AES-256-CBC-SHA - what is the format of this key?
0
votes
2answers
246 views

Should an AES byte key generated with OpenSSL be converted to hex?

I am generating a key & iv with Ruby's OpenSSL wrapper for an AES CBC 256 setup: ...
1
vote
0answers
77 views

Public-key based on roots of polynomial

In general it's hard to calculate the roots of a given polynomial P(x). But the other way back calculating the coefficients is much easier (Vieta's formulas). If this is a one-way function, is it ...
3
votes
1answer
1k views

Why is Serpent faster than AES in this benchmark?

I have a laptop without the AES-NI CPU instructions but with SSE4.1. I'm using Linux and tried the (in-memory) cryptsetup benchmark to get the rough tendency which returned: ...
3
votes
1answer
105 views

Quadratic Sieve: what's the next step after it fails?

Factoring some 20-45 digit values n with a (simple) quadratic sieve, the quadratic sieve may end up with pairs of x and y s.t. $x^2 \equiv y^2 \pmod n$, but neither x+y nor x-y has a nontrivial gcd ...
1
vote
0answers
71 views

Does a dynamic accumulator exist yet? [closed]

I’m looking for a one-way accumulator which can safely add new members (deletion is not necessary) and does not rely on a trusted party in any way. I’ve been looking for one, I need it for this ...
3
votes
1answer
80 views

What is the importance of the $r$ and $c$ values for the Sponge Construction?

What is the importance of the $r$ and $c$ values? Keccak[r=1600,c=0] is stated on a calculator on the Keccak website to be a checksum. But I figured if c=0, then there's only one possible output? ...
1
vote
0answers
140 views

Is this a secure (and correct) sign-then-encrypt technique for transferring messages?

After reading some information on the way iMessage works I have been working on writing some code to try my hand at securely transferring messages in a similar manner and I wanted to confirm that the ...
1
vote
1answer
140 views

Is the term “Elliptic Curve Discrete Logarithm Problem” a misnomer?

I have just started studying Elliptic Curve Cryptography, and I have this doubt. In ECC the group operation is addition (and not multiplication). So, why is ECDLP stated as a variation of the discrete ...
1
vote
1answer
123 views

Why concatenate the key a second time in HMAC? [duplicate]

On Wikipedia it is said that HMAC is basically (without taking into account padding): $H(key\ \Vert\ H(key\ \Vert\ message))$ where $\Vert$ denotes concatenation. I understand the need to hash ...
1
vote
2answers
80 views

Subexponential algorithms for DLP in $\mathbb{Z}_s \times \mathbb{Z}_t$

Consider the accepted answer to the question: Why are elliptic curves better than cyclic groups? It seems to suggest there are subexponential algorithms (i.e., algorithms with running time $$ ...
4
votes
1answer
159 views

Entropy when iterating cryptographic hash functions

Consider a cryptographic hash function that maps $n$-bit strings to $n$-bit strings: $$ \DeclareMathOperator{\H}{H} \DeclareMathOperator{\SHA}{SHA-256} \H(x) : \left\{0,1\right\}^{n} \mapsto ...
1
vote
1answer
266 views

How do the following new (2013) ECC curves compare in security or efficiency? [closed]

I read about the following "safe" ECC curves and notably, secp256 and all the NIST curves are marked as "unsafe" when compared to more modern curves. I need a curve for signing or encryption, (or ...
1
vote
0answers
74 views

Problem implementing MixBytes functionality in Groestl

Disclaimer: School work. I am trying to implement Groestl through Java, and have got stuck on the MixBytes section which can be found here section 3.4.5 page 11. As per the description of matrix ...
-1
votes
1answer
62 views

Meet in the middle attack - message and key

I clearly understand the story of Alice and Bob: Alice and Bob are going to use double DES. They know the keys K1 and K2. Alice sends to Bob the encrypted message c= EK1(EK2(m)). Bob decrypts the ...
4
votes
1answer
344 views

What prevents a padding standard to cause a data loss?

In here different byte padding standards are listed as ANSI X.923, ISO 101.26, PKCS7, ISO/IEC 7816-4 and zero padding. All of them seems to apply padding to the last byte blocks. Odds are rare but ...
-1
votes
1answer
138 views

Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
-1
votes
1answer
148 views

Hash Based Encryption (fast & simple), how well would this compare to AES? [duplicate]

First of all, I know it's a very bad idea to invent your own encryption algorithm. It's better to use existing known, trusted, extensively tested and studied algorithms with a proven track record. The ...
4
votes
2answers
488 views

Randomness test question from FIPS 140-1 and comparison with 140-2

In FIPS 140-1 there are 4 statistical random number generator tests (The Monobit Test, The Poker Test, The Runs Test and The Long Runs Test. Then FIPS 140-2 came along and supposedly tightened the ...
3
votes
1answer
285 views

Why does Openssh use only SHA1 for signing and verifying of digital signatures?

I am learning SSH protocol. With my current understanding of SSH protocol, I think that message digest algorithms for using in digital signature should be derived from Key Exchange. But Openssh ...
4
votes
1answer
111 views

Should different key pairs be used for signing and encryption?

In the recent iOS Security white paper from Apple (February 2014), the section on iMessage discusses using two different asymmetric key types as part of its standard operation: When a user turns ...
2
votes
1answer
100 views

Why do we apply the concept of circuit in homomorphic encryption schemes?

I am a beginner to the concept of homomorphic encryption. One thing that makes me very confused is why we use the circuit concept or approach to homomorphic encryption. Gentry's paper does not discuss ...
1
vote
1answer
284 views

Difference between known-plaintext attack and forward search attack

I am looking at the different attacks on RSA. I came across known-plaintext attack where the public key can be used to encrypt all possible messages until it finds a match on the sent encrypted ...
4
votes
1answer
204 views

Difference RSA keypair creation openSSL and openPGP?

Creating a 2048bits RSA keypair I figured that doing this using openssl takes as an input 32bytes of "randomness" from /dev/urandom gpg (openGPG) takes as input ...
4
votes
0answers
128 views

How can I create an RSA modulus for which no one knows the factors?

It's easy to create an RSA modulus where almost no one knows the factors: for example, I can generate two 1024-bit primes $p$ and $q$ and set $n=pq$. If I publish $n$, I will be the only person in ...
0
votes
3answers
159 views

Question on RSA trapdoor permutation

You plan to use a public-key cryptosystem based on the RSA trapdoor permutation in three different real-life applications, in which the attacker has, respectively, only one of the following resources: ...
2
votes
1answer
124 views

Verifying multiplicative inverse on a prime field in NIST's ECDSA_Prime.pdf

I am trying to learn about the Elliptic Curve Digital Signature Algorithm (ECDSA) by verifying the results in some example calculations. I found a PDF of example ECDSA calculations from NIST here: ...
1
vote
0answers
93 views

Trying to calculate the strength of a Bitcoin brain wallet created with a custom diceware password

I want to create a brain wallet using a custom diceware since I don't like the original one. Instead of 7776 words it has 46656 because I use 6 dice for each word instead of 5, and also it only has ...
1
vote
2answers
513 views

RSA problem if i choose two specific small prime numbers?

I know that rsa normally is made to make it with big integers, but i trying to make the algorithm myself (with the help of wikipedia) and I´m making it with small numbers to track the problems easily. ...
9
votes
3answers
474 views

Elliptic Curves of different forms

Looking at http://safecurves.cr.yp.to/ to find a safe curve, I find that most curves described here are of a different form from that generally used. In Bouncy Caslte, for example, ...
-1
votes
1answer
42 views

Affine encryption function

Let $f(x) = ax + b$ be an affine encryption function. $a$ and the cardinal of the field of our keys $K$ (in English, 26) must be coprime so that the encryption ...
5
votes
2answers
309 views

Reusing AES-CTR Keys and IVs for File Encryption

I’m implementing some file encryption module with random-access capability and AES-CTR seems the right way to go. I understand that reusing Keys and IVs can expose the file to ‘Stream Cipher Attacks’ ...
5
votes
1answer
157 views

What functions allow for practical indistinguishability obfuscation?

Recently, there has been a major theoretical breakthrough in program obfuscation, in the area of indistinguishability obfuscation. Background: Indistinguishability obfuscation is a form of program ...
2
votes
0answers
63 views

Obfuscating point-like functions

There are standard schemes for obfuscating a point function; I'm wondering if we know how to obfuscate a slight generalization of a point function. I'll elaborate more precisely. Definition 1. A ...

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