Cryptography Stack Exchange
Cryptography Stack Exchange

Most Popular

more tags
1500 questions
25
votes
3 answers

Are there any practical implementation of a homomorphic hashing or signature scheme?

A homomorphic hash function is a function $H : A \to B$ between two sets with some algebraic structure $(A, *)$ and $(B, \star)$ such that $H$ is collision resistant, i.e. it is hard to find $x \neq y$ such that $H(x) = H(y)$ and $H$ is a…
sashank
  • 6,234
  • 4
  • 36
  • 68
25
votes
4 answers

Is sharing the modulus for multiple RSA key pairs secure?

In the public-key system RSA scheme, each user holds beyond a public modulus $m$ a public exponent, $e$, and a private exponent, $d$. Suppose that Bob's private exponent is learned by other users. Rather than generating a new modulus, Bob decides to…
Mohammed Fathi
  • 251
  • 1
  • 3
  • 3
25
votes
1 answer

Why is SHA-3 robust against Length-Extension Attacks?

If a length extension attack can occur because of $H(\text{K}\mathbin\|\text{Message})$, what changed in SHA-3 from SHA-2 that prevents this from occurring?
elberman
  • 351
  • 3
  • 3
25
votes
4 answers

Is using the same IV in AES similar to not using an IV in the first place?

So if I understand how an IV works with AES, I'm supposed to generate a different IV for every message because using only a key, I will get the same encryption if the message was encrypted twice (which is not secure) thus we use the IV which is some…
Ali_Nass
  • 353
  • 1
  • 4
  • 8
25
votes
5 answers

Can a hard drive store clear text data that is physically impossible to retrieve?

I'm trying to study how HSM and TPM works when storing secret data in clear text. How can they achieve physical impossibility in retrieving secret data? I get the point in software, if you just have input and no outputs then it should be impossible…
einstein
  • 431
  • 5
  • 8
25
votes
1 answer

What size of initialization vector (IV) is needed for AES encryption?

What size of initialization vector (IV) is needed for AES encryption? I am using either CBC or CFB modes. Knowing that AES is a sysmmetrical block-cipher algorithm with a 128-bit block size, I think the answer for IV is still 16 bytes or 128 bits…
wei3923
  • 361
  • 1
  • 4
  • 4
25
votes
1 answer

Memory-hard password hash in practice?

Dan Boneh, Henry Corrigan-Gibbs, and Stuart Schechter have proposed Balloon Hashing: A Memory-Hard Function Providing Provable Protection Against Sequential Attacks (in proceedings of AsiaCrypt 2016). Taking the abstract at face value, it is a blow…
fgrieu
  • 149,326
  • 13
  • 324
  • 622
25
votes
5 answers

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?
John Gietzen
  • 1,515
  • 2
  • 15
  • 16
25
votes
1 answer

How are the names of cryptographic algorithms (like RSA, AES, SHA-256, Curve25519, etc.) pronounced?

I'll have to give a spoken presentation on cryptography and I don't want to make any pronunciation mistakes. Therefore I'm asking how I should pronounce acronyms like RSA, AES, SHA-1, SHA-256, IGE and CBC, Curve25519, ECDH, MAC, HMAC, etc., both in…
M-elman
  • 1,278
  • 3
  • 16
  • 24
25
votes
3 answers

FIPS 140-2 Compliant Algorithms

Is there any reference to check the list of encryption & signing algorithms which are compliant to FIPS 140-2. After an exhaustive search I could find only "AES". Any suggestions would be much appreciated.
Siva Arunachalam
  • 353
  • 1
  • 3
  • 6
25
votes
2 answers

What's the difference between PBKDF and SHA and why use them together?

I've been reading a little bit about hashing lately and according to AgileBits, they use "SHA512 within PBKDF2" in their new vault file. I've looked in Wikipedia for both names and I know PBKDF2 is a key derivation function and SHA is a…
Danowsky
  • 353
  • 1
  • 3
  • 4
25
votes
3 answers

What differentiates a password hash from a cryptographic hash besides speed?

I understand that password hashes like bcrypt have the principal property of taking a long time to run, but I'm wondering what if anything about password hashes make them superior to merely running a fast cryptographic has a bunch of times. In…
Steven
  • 353
  • 2
  • 6
25
votes
5 answers

Developing algorithm for detecting plain text via frequency analysis

I'm currently attempting the Matasano Crypto Challenges as a basic intro to cryptography. For solving some of the earlier challenges I utilised n-grams to determine which is going to be the most likely English plain text. It has been quite…
CryptoNoob
  • 253
  • 1
  • 3
  • 6
25
votes
4 answers

How many RSA keys before a collision?

I was wondering how many possible private/public keys exist? If a million people – for whatever reason – would try to generate 5 keys each in the same minute (on the same date and time) is there a high chance of collision? I believe GUID would…
Nick wheatley
  • 363
  • 1
  • 3
  • 5
25
votes
3 answers

How robust is discrete logarithm in $GF(2^n)$?

"Normal" discrete logarithm based cryptosystems (DSA, Diffie-Hellman, ElGamal) work in the finite field of integers modulo a big prime $p$. However, there exist other finite fields out there, in particular binary fields $GF(2^n)$. There is a…
Thomas Pornin
  • 88,324
  • 16
  • 246
  • 315
1 2 3
…
99 100