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location Frankfurt, Germany
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visits member for 3 years
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1d
awarded  Popular Question
1d
comment Public key Issue - same key pair as existing one?
Cryptography is all about attacks being "very unlikely". Consider AES128 - the attacker can guess correctly with probability $2^{-128}$ with a single guess. The probability of colliding RSA keys is much smaller than that if you use perfectly random primes.
2d
comment ECDH anonymous key exchange to avoid PKI
Take a look at djb's curvecp and trevor perrin's noise protocol. They're relatively simple protocols where peera are identified by an ecc public key.
Jul
25
comment Does 3-DES take approximately the same time to encrypt 1B and 1KB?
Which mode of operation are you using? A bitsliced implementation could exhibit unusual scaling with message length, but doesn't really fit your description. Perhaps your benvhmark is flawed, so I'd like to see your code.
Jul
21
awarded  Yearling
Jul
17
comment Are there any reasons for using SSL over IPSec?
I think this fits security.se betterthan crypto. @mikeazo can you talk to the sec.se mods and possibly migrate?
Jul
12
comment McEliece and cryptanalysis
I'd expect grover to be applicable to some degree.
Jul
9
comment Is calculating a hash code for a large file in parallel less secure than doing it sequentially?
Note that Merkle-Damgard has a similar loss of second pre-image security, so compared to SHA-2 the security loss is only due to the additional compressions the tree adds, which should account for less than a bit. The workarounds are pretty similar too, either add unique node tagging or use a wide-pipe.
Jul
8
comment What exactly does a key do?
If you have an $b$ bit key, there are $2^b$ possibilities. The base 2 logarithm $\log_2$ is the inverse of the exponential function $2^x$. So with 26 possible keys, you get $\log_2{26} \approx 4.7$ or equivalently $2^{4.7} \approx 26$.
Jul
8
comment What exactly does a key do?
In that sample you could consider "Shift by $x$" the algorithm (Caesar encryption) and $x=2$ the key. This would be a $\log_2{26}\approx4.7$ bit key.
Jul
6
comment Convergent encryption has dictionary attack, but why hash function doesn't?
Sending the hash of the plaintext suffers from the same problems as convergent encryption. The best writeup of the security properties of CE I've seen so far is zooko's Drew Perttula and Attacks on Convergent Encryption
Jul
4
revised Use ElGamal to solve Diffie-Hellman problem
edited tags
Jul
4
comment Use ElGamal to solve Diffie-Hellman problem
AFAIK ElGamal only reduces to the decisional DH problem, not the the computational DH problem. So this proof shouldn't exist
Jul
2
awarded  Nice Question
Jul
2
awarded  Curious
Jul
1
comment Types of cryptography
You should read Structure vs. Combinatorics in Computational Complexity
Jul
1
comment Types of cryptography
The underlying problem is called AES. Typical symmetrical schemes don't reduce to an elegant mathematical problem. They rely on the complexity emerging out of the interaction of many simple operations. In a way RSA/DH etc. are structured whereas AES is unstructured.
Jun
30
revised Combining Random Hashes - avoiding collisions and ensuring randomness
added 579 characters in body
Jun
30
comment Combining Random Hashes - avoiding collisions and ensuring randomness
@Navonod SipHash has been designed with a uniformly random key in mind, so you're not using it as intended. But since your requirements are much weaker than what it's designed to offer, that might still be okay for you.
Jun
30
comment Does collision resistance imply (or not) second-preimage resistance?
If you have a two block message you can run a meet-in-the-middle attack since the primitive function is invertible. This should break (second) preimage resistance with cost $2^{c/2}$ where $c$ is the capacity. (I didn't look into the memory requirements, they might be unrealistically large) This is the reason why SHA-3 uses $c=2 n$.