9,771 reputation
12448
bio website github.com/CodesInChaos
location Frankfurt, Germany
age
visits member for 3 years, 2 months
seen 10 hours ago

Nov
10
comment How can two (or more) parties share and agree upon a common random seed?
Since collision resistance is required, the security level of 64 bits provided by a 128 bit hash is insufficient.
Nov
10
comment Why don't we use MACs to store passwords?
For smaller websites a HSM is too annoying to deploy. But I'd expect big websites like google to encrypt their password hashes with HSMs.
Nov
10
comment Can Diffie-Hellman generate values in a specified range?
btw. DH never returns 0 if both sides follow the protocol. Only way to obtain 0 is if one side uses 0 as public key $A$, which is obviously broken and doesn't result from computing $A=g^a$ for any private key $a$.
Nov
10
comment Can Diffie-Hellman generate values in a specified range?
As I said, simply hash the shared secret with e.g. SHA-2. Then truncate to one byte.
Nov
9
comment Can Diffie-Hellman generate values in a specified range?
@JaimeASV Deriving an 8 bit key is trival using a hash function. But what's the point of using such a small key? Symmetric keys should be at least 80 bits, preferably 128. (and obviously 17 is much too small as well, you need primes larger than a thousand bits to be secure)
Nov
9
comment Decryption or attacking DES encrypted file
Short answer: brute force is feasible thanks to the small key-space
Nov
9
comment How do I test my encryption? (absolute amateur)
The absolute minimum is a specification using typical notation and a reference implementation in c. You should also consider an attacker who knowns or even chooses both message and ciphertext. If such an attacker can break your scheme then it's very weak by modern standards.
Nov
8
comment How do I sign data that's been encrypted using public key? (RSA)
You should sign with your own private key, not with the receiver's public key. You need to create your own key-pair to do so.
Nov
8
comment What is the difference between various modes in FPE?
It's even worse, FFX contains several different modes plus a bunch of parameters.
Nov
7
comment Are there any bijective one-way functions not based on number-theoretic hardness assumptions?
I don't see a requirement in the OP that it should be easy to invert when knowing a secret parameter.
Nov
7
comment Are there any bijective one-way functions not based on number-theoretic hardness assumptions?
@D.W. Some people place a much higher trust in unstructured problems than in highly structured number theoretic problems.
Nov
6
comment Would this program be useful in cryptography?
@user8911 You shouldn't just benchmark multiplication time. Part of key-gen with unknown primes is the primality test. You can't use well known primes like mersenne primes, those could be trivially factored. But just obtaining the key isn't the problem. You actually need to be able to sign/decrypt data with it. Even with karatsuba multiplication that will be pretty expensive. With numbers that size you need to use fancy algorithms, for example a fourier transform based one.
Nov
6
comment Would this program be useful in cryptography?
Have you tried running RSA on that number? By my estimation it'd take about a week for a single private key operation unless you implement advanced multiplication algorithms.
Nov
6
comment What does it mean if second half of 8-char string encrypted in 3DES is always identical?
Is there any reason to believe that it's zero padding and not e.g. PKCS7? I'd expect most paddings to show the same behavior.
Nov
5
comment Is it true, that non-military cryptography appeared in 50's and 60's only thanks to leaks from the NSA?
It's an influence from secret military crypto/NSA on civilian crypto. Not technically a "leak", but certainly sounds like the kind of thing the OP is interested in.
Nov
5
comment Is it true, that non-military cryptography appeared in 50's and 60's only thanks to leaks from the NSA?
DES was developed by IBM with input from NSA (who at least strengthened it against differential crypto-analysis and reduced the key size). I do not know how big the influence of the NSA on DES was.
Nov
4
comment random access stream cipher
There are random access stream ciphers, such as AES-CTR or Salsa20. But they are problematic since they can easily lead to two-time-pads. I think the closest you're going to get is XTS which needs to encrypt a few bytes close to the data you want to read.
Nov
4
comment McEliece Public Key Encryption
Zero is also an acceptable error probability.
Nov
2
comment RSA 896 vs 1024 vs 2048 in Javascript?
Since SSL already blocks most attacks, the gain by using JS crypto on top of that can only be meaningful with keys that even a powerful attacker can't break. At minimum 2048 bit RSA or 224 bit ECC.
Nov
1
comment How to Distribute the Shares using Secret Sharing for arbitrary Monotone Access Structures
@DrLecter I'm not sure if your edit made the question requirements stricter. The OP might be happy with different weights for each secret holder without being handle the general case.