9,442 reputation
12345
bio website github.com/CodesInChaos
location Frankfurt, Germany
age
visits member for 3 years
seen 1 hour ago

Jul
21
awarded  Yearling
Jul
21
comment why hash(hash(str)) is bad?
If you're talking about password hashing then it's bad because it doesn't have a salt (which needs to different for each user) and it's bad because it's fast. Rainbow tables are largely irrelevant, what's the real threat are GPUs. Without salt all hashes in a database can be attacked at once, with salt they need to be attacked individually.
Jul
20
comment Is generating public key inevitably slow in classic Diffie-Hellman if the private key is large?
I think you can still choose a small value for x (say 256 bits) without losing much security even with a 3000 bit q. A large q is mainly problematic for DSA, not DH.
Jul
20
comment Can you explain what the AES paper means by “sharing active S-boxes”?
@e-sushi I don't think this is a reference request. It's asking for for clarification of certain concepts used in a notable paper. It's limited in scope and doesn't lead to link-only answers. So I consider it on topic.
Jul
20
comment How difficult is it to find the “pre-image” of a block cipher?
@samoz If $M_2$ isn't fixed then Thomas' suggestion works for every key.
Jul
20
comment Is HMAC-MD5 considered secure?
Collisions are irrelevant in typical MAC usage scenarios.
Jul
20
revised Quadratic residuosity problem reduction to integer factorization
added 63 characters in body
Jul
19
comment Generating a secure random number in javascript
Using strong crypto in the RNG is the easy part. The real problem is entropy gathering. Which sources to use, and how to estimate the entropy. One really common issue is allowing consumers to read from the PRNG before enough initial entropy has been gathered.
Jul
19
comment Jumblar: Using map locations as passwords
The entropy contained in a single location is pretty low, so the generated password might be weak.
Jul
18
revised What is meant by $\tilde\Omega(\lambda^4)$?
deleted 191 characters in body; edited tags; edited title; edited tags
Jul
17
comment AES 256 Encryption - Is it really easy to decrypt if you have the key?
@bhs Then get out a time machine and travel back a few centuries. It is a core principle of modern crypto that it must be secure if the attacker knows everything about the scheme, except the key.
Jul
17
comment How can scrypt be improved to counter GPU mining
One can simply adjust the memory use parameter of scrypt. Litecoin chose a really small amount of memory. It's also possible to design a new scheme that doesn't allow certain time-memory trade-offs the GPU implementation takes advantage of.
Jul
16
comment Birthday Attack
That 2H looks weird. Shouldn't that be in the denominator?
Jul
16
reviewed Approve suggested edit on Birthday Attack
Jul
16
comment Generating a secure random number in javascript
Your approach is certainly much worse than hashing all the raw entropy with SHA-2 and then expanding it to the desired size.
Jul
16
comment Generating a secure random number in javascript
See Generate cryptographically strong pseudorandom numbers in Javascript? on security.SE
Jul
16
reviewed Approve suggested edit on why public key cryptography (RSA) is use in sites like Google, facebook (what is the need to ecode data in these sites)?
Jul
15
revised Technical feasibility of decrypting https by replacing the computer's PRNG
added 2 characters in body
Jul
15
comment How can Alice prove that a message has not been tampered with?
What do you mean by privileges? Can Bob use the message to claim some privileges from Carol? In that case a simple digital signature should do the trick. Bob can modify the message, but carol won't accept it.
Jul
15
comment Primality testing (deterministic vs. non-deterministic)
On real hardware all algorithms are probabilistic and something like $2^{-200}$ is certainly smaller than the probability of your hardware messing up the computation. So deterministic algorithms don't really offer a practical advantage.