Reputation
4,895
Top tag
Next privilege 5,000 Rep.
Approve tag wiki edits
Badges
1 13 36
Newest
 Enlightened
Impact
~147k people reached

Mar
12
comment Method and explanation for calculating difference in speed between DES and RSA
The question makes no sense. You don't encrypt the same type of data with RSA or DES, the comparison is meaningless. Why should you care that RSA is "100 times slower than DES"? You're not going to be encrypting megabytes of data with it. It's a useless metric, things like "encryptions/signatures/verifications per second" are much more sensible.
Mar
11
reviewed Approve Tree hash and multithreading for parallelism
Mar
10
comment Where to store the private key and the public key in a communication protocol
"And i decided to create my own protocol about that." what motivated this change of mind? Generally, it's very dangerous and irresponsible to invent your own crypto protocol.
Mar
9
comment Is this method for exchanging private key using RSA sound?
let us continue this discussion in chat
Mar
9
comment Is this method for exchanging private key using RSA sound?
The randomness comes not from the group parameters, but from the $a$ and $b$ individual secrets of each party, which are selected randomly. Then the shared secret is $g^{ab}$ which is therefore unique to each session. The Wikipedia article is pretty good, if you haven't read it already (though I recommend not to implement it yourself). I cannot help about the C# implementations, though.
Mar
9
comment Is this method for exchanging private key using RSA sound?
Ah, sorry, I did not see that the keys were encrypted with each other's public keys. Ignore my last message. If you already know each other's public keys, then yes, there should be no problem. But there are a few practical issues (not security, but usage). I'll let others elaborate. But I don't quite understand why you don't want to use DH. The shared secret obtained from DH changes for every session, even if you keep the same group parameters.
Mar
7
awarded  Nice Answer
Mar
7
reviewed Edit Examples of applications that use the Schnorr digital signature?
Mar
7
revised Examples of applications that use the Schnorr digital signature?
Example application provided - OpenSSL
Mar
7
comment Strength of Combining Hash functions
@user5195 Which one? I enumerated two of many possible properties (see CodesInChaos's comment above mine).
Mar
7
comment Strength of Combining Hash functions
@user5195 Define "break the hash". Do you mean successfully find a collision, find a pre-image, ..?
Mar
5
comment What should I be aware of when implementing algorithms myself?
I suppose it would be, once you or someone else has gone over it and checked there is no suspicious code in it. But any realistic application is going to need at least performance, security, or certification, so there is no incentive to use an alternative library over, say, OpenSSL, or BouncyCastle, except in the most trivial of uses. There are a lot of subtle threats lurking around even this contrived scenario which I can't enumerate (correctly handling padding, etc..) and while it would be a good coding exercise - I did it myself a few months ago - I would not expect widespread use.
Mar
5
comment What should I be aware of when implementing algorithms myself?
just don't. I mean, yes, if everything passes the test vectors, there is a good chance the implementations are, functionally, correct. But you are ignoring side channel attacks, backdoors, performance, portability, ease of use, patents on algorithms, etc.. which require careful review by experienced people. So it would be at best unsafe to let other people use a hobby cryptography library.
Mar
5
comment Security relevance of random factor in Paillier
Revealing $r_1 \cdot r_2 ~ \text{mod} ~ n^2$ will not reveal $r_1$ and $r_2$, since there are exponentially many pairs of solutions, and only one will allow the recovery of $m_1$ and $m_2$ given the two ciphertexts.
Mar
2
comment Security of Pohlig-Hellman exponentation cipher?
Looking at the requirements for the hardness of the discrete logarithm problem (DLP) would be a good start. Indeed, $p$ needs to be chosen with care, a large random prime simply won't do. Size is only half of the story. As in $\log{(p)}$, I mean.
Mar
2
comment How to solve the reverse of an equation that uses MOD?
@hsikcah en.wikipedia.org/wiki/Modular_exponentiation
Mar
2
reviewed Approve How is CipherCloud doing homomorphic encryption?
Mar
1
comment Are common cryptographic hashes bijective when hashing a single block of the same size as the output?
@StephenTouset And even then, SHA-512 is more expensive to compute than iterating a counter, so you can add a few more bits of required computational work to that.
Feb
28
comment Is SHA-1 collision free on data up to 20 bytes long?
@SmitJohnth That is because there is no mathematical proof. Modern hash functions have structures that aren't very exploitable mathematically, by design. The best we can do is either brute-force it and try to find a collision, but this is expensive (it's supposed to be infeasible, actually) or assume that SHA-1 is a perfect random function and use that to calculate the likelihood of bijection, and the duplicate's answers address both these approaches. There simply is no other known way on a non-broken hash function.
Feb
28
comment Question about why RSA is hard to attack
Note the two approaches are fundamentally different, the first one recovers the plaintext (and says nothing about $d$) and the second one recovers $d$.