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Jul
31
comment ElGamal in $Z^*_{p^n}$
Another way (and, it turns out, an equivalent way) of looking at it is that if we know that if we have a solution for $a^x = b \bmod 3^n$, then we can easily find a solution for $a^x = b \bmod 3^{n+1}$; hence we can start with $n=1$, and work our way up.
Jul
30
reviewed Approve Is there a proof for showing any cryptogram is crackable?
Jul
30
reviewed Approve Simply put, what does perfect secrecy means?
Jul
30
reviewed Leave Closed What is the definition of “the correlation” and “the difference propagation probability”?
Jul
30
answered Can we solve the Hidden Number Problem in $GF(2^n)$?
Jul
29
comment I don't know whattype of cipher this is
My guess is that it's some sort of transposition cipher (the letters are rearranged)
Jul
28
revised Is Paillier cryptosystem commutative?
Paillier addition is not a field operation (the power is a non-prime-power). It is a group operation, and that sufficies.
Jul
28
answered In which step does AES use the key to encrypt data?
Jul
27
comment Library to find an addition chain for a large number?
What do you mean by 'good'? The simple-minded binary method gives a decent one (within 50% of optimal for random inputs), and is completely trivial to compute. If that's not good enough, how close to optimal are you demanding?
Jul
27
comment Permuting Small Sized Set in Practice
I believe you need to rethink what security means in this context. It doesn't mean that the attacker can't take a guess at the permutation (and have a $1/|S|!$ chance of getting it correct). Instead, it's that the attacker doesn't get any additional information about the permutation. That is, even if $|S|=2$, the attacker knows that either the two elements remain where they are, or that they are swapped; but he doesn't know which it is.
Jul
27
answered Reduction to cdp,dl or cdh?
Jul
27
comment Reduction to cdp,dl or cdh?
Where does the randomization come into play? $f(x) = g^{sk \cdot x} \bmod p$ (for fixed $g$, $sk$, $p$) looks determanstic.
Jul
27
comment Construction of ElGamal signature?
As for a hint to #1, if you know $s$ and $r$ with $s = k^{-1}(m + ar)$ (for some unknown $k$, $a$; what would you need to adjust to make an $s' = k'^{-1}(rm + ar')$ (for some $k'$, $r'$ that are related to the original $k$, $r$)? I'd suggest trying to figure out what $r'$ needs to be first; then going back to the $r = g^k$ relation to deduce what $k'$ needs to be.
Jul
27
answered Ephemeral key is held constant in ElGamal
Jul
23
comment parallel shifters
You might want to revise your question - I really can't make heads or tails of it. You might want to outline what problem space you're looking at (e.g. does 'register' mean a CPU register, or a set of flipflops on an FPGA?); you probably want to be a bit more explicit about the question as well.
Jul
22
revised Fast attack on approximate GCD problem?
added 117 characters in body
Jul
22
answered Fast attack on approximate GCD problem?
Jul
20
comment How many bits to flip in an RSA public key to do signature forgery?
@dannycrane: that was discussing the $e=3$ case; if $n = pq$, where $p$ and $q$ are primes, then $p=2 \pmod{3}$ (because that's a requirement that RSA makes if $e=3$) and $q = 2 \pmod{3}$ (ditto), and hence $pq = 2\cdot 2 = 1 \pmod{3}$. As for what $n - n'$ is nonzero mod $e$, well, flipping bit $k$ of $n$ will either increase it's value by $2^k$ (if the bit was original 0), or decrease it by $2^k$ (if it was 1). Hence, $n - n'$ is either $2^k$ or $-2^k$. As $e$ is odd, then neither $2^k$ nor $-2^k$ will be a multiple of $e$, and that's what $(n - n') \bmod e \ne 0$ means
Jul
19
answered What is the run-time on finding collisions with MACs,…?
Jul
19
reviewed Reviewed Is a book cipher provably secure?