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Jan
27
awarded  Enlightened
Jan
26
reviewed Edit What is a block cipher?
Jan
26
revised What is a block cipher?
Better title and improved grammar
Jan
19
answered AES CBC mode or AES CTR mode recommended?
Jan
10
answered Is it possible to break a hash-based block cipher?
Jan
10
awarded  Nice Answer
Jan
9
reviewed Approve Why is ciphertext from low entropy plaintext not compressible?
Jan
8
answered Why is RSA usually limited to messages up to 1 block
Jan
6
answered Simple homomorphic crypto for 32-bit integers
Jan
3
answered Does the elliptic curve (EC) cryptosystem outperform RSA and DL cryptosystems?
Dec
30
answered Efficient Symmetric Mutual Entity Authentication Protocol
Dec
22
awarded  Good Answer
Dec
7
answered Are really, really long passwords any securer than short ones?
Dec
7
reviewed Approve RSA 4096 bit key benchmark
Nov
30
comment Exhausting the entropy of a hash function
There are details. There are also online dictionary attacks, which are performed against the live target server, without knowing the hash value. Specific preimage resistance of the hash function is irrelevant for that. But if the attacker knows the hash value, then yes, there is no need, even academic, to push the password entropy beyond the preimage resistance of the hash function.
Nov
30
answered Exhausting the entropy of a hash function
Nov
29
answered Constructing RSA private key, given public key
Nov
29
answered What cipher mode is suitable for independantly decryptable short messages?
Nov
24
answered Does a trace of SSL packets provide a proof of data authenticity?
Nov
23
comment Mapping between subgroups and the integers
$q$ is a prime so it is odd ($2$ is the only even prime). Therefore $q = 2k+1$ for some integer $k$. So, $p = 2q+1 = 4k+3$, which means that $p = 3 \mod 4$. Whe computing modulo a prime $p$ which is equal to 3 modulo 4, $-1$ is not a quadratic residue, so $x$ and $-x$ cannot be both quadratic residues (but one of them necessarily is).