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Mar
13
reviewed Close Of what use is my code for finding prime numbers of a certain size?
Mar
13
answered Why is this a fix to Bleichenbacher's attack?
Mar
13
awarded  Nice Answer
Mar
12
comment Is this discrete log generalization a well known cryptographic assumption?
@RandomGuy: if group order is prime, then it is always cyclic. Otherwise, you have a good point: that would mean that I would need to omit the 'perhaps we can handle it if the group order is composite' statement at the end, or at least, qualify it.
Mar
12
answered Is this discrete log generalization a well known cryptographic assumption?
Mar
11
comment Encrypt-then-MAC: Do I need to authenticate the IV?
Correction: assuming we're talking about CBC mode, Mallory can predict the result of the modification; if he flips bit $i$ of the IV, this will result in flipping bit $i$ of the decrypted text. What this means is that if Mallory knows the first 128 bits of the correct decrypted message, he can replace that with any other 128 bit value of his choosing.
Mar
11
reviewed No Action Needed Algorithm: How to use x and y mouse movement co-ordinates to generate random data?
Mar
10
reviewed Close Decrypting DES with decrypted and encrypted data
Mar
10
reviewed No Action Needed what is the current actual budget - as of 2015 - needed to build a DES breaker machine?
Mar
10
reviewed Reviewed Reusing the random exponent for ElGamal encryption with different plaintexts
Mar
10
reviewed Close Standard serialization format for libsodium-based messages
Mar
10
reviewed Close how to integrate 2-3 algorithms to encrypt large data fastly and securely insted using AES?
Mar
10
reviewed Close Known plaintext, unknown 128 bit block cipher
Mar
10
comment Transport SA bundled inside a tunnel with encryption applied before authentication?
The standard way to do what you're doing is to use ESP in tunnel mode, with the ESP performing both encryption and authentication transforms (or alternatively a combined mode transform). Is there a specific reason why this isn't an adequate solution?
Mar
9
comment What happens to entropy after hashing?
@KarlZorn: I have no idea what you mean by 'entropy computed at byte or character level'. In addition, as how E(H(X))/E(X) acts depends a great deal on the precise distribution X (for example, consider a distribution which is defined such that only values $x$ with $H(x)=0$ have nonzero probabilities), it's not clear that your $f(x)$ is actually well-defined.
Mar
5
answered Will SHA1 or Other Hash Functions Ever Contain Quotes
Mar
4
comment Which characters to take into account when calculating unicity distance?
@GeorgeG: in addition to Ilmari's correct comments, there's another issue with unicity distance -- it's not very useful. Not only does it vary depending on the plaintext and the capability of the attacker (as Ilmari points to), in practice (and with real plaintext distributions) it's tiny -- somewhat larger than the key size. When we use AES to encrypt something, we're generally interested in encrypting more than 24 or 32 characters. Hence, we cannot depend on unicity distance; instead, we must rely on the computation complexity of breaking AES.
Mar
4
comment Find the prime factorization in the DLP
@RobertNACIRI: actually, I misspoke; it's $3x-1 \bmod (p-1)(q-1)/4$ which is 0 with high probability. In any case, if we have a value $k(pq-p-q+1)/4$ (for modest $k$), and $pq$, how can we rederive $p, q$?
Mar
4
comment Find the prime factorization in the DLP
@RobertNACIRI: I assumed that this was the question crypto.stackexchange.com/questions/24251/… (asked better); there, we assume that, given $g$ and $h$, we can find $x$ (and are asked to show that that implies an easy factorization method)
Mar
4
comment Find the prime factorization in the DLP
@mikerussel: no, your first statement was correct; there exists an integer $k$ such that $3x-1 = k(p-1)(q-1)/2$. Now, how big can $k$ be? Hint: $x < (p-1)(q-1)/2$, as it's the minimal $x$ value.