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Feb
8
comment Is $f(x)\oplus x$ a one-way function?
@Maeher : $\:$ To make do with merely superlogarithmic-length $x_{\hspace{.02 in}1}$ (or even polylogarithmic-length), one would need $\hspace{.02 in}f$ be be secure against SUBEXP-time adversaries. $\;$
Feb
8
comment How does CTR-ESSIV work ? (cryptsetup Linux)
en.wikipedia.org/wiki/… $\;$
Feb
8
comment Is $f(x)\oplus x$ a one-way function?
I think $x_{\hspace{.02 in}1}$ should be replaced with $x_{\hspace{.02 in}1}'$. $\:$ Also, one can let the construction have slightly better $\hspace{.4 in}$ efficiency in general by letting $\hspace{.04 in}f$'s input and output lengths be $m$ and $n$ instead of $n/2$ and $n/2$. $\hspace{.64 in}$
Feb
8
comment Simple multiplication as an encryption method
$K \: = \: C \div M \;\;\;\;$
Feb
8
comment Hash function as secure as one-time pad?
@MaartenBodewes : $\:$ Alternatively, it could require that the messages be chosen non-adaptively. $\hspace{.55 in}$
Feb
7
comment Hash function as secure as one-time pad?
There are almost-universal hash families and information-theoretically secure MACs. $\hspace{1.3 in}$
Feb
7
comment Hash function as secure as one-time pad?
"just the same as a hash function" in what sense? $\;$
Feb
7
comment Boneh-Boyen like signature scheme
BLS $\;$
Feb
7
comment Misunderstanding Broadcast Encryption
@hackartist : $\:$ The admin can use a digital signature scheme, for each message, encrypt the message-key separately for each approved user. $\;\;\;\;$
Feb
7
comment Misunderstanding Broadcast Encryption
I'm just alluding to the fact that in that case, anyone could unlock anything by $\hspace{1.49 in}$ locking on and then removing their own lock. $\:$
Feb
6
comment Misunderstanding Broadcast Encryption
The combination of encrypt(message, key1) -> code1 with encrypt(code1, key2) -> code2 and decrypt(code2, key2) -> message make me wonder how this is related to cryptography. $\;$
Feb
6
comment Can you exchange a shared key without any hardness assumptions?
(... continued) $\:$ outputting $\perp$ if more than $L$ bits of randomness would've been used or either of them would've reported failure, and outputting the resulting transcript otherwise. $\:$ If Alice and Bob together use at most $L$ random bits and succeed, then a preimage of the transcript under that function yields the agreed-on key. $\:$ If there might be undetected failure, then one would have to read Clint's comments to his answer on the page I linked to in the other comment thread. $\;\;\;\;\;\;\;$
Feb
6
comment Can you exchange a shared key without any hardness assumptions?
@Ike : $\;\;\;$ Not quite; his proof implies that the attacker can make their failure probability an arbitrarily small inverse-polynomial function of the security parameter. $\:$ Choose some length $L$, and consider the function from strings of length $L$ to the union of $\{\hspace{-0.02 in}\perp\}$ with the set of transcripts which is given by trying to run Alice and Bob using the input string as the random bits, $\:$ (continued ...) $\;\;\;\;\;\;\;$
Feb
6
comment Can you exchange a shared key without any hardness assumptions?
"also sending the hash of the plain text" ... would reveal "the hash of the plain text". $\hspace{1.35 in}$
Feb
6
comment Can you exchange a shared key without any hardness assumptions?
That's right. $\:$ One can additionally consider the case in which Alice and Bob don't have the same "CA"s. $\:$ However, "sending random bits in it to each other" isn't good enough, since it doesn't have a high-enough probability of detecting a small difference. $\;\;\;\;$
Feb
6
comment Stream cipher key length to send
Well, a steam cipher's key usually has a different length from "the length of the message". $\hspace{1.01 in}$ (Of course, nothing stops one from using it to send a message with the same length as the key.) $\hspace{.71 in}$
Feb
6
comment Can you exchange a shared key without any hardness assumptions?
@ike : $\:$ If "many possible inputs would result in the same transcript", then one needs to read Clint's comments to his answer on the page I linked to. $\;\;\;\;$
Feb
6
comment Can you exchange a shared key without any hardness assumptions?
cstheory.stackexchange.com/q/8697/6973 $\;$
Feb
3
comment PRF based on the GGM construction
"dynamic search symmetric scheme" $\: \mapsto \:$ "dynamic searchable symmetric encryption" $\;\;\;$ ? $\hspace{.81 in}$
Feb
3
comment Python implementation of a blind signature scheme which doesn't involve RSA
@CodesInChaos : $\:$ Another pitfall is that you should make sure that the public key defines a permutation. $\;\;\;\;$