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Sep
16
revised Is Rabin's cryptosystem secure against known-plaintext attacks?
rephrased body to make it ask a question
Sep
16
awarded  Tumbleweed
Sep
15
comment Implementing a web app where the server cannot decrypt its own data?
@inxilpro : $\:$ Allow users to install an application if they wish, and list the SHA256 hashes of each version of that application. $\;\;\;\;$
Sep
15
comment Implementing a web app where the server cannot decrypt its own data?
@jfriend00 : $\:$ "This" is the part of the OP that comes after your quote. $\;\;\;\;$
Sep
14
comment Is appending the hash of the plaintext to the end of an encrypted message sufficient to ensure integrity?
No. $\:$ No. $\:$ Yes; the attacker might know the hash of the to-be-forged plaintext, without knowing the whole plaintext. $\;\;\;\;$
Sep
14
comment RSA-KEM construction
Only if the mode of operation has the type of security I described. $\;\;\;$ The KDF doesn't come in. $\hspace{.58 in}$ If length(C2) < length(C1) then send $\:$1 || [prefixfree](en.wikipedia.org/wiki/Prefix_code)(C2) || C1$\:$ else send $\:$0 || [prefixfree](en.wikipedia.org/wiki/Prefix_code)(C1) || C2$\;$. $\hspace{.28 in}$
Sep
14
comment Help to understand the chameleon hash function?
@Alex : $\:$ Identity-Based interactive key exchange can be built from identity-based signatures and [a PKE scheme that is allowed to use trusted public parameters]. $\;\;\;\;$
Sep
14
answered RSA-KEM construction
Sep
13
comment Does NTRU provide Perfect Forward Secrecy?
Note that there are subtleties involved in that. $\;$
Sep
13
comment Does NTRU provide Perfect Forward Secrecy?
What is "the long term channel"? $\;$
Sep
13
answered Why are we advising PKI if we know that quantum computers will break them?
Sep
12
comment Equal length of primes in paillier cryptosystem
One could compute $q$ as 1 more than [something-coprime-to-$p$ times something-smaller-than-$p$]. $\hspace{.48 in}$
Sep
12
revised Can we use numbers as a pad in the Vernam cipher - why or why not?
fixed grammar and capitalization
Sep
11
comment Regarding Key Strength with DES and Blowfish
This paper gives an attack whose heuristic expected runtime is $O(2^{91-(m/2)})$ for $\: 10\leq m \;$. $\hspace{1.03 in}$
Sep
11
comment How can AES be considered secure when encrypting large files?
en.wikipedia.org/wiki/Block_cipher_mode_of_operation $\;$
Sep
11
comment Quantum key exchange skepticism/confusion
It looks to me like intercept-and-resend only gives the upper bound $\: u = 25\% \:$ when the receiver might measure what was resent almost completely correctly. $\:$ Is there some way to show the 25% upper bound even if one assumes a lower bound on the error in that situation? $\;\;\;\;$
Sep
11
comment How can I know when a file was signed?
"Sending it to a 'secure' time and location server (assuming that exists).", would what? I believe most systems "just take Computer time".
Sep
11
comment How can I know when a file was signed?
Even sending your "signature to a 'trusted' time server, which timestamps" your "signature and signs it" would not necessarily be enough, since after learning your private key, it might be easy for the thief to find a new message for which that signature is valid. One could use forward-secure signatures.
Sep
10
comment Quantum key exchange skepticism/confusion
@FrédéricGrosshans : $\:$ I have no idea how physically plausible such an assumption is, but would a noticeable lower bound on the error rate for measuring adversarially produced quanta break the proof of the 25% upper bound? $\;\;\;\;$
Sep
10
comment Quantum key exchange skepticism/confusion
Also, after reading Frédéric's answer, I now believe that instead of using fuzzy extractors, it would be better to use one or more (the same number each) secure sketches, universal hashes, and strong extractors‌​. $\:$ (The strong extractors do not need to be based on the leftover hash lemma.) $\;\;\;\;$