Cryptography Weekly Newsletter

Cryptography newsletter

Top new questions this week:

Logjam on Elliptic Curves?

I think we're all aware of the Logjam attack. From now on we know that re-using primes for DH is a bad idea. But we also say that elliptic curves are safe from the attack (relying on the NFS), ...

elliptic-curves diffie-hellman discrete-logarithm logjam  
asked by SOJPM 7 votes
answered by Samuel Neves 5 votes

RSA with probable primes

I am a bit of a newbie to RSA encryption, so please be patient. I understand that for a 4096 bit RSA, the numbers p and q should be prime. And to have the best security, the p and q should both be ...

rsa prime-numbers  
asked by Jug 5 votes
answered by fgrieu 5 votes

Hard-core predicates: should the adversary be given $1^n$?

In most (all?) classical sources such as the book of Goldreich (2001), hard-core predicated are defined thus: A polynomial-time computable predicate $b : \{0,1\}^* \to \{0,1\}$ is a hard-core of a ...

one-way-function security-definition hard-core-predicate  
asked by fkraiem 5 votes
answered by Guut Boy 0 votes

possible MITM attack against servers that used to support weak DH?

from reading the TLS 1.1 RFC, it looks like it would be possible to break a previously recorded TLS <1.2, 512-bit DHE ServerKeyExchange and then send it (unmodified, with the original, valid ...

diffie-hellman ssl man-in-the-middle  
asked by lily wilson 4 votes
answered by SOJPM 1 vote

Logjam: "composite order subgroups" explained for TLS developers and system admins?

I have read the recent logjam paper Imperfect Forward Secrecy: How Diffie-Hellman Fails in Practice. On page 11 in the Recommendations section, they state: Avoid fixed-prime groups In the medium ...

diffie-hellman group-theory  
asked by Mike Ounsworth 4 votes
answered by cpast 7 votes

How can a block cipher in counter mode be a reasonable PRNG when it's a PRP?

Wikipedia claims: A secure block cipher can be converted into a CSPRNG by running it in counter mode. This is done by choosing a random key and encrypting a 0, then encrypting a 1, then encrypting ...

csprng  
asked by Anon2000 4 votes
answered by CodesInChaos 5 votes

Can spatial filters be used to factor composite numbers?

$Z=(N-XY)^2$ is a surface with absolute minima ($0s$) anywere $Y=N/X$. I know this question is naiive, but shouldn't it be possible to apply a lossy compression filter to this function which ...

factorization  
asked by zQAycX 2 votes
answered by kodlu 2 votes

Greatest hits from previous weeks:

Difference between encrypting something and hashing something

What is the difference between encrypting something and hashing something? in what situations would I want one or the other?

encryption hash  
asked by Joel B 7 votes
answered by Thomas 6 votes

How does TLS_FALLBACK_SCSV help?

After reading through https://tools.ietf.org/html/draft-ietf-tls-downgrade-scsv-0, I could understand that this option is recommened for use when one has legacy SSL Servers which only support SSLv3. ...

ssl openssl  
asked by dpb 2 votes
answered by lxgr 6 votes

Can you answer this?

Hardening of random number generators

Boxcryptor uses various CSPRNGs and apparently hashes the output using PBKDF2 to derive the final key. Even though the choice of PBKDF2 is probably not semantically correct (PBKDF2 is intended for ...

key-derivation pbkdf-2 csprng  
asked by Paya 1 vote
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