Cryptography Weekly Newsletter

Cryptography newsletter

Top new questions this week:

If you hashed a hash an infinite number of times would you end up with a unique hash?

If you took a hashing algorithm for example MD5 and repeatedly passed the output hash back into the algorithm an arbitrarily large number of times would you eventually end up with one unique hash? My ...

hash entropy  
asked by Alex Lewis 8 votes
answered by Thomas Pornin 23 votes

Is it possible to break enigma code with a todays laptop

I have a 500 characters enigma encoded text. Random rollers were used (not the ones from wikipedia). I know of this flaw. I can guess some words that sould be in the text, but this probably doesn't ...

encryption history  
asked by kyra 7 votes

Can cycle finding techniques reduce the memory usage of the MitM attack against 2DES and 3DES?

A 2DES like cipher $c=E^{(2)}_{K_2}(E^{(1)}_{K_1}(p))$ where both halves have an $n$ bit key is vulnerable to a meet-in-the-middle attack. Meet-in-the-middle using a big table Create a table ...

meet-in-the-middle-attack  
asked by CodesInChaos 5 votes
answered by fgrieu 1 vote

Adding two public keys

secp256k1 (the signature scheme used by Bitcoin) has the interesting property that you can add two public keys to get a combined key that requires both private keys to produce signatures for. Is ...

ecdsa  
asked by Nick ODell 4 votes
answered by D.W. 4 votes

Has human-generated entropy ever been a real problem?

I know the topic of human brains generating random numbers has been discussed here and in Cognitive Sciences before, but I am interested in a particular part of it: In an introductory book to ...

entropy  
asked by user2891462 4 votes
answered by gowenfawr 7 votes

Can Grover's algorithm be parallized?

Using a quantum computer, Grover's algorithm can search an unordered list of length $N$ in time $\sqrt{N}$. Applied to cryptography this means that it can recover $n$ bit keys and find preimages for ...

post-quantum-cryptography  
asked by CodesInChaos 4 votes

Non adjacent form of an integer is unique

I have tried to look up the proof for NAF (Non-adjacent form) being unique for every integer, but as far as I have seen, textbooks only mention it as a property of NAF, but no proof is given. Also I ...

elliptic-curves number-theory  
asked by Vi Jay 3 votes
answered by fgrieu 5 votes

Greatest hits from previous weeks:

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

How does asymmetric encryption work?

I've always been interested in encryption but I have never found a good explanation (beginners explanation) of how encryption with public key and decryption with private key works. How does it ...

public-key  
asked by Senad Meškin 23 votes
answered by Thomas Pornin 21 votes

Can you answer these?

How to securely map an element from an smaller domain to the other element in a large domain

Problem: I have a small sized domain, say s-bit. It's clear that the probability for an adversary to guess an element is $ \frac{1}{2^s}$. I need to make the probability negligible. However, I need to ...

public-key provable-security encoding  
asked by user13676 1 vote

Double-and-add/Montgomery VS blinding

I'm having a hard time understanding why people use constant-time techniques to counter time-attacks, when blinding seems as good and cheaper to implement. Why do people avoid blinding in ECC?

elliptic-curves montgomery blinding time-attack  
asked by David 天宇 Wong 1 vote

Prime factorization

What is the largest integer that can be factored by modern algorithm like Msieve and GGNFS in a time less than 5 hours with normal computers? For example, can an integer like ...

factorization  
asked by Lisbeth 3 votes
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