Cryptography Weekly Newsletter

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Top new questions this week:

Why are primes important for encryption

Why are primes so important? Why can't we just use a random number? My guess is that it's because finding a random prime require more computing power, than finding a random number. Can anybody confirm ...

encryption prime-numbers  
asked by KaareZ 12 votes
answered by Philipp 16 votes

Why is authenticated CFB mode insecure?

I read that the following adaptation of the CFB block cipher mode into an authenticated mode is prone to chosen plaintext attacks, yet Im still unsure how to prove it: Let $P_1,P_2,\ldots P_n$ be the ...

block-cipher modes-of-operation authenticated-encryption cfb  
asked by NumberFour 7 votes
answered by poncho 7 votes

What is the difference between uniformly and at random in crypto definitions?

Very often in the description and analysis of a cryptographic protocol there is a need for a an element $k$ that is sampled uniformly AND at random. Is there a redundancy in the definition with ...

asked by curious 5 votes
answered by DrLecter 7 votes

Dancing confusion with Daniel J. Bernstein's stream ciphers

I know of Salsa20 which won the ESTREAM competition. This is dated of 25 Dec 2007. There is also the ChaCha20 stream cipher ( This claims to increase the amount of diffusion ...

encryption algorithm-design stream-cipher cipher salsa20  
asked by x9c8v7 4 votes
answered by CodesInChaos 5 votes

Extending pseudorandom generator by one bit using exclusive-or of previous bits

Is it possible to have a pseudorandom generator that extends its output by 1 bit by simply appending the exclusive-or of all the previous bits? I know the output of a pseudorandom generator is ...

asked by user1742646 4 votes
answered by yyyyyyy 7 votes

Does RSA operate over a Finite Field (Galois Field)?

Is it correct to say that RSA operates over a Finite Field (Galois Field)? In this case GF(p)? I do understant that the modulo in RSA is not itself a prime number, but all the operations ...

rsa finite-field  
asked by BolshoiBooze 3 votes
answered by yyyyyyy 4 votes

Decrypt all RSA ciphertexts if you can break 1% of them

I was given a cryptography question during an interview the other day. Imagine you are given an efficient algorithm which for a given RSA public key (n,e) is able to decrypt 1% of the messages ...

asked by simon 3 votes
answered by CodesInChaos 4 votes

Greatest hits from previous weeks:

Cryptography vs Security

This may sound a little bit of basic but here it goes… Which of the following is correct? “Cryptography is under the security field”, or “Security is under the cryptography field?” Cryptography ...

asked by Giliweed 5 votes
answered by e-sushi 13 votes

How is SHA1 different from MD5?

On the surface, SHA1 and MD5 look pretty similar. Their diagrams include chunks of bits, bit rotation, xor and special functions. Their implementations are roughly the same length (at least the ones ...

hash md5 sha-1  
asked by qwr 8 votes
answered by Thomas Pornin 11 votes

Can you answer this?

How does Schnorr signature actually work?

I'm trying to get a grip on how Schnorr signature works. Suppose Alice sends Trent a tuple $(P, M)$, which contains a payload and a message to be signed by him. She then passes the certificate to Bob ...

signature blind-signature schnorr-signature  
asked by Kate 1 vote
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