Cryptography Stack Exchange Community Digest

Top new questions this week:

Why is this not a viable key exchange algorithm?

I was just wondering why this kind of algorithm can't be used instead of, say, Diffie-Hellman to exchange keys: Alice decides on a key she wishes to share with Bob. Alice generates a stream of bytes ...

public-key diffie-hellman algorithm-design key-exchange  
asked by guest 9 votes
answered by kelalaka 31 votes

Can a PRF distiguisher invoke the function's algorithm?

The definition of a function $F:\ \{0,1\}^n\times\{0,1\}^n\to\{0,1\}^n$ being a Pseudo Random Function Family (PRF) is that it's implementable by a P.P.T. algorithm $\mathcal F$, and there is no P.P.T....

provable-security pseudo-random-function  
asked by fgrieu 4 votes
answered by 0kp 4 votes

Does varying ChaCha rounds add any security?

This paper introduces 'Freestyle' a randomized, and variable round version of the ChaCha cipher. It uses the concept of hash based halting condition, where a decryption attempt with an incorrect key ...

encryption hash stream-cipher chacha salsa20  
asked by Modal Nest 3 votes

Does it make any sense to sign a GCM authentication tag with RSA?

To achieve double insurance for authentication, can we sign the GCM final tag with using RSA? with RSA, no one is able to create his own tag since the private key is not known. However, according to ...

rsa authentication gcm  
asked by Pi-Turn 2 votes
answered by Maarten Bodewes 2 votes

Why Fiat-Shamir based signatures incur a security loss?

I read here that assuming we have a Fiat-Shamir (FS) signature $\Sigma$ that is secure based on the hardness of a particular hard problem $\Pi$. Then, the security proof of $\Sigma$ in the classical ...

signature fiat-shamir  
asked by tinker 2 votes

Crypto scheme to map data to users in a way that is anonymous to database server

I am trying to finish a paper on censorship resistant data-sharing systems in semi-centralized ways. I know the below threat model can be mitigated by using decentralized system, but I am looking for ...

encryption one-time-pad identity-based-encryption database anonymity  
asked by skydanc3r 2 votes
answered by cisnjxqu 1 vote

How to encrypt many files with AES-GCM, without running the key derivation function each time?

Linked question: AES encrypting multiple files With a password, I have 100k files to encrypt. (Maybe 100k files today; or maybe 50k today, 10k tomorrow, and 40k ...

aes key-derivation file-encryption aes-gcm  
asked by Basj 2 votes
answered by fgrieu 1 vote

Greatest hits from previous weeks:

Should we sign-then-encrypt, or encrypt-then-sign?

We regularly want to send messages that are both (a) encrypted, so passive attackers can't discover the plaintext of the message, and (b) signed with a private-key digital signature, so active ...

encryption public-key signature protocol-design hash-signature  
asked by David Cary 121 votes
answered by D.W. 90 votes

Chinese Remainder Theorem and RSA

Wikipedia has a nice section regarding the speedup of the RSA decryption using the Chinese Remainder Theorem here. I need to understand the implementation of a similar speedup for the encryption ...

rsa homomorphic-encryption  
asked by Mihai Todor 15 votes
answered by poncho 23 votes

Impacts of not using RSA exponent of 65537

This RFC says the RSA Exponent should be 65537. Why is that number recommended and what are the theoretical and practical impacts & risks of making that number higher or lower? What are the ...

public-key rsa  
asked by goodguys_activate 66 votes
answered by fgrieu 61 votes

Can I remove newlines in a public key?

Can I remove new lines from the RSA public key file to get a one line string? So the question is if the key looks like this AAA BBB CCC or ...

rsa public-key keys encoding ssh  
asked by xpepermint 37 votes
answered by otus 29 votes

Can you help me understand what a cryptographic "salt" is?

I'm a beginner to cryptography and looking to understand in very simple terms what a cryptographic "salt" is, when I might need to use it, and why I should or should not use it. Can anyone offer me a ...

encryption hash passwords salt password-based-encryption  
asked by Bhavik Ambani 119 votes
answered by MartinSuecia 171 votes

What is the difference between a digest and a hash function?

I was wondering about the difference between these two terms... What is the difference between a digest and a hash function?

hash terminology  
asked by sekmo 54 votes
answered by Awn 69 votes

Can you explain Bleichenbacher's CCA attack on PKCS#1 v1.5?

I've studied that the Bleichenbacher's CCA attack on PKCS#1 v1.5. is a base to many versions of attacks in the area. I'm trying to understand that attack, but every explanation I saw starts with the ...

encryption rsa public-key chosen-ciphertext-attack  
asked by Bush 62 votes
answered by Thomas Pornin 102 votes

Can you answer these questions?

Fisher Yates on "faulted" random number generator cryptanalysis

For the sake of curiosity and fun, i have implemented a C# program that operate as deck dealer on 40 cards deck (following the Fisher Yates shuffeling algorithm https://en.wikipedia.org/wiki/Fisher%E2%...

cryptanalysis random-number-generator randomness pseudo-random-permutation shuffle  
asked by Skary 1 vote

Rounding function used in Saber Key Exchange

In Saber: Module-LWR based key exchange, the authors use a rounding function called $\textit{bits}$, defined (in page 3) as follows: $bits(x, i, j)$, with $j \leq i$, gives $j$ consecutive bits of a ...

key-exchange post-quantum-cryptography lattice-crypto nist lwe  
asked by a196884 2 votes

Is it OK to use a doubled key for XTS-AES?

https://en.wikipedia.org/wiki/Disk_encryption_theory#Xor%E2%80%93encrypt%E2%80%93xor_(XEX) reads: The standard supports using a different key for the IV encryption than for the block encryption; this ...

aes xts  
asked by fadedbee 1 vote
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