Cryptography Stack Exchange Community Digest

Top new questions this week:

"official" guidelines about the minimum length of a truncated hash

I am looking for some reference documentation suggesting a minimum reasonable length for a truncated hash (specifically, a truncated SHA-256 hash) to ensure preimage resistance. Obviously, truncating ...

hash sha-256 preimage-resistance standards  
asked by user975176 8 votes
answered by kelalaka 7 votes

Distance between consecutive primes distribution

In several prime generation schemes I saw we pick a random number uniformly at random from a wide range and find the next prime after it. Obviously with such a scheme some primes are more likely than ...

random-number-generator prime-numbers number-theory  
asked by Meir Maor 7 votes
answered by Meir Maor 3 votes

Would creating a custom human language be stronger protection than encrypting a known human language?

There are some languages that people haven't been able to read (Cretan Hieroglyphics for example). Does that mean that you can better protect data by making your own language than by encrypting an ...

terminology decryption  
asked by Mike 5 votes
answered by kelalaka 6 votes

How do encrypted radios perform key exchange?

I'm having difficulty finding documentation for the over-the-air protocols used by encrypted public safety radios. It seems that most systems are based on Project 25, previously known as APCO Project ...

asked by vy32 5 votes

ECC: Lightweight proof of correct exponentiation

In the context of ECC. There's an EC point $P$ which is supposed to be a known power of another known point $G$ (generator). That is: $P = [k]G$ (in additive notation) This should be verified on an ...

asked by valdo 3 votes

Breaking RC5 without rotations

I'm trying to follow Schneier's self-study course in cryptanalysis and am ashamed to say I am stuck on the very first problem of breaking 8-round RC5 without any rotations (i.e. just XOR and modular ...

asked by Seawaves32 2 votes

Help with cryptanalysis of branching in schemes based on Multivariate Public Key Cryptography

I'm familiarized with the structure of branching found in Multivariate Cryptography, as it allows us to partition a $n$-tuple over $F_{q}$ into a $k$-tuple where the $i$-th element is in ...

public-key cryptanalysis post-quantum-cryptography linear-cryptanalysis multivariate-cryptography  
asked by kub0x 2 votes

Greatest hits from previous weeks:

What are the differences between a digital signature, a MAC and a hash?

A message may be accompanied with a digital signature, a MAC or a message hash, as a proof of some kind. Which assurances does each primitive provide to the recipient? What kind of keys are needed?

hash signature authentication mac non-repudiation  
asked by Flimm 167 votes
answered by Flimm 192 votes

What is the difference between .pem , .csr , .key and .crt?

I'm new to SSL / TLS and I want to work with the OpenSSL toolkit. I don't know what .pem and .csr stands for? I do know that .key is the private key and .crt is the public key.

asked by Richard R. Matthews 51 votes
answered by Maarten Bodewes 72 votes

How does one attack a two-time pad (i.e. one time pad with key reuse)?

My question might appear the same as the question Taking advantage of one-time pad key reuse?, but actually I did read all the answers and none of them helped me with the details I need. I am new to ...

cryptanalysis one-time-pad key-reuse  
asked by Samer Makary 68 votes
answered by poncho 76 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 AAA\n\rBBB\n\rCCC\n\r is this the same as AAABBBCCC

rsa public-key keys encoding ssh  
asked by xpepermint 32 votes
answered by otus 27 votes

How to check a file was encrypted (really & correctly)

I would like to audit how an implementation of an encryption algorithm is really performed with the following given data of the problem: the encryption mechanism is reversible (this isn’t a ...

cryptanalysis file-encryption  
asked by dan 17 votes
answered by Gilles 'SO- stop being evil' 29 votes

How is CipherCloud doing homomorphic encryption?

Much of the literature and latest papers suggest that homomorphic encryption is still not practical yet. How is CipherCloud able to achieve this? Does anyone have an idea? Their website does not ...

homomorphic-encryption database  
asked by sashank 89 votes
answered by CodesInChaos 86 votes

What are the advantages of TOTP over HOTP?

HMAC-based One Time Password (HOTP) was published as an informational IETF RFC 4226 in December 2005. In May, 2011, Time-based One-time Password Algorithm (TOTP) officially became RFC 6238. What ...

one-time-password hotp  
asked by Jader Dias 59 votes
answered by B-Con 58 votes

Can you answer these questions?

Attackability of one-time MAC when using block mode

Consider an encrypted message m which is encrypted with AES-CBC, so in addition to the message there is an IV supplied initially. If I understand correctly the IV and afterwards the prior ciphertext ...

block-cipher mac one-time-pad  
asked by Strernd 2 votes

Keeping a backup of asymmetric keys with the help of a certificate authority without losing the privacy

First I'll explain the problem, then I will also give a solution(it might be wrong) I've found for it, you let me know what you think about this solution and whether you have a better one. Assume a ...

public-key certificates integrity  
asked by aderchox 1 vote

Double discrete logarithm on elliptic curve

Background: I am attempting to implement the paper Publicly Verifiable Secret Sharing. I managed to get it working using modular groups, but when I want to make it more efficient by transferring to ...

elliptic-curves discrete-logarithm group-theory  
asked by joakimb 1 vote
answered by poncho 0 votes
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