# All Questions

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### Can we develop a working asymmetric crypto message protocol without an asymmetric encryption algorithm?

Our crypto libraries have: DSA (4096, 512) DH (4096) AES (256) SHA (512) Let us say these are implemented directly in hardware so that trying to pull the pieces out is not possible, and the CPU ...
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### One-wayness proof of Elgamal

Here in the proof of Elgemal one-wayness: Consider an adversary V that can invert random Elgamal encryptions with $ε$ probability. $V *$ : Adversary to compute the Diffie-Hellman function: ...
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### Why is the simulation required in these identity-based encryption security proofs?

In identity-based encryption papers (i.e.this) it is very difficult for me to understand security proof. I don't know why they prove assumption (BDH, BDDH) for security of their scheme. Some uses ...
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### Is using a rolling code as a constantly-changing shared secret effective for signing?

I am your average developer looking for some crypto-related guidance. I am trying to have assurance that a received message is from a particular sender, but have no need for the message content to be ...
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### In PKCS#1 V2.2, should MGF be based on the same hash function that RSA-OAEP-ENCRYPT uses?

In Section 7.1.1 of PKCS#1 v2.2 there are two options for RSAES-OAEP-Encrypt given: Hash MGF Appendix B.2.1 of the same document states that MGF1 is based on a hash function. Is MGF1 based on the ...
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### Why would Carter-Wegman-style message authentication not be broken by P = NP?

Researching about the implications of P = NP to cryptography I found someone say that the only cryptography left standing would be the one time pad and Carter-Wegman-Style message authentication. ...
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### Are there encryption schemes with which it takes (significantly) longer to encrypt than to decrypt?

Are there encryption schemes with which it takes (significantly) longer to encrypt than to decrypt? I am thinking of a specific situation in which a server continuously receives encrypted messages ...
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### How do you do a linear feedback shift register?

I saw a video on YouTube by Daniel Rees. The video was about stream ciphers and showed how to do a linear feedback shift register. The example that was used to demonstrate how to do it is was like ...
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### Some Question about Security Proof of authenticated identity-based encryption

In authenticated identity-based encryption by Benn Lynn, in proof of security, I have a little difficulties in understanding. In key extraction queries,if attacker request for guessed ID, then B fails....
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### AES sbox security issue - power analysis attack?

I was wondering about whether the usage of a precomputed sbox (kind of a lookup table) could be a serious security issue when using AES. I am new to power analysis attacks, so it is hard to ...
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### The Encode algorithm of Garbling scheme is probabilistic or deterministic?

In general the garbling scheme works as follows: Garb(1^\lambda, C): on input the security parameter \lambda in unary and the circuit C, it outputs a garbled circuit \widehat{C} and a garbling key ...
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### Advantage of attacker in CPA secure IBE

In CPA secure IBE systems, the advantage of attacker (A) is defined as absolute value of $$Pr[b=b^{'}]-\frac{1}{2}$$ Can someone please explain this to me in a few words? Where exactly does that ...
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### Distinguish two ciphers in Ring-LWE?

I am fairly new to this topic. so my question is: if I have $A=e_0a+e_1$ and $B=e_2a+e_3$ where $a$ is the agreed public parameter, $e_i \leftarrow \chi$ (drawn from the error distribution). if the ...
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### What is many:1 and collision in MD5?

This is in reference to this answer on Stackoverflow. If you read the first paragraph of the answer, you'll find this line: It's always a many:1 mapping (meaning there will always be collisions) ...
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### Why security proof uses random oracles in identity-based encryption?

In identity-based encryption, users decrypt the ciphertext by using private keys. Without private key, no one will be able to decrypt.In security proofs like here, random oracles are used with the ...
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### In what sense addition modulo $n$ ($n>2$) isn't linear in the field $\mathbb{F}_2$?

I've been reading the Reason why “XOR” is a linear operation, but ordinary “addition” isn’t? question, in which one of the answers states that addition modulo $n$ ($n>2$) is linear in $\mathbb{Z}_n$...
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### Encrypt a small amount of data with a password derived from PBKDF2

I have a small amount of data (about 128 bits) to secured with a strong password. I plan to run PBKDF2-SHA2-256 on the password and a 128 bit random salt to generate a 256 bit derived key. Then with ...