# All Questions

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### Diffie-Hellman: *assumed* largest prime factor of order of $g$?

I've read in several places: some of my confusions about DDH assumption - comment by Thomas Pornin on his own post Is there a key length definition for DH or DHE? - the answer by Tom Leek that ...
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### Homomorphic OR operations

Is there an encryption scheme that provides efficient homomorphic OR operations at the ciphertext space? Of course any fully homomorphic encryption can be used but I do not require or want additional ...
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### Zero-Knowledge Proof of a polynomial

I have two secret values $L_1$, $L_2$, and two Pedersen commitments $C_1 = C(L_1)$, $C_2=C(L_2)$. The commitments $C_1$, $C_2$ are public. Given a challenge $c$, I want to output $d = c*L_1+L_2$ and ...
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### Are there AES128 keys such that first round key equals last round key?

I am looking for AES128 keys such that the last round key is exactly the first round key (which is simply the key). Any pointer to a proof that they exist or that they don't would be welcome. In the ...
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### Translation of Schorr Ring Signature to ECSchnorr Ring Signature

I have to write an EC version of Schnorr Ring Signature Scheme. I've already wrote regular ECSchnorr Signature Scheme using this (page 128). I've found a scheme of Schnorr Ring Signature Scheme (page ...
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### Alice answering Bob without knowing he question

I'm a student and I don't know how to solve the following problem : Alice is proposing a 10 questions list to Bob. Bob choose only 1 question and wants to know the answer without Alice knowing the ...
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### Best modern cipher for morse code?

I am looking for a modern cipher to encode morse code, ie. input is [A-Z 0-9] (base36 as I learned in the comments below) and output is the same, one character at a ...
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### Lightweight Asymmetric encryption algorithm

I'm an embedded systems researcher, and new in the crypto field. Actually, I need to know if there are any lightweight asymmetric encryption algorithm especially considering the time needed for key ...
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### Lightweight Asymmetric encryption algorithm [duplicate]

I'm an embedded systems researcher, and new in crypto field. Actually, I need to know if there are any lightweight asymmetric encryption algorithm especially from time needed for key generation. I ...
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### Why use Diffie-Hellman key exchange over RSA (or any public-key encryption)?

In Diffie-Hellman key agreement between Alice and Bob, Alice computes and sends $g^a$ to Bob, and Bob computes and sends $g^b$ to Alice. Alice then computes $(g^b)^a$, and Bob computes $(g^a)^b$; ...
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### Cyclic group collision resistant keyed cryptographic hash function

I am self-studying cryptography from a book and have come across a really difficult question that's doing my head in. I would be very grateful if somebody can help me out here with this difficult ...
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### Elliptic Curve ElGamal and DSA - smooth group order and element of large prime order

In regular ElGamal and DSA, we choose large primes $p$ and $q$ such that $p\equiv 1\pmod{q}$, and a group element $g$ of order $q$ by computing $a^{(p-1)/q}$ for some random $a$. This is to prevent ...
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### RSA incorrectly translates for small keys [duplicate]

I've been learning about RSA and wrote my own implementation. I don't pretend to have intuitive understanding of RSA or that I understand why it works, but I believe to have some basic understanding ...
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### Adding parameters to sponge's capacity

Is it safe to XOR parameters like domain, length of the message or block counter into sponge's capacity or that gives attacker control over capacity? For example NORX XORs domain into capacity. Does ...
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### DES: How to find the Inverse of the Initial Permutation?

I am doing a DES problem by hand and I want to know how you calculate the inverse of the initial permutation. I know what the permutation is, but how do you find it based off the given initial ...
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### Data Leakage and Data Switching

I have two secret values $a$ and $b$ (i.e. they are arbitrary values). I mask them as follow: $v_1=r_1a+r_2$ $v_2=r_1(b-a)$ where $r_1$ and $r_2$ are uniformly random values. I send $v_1$ and $v_2$ ...
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### Hash functions vs Stream Ciphers in terms of Speed

We know that it's possible to create a hash using a stream cipher (for instance, RC4 or AES in Counter Mode). As stated here: "A Pseudo Random Generator (PRG) and a hash function are both Pseudo ...