# All Questions

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### How to find out the method used to encrypt [closed]

How to find out the method used to encrypt the string 123456 which results in the value: 6g9SkDLIKa8l2VhafFnHvg==?
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### Choice of multiplication polynomial in Rijndael s-box affine mapping

The Rijndael specification details the design choices for the s-box in section 7.2. They describe the choice of affine mapping as follows: We have chosen an affine mapping that has a very simple ...
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### Does collision resistance imply (or not) second-preimage resistance?

I've seen contradictory results. Sometimes hash functions are collision-resistant but not necessarily second-preimage resistant. I've seen this kind of things in papers from Bart Preneel: “Security ...
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### Condensed ElGamal + AES

In normal ElGamal encryption, the encrypted message is a pair (gb, gabM) - that is, the actual "encryption" is simply multiplication by the shared secret ...
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### How to convert projective to jacobian co-ordinate in ECC?

I am doing a small project using elliptic curve in cryptography. My doubt is, can I directly convert a projective to a Jacobian coordinate system without using the affine conversion in elliptic curve ...
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### Public Key Cryptography: Diffie-Hellman Key Exchange

Please watch this video it's very short. If you already know cryptography and really good at it please start from 3:51. I didn't understand the step at 4:39, can someone here to explain? Why is ...
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### Empty message Hash length

I am learning Hash Algorithms and in a presentation (PDF) about these algorithms I read that: Length of $h(m)$ much shorter then length of $m$. Now my question is: What if we talk about an ...
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### Combining Random Hashes - avoiding collisions and ensuring randomness

I have a series of integers which I want to convert to random integer (64 bit). The idea here is to produce random numbers very quickly. The issues that good quality random numbers are required with a ...
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I was researching about hash, and I thought, If sites store passwords with hash algorithms, then can't this happen: User A has the password 'hello' User B finds out the hash code of the password of ...
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### moduli in SSL certificates [closed]

this is normally seen in a typical SSL certificate. For the modulus, I know that it is represented in hexadecimal form, but why is there a semicolon (:) after every group of 2 digits? ...
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### Indistinguishable encryptions in the presence of an eavesdropper equivalence

I'm trying to prove that definition 5 and definition 6 in this document are equivalent. This is what I've done at the moment: Asume that the scheme has Indistinguishable encryptions in the presence of ...
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### Large text file encryption per line

Some background: I receive data in text files of over 16 million records (lines). I need to be able to encrypt the first column in that file so that it cannot be deciphered. This process will be ...
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### Is it possible to get better randomness by using multiple PRNGs?

I don't know if this question even makes sense, but: Is there be any benefit or impact to some sort of hierarchical (e.g. a PRNG drives the decision for which PRN to pull from a set of PRNGs) or ...
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### In public key cryptography, how many keys are required for secure communication between n parties?

In public key cryptography, how many keys are required for secure communication between n parties? In my view the answer should be $n^2$. Reason: There are ‘$n$’ Parties. Every Party has One (1) ...
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### Are poly1305 authenticators distinguishable from random data?

Assume Alice authenticates a message $M$ with nonce $N$ and secret key $K$, creating authenticator $A$. She then sends $A$ across the network. The Poly1305 paper does not seem to specify whether it ...
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### How to prove NIZK proof of knowledge?

Assuming we have an El-Gamal pk tuple $(G,q,g,g^s)$. Someone, knows only the first three parameters. In round $i$, I send him $X_i=(g^s)^{t_i}$ (the $t_i$ values are chosen randomly for each round), ...
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### Deriving 2 keys using HKDF

I have an encryption scheme that uses a 256-bit master key, from which 2 separate keys (one for AES-256-CTR encryption and one for a HMAC-SHA256) are derived using HKDF. However, I'm not sure exactly ...
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### OpenSSL: do I need multiple EVP_CIPHER_CTX structures? [migrated]

This may need to be on StackOverflow instead. I have a single-threaded client/server application that needs to do both encryption and decryption of their network communication. I plan on using ...
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### Is there a deterministic number generator that allows me to share some (not all) numbers I've generated using a smallish seed?

I was just wondering, is there a type of deterministic number generator that allows me to share some (not all) numbers I've generated using a smallish seed? I have pairs of random numbers and need to ...
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### How do I decide what mode to use?

I'll be using AES from OpenSSL. I understand why I don't want to use ECB from reading pages like this Wikipedia article, which has a great example of what happens when you attempt to encrypt with ...
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### Modulo settings for successful encryption?

I saw this awesome video which shows how encryption works using "discrete logarithm". The example says: $3^x\mod17$. I understood that $3$ is called “generator”, because it has no "straight" root and ...
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### DH “prime size” security in OpenSSL

There's a program that uses the following OpenSSL function... DH_generate_parameters(256, 5, NULL, NULL) ...to create DH parameters which are later used for ...
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### What does it mean for an adversary to run in PPT?

I've been reading this question where a detailed description of mine is given, I've understood that a polynomial-time adversary is an adversary for which the only feasible strategy are those that take ...
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### Is email an example of public-key cryptography?

It seems like email is at least analogous to public-key cryptography, the public portion of the key being your email address, and the private portion of the key being the password to the email ...
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### How can I find the multiplicative inverse in the first transformation of the SubBytes() transformation in AES?

In FIPS-197 §5.1.1 , it says the first transformation in the SubBytes() transformation is: Take the multiplicative inverse in the finite field $\text{GF}(2^8)$ described in Sec. 4.2; the ...
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### Is it possible to perform a rudimentary asymmetric key encryption algorithm by hand?

I have at least three, distinct motivations for having a simple way to use asymmetric key encryption by hand or without modern computers. First, I was recently demonstrating to a 12-year-old how ...
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### Pseudo Random Generator with fixed Hamming Weight [closed]

I'm searching for way to generate secure pseudo random sequence with a fixed Hamming weight using a seed. I found below code but I need a seed to generate a sequence ... (and need know if is possible ...
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### Public and private key lengths

I am generating RSA Public and Private keys with node.js instead of reading them from pem/crt files as I can hide them inside a private object using this module https://www.npmjs.org/package/private ...
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### Could scrypt salts contribute to entropy if passwords & salts are only stored in human memory?

I'm unsure of how exactly the salt is manipulated by scrypt and its potential contribution if any to overall password entropy if passwords & salts are stored only in human memory for a ...
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### Description of signatures with message recovery (as in ISO/IEC 9796-2 and EMV Signatures)

I'd like to get an overview of how the signatures with message recovery work, especially in case EMV and other smart card systems. Is there a nice overview available without being required to read the ...