# Tagged Questions

An asymmetric cipher is an encryption scheme using a pair of keys, one to encrypt and a second to decrypt a message. This way the encrypting key need not be kept secret to ensure a private communication. Similarly in public key authentication, the verification key can be public and the signing key ...

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### Some confusions about Repeated Doubling Algorithm?

The following repeated point doubling algorithm is taken from the book Guide to Elliptic Curve Cryptography by D. Hankerson, A. Menezes, and S. Vanstone on page#93. Clearly, this algorithm is ...
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The following snapshot of the algorithm is taken from the book Guide to Elliptic Curve Cryptography published by Springer 2004. I don't understand that why at the statement 9.1 if both $T_1$ and $... 2answers 208 views ### Alice answering Bob without knowing the 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 ... 2answers 634 views ### Why is hybrid encryption more effective than other encryption scheme? Currently I am learning about Hybrid Encryption but I was not able to find any good study material. Below is my understanding: One of the reason why we use ... 4answers 899 views ### Why is public key cryptography (RSA) used in sites like Google or Facebook? The RSA algorithm is used for encryption (plain text to cipher text) and decryption (cipher text to plain text) of data. What is the need for using public keys in these sites; why is data is encrypted ... 1answer 134 views ### UKS attack on KEA protocol I'm trying to understand the UKS attack on KEA protocol. This is described in this paper: Security Analysis of KEA Authenticated Key Exchange Protocol So to summarize: KEA protocol: UKS ... 1answer 170 views ### How to generate a bilinear group of prime order p for key generation I am trying to implement an IEEE Paper In Cryptography. I read many reference regarding an RSA key generation. But i am confused with above statement. Please someone explain me What it says with ... 1answer 240 views ### Authentication by hardcoding public key in client software It would seem to me that mobile applications could reduce network traffic by hardcoding the server's public key into the app. The idea being that they could then encipher a secret to share with the ... 1answer 68 views ### Can I always derive a key pair from password+salt with libsodium? I'm using libsodium to create public/secret key pairs from a password and salt combination by using crypto_pwhash_scryptsalsa208sha256 to generate a seed and ... 2answers 105 views ### Is there a theorem to determine the elliptic curve parameters based on the group order? By Hasse's theorem we know that range of the group order of the elliptic curve. And similarly, there exist a theorem on the admissible order of elliptic curves. Suppose by the theorem on the ... 1answer 25 views ### How to run a (provably probably) secure global referendum? The following question is extremely broad and speculative, for which I apologize, but it strikes me as exceedingly important, so I will ask it nonetheless. Suppose an event of global significance ... 0answers 49 views ### Given a public-key encryption and signature scheme, define a new primitive I'm new to cryptography and am currently working on the following question: Say you are given a public-key encryption scheme$\Pi_e=(\mathcal{K}_e,\mathcal{E},\mathcal{D})$and a signature scheme$...
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Someone posted this on reddit a few days ago, and I haven't found much about it except for links back to the same page. Here's the article http://programmingpraxis.com/2016/01/19/rsa-encryption-...
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### Large Volumes of Asymmetric Encryption

First of all, I apologize in advance if I use any incorrect terminology. I am just getting my feet wet when it comes to cryptography and there is a lot to learn. For the past 12 months we have been ...
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### Calculate if a digital signature is valid

In the book An Introduction to Mathematical Cryptography, it mentions a section on digital signatures and a theoretical example. I am having difficulty understanding the book and I was wondering if ...
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### RSA encryption with private key, decryption with public key (again)

First of all let me point out that I am aware of all the theory behind asymmetric encryption and signing, and other related areas like signcryption, etc. It seems that mathematically it is possible to ...
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### How does certificate-based encryption solve key revocation problem?

How does certificate-based encryption solve key revocation problem? For example, if a user accidentally reveals its secret key or an attacker compromises it, the user may request revocation of its ...
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### How does a client verify a server certificate?

As far as I know, when I request a certificate from Verisign (for example), and after they approved that me is me, they create a certificate (for me) which contains the digital signature and public ...
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### UKS attacks. Dangers & Prevention?

I am trying to understand how to prevent a UKS (unknown key-share) attack, but I am having trouble finding many resources out there to help. Let's imagine a hypothetical secure messaging application ...
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### How can public key not reverse encryption if the algorithm is known? [duplicate]

I've been reading about WhatsApp getting "end-to-end" encryption, and when reading about it, I've notice something. If I want to send a message from cell $A$ to cell $B$, since there's a public key, ...
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### Do I need to use a MAC with asymmetric encryption?

The internet has drilled into me that when I delivery any symmetrically encrypted data, I should also deliver a MAC to authenticate it before any decryption occurs. Do I also need to do this if I use ...
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### Security implications of public nonce

I'm planning to use the crypto_box() functions of Nacl (or, alternatively, the crypto_box_easy() functions of libsodium) to ...
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### Is javascript RSA signing safe?

I'm currently working on a secure open source messaging system (https://github.com/DSMNET/DSMNET). I'm currently using the cryptico.js (https://github.com/wwwtyro/cryptico) library to encrypt all the ...
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### CCA on PKCS#5 using error feedback

My question is about attacking PKCS#5 with CCA using the error feedback. What we learnt in class about PKCS#5: CBC requires padding to whole block boundary PKCS#5: standard padding If ...
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### Single public key for NaCL signing and encryption?

Bob wants to use NaCL (specifically the Python NaCL library) to both a) sign some publically available plaintext for anybody to authenticate as being written by Bob and b) encrypt some other secret ...
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### How big an RSA key is considered secure today?

I think 1024 bit RSA keys were considered secure ~5 years ago, but I assume that's not true anymore. Can 2048 or 4096 keys still be relied upon, or have we gained too much computing power in the ...
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### Asymmetric password encryption - Viable? Which algorithm?

We have an application that requires cleartext passwords for user authentication because of the authentication mechanism in use (RADIUS/CHAP), which unfortunately we cannot change. Since we don't want ...
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### Why does the recommended key size between symmetric and asymmetric encryption differ greatly?

In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key ...
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### ECDSA vs ECIES vs ECDH

Recently I started studying Elliptic Curve Cryptography and I just loved it. I want to transfer some big data (like 3KB), What is the best method, ECDSA, ECIES, or ECDH (and why)? I am confused, how ...
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### How should I implement a secure recovery of encryption?

I want to create a system to host as securely as possible encrypted data in a way that not even the system can know the content of the data, but that it could be recovered. I would like to know how ...
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### Cloneability of AES-128

I would like to implement an anti-counterfeiting scheme for tools my company manufactures. This would ideally be done via RFID/NFC tags. However, the environment in which these tags operate would ...
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### Does keeping a public key private or using multiple encryption help?

I recently had a discussion with a friend of mine about cryptography. As we are both no experts, I thought that I could better resolve are dispute here. My friend said that when he used public key ...
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### Why $e>n^{3/2}$ prevents Wiener's attack

Here's the Wiener's attack as I understand it. Suppose $n=pq$ with $q < p < 2q$, and $d < n^{1/4}/3$ where $ed=k\phi(n)+1$ and $e < \phi(n)$. \begin{align*} n-\phi(n) &=n-(p-1)(q-1)...
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### Public-key encryption with associated data

In the symmetric-key world, we have authenticated encryption with associated data (AEAD). I'm looking for something similar, but for public-key encryption: public-key encryption with associated data (...
Suppose we have $(n,e)$ and the ciphertext $c$ where the public exponent $e$ is of the same length, 1023-bit, as the modulus $n$. It is also assumed that the factors of $n$ are balanced. The message ...