# Questions tagged [public-key]

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 private.

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### Are there groups where the computational Diffie Hellman problem is easy but the discrete log problem is hard?

I know that there are elliptic curve groups, used in pairing-based cryptography, where the decisional Diffie Hellman problem (ie. given $g$, $g^a$, $g^b$ and $c$, determine if $c = g^{ab}$ is easy but ...
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### In a lattice, how can one define a good basis and a bad basis?

When it comes to lattice based cryptographic systems, all the literature talks about, good bases and bad bases. How does one define what a good basis is and what a bad basis is?
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### RSA: revealing the modulus factorization by choosing a bad message

I started reading the book Cryptanalysis of RSA and its variants by M. Jason Hinek and I stumbled upon a phrase that intrigued me: plaintext messages that are relatively prime to the modulus (i.e....
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### Is a private RSA key vulnerable to a chosen plaintext encrypted with that private key?

I grasp that having known plaintext encrypted with the public key doesn't provide a means of discovering the private key (that being the whole point...). But if one were in a situation where they ...
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### Can I switch out a private RSA Key, so that when decrypting a message, it is decrypted to a different message?

Here's a task I've been struggling with: Say I have an encrypted message $c$, and a desired plaintext $m$. How can I define a valid private RSA Key $(d,N)$, so that $c^d \bmod N = m$ Note that the ...
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### Single Ciphertext which can decrypt with multiple keys

Say we have a public key system where we have 2 users, Alice, and Bob each has a public and private key. We also have a publicly available server which stores a message. I want to encrypt this ...
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### Using public key cryptography with multiple recipients

I have a message that I want to send to multiple recipients. Can I encrypt the message separately with each of the recipient's public keys, then send the message thus encrypted to the respective ...
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### How do public key rings work in cryptographic applications?

I am wondering if there are any links to articles or resources available online, or explanations that you can give, that would help me to understand the concept of a public key ring, and why I might (...
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### Raw curve25519 public key points

I'm trying to understand curve25519, and ECC public points. I'm playing with Minisign, to better understand the fundamentals of ECC. Minisign uses curve25519 and outputs public keys as base64 ...
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### What kind of attack could one perform if you generate private keys using SHA3(master_key || nonce)?

I'm aware HMAC is more appropriate than SHA3(master_key || nonce), but I do not understand what kind of attack could be performed against that strategy. How could ...
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### Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?

With a standard authenticated encryption scheme (or MAC), Alice and Bob share a symmetric key. When Alice sends something to Bob, Bob can check that it is authentic. At that point, Bob can deduce ...
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### What other one-way functions are used in cryptosystems?

For RSA and El Gamal (and most other public key cryptosystems), one of the key ideas is that factoring and finding discrete logarithms are hard. There are other systems that rely on certain properties ...
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### Does Cramer-Shoup allow re-randomization?

Is it possible to re-randomize a ciphertext with the Cramer-Shoup System? I have some Cramer-Shoup ciphertexts and i want to re-randomize them, so they look different and are unlinkable to there ...
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### Client and server using same SSL certificate - any issues?

I'm working on software where multiple components will communicate with each other using SSL. There would be one central component acting as a server, which would also require the clients to present ...
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### Get RSA PlainText without Knowing Private Key

If I have an algorithm,RSA-Crack(), that, for a given RSA public key (n,e), is able to decrypt 1% of the messages encrypted with that key (without knowledge of the corresponding private key).Can there ...
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### Has any alternative to RSA and Discrete Logarithm been standardized for deployment?

Suppose RSA and Discrete Logarithm over any group (including elliptic curves) gets broken what other schemes we have for DEPLOYMENT IMMEDIATELY do we have to rescue the internet from collapse? So ...
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### Layered encryption in mixnets with post-quantum cryptography

I am trying to implement a mixnet using post-quantum public-key crypto. Each message may be encrypted by up to 10 levels of public keys, shuffled, before the layers of encryption are stripped off one ...
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### Key Exchange & key Distribution in symmetric key cryptography

I want to know whether there is a difference between key exchange & key distribution in private key cryptography as well as public key cryptography? or is it the same term?
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### Can an U2F public/private key-pair for signatures be used for encryption?

I understand that this might be more a process question: Given a U2F device which supports signatures using ECDSA public/private key pairs, is there a way to use the signing function of such a device ...