# 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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### Given a 'good' basis for a lattice, how can we solve the CVP?

I'm doing a little bit of reading about lattices. I read that if we can find a 'short' basis for our given lattice, we can solve CVP and SVP very efficiently. However, the paper didn't describe an ...
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### Zero knowledge proof for Paillier addition under multiple keys

Suppose $m_0, m_1, m_2 \in \mathbb{N}$ such that $m_0 = m_1 + m_2$, $m_i > 0$ (none of them can be 0 or lower) Under a Paillier cryptosystem, set $e_0 = E(m_0, r_0)$ for a public key $(g_0, n_0)$ ...
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### What public-key encryption protocol can use the same key pair as ECDSA?

Assume we wanted to use the same ECDSA public/private key pair (drawn for standard ECC parameters, perhaps P-256) for both its intended use (public-key signature), and for public-key encryption; this ...
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### Cryptomania and NP $\cap$ co-NP

Cryptomania is usually presented as the Impagliazzo's world, which gives us public-key cryptography under the assumption that trapdoor OWFs exist. For purposes of constructing public-key cryptography ...
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### How did G.H. Hardy's work contribute to today's public-key cryptography?

I know that Hardy's work in number theory was used by Clifford Cocks in 1973 to develop the basis for public-key cryptography. What specifically was this work, and how is it used today in ...
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### Have time-release servers been implemented?

Conceivably, Alice could release a public encryption key and promise to release the private decryption key on a certain date. That way anyone could use that encryption key, combined with others from ...
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### Key strength comparison: symmetric key vs RSA/DH key

I came across different reputable sources quoting different equivalent symmetric key strengths for RSA/DH keys. This NIST paper (page 67) states the following offer corresponding security strenghts (...
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### How can a public-key encryption scheme be used to construct a commitment scheme in the CRS model?

For a PKE scheme $(Gen, Enc, Dec)$, the most 'obvious' idea is to commit to an encryption of a bit and in the reveal phase maybe send $r_g$, $r_e$ where $r_g$ is the randomness of $Gen$ and $r_e$ is ...
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### What are some examples of out of bound channels that work over the Internet in practice?

If I want to verify a public key (be it RSA, PGP, etc.) with another client over the Internet only, what are some viable out-of-bound channels for verification? Which channels have been used in ...
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### Recursive RSA encryption

I have a ciphertext $C$ encrypted with public key $pub_C$, which contains ciphertext $B$ and $pub_B$, $$C= E_{pub_C}(B\mathbin\|pub_B)$$ Ciphertext $B$ is encrypted with $pub_B$ and contains $pub_A$ ...
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### Verify commitment C commits to the same value that E encrypts

Given the following (using additive notation): $G$ - generator of an elliptic curve group of order $q$ $s$ - secret drawn uniformly from the distribution $1..q$ $k$ and $K$ - a private public keypair ...
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### Asymmetric encryption, multiple recipients, traitor must share private key

Is there an asymmetric encryption scheme, or public-key encryption, where multiple recipients can access the data, but in order for one of the recipients to leak the key to the data, they would need ...
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### A proposal for randomization of Niederreiter cryptosystem

The Niederreiter cryptosystem is a public key cryptosystem using Goppa code. Unfortunately it it is insecure unless it is a binary code. So I thought I could insert random linear codes into randomly ...
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### Security of an Elliptic Curve Public Key with a "Small" x-coordinate

Consider an elliptic curve over a finite field $F_p$ with $p$ prime and order $n$. Let $Q$ be a generator for the field. Given a public key point $P = aQ$, suppose we have an algorithm that finds an ...
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### How do pairings behave on G2/twist points off the prime order subgroup?

$\newcommand{\F}{\mathbb{F}}$ Consider the ate pairing defined on a curve $G_1 = E(\F_q)$ and $G_2 = E'(\F_{q^r})$ where $E'$ is a twist of $E$ with the twisting isomorphism defined over $\F_{q^r}$. ...
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### Quantum Resistant Algorithms and types: PKE vs PKEs vs KEM vs KEMs vs DSS

I am trying to wrap my head around the second round Quantum Resistant Algorithm candidates currently under the NIST PQC Effort. Can someone verify if the following is a correct summary of the 17-...
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### Derivable encryption key - BIP0032 parallel

I wish to find an asymmetric encryption algorithm that supports key derivation, BIP0032 style. Meaning that I have some SEED [PRIV] and I give someone some public data [PUB], then given new public ...
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### Concept for a RSA "repeater". Is it sensible?

I have been using RSA signed/encrypted mailing a lot recently. Naturally, I wanted to use RSA mailing also on my phone, not only on my computer. However, I feel uneasy having my private key on my ...
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### GPG Sub Key Renewal Questions

Last year, I followed this guide to create two GnuPG Smart Cards; one card with the Primary Key and the other card with the Sub-keys. I noticed that the sub keys were close to expiring so I renewed ...
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### What standards of ECC point compression exist?

The method that I used before to decode EC point from public key led me in a dead end. So I just want to know what yet I could try. I've got a public key that I don't know how to decode and I am ...
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### Where shoul I store private/public keys and how should I share it?

I'm new in terms of encryption and I have to encrypt the data between two Java Spring applications, one have serves as MVC framework and other as Web Service, I'm implementing an asymmetric encryption ...
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### Curve25519 / Ed25519 - Generate a private key from this term

I have 2 key pairs $(x_1, y_1)$, $(x_2, y_2)$. I also have $a =$random 256-bit array and $b =$256-bit of defined values from me. I know the values for $(x_1, y_1)$, $x_2$ and $b$. But I miss the ...
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### P2P Website/Database Encryption Process

Sorry if this doesn't fit the guidelines, but I believe it is a conceptual issue that is not opinion-based and can be reasonably answered in a single authoritative answer (I'm also struggling to find ...
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### Asymmetric encryption property required in an authentication protocol

We want to choose an asymmetric encryption scheme for use as follows: A device holds its private key, with the corresponding public key known and trusted by all. The device also holds a small $b$-bit ...
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### Can proofs be relayed to derived keys?

I am aiming to find out if this problem/puzzle can be solved with cryptography at all. Say there are these two parties: Subject S which has a master private/public key pair (MPriv, MPub) and a set of ...
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### Encryption design for user data with service access

I'm looking to provide users with a way to give a service sensitive information, which the service can freely use up until the user decides otherwise. I want to encrypt the data at rest (and of course,...
The original Station-To-Station (STS) protocol is as following: Alice : Generate $x$ Alice → Bob : $g^x$ Bob : Generate $y$, compute $g^y$ Bob : Compute $K = (g^x)^y$ Bob : Sign-then-Encrypt \$(g^y, g^...