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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Guidelines for cryptographic key generation

I was wondering whether you know can point me to some general (basic) principles/guidelines one should follow for generating cryptographic keys? I have looked at NIST 800-133, but was hoping for some ...
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Identifying a bad public key

The great thing about public key cryptography is that anyone can generate a keypair, keep the private key secret and publish the public key anywhere they want. This is used in CAs where an ...
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Why isn't ElGamal a symmetric-key scheme?

I was asked about this question by a friend. He considers that Alice and Bob share a secret key s=g^(xy). So why isn't it considered a symmentric-key scheme? ...
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Why Nonces and timestamps are used in Public key authority?

why the nonces(N1 and N2) and Timestamps(T1 and T2) are used in Public key Authority? which of them prevent replay attack?
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Importance of the order of public/private key application to a signed encrypted message [duplicate]

Let's say two users (U1, U2) each have a private key they keep to themselves, and each broadcast a corresponding public key to the world. Let's then say that U1 wants to send a signed encrypted ...
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How can a message encrypted with the public key be decrypted with the private key?

I've been reading about encryption and have a basic understanding of the concept. What I don't understand, however, is how a calculation with one key can result in a number that, through calculation ...
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How to exchange a common key to a group of person using Elliptic-curve Diffie–Hellman (ECDH)? [duplicate]

In ECDH, when two persons want to share private keys, they first select a point $G$ on the elliptic curve and after that, each of them picks a random integer $a$ and $b$, respectively, and multiply ...
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Decentralized / Distributed Private Key Generation between Untrusted Parties?

I found an interesting concept in this paper, page 13, (Link to the paper) called "Decentralized private key generation", as follows: "Decentralized private key generation – Multiple Enigma nodes ...
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Share secret non-interactively in a verifiable way

In an application, I need to share a secret (random number) with a Group of known receivers over a public channel (a Blockchain) but each receiver needs to be able to check that the others received ...
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How to find at least one private key from a large list of compressed public keys secp256k1

Not long ago I saw a discussion on the Bitcoin Talk forum: https://bitcointalk.org/index.php?topic=5060735.msg50736695#msg50736695 Please give advice and working methods? Is it possible to find at ...
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Minimal secure index of quasi-cyclic codes for code-based cryptography

It is well-known that keys (generator matrices) of code-based cryptography are very large for its practical usage. To reduce them scientists propose to use families of quasi-cyclic codes. I remind ...
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Can you compress an elliptic curve private key in half?

According to this, a $n$-bit key offers about $n/2$ bits of security. That got me wondering, can you compress the key in half? At first blush, no, because the key is essentially a random number, and ...
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How to encrypt sensitive files in a business application? Is it needed? [closed]

I'm currently working on a business Java application, and we store sensitive files related to our users. What is the appropriate approach to store them securely? Is it viable to encrypt/decrypt all ...
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584 views

If H(m) = 0 for some m, how can a DSA signature be forged?

If we know for some message $m$ that $H(m) = 0$, how can we forge a DSA signature with only the public key? I got that $g^s*r = (g^x)^r$ where $x$ is the private key, but that's one equation with 2 ...
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cryptographically signed streaming data

On a high level the question is: how does one cryptographically sign streaming data? Here is the context: a number of people are continuously streaming data to me the data is public and does not ...
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RSA: why does $m^{ed}$ equal the original message?

Trapdoor functions are defined as that a secret key reverses the function. It seems to me more that it causes a cycle to repeat, similar to how $n^k \bmod k$, when $k$ is a prime number, equals $n$, ...
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What attacks does future secrecy protect against?

Consider messaging between 2 parties. A sequence of messages are exchanged between the parties using encryption. We consider an attacker that has at a minimum a log of all the (encrypted) messages ...
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What's wrong with RSA and OpenSSL?

We all know that signing a document is to encrypt its hash using signer's private key. https://commons.wikimedia.org/wiki/File:Digital_Signature_diagram.svg I've been searching the web for days, ...
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Using secp256k1 keys for encryption

We are making a system where users can share files with other people but nobody should be able to figure out that all these different files belongs to same user on blockchain. these are the steps we ...
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Choosing K in ECDSA SECP256K1

I am working on a very resource-constrained environment. Using a standard peer reviewed library isn't possible because it won't fit within the RAM requirements of the device (~5K unused ram without ...
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1answer
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Why is encryption slower than decryption in elliptic curve cryptography (ECC)?

While performing encryption using public key and decryption using the private key, I am always finding that encryption takes more time than decryption in elliptic curve cryptography (ECC). It's the ...
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Ciphertext indistinguishability under a noisy channel w/ error correction

The objective is to broadcast information over a noisy digital channel (corruption rate of say, 10-20 %, where bits flip). Assume the broadcasting software is public and there is no possibility of ...
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Zero-knowledge proof for Paillier parameters

For RSA one can give a non-interactive zero-knowledge proof that RSA with parameters $(e,N)$ form a permutation and a proof of knowledge of the associated RSA secret key. For example, such a proof can ...
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What are the inverse operations in elliptic curve cryptography?

Public-private key cryptography is based on inverse operations that use separate input. In elliptic curve cryptography, what are those inverse operations?
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Is it possible to use X.509 for a symmetric-key algorithm?

I read on wikipedia what is X.509: In cryptography, X.509 is a standard defining the format of public key certificates. X.509 certificates are used in many Internet protocols, including TLS/SSL, ...
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find $a$ and $k$ for a given el gamal cryptosystem

I am given this question: Suppose Alice is using the ElGamal Signature scheme with parameters $p = 31847$, $\alpha = 5$, and $\beta = 25703$ Assuming that we have received signed messages $(x_1,(\...
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What is a (smooth) projective hash function?

I recently came across the term "smooth projective hash function", and I see that there are many constructions nowadays that rely on them, especially some PAKE constructions. But, I didn't exactly ...
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How to multiply two Public Keys in Elliptic Curve in Go

I am working on a messaging client similar to Signal. I am stuck on implementing Tripartite Diffie-Hellman handshake in which three DH exchanges are combined to authenticate both parties and produce ...
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Are the first 4 bytes of a Ed25519 public key random?

We are using the Ed25519 signature scheme (which uses Curve25519). A key pair is generated by generating the secret key from random data and then computing the 32-byte (256-bit) public key from said ...
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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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639 views

Is it possible to implement the Signal Protocol without a server?

My question is regarding the Signal Protocol[1]. Is it possible to implement the protocol securely, without a server? (I have no particular motivation for the question other than to understand better ...
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Zero Knowledge for Low Entropy Witness

For any PPT prover ($p$) and verifier ($v$), imagine I have a low entropy witness, say smaller than $2^8$. Now, let us say I have a dlog statement in the form of $y = g^w$. Theory says I could use a ...
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RSA-OAEP Padding scheme

Honestly I'm really confused about padding in RSA scheme. I don't study computer science, and I'm a beginner learning cryptography (self-taught). Can anyone give me suggestions?
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Mathematical explaination of file encryption for multiple persons with multiple keys

Let's say I want to encrypt a document which only can be read by John, Mike, and Dave. This can easily done with PGP/GPG: Import John‘s, Mike‘s, and Dave's public key Encrypt the document using those ...
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What is this called: encrypt $X$ with key $E$, decrypt $X$ with key $D$?

I am a software developer interested in developing an application with cryptography. I can explain what I want to accomplish, but I do not know the technical terms for the cryptographic functions I am ...
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How are the primes used to generate RSA keys?

I am confused about how keys in RSA asymmetric encryption are generated and what the implications for open communications are. Textbooks say the one-way function is merely two primes (with some ...
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Is there a symmetric-key algorithm which we can use for creating a signature?

I know that in the asymmetric-key algorithm the RSA signature exists but what about the symmetrical ones?
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Using NewHope key exchange between browser and BouncyCastle implementation

I have been looking around with some new Post-Quantum secure key exchange methods, such as McEliece, NTRU and SIDH, but none of these seem to be working nicely between the browser and the BouncyCastle ...
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Curve25519's Y coordinate of Basepoint origin

The paper High-speed high-security signatures by Bernstein et al. introduces the Edwards curve Ed25519. Concerning the base point $B$, it says that $B$ is the unique point $(x,4/5)∈E$ for which $x$...
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What is the benefit of zero knowledge identification (Fiat Shamir) over a standard digital signature?

Let's say there is a public key $v$. Peggy has to prove to Victor that she has the corresponding private key $a$. Of course she doesn't want to disclose $a$ to Victor, but just to prove that she has ...
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Isogeny of elliptic curve

If we have two elliptic curves $E$ and $E'$ and the points of both elliptic curves are same. Then all the points of $E$ map to all the points of another elliptic curve $E'$. For example $E$ has ...
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What is the relationship between attribute based encryption (ABE) and access control?

So if possible could someone tell me or at least recommend a book.
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Is there a feasible way to generate an RSA key manually the same way as it is for an ECC one?

In elliptic curves, a private key is just a random number, and one relatively small compared to other crypto systems (256 bits for ECC vs 4096 bits for RSA for example). Suppose I don't trust ...
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Audio Files and Digital Bearer Instruments

Is it possible to combine Audio Files and Public Key Cryptography creating a Digital Bearer Audio File that is in complete control of the owner who would then have the ability to grant access to ...
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How does encryption work in elliptic curve cryptography?

So I think I understand a good amount of the theory behind elliptic curve cryptography, however I am slightly unclear on how exactly a message in encrypted and then how is it decrypted. So my ...
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63 views

Difference between Identity-based encryption and multiple key-pairs of public key encryption?

What is the difference between Identity-based encryption and multiple key-pairs of public key encryption scheme?? Suppose trusted key generator generates a bunch of public and private key pairs $(k_{\...
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Diffie-Hellman: Recommendation of the base size?

Based upon choosing a prime $p$ of recommended length and $N=2p+1$, where $N$ is also prime, and $a^2$ is not congruent to $1 \pmod N$, and $a^p ≡ 1 \pmod N$, I believe you can rely upon $a$ as having ...
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Why do we need a digital signature?

First of all, I want to say that I'm totally new to cryptography. I searched on crypto stackexchange but couldn't find the answer to the following question.(probably because it's easy, but I still don'...
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Why doesn't the formula work when checking two ECDSA signatures?

There are two generated ECDSA signatures X - Private key S = ((Z + (X * R)) / K) mod n S` = ((Z` + (X * R`)) / K`) mod n G - Base point, of order n; ...
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Can deterministic ECDSA be protected against fault attacks?

In a paper by Barenghi and Pelosi, it was described that fault attacks could be used to derive the secret key when using deterministic ECDSA as described in RFC6979 by @Thomas_Pornin Deterministic (...