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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Encrypting a broadcast message decryptable by a subset of receivers

I wasn't certain how to title this request/problem, but here goes: I'm A, and I want to send a message that is received by B, C, D. Each receiving entity here is part of some set of domains D1, D2, D3:...
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Static vs ephemeral diffie-hellman

I feverishly searched the web and couldn't find a clear explanation about what exactly is "Ephemeral diffie-hellman". Let's briefly recall how diffie-hellman basically works: Bob and Alice ...
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Is blinded mixing possible?

Alice creates ordered set of $N$ public messages $(m_1,...,m_N)$ and sequentially sends them to Bob. Bob evaluates $N$ functions $E_i(m_1,...,m_N)$ (possibly using a secret random value $r$ and/or his ...
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One way shared key encryption with NaCl - is it safe to generate a throwaway keypair for the encrypting party

So, I need users to be able to pass me information that no one else can read, so I've generated a secret key. Using NaCl I create a key pair from that secret key and I share the public key of the key ...
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Algebraic Variants of NTRU

There are a large number of algebraic NTRU variants: for example, in some (such as ETRU), the underlying ring has been changed to the ring of integers of a certain number field; there is GR-NTRU, ...
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Diffie Hellman with Smartwatch

I am trying to reverse engineer the Handshake wit a Smartwatch by sniffing the BLE traffic. There is what I figured out and were able to reproduce: The manufacturer-app requests a random number from ...
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How is the session key more secure than the public key?

From the website of GNU Privacy Guard (GnuPG): If an attacker could decrypt a session key it would only be useful for reading the one message encrypted with that session key. The attacker would have ...
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Why is a hash function required for building Public Key Encryption from a Trap Door Function

This is from Dan Boneh's Coursera Lectures - Week 6 - Constructions. https://www.coursera.org/learn/crypto/lecture/nTRhL/constructions Here he picks a random x from X. And then Hashes X to get the ...
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Recommended length for a nonce in hashed-based authentication

Considering the following variation of the SKID3 protocol (1) $A \rightarrow B: r_A$ (2) $B \rightarrow A: r_B || \operatorname{MAC}(r_B||r_A||A)$ (3) $A \rightarrow B: \operatorname{MAC}(r_B||r_A||B)$...
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Making a secure file sharing scheme usable

I am trying to realize a secure file sharing scheme based on asymmetric crypto. Users will access this via browser. In short, it works like this: Users register and set their username and password. ...
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Deterministic generation of secure private keys from parent private key

is it possible to generate set of child private keys from one parent private key, generated by ECC for example, securely? So that new private key (and derive public key) could be used for encryption ...
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How GGH/HNF public key cryptosystem encryption process works

I'm reading paper Lattice based cryptography which at section 5 page 14 it describes GGH\HNF scheme that i can not quite get it and i need help. The private key is a “good” lattice basis $B$. ...
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Is there a secure way of allowing users of my app to selectively share data from an external service?

Is there a secure way of allowing users of my app to selectively share data from an external service with my app? In order for the users of my app to get their personal data from the external service ...
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What is the need for Diffie-Hellman key exchange when we have asymmetric encryption?

I am new to cryptography and I am having a hard time understanding what is the need for DHKE procedure. I think I fully understand the principle in which it happens and also the mathematics behind it ...
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Encode ASN.1 PKCS#8 Private Key with Public Key and attributes

I'm trying to encode an Ed25519 private key as a PEM file based on this document https://www.rfc-editor.org/rfc/rfc8410#page-7 . I'm using an ASN.1 encoder written in Dart, and I can encode the ...
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More than one private key for RSA

In an RSA-encryption scenario, Bob's public key pair $(n, e)$ is $(143, 43)$. An attacker Mallory tries brute-force and comes to $d = 7$ as the private key. The value of $φ(143) = 120$ is not known to ...
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Decrypting message as MSB in regev scheme

I was watching this FHE video and it define Regev encryption scheme as fallow : kyegen: sk : choose $t = (1,s)^t \in \mathbb{Z}_q^{n+1}$ pk = $A \in \mathbb{Z}_q^{m*(n+1)}$ random except $[A * t]_q$ ...
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Is inverse polynomial in a finite field NP hard?

In ECC we have: if we know $G$ and $P=kG$, it is very difficult to find $k$. I wonder whether or not in NTRUEncrypt: if we know $h$ and $P=rh$, it is difficult to find $r$?
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Finding MSB in RSA

Scenario: Alice and Bob send each other encrypted AES (128) messages. In order to change key, Alice has a public RSA key (2049 bits). Bob has Alice's public key. Bob picks a random AES key, encrypts ...
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I need a pathway for studying Lattice-Based Cryptography

I realize that I need a study pathway for post-quantum cryptography. I started to study post-quantum crypto by reading NIST PQC 3rd-round submissions of the lattice-based schemes (let's start with the ...
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Is there a problem with this specific RSA protocol?

So a protocol uses two random primes $P$ and $Q$ with the equivalent bit length of around 2048 bits, multiplies to form $N$. The encryption function in detail is: $m^e \bmod\ N$ $(\text{512-bit-random-...
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What is the more accurate way of stating the correctness of a PK encryption scheme?

Is it more accurate to state that a public key encryption scheme is correct if for all $m \in M$ and $(pk, sk) \in \operatorname{Gen}(1^k)$ a. $\operatorname{Dec}_{sk}(\operatorname{Enc}_{pk}(m))=m\;$ ...
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I don't understand Digital Signature

Why did we call it digital signature if an attacker can pretend to be Bob? Bob hashes his message, encrypts the hash with Alice's public key, and sends it to Alice with the original message. Alice ...
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Post-quantum asymmetric encryption algorithms

One could use Falcon-512 for establishing a private and public key for an asymmetric context. Whereas in a symmetric context, we could use firesaber/saber/variants in order to obtain a shared secret ...
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Encryption in SET protocol

I have a rough idea of what is symmetric and asymmetric encryption, but I can't apply the idea to the SET protocol (Secure Electronic Transaction Specification), so how the symmetric and asymmetric ...
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How does one associate the actual identity of a person or organization with a decentralized ID?

In SSI (Self-Sovereign Identity), anyone can generate their own DID (Decentralized ID). No authority or authorization is needed to create one. Since a public key pair is associated with DID, the ...
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RSA algorithm implementation

$$m^{ed} \equiv m \bmod n$$ $n =pq$, so by Chinese Remainder Theorem it is equivalent to $$m^{ed} \equiv m \bmod 𝑝, m^{ed} \equiv m \bmod q$$ where $n=p\cdot q$ So how did 2 come from 1 by the ...
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SSL Pinning security: can MitM generate the same public key?

This is a very newbie question. SSL Pinning is "safe" in assumption that only the real server can decrypt the public key. By design, it should be almost impossible to find the private key ...
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Can I base a public-key cryptosystem only on a hash algorithm?

Could I base a public and private key system on just using a hashing algorithm? For example: privKey = sha256( randomGenerator() ) pubKey = sha256( privKey ) Why ...
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What grade of protection does a private key's passphrase provide at best?

Does a passphrase with high entropy provide the same level of security as the private key itself? General scenario: An attacker has access to a private key file that is protected with a passphrase ...
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Zero knowledge proof of symmetric keys and encrypted texts resulting in the same text, if the symmetric keys are encrypted with asymmetric ones

Suppose I have: text T, symmetric keys X, Y encrypted text T with symmetric keys X, Y = TX, TY accordingly asymmetric key Z, used to encrypt X, Y to transmit them to a person. Let the encrypted ...
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Key and Message generated on Client, and validated by Server

(Sorry in advance for my blurry thinking on this: I'm a programmer, not a cryptography expert.) I have a Client/Server web application. The Client needs to be able to alter the local state in ways ...
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Is it possible to retrieve the original hash of a digital signature using a public key?

I am running a server that is receiving packets. Each packet is signed with an RSA 512 SHA-256 digital signature. I have a public key and exponent that I use to verify the digital signatures. I'm ...
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How many public keys and private keys are needed for RSA?

I am just learning about RSA encrytion and I am somewhat confused. First two prime numbers $p$ and $q$ must be chosen and multiplied to get $n$. Then we compute Euler function $\varphi (n) = (p-1)(q-1)...
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Why in RSA do we use mod n rather than mod phi(p⋅q)?

When we pick $e$: $$e \in \{1,2,3,4,...,\phi(p\cdot q)-1\}$$ where $\gcd(e,\phi(p\cdot q))=1$. Similarly when computing $d$ which is the modular inverse of $e$ (the private key) we use the extended ...
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R, S, and Z values in a transaction using the Transaction ID

How can i get the R, S, and Z values and the Public Key using a transaction IDE i have? I knew of a website called 2coin.org which provided these values but now the website is no more active and it ...
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How can JWE support an integrity check given that it uses a public key to encrypt the message?

As far as I know JWE (JSON Web Encryption) supports both integrity and confidentiality. I agree about the confedintiality because only the recepient with a private key can decrypt a message. What ...
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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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Why is this not a viable key exchange algorithm? [duplicate]

I was just wondering why this kind of algorithm can't be used instead of, say, Diffie-Hellman to exchange keys: Alice decides on a key she wishes to share with Bob. Alice generates a stream of bytes ...
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What would be the most recommended AES && RSA Keys for production?

While I am a front-end developer and not a security expert programmer, I am worry about the keys I am using for my AES && RSA encryption. Please help me to understand: Is the following keys ...
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Can the ECDSA still work without present of hashing function? [duplicate]

According to walkthrough steps for ECDSA topic from wikipedia as shown below, What if the impact if we don't apply the hashing function (highlighted in blue in the image) to the raw messages? Although ...
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Using different hashing function with ECDSA

I came across an IC device configuration & security flow and the details are illustrated in image below. I'm wondering must the ECDSA pair with the SHA Hashing function? Alternatively, what if ...
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Prove that you have the data when hash is public

I am designing an online service where users can upload files (3d models) for processing. I want to speed up things when the same file is uploaded by many different users by allowing them to post a ...
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A secure public-key cryptosystem

Is there any public-key cryptosystem that is (possibly) secure against $NP\cap coNP$ adversary?
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Are there any public-key encryption schemes based on DLog?

There are public-key encryption schemes based on many different mathematical hardness assumptions, like the hardness of Decisional Diffie-Hellman problem, the hardness of the Factoring problem, the ...
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Can every signature scheme be transformed into a public-key encryption scheme? [duplicate]

I am reading about Signing vs. Public-Key encryption and a question pop up in mind that is it possible to transform any signature scheme to a public-key encryption scheme?
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How long to reestablish PKI if Diffie Hellman and Factoring are in classical $P$?

Supposing there is a classical (no need quantum) $O(\log N)$ algorithm to factor integers $N$ and supposing there is a classical (no need quantum) $O(\log p)$ algorithm to find $g^{xy}$ given $g^x$ ...
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Zero knowledge proof of Paillier cryptosystem

I have read the paper recently and I am curious about part 3. According to part 3, Bob sends a zero-knowledge proof such that $c_B=b\times_{E}c_A+_E E_A(\beta')$. Then Alice should first decrypt the ...
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testing for a curve25519 public key

The following suggest that it's possible to test 32 bytes mathematically to determine if they might constitute a Curve25519 public key: Bernstein, Hamburg, Krasnova and Lange 2013 https://safecurves....
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Can there be different representation of the same public PGP key?

I have two PGP public key files: File1 was created with Kleopatra / Gpg4win. File2 was created by the following procedure: Import File1 as public key for EmailAccount1 into Thunderbird 78.4.0 Send ...

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