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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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Looking to verify my understanding of RSA math

I want to explain RSA to a programming audience with no cryptography background and I want to be sure my explanation is correct. The goal is to help them understand how RSA works under the hood. You ...
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Reason for including the public key of the key agreement in the KDF

I found the following text when looking up KDFs: In comparison, the so-called DHAES mode in IEEE 1363a mandates to use the binary representation of the sender’s public key as an input parameter. ...
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Can we build a zero knowledge mapping using public-key encryption?

I'm trying to understand if this design is possible. I want to build a mapping that is zero-knowledge, between a (pubkey, proposalId) => bytes form, without ...
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what is the name of the following protocol? [closed]

I have 2 parties (A and B) who don't trust each other. My goal is to design a protocol so I ensure they trust each other. I'm thinking of a name to such protocol like "with No A2B Prior Trust"?
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In NIST modulus and key size recommendations is `group` equivalent to modulus and `key` equivalent to exponent?

Looking at the following NIST recommendations for a discrete logarithm, for 2016-2030 and beyond they list 3072-bit number for the group and 256-bit for the ...
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149 views

Diffie-Hellman private key recover with non-prime modulus

Say we have a classic Diffie-Hellman key exchange. We have the following parameters of a public key: p,g,y Where $p$ is the modulus, $g$ is the base, $y$ is the ...
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51 views

Find hash and signature algorithms used in an X.509 certificate signed with RSASSA-PSS

I'm trying to understand the new PSS scheme, but having trouble figuring out how to parse it properly. When receiving a certificate with OID of RSASSA-PSS, how can I know which hash and signing ...
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Is it necessary to study the KPA security for asymmetric encryption algorithms in addition to CPA security? [duplicate]

In a KPA attack model, an adversary $\mathcal{A}$ has access to pairs of messages $(m_i,c_i)$ which are encrypted using some asymmetric algorithm. However, assuming either El-Gamal or RSA algorithms, ...
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Mitigating leakage of asymmetric encryption scheme leaking the length of plaintext

Asymmetric encryption schemes do leak something about the encrypted plaintext: the length of the plaintext. How can this be mitigated? My solution: Padding the plaintext with some string of the ...
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54 views

How can you derive a P-256 public key from the X and Y points

Deriving a secp256k1 public key is also possible. For whatever reason, I'm only being provided X and Y, not the public portion. I just need to get the binary representation of the public key given ...
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37 views

Finding a secret key corresponding to a public key

As far as I know, a secret key corresponding to a given public key is not unique. So, for example, there are actually multiple secret keys that can produce the same digital signature under RSA ...
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If finding a private key from a public key is [co-]NP-complete, does NP=co-NP?

In a given public key cryptosystem, if the problem of determining the private key from the public key is NP-complete or co-NP-complete, does that imply that NP = co-NP? Complexity theory is ...
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Private key which becomes invalid after specific timestamp

Sorry for my dumb question, as I'm not crypto guy. Is there any algorithm, which allows to encrypt some message with the public key, but the associated private key is only valid for specific period ...
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Could any one suggest alternative Zero knowledge proof protocol to Schnorr protocol ZKP?

I read that Schnorr protocol cannot be proved zero knowledge on that link: Perfect zero knowledge for the Schnorr protocol? Could any one suggest alternative Zero knowledge proof protocol so a prover ...
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Does public key encryption support a large message size? [duplicate]

I'm somewhat new to encryption. I see that the actual RSA sizes are 1024 and 2048? Can those key sizes support data blocks of 128 MB?
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Python, Encript a message with two different public keys. (Crypto.PublicKey ) [migrated]

as a title I would like to use python to encrypt a message with two different private keys. In this situation I am using a module called Crypto.PublicKey . In the following code, I can do the ...
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Does libsodium sealed box leak key ids?

I am using python and libnacl, which is a libsodium wrapper, to develop an application where users can deposit encrypted data. Alice uses ...
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1answer
25 views

Give a CPA-attack on Elgamal when used with $\mathbb{Z}_p^*$

We know that if the decisional Diffie-Hellmann problem is hard then the Elgamal encryption is CPA-secure. One show that if the chosen group is $\mathbb{Z}_p^*$ then the decisional Diffie-Hellman ...
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Is it possible to derive a public key from another public key without knowing a private key (Ed25519)?

I have a following use case: User has his master public (sk) - private (pk) key pair (Ed25519). In DB we store a public key. Is ...
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Are all block and stream ciphers symmetric?

I'm trying to categorize my knowledge. Can I place block ciphers and stream ciphers under symmetric with RSA/DH under asymmetric?
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Understanding Public key and Private key

I try to understand the private and the public key concept, and need some validation about my statements: If I encrypt a message with public key, I can only decrypt with private key. If I encrypt a ...
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43 views

Understanding TLS certificate

I'm newbie in the word of TLS, and need some verification about my picture. I can use TLS with 3 or 2 participants: 3 participants: Client, server, CA (certification authority). The CA is where the ...
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McEliece cryptosystem

There is something intriguing me about this cryptosystem. That is : Let $(S, G, P)$ be the secret key: $S$ : invertible matrix $G$ : generator matrix for some linear code $C$ $P$ : permutation ...
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Why is a smaller value preferred for the public key in RSA?

For my practice implementation of the RSA cryptosystem I use a random value generation function such the value of public key e holds: The public exponent $e$ and the modulus $n$ should be $e<\phi(...
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48 views

Can you construct a key agreement system from public-key-encryption system?

Can you construct a key agreement system from public-key-encryption system? If so, how? What about vice versa?
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How does openssl signature verification work?

I would like to know how openssl verifies a digital signature? I know that it uses this command to verify a signature: ...
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What is the difference between $\bmod{p - 1}$ and $\bmod p$

I have a doubt in my research work, can anyone tell me; What is the difference between $\bmod {p-1}$ and $\bmod p$
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Temporal or spatial digital signatures

Digital signatures allow authentication of content based on a secret held by the signing entity. Are there any existing schemes, proposals or even services for letting "location" or "time" sign the ...
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35 views

ElGamal variant

I came across this problem, while currently reading "Introduction to Modern Cryptography" by Katz and Lindell. I am new to crypto and just trying to go through the book and solve the exercises, ...
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1answer
73 views

Can POS devices really generate random numbers?

I am doing an implementation of a system designed by a payment company and I am a little skeptical about the way they have designed the end to end cryptography. The system is as follows: There are ...
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48 views

Simple but secure method to share secret (128 bit AES key) though an untrusted relay

I am creating an end-to-end encrypted group messenger, and am looking for a way for online members of the chat to a arrive at a shared secret that can be used as a cryptographic key. This will ...
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Security of the Needham-Schroeder public key protocol after a minor adjustment

I'm preparing for a computer security exam by going through some past paper questions. And I came across this particular one that I could not answer: We have the Needham Schroeder Public Key Protocol:...
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Are compressed pairings used for Barreto-Naehrig curves in practice?

In 2009 Galbraith and Lin wrote the article "Computing Pairings Using x-Coordinates Only" https://link.springer.com/article/10.1007/s10623-008-9233-3, where they proposed to compute pairings on ...
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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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How many keys in a Hybrid Cryptosystem?

If symmetric cryptosystems have $C^2_n$ keys, and asymmetric systems have $2n$ keys, how many does a hybrid system have? This was in an online quiz from school Company A is considering to adopt ...
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Is it acceptable to add a setup algorithm in the public key encryption?

I saw in the paper How to Use a Short Basis: Trapdoors for Hard Lattices and New Cryptographic Constructions at page 29 that key generation algorithm of PKE can use a common random matrix $A$. Is it ...
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Verifying valid public key and finding private key? [duplicate]

A naive user of RSA has announced the public key $n = 2903239, e = 5$. Eve has worked out that $n = 1237×2347$. Verify that the public key is valid and explain why the private key is $d = 2319725$. [...
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Does Elliptic Curve Integrated Encryption Scheme (ECIES) provide IND-CCA2 security?

I am looking for a faster alternative to RSA with OAEP as a IND-CCA2 public key scheme. Elliptic Curve Integrated Encryption Scheme might be a candidate, but I am not sure if it provides IND-CCA2 ...
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How to create a private key using $n,e,d,p,q$ where $n$ is prime

Someone has incorrectly created a public/private key pair where $N$ (modulus) is a prime number. This makes $p$ and $q$ trivial as they they are $n$ and $1$. $d$ is solved from $d \cdot e = \bmod (...
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zero knowledge proof of encryption

I am trying to see if there is a way to prove that a ciphertext c was encrypted under a given Public Key, Pk, without revealing the plain text message m.
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Rolling Code via Encrypted Index vs Pre-Generated Keys

I am planning on designing a system that needs a password to be operated, using a rolling key. Now I am facing two options, as far as I am concerned: Having an index saved, which will be incremented ...
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55 views

Definition of Short Authentication String

I am studying for my cryptography final and I passed by the following term: short authentication string. Please, can anyone explain it to me, thank you very much.
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71 views

Comparable or partially homomorphic public key derivation for signatures?

Are there any public key signature schemes that can be compared blindly or partially homomorphically based on the private key without knowing the private key? Example: let's say I derive a public key ...
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58 views

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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Digital signature

I learned that a digital signature is encrypted using private key and is decrypted using public key. How does the verifier gets the public for verifying the signature? If a person has to request ...
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1answer
51 views

Public key on Server Key Exchange Generation vs Public key on Server's Certificate

To understand the distinction between TLS 1.2 and TLS 1.3. I am stuck in the past understanding for TLS and the current reference I am studying: As I know certificate goes with owner's public key, ...
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179 views

Creating multiple “public” keys from one private key

Is it possible to create a public key out of a private key, then create another public key from the first public key. And treat the first public key as a private key (So you have two levels of private ...
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616 views

RSA using 2 as a public exponent

I'm failing to see why 2 can never be used and what weaknesses would be associated with doing so. There's a similar question asking why it has to be in the form of $2^n$+1 but why not $2^n$
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Pseudonymous publication of a series of texts online when a bad guy is expected to join in with fakes: will this approach to PGP verifiability work?

Alice wishes to publish under a pseudonym a series of texts online. She expects the texts to circulate, and she will not include any way of contacting her. Bob will not know the identity of the ...
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90 views

Why ECDSA has its form?

According to Wikipedia, if Alice wants to sign some message, she computes $s = k^{-1} (z + r d_A)$ then sends $(r, s)$ to Bob. I don't understand why they use this particular formula $s = k^{-1} (z + ...