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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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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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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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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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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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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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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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Post-quantum candidates for asymmetric cryptography with small key sizes

One of the things that I have come to like about elliptic curve cryptography is that the key only needs to be twice as long as the desired security level. That's a very small expansion (I also like it ...
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1answer
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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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2answers
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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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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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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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1answer
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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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Asymmetry between public key and private key: digital signatures use the private key for “encryption”?

I have a misunderstanding concerning public key cryptography...would be very helpful if you answer the questions... Digital signatures: You use your private key for "encryption" and they use your ...
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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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2answers
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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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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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How does one verify a GPG/PGP key revocation?

After revoking a key and sending the revocation to MIT's keyserver, I noticed that the key is listed as such: ...
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5answers
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Does RSA work for any message M?

I decided to read the original RSA paper A Method for Obtaining Digital Signatures and Public-Key Cryptosystem because of a question I had about RSA (which is not the question I'm about to ask, but ...
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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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1answer
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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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1answer
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How is the message digest related to Signatures and Encryption?

I was studying about 'Data Security' and I found out this one thing confusing. What is a message digest? I got it is the hash of the message. Is the message here referring to the plaintext or cipher ...
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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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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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2answers
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ECDSA vs ECIES vs ECDH

Recently I started studying Elliptic Curve Cryptography and I just loved it. I want to transfer some big data (like 3KB), What is the best method, ECDSA, ECIES, or ECDH (and why)? I am confused, how ...
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2answers
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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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1answer
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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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1answer
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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1answer
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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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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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4answers
851 views

Where should I store the private key (RSA) in a web application?

My web application receives encrypted data from another server encrypted with RSA keys. Where should I store the private key (RSA) in a .NET web application (Windows)? It seems that putting in it in ...
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1answer
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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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1answer
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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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278 views

RSA - factorizing $N$ to get $p$ and $q$

I need to decrypt a message encrypted using RSA. I only know the public keys $n$ and $e$. I need to get the private key $p$ and $q$ in order to get the decryption exponent $d$. Now to do so, I know ...
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1answer
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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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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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2answers
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What's the fundamental difference between Diffie-Hellman and RSA?

What is the difference in the purpose of DH and RSA? Aren't they both public-key encryption?
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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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0answers
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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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2answers
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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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1answer
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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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1answer
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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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1answer
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The goal, the method, and the interface of the signcrypt primitive.

Some time ago, I proposed making the site more educational by teaching correct cryptographic programming. The proposal had had somewhat good reception, but was met with cold ice as there had been ...