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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Proof by reduction for for digital signature scheme $S_2((sk_0,sk_1), m):=(S(sk_0,m), S(sk_1,m))$

Let $(Gen,S,V)$ be a secure signature scheme (existentially unforgeable under a chosen message attack) with message space${\{0,1\}}^n$. Generate two signing/verification key ...
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Same private key for signing and decryption

I am designing a service which identifies records with public keys. All other fields are encrypted with that public key and protected by a HMAC. For authentication, I am thinking about signing ...
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How to devise cryptographic system with data-sharing ability and password reset

I originally posted this in the security.stackexchange forums but then I was directed to this one which seems more befitting for my question. I am writing a C# .NET application. For my application the ...
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How does CL signature work?

I'm studying the CL signature that how can it works. However, I cannot understand how equation (42) is calculated. What is the last three factors? The value T is as follows: $$T \leftarrow(A')^{\...
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Can we defends against RSA Timing attack when we use java.math.BigInteger.modPow?

I think that Montgomery and sliding window techniques are applied within java.math.BigInteger.modPow (and more specifically ...
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Could someone please explain the implementation of public-private key encryption for storing passwords?

As someone new to cryptography,I have a question about how logins work on websites. I understand mathematically how asymmetric encryption works and how https web requests work to securely send ...
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Which public-key cryptosystems are used the most?

Does anybody know if there is some kind of measure on how often public-key cryptosystems like El Gamal, RSA,... are implemented. Which ones are most common?
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How do NTLMv2 hashed passwords work?

We have an application which embeds NTLMv2 password hashes into its configuration. In attempting to assess the security of this practice, I'm not finding much straightforward information about how an ...
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Authentication using a nonce

For an authentication problem imagine the following scenario with two devices: 1 server 1 client. The client starts a conversation with the server and sends him his public key. All public keys in ...
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What is the code when looking at the LPN problem?

We are given the problem in this question. We know that we have to use the algorithm $A_D$ in order to get $e_i$. Our idea is that we construct a vector $l$ of $l_i$'s by getting $n$ samples from the $...
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How to get fixed m from different pairs of n, e and c in RSA?

In RSA cryptosystem, if I have two (or more) pairs of public key and also the corresponding ciphertexts, can I get the fixed message from them? I cannot think up any good idea for now.
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Can we use HMQV in an asynchronous setting?

Following the HMQV paper, to perform a key-exchange, Alice ($\hat{A}$) and Bob ($\hat{B}$) perform the following: $\hat{A}$ generates the long-term key pair ($sk_A= a$, $pk_A =g^a$) and the ephemeral ...
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Encrypt encryted message vs DS

In digital signature The encrypted message is signed by the sender private key and verify using sender public key. The encrypted message is encrypted with another public private key pair which the ...
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Signing a secret key with ECDSA

Assume Alice and Bob both separately come into possession of the same randomly generated 256 bit secret key. Alice has Bob's public ECDSA key. Alice wants to verify that Bob has possession of the ...
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Are My Answers for This RSA Question Correct?

I am very new to cryptography and so I am looking for feedback on this question on RSA. Please let me know if I have made any mistakes, Thank you! (a). RSA Algorithm: -choose two primes p,q -...
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Is the password based key exchange secure even if the public key is known to adversary?

I am assuming the answer for part 1 to be a "NO" as the adversary knows the public key he can get the password by offline attack IN part 2 : the answer is "yes" as the public key is freshly generated ...
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E2EE encrypted chat where messages are only readable by participants and admin users

As the title suggests, is there a way to have an E2EE chat between two users, and have them be visible later by an admin user. I know this defeats the point of E2EE, but i want to have the messages ...
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Secure asymmetric encryption with 32byte ciphertext

I need securely asymmetrically encrypt the up to 16 bytes plaintext and receive up to 32 bytes ciphertext. I found that ElGamal produces ciphertext that is 2 times keysize. So I would need to use ...
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Protect student log data through public-key encryption and a trustee

I am looking for an GDPR-conform way to log student behavior in an online learning system (Moodle). In the system, students are offered a course to be examined in a field study. According to the GDPR, ...
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Diffie-Hellman + Asymetric encryption kept simple, or alternatives to TLS

I am working on a system that includes our dear friends Alice, Bob, and a server that is only partially trusted. I have spent the majority of the day reading up on various cryptography methods, but I ...
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Unable to determine plaintext from ciphertext

Given the letter-number cipher: a=00, b=01, c=02, etc., encrypt the word 'hi' and decrypt its ciphertext using RSA. The public key is (5,35) and the private key is (29,35). I know that 'hi' is ...
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Encrypt and decrypt data accessible by two users on the web on multiple devices

I am currently building a website where a user will be able to upload a file to my server and another user will be able to download the file. Now i want to add encryption to this with the following ...
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Least knowledge ephemeral PKI?

I'm trying to build a PKI for document signing but only using 2nd party auth and no client persistence. I'm assuming I'd need to use something like a SCrypt key of the user credentials for the user'...
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Fully Homomorphic cryptographic Scheme?

Given two FHE schemes FHE1 and FHE2 in which one of the two scheme is secure and other is not (we have no idea which is secure). Construct a FHE scheme which is secure using the given two scheme.
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Three Pass Protocol Question!

Alice and Bob have agreed to use the Three Pass Protocol. p=1009 Alice chooses the encryption exponent e_A = 101 Bob chooses the encryption exponent e_B = 209 Now Alice and Bob send three ...
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XTZ Private Key

The BIP39/44 off-line tool does not contain XTZ coin. Therefore, I cannot derive (from my 24 words) my ledger nano s private key associated with my Public key for my Tezos account. Is there another ...
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Same ephemeral key for 2 uses

I am theorising an onion routing network, and I have a question about ephemeral keys. This is the basics e2e connection encryption protocol. ...
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Is it possible to generate a membership proof using an RSA accumulator without knowing all the accumulated values?

I am currently learning about RSA accumulators and this was just a question I had since in most available implementations I see in Github accumulated primes are stored in hash tables and they are ...
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Lifting point to quadratic twisted curve

How to lift point to it’s quadratic twisted curve? I use secp256k1. Is the diiscrete log still same? Thanks before
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Computing PGP ed25519 and curve25519 keygrips?

There are public key algorithmic differences for how PGP computes fingerprints and keygrips. For the v4 protocol, fingerprints are not exclusively computed from public keys while keygrips are. RFC ...
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I need two types of easily crackable asymmetric and symmetric encryption

I have a school project in which I'm comparing asymmetric and symmetric encryption. I need two different types of easily crackable encryption, one symmetric and one asymmetric. I am planning on ...
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Define a Decryption algorithm on a given group-based Cramer Shoup lite scheme

I am currently working on public key encryption schemes and I want some help to figure out how decryption algorithms work. Suppose we have a public key $pk = (G,p,g,e)$ with $e \in Z^*_p$ . (where $G$ ...
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How to intuitively realize the Diverse Group System in the Hash Proof System(HPS)?

In the paper Universal Hash Proofs and a Paradigm for Adaptive Chosen Ciphertext Secure Public-Key Encryption by Cramer & Shoup, projective hash family derived from group system can be easily ...
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Efficient receiver determination of public posted cipher

Assume there is a global message board, that people use to send messages to other people. Of course no one else but the receiver should know the content of the message, so senders use asymmetric ...
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Symmetric key crypto secure communication infrastructure

Imagine that public-key crypto stops working. Are there any academic proposals out there that would explain how we could implement commercially viable secure communication based on the current ...
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Where to store public key of an asymmetric cryptosystem?

I am developing an application that uses ECIES encryption and I am currently storing private keys in secure place on each peer and storing public keys in a shared database (accessible by all peers). ...
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Will CT (Certificate Transparency) override the use of CAA and/or DANE/TLSA records?

I'd want to know if some of these competing technologies has more chance to survive. It seems they are thought to solve a similar problem by different manners and I'd want to stick to the most ...
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What is the current state of the Conjugacy Search Problem in Matrix and Permutation Groups?

It results that I have come with a mathematical approach to solve the CSP (Conjugacy Search Problem) where the platform group $G$ is either a permutation group or a Matrix Group. From my part I ...
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Resetting a shared private key

I have a scenario with a user that needs to operate on common data from multiple devices but the link to the server is often offline. Unfortunately in the environment, I trust anything not directly in ...
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Are the existence of secure IBE and secure PKE equivalence?

Of course, if there is a secure IBE (e.g. IND-ID-CPA), then there exist a secure PKE (e.g. IND-CPA). I want to know the inverse proposition is true or not.
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Can Paillier Encryption has independent decryption key?

As Pailliear cryptosystem secret key $\lambda$, depends on primes $p$ and $q$. As $\lambda = \operatorname{lcm}(p-1,q-1)$. I want decryption key to independent from $p$ and $q$. It can be possible ...
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How to get a random point of a specific EC group with cofactor Not-Equal 1?

We got a EC group generated with point G, and the cofactor of E(G) is with the similar size of the Order. Now we need a random point of E(G) and not revealing the "logarithm" of the random point, so ...
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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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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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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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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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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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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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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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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 ...