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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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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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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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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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76 views

Cryptographic equivalent of family coat of arms

As a layman when it comes to cryptography, I have recently been asking myself if there was a cryptographic equivalent of a family code of arms. I'm thinking of something asymmetric, that is future ...
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I need help understanding and answering this question about RSA Enc/Dec [closed]

Let's assume, Alice's public key is ($N = 15,\space e= 3$), private key is ($N=15, \space d=3$). Bob sends message $m = 5$ by encrypting it with Alice's public key. Attacker Eve intercepts that ...
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48 views

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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Difference between Sibling Intractable Function Family and Secret Sharing? [closed]

What is the difference between any Secret Sharing Scheme Link and Sibling Intractable Function Family (SIFF) Link?
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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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1answer
46 views

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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44 views

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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How do pairings behave on G2/twist points off the prime order subgroup?

$\newcommand{\F}{\mathbb{F}}$ Consider the ate pairing defined on a curve $G_1 = E(\F_q)$ and $G_2 = E'(\F_{q^r})$ where $E'$ is a twist of $E$ with the twisting isomorphism defined over $\F_{q^r}$. ...
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How does the key agreement process take place in Virgil E3Kit SDK for end to end encryption?

I'm using Virgil E3Kit SDK to implement end-to-end encryption in my App. Their E3Kit SDK is very effective and not too hard to understand, but I still don't understand how does the key agreement ...
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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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64 views

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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109 views

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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Computational hardness in two different cryptographic problems [closed]

What is computationally hardest, finding the private key corresponding to a given public key, or, finding a pre-image that hashes to a public key for a key pair (any pair) where you control the ...
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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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1answer
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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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Load key “ec256.pem”: invalid format is thrown on trying to generate public key from private key [migrated]

I am trying to generate public/private key pair using ECDSA curve secp256k1 On generating public key from ec256.pem (private key) the following error is thrown "Load key "ec256.pem": invalid format" ...
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man-in-the-middle attack on text-book RSA PKE

I am attempting to solve the following problem: I know the following: 3 messages are being sent between Alice and Bob, all messages are encrypted with the known public key $(d,N)$: Alice sends ...
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1answer
32 views

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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Why public key has two parts in my secure messaging client similar to signal

I am working on a Golang code similar to Signal protocol. I need to modify it. I am confused on tripartite Diffie-Hellman handshake part of code, i.e. why public key has two separate parts as compared ...
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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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2answers
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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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2answers
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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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1answer
103 views

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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1answer
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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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1answer
300 views

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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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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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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1answer
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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 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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Secure multi-party computation for digital signature

Is there any practical algorithm that will allow to use public key cryptography (RSA or ECC) in the following way There are N parties. Up to M are malicious adversaries (were trusted, but got taken ...
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Purpose of the ZKPoPK in the original SPDZ protocol

What is the purpose of ZKPoPK in the SPDZ paper? And will the following can detect the active adversaries in 2 party spdz excluding ZKPoPK step? Each party sends a commitment on his MAC key ∆_i ...
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1answer
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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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1answer
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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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1answer
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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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1answer
114 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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86 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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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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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 ...