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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Determining the algorithm used to generate a digital signature

I have a string "abcd pqrs". This string is digitally signed with an X.509 certificate (with its private key) and it produces a signature. From the signed string, is it possible to find out what ...
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How to construct the blind factors in practice?

I'm Implementing a protocol that uses masking techniques (or blinding factors), so we can mask a value $y_0$ as $m_0=y_0 \cdot r_0$ where $y_0 \in \mathbb{Z}_p$ and $r_0 \stackrel {R}\leftarrow \...
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Zero-knowledge commitment verification

Assume everything takes place in a prime field. Given the following: $g$ - generator $s$ - secret $E(K, m)$ - a public-key encryption function using public key $K$ and plaintext $m$ The ...
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53 views

Homomorphic Public/Private Key Encryption Scheme for Floating Numbers

Is there any public/private homomorphic encryption scheme that directly works on floating numbers or vectors of floating numbers? In our application, we want to find out if $$v_1 \approx v_2, \qquad\...
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Multiple sender single receiver Encryption

I had this article given to me by my teacher, and I would like to enhance it. It's titled Modified El Gamal Algorithm for Multiple Senders and Single Receiver Encryption. I planned on having the ...
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asymmetric encryption with rekeying in an untrusted environment

Alice can retrieve asymmetric encrypted messages (let's call one of them C1 and the Message itself M) for her from an untrusted environment (let's call it Eve). She owns her private key K1 and has ...
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How do I calculate key rotation schedules?

tl;dr: How do I formulaically determine key rotation schedules for different kinds of keys and use cases? The organization I'm a part of for utilizes both symmetric and public/private key encryption ...
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34 views

Asymetric encryption, multiple recipients, traitor must share private key

Is there an Asymetric encryption scheme, or public key encryption, where multiple recipients are able to access the data but in order for one of the recipients to leak the key to the data they would ...
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58 views

I need to send 16 bytes using ECC keys on a resource-constrained device

I have a system where a resource-constrained device has to send 16 bytes. It has its ECC key pair, and a peer's Public ECC Key. We're using the p256 curve. The device also has an AES-128 hardware ...
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How can I prove that the plaintext of an elgamal ciphertext is the discrete log of an element?

Is there any (efficient) method to prove that the plaintext of an ElGamal ciphertext is the discrete log of an element? In the scenario I concerned, I have an El Gamal key pair $(pk, sk) = (g^y, y)$....
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Looking for commutative asymmetric cipher for data matching

I need some crypto operation for matching data privately between two peers (let say Alice and Bob). Alice should be able to encrypt her data with Alice and Bob public keys and pass the cipher text to ...
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47 views

Is there a public-key system that can chain?

Does there exist any asymmetric cryptosystem that has the following properties: If I know somebody's public key PBK_1 and my own key pair (PVK_2,PBK_2), I can construct a new public key PBK_3 such ...
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RSA How to find the exponent ($e$) of the Public key with the values $p$ $q$ and an example are given

I'm wondering if it's possible to find the public exponent ($e$) with an example and the (rather small) values of $p$ and $q$ given. Currently the only option I found is bruteforcing this value, but ...
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ECC with 512bit compatible curves

I understand that given solutions for solving a discrete logarithm problem are on the order of 𝑂(2𝑛/2), ergo, 256bit private keys based on 25519 or secp256k1 have an effective bit strength of ...
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How does the KeyGen of Merkle's improvement of Lamport's OTS work?

In his paper [1] on page 17 and 18, Merkle proposes an improvement on Lamport's OTS by only signing the 1's in the message in combination with a checksum of the amount of 0's in the message. I get the ...
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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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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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71 views

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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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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23 views

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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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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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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TPM 2.0 Reissued EK Cert

Unlike the TPM 1.2 module, the TPM 2.0 specification allows the platform user to create own ...
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104 views

Security of BLS under additional information on the secret key

Question A Is the BLS signature scheme still secure if an adversary in addition to the public key $ pk = g_2 \, sk \in \mathbb{G}_2 $ also obtains additional information on the private key $ sk $, ...
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Private Key Sharding - How is it Secure in a Distributed Network?

In a Distributed Network in order for a private key not to be compromised sharding will have to take place off the network, correct? If so: Why is it when a Distributed Network shards private keys ...
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Can one design an asymmetric encryption scheme based on any secret sharing scheme? Are they that closely related?

I've seen both asymmetric encryption and secret sharing schemes based on graph 3-coloring, and I'm curious if this is a coincidence due to some peculiar property of graph 3-coloring alone.
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ECC Curve25519: How to generate this kind of private key? / Strange key exchange mechanism

I'm currently reverse engineering a program that uses Curve25519 key exchange in network communication. I have only a basic understanding of ECC, so maybe this thing just seems strange to me. The ...
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How to define a FHE scheme whose plaintext space is infinite using boolean circuits?

There are many kinds of fully homomorphic encryption scheme by using boolean circuits. And the plaintext space $\mathcal{P} = \{ 0,1 \}$. If there is a -bit FHE scheme, we can construct a FHE scheme ...
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47 views

Seeking Fast Bloom Filter for Anonymous Address

I had an idea to use something like public message boards to pass secrets anonymously and non-interactively (similar to TV/Movie Trope : http://tvtropes.org/pmwiki/pmwiki.php/Main/PublicSecretMessage )...
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Why only ABE is used in ABAC

Why ABAC access control model uses ABE not RSA or any other public key cryptography? Moreover what is the relation of ABAC with public key cryptography (ABE/RSA)?
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ECDSA: Is it possible to generate from known signature (Key, message) valid signature (-Key, message)?

Let Alice has private key $R_1$ and known to Bob public key $P_1$. She generates signature for some message $M$ and shows it to Bob. Could Bob generate signature for the same message $M$, but for ...
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Any algorithm with a pair of master keys and multiple pairs of subkey for a secure key escrow?

Note: This question looks like my other question — Any algorithm with a master key for decrypting private key encrypted messages? — which is perfectly answered by @real-or-random, but this one is ...
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Benefits of using SSL certificate over a raw key pair for non-browser use?

For applications not involving CA signed certificates – or web browsers for that matter – it would seem to be easier to use a raw key pair if possible, rather than deal with potential formatting ...
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How does the authd protocol work?

So far, I have been able to research on what it is: authentication; authorization; using resource authd. I still have not come across a definitive answer or ...
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135 views

Using NewHope key exchange between browser and BouncyCastle implementation

I have been looking around with some new Post-Quantum secure key exchange methods, such as McEliece, NTRU and SIDH, but none of these seem to be working nicely between the browser and the BouncyCastle ...
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201 views

BLS aggregate signatures for relay node non-interactive incentive accounting

This is a practical application of cryptography question and I hope this is the right place to ask it. Any advice would be very much appreciated. I'm looking for a low-bandwidth, non-interactive ...
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139 views

Why are garbled circuits selectively secure?

In Adaptively Secure Garbled Circuits from One-Way Functions, the authors wrote that the adversary may be able to influence the choice of the input $x$ after seeing the garbled circuit, so we need a ...
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What is the main difference between Anonymous HIBE and Anonymous Predicate Encryption?

What is the main difference between Anonymous HIBE and Anonymous Predicate Encryption? In my opinion, both work for the same concept in different ways.
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What's wrong with this construction? ECDHE+AES

Let's say I want to use ECs to do asymmetric encryption. Suppose both sides have generated EC keypairs and have exchanged their public keys. I run ECDHE, and get a derived secret. I would then either ...
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Beginners question about revealing randomness in probabilistic asymmetric encryption

I am encrypting "1" with probabilistic encryption with a foreign public key (I don't have the private key for it) which results in an encrypted file e. Can I prove to a third party, that e contains ...
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Cryptographic Tagging of Information over an Insecure Channel

Is there an efficient algorithm for the tagging and location of information over an insecure channel, where two parties (the tagger and the intended recipient for the tag) can recognize a piece of ...
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Is there a public key encryption for permutations which is homomorphic under permutation composition?

I'm brainstorming an idea for extending our Latin square autotopism secret sharing scheme (proposed here [open access]) to a repairable scheme. I seek a cryptographic method, which may or may not ...
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364 views

Create digital signature with input from multiple users?

Suppose that users A,B and C want to create a digital signature together. The users do not trust each other so, they need to create a signature that receives input from all of them. The best way I ...
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Shall I use individual or common signing keys for different roles?

I have a server S to which a client system can establish connections using predefined roles R1, R2, ...Rn. For mutal exchange of data and for authentication with GCM/GMAC a set of symmetric AES-128 ...
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135 views

zero knowledge messaging implementation

I understand that messages are encrypted using a symmetric algorithm such as AES, and the symmetric key is encrypted using an asymmetric algorithm such as RSA. In my particular implementation, the ...
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180 views

How are attributes encoded in private keys in Attribute-Based Encryption?

I understand how private keys are generated from public keys in a setup like Bitcoin (using ECDSA). I understand that anyone can verify they have the 'correct' private key using a digital signature ...
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358 views

Authentication on top of Bluetooth JUSTWORKS encrypted channel

I have an embedded device with which I need to establish a secure Bluetooth LE connection. Unfortunately, the device does not have a display. However, the device will have a private key whose ...
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159 views

Isomorphic curve vs isomorphic curve group

It is said that if two elliptic curves $E_1, E_2$ defined over a finite field $K$ are isomorphic, then $E_1(K), E_2(K)$ groups are also isomorphic. But the converse is not true. Now, By definition, ...
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Digital Dead Drops or guaranteed significant uncertainty of identity over TCP/IP for a large set of users

Client is part of a Set members. Every distinct object in members has in common, that they do want to communicate to the Server without the Server or other objects of members knowing the origin of ...
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To utilize asymmetric cryptography in symmetric manner - demand-of-security-definition?

Cryptography can largely be divided into two classes: asymmetric and symmetric. Like homomorphic encryption now greatly restricted in the asymmetric cryptography, the difference of asymmetric and ...