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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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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68 views

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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53 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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135 views

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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53 views

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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123 views

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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188 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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223 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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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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71 views

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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53 views

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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112 views

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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375 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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36 views

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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149 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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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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402 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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199 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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36 views

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 ...
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What are the most appropriate PKI based cryptographic protocols for peer to peer communicaton?

I've been trying to find out which is the most appropriate PKI based cryptographic protocol for peer to peer communication. I do understand that they vary with respect to the peer to peer architecture ...
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Key Distribution Center Key Protocol Analysis

As shown in the image, why is Circle 1 to be B and Circle 2 to be A? Why is not the opposite, that is, Circle 1 to be A and Circle 2 to be B? like this picture From my understanding, Notation B in ...
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257 views

Simulation-Based Proof: When a Secret Key is Involved

Assume we have a protocol in which a party receives an encrypted random polynomial. The polynomial is encrypted using his public key. We want to construct a simulator for this party (so this party ...
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106 views

Given a public-key encryption and signature scheme, define a new primitive

I'm new to cryptography and am currently working on the following question: Say you are given a public-key encryption scheme $\Pi_e=(\mathcal{K}_e,\mathcal{E},\mathcal{D})$ and a signature scheme $\...
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66 views

Is it possible to re-generate ECPublic key from raw private key and curve params?

As per my understanding, in Elliptical curve cryptography, the EC PrivateKey is nothing but a bigInteger value. If you know the curve specs and you have this private BigInteger value (which I am ...
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Can I expand the modulus of an encryption scheme?

Take the lifted ElGamal as an example: suppose the original ciphertext is $<g^y \bmod q,g^m\bmod q>$. After some calculations, $m$ could be large enough to do modular. But I don't want $m$ to be ...
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Is it possbile to get same set of public and private keys twice while creating CSR ? If so where does the conflict happens !?

I'm new to cryptography and please clarify if my below assumption is wrong. Lets assume, that two different banks creating CSR and they get identical public and private key pairs of RSA. In such ...
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247 views

CPA-security proof of “l-padded RSA” encryption scheme

The 10.9 exercise from the Katz-Lindell textbook creates a lot of confusion, let me state it here. Consider the following experiment for an algorithm $A$ and a function $l$ with $l(n) \leq 2n-2$ for ...
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317 views

RSA Signature Forgery

We all know that x509 certificates carry a signature that represents the certificate digest encrypted by the private key of the issuer. I believe that the digest is encrypted only providing one block,...
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Non-interactive zero-knowledge proof for discrete logarithm without random oracle

Is there any non-interactive zero-knowledge proof for discrete logarithm without random oracle over the group $\mathbb Z_p$?
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Registration and log in through public key cryptography?

I read about zero knowledge proofs. Let's say you want to create an account at a website. You choose a password $p$ and from $p$ you derive deterministically a public & private key pair $(e,d)$ ...
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59 views

How to securely map an element from an smaller domain to the other element in a large domain

Problem: I have a small sized domain, say s-bit. It's clear that the probability for an adversary to guess an element is $ \frac{1}{2^s}$. I need to make the probability negligible. However, I need to ...
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Obliviously computing the Least common multiple of two poylnomials

Consider I have two polynomials $f_1$ and $f_2$ of the same degree. I want to secure them (using any kind of encryption except FHE) and outsource them to an untrusted server. I want him to compute the ...
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RSA OAEP: prevention of partial decryption of ciphertexts

I'm trying to understand RSA encryption (as a beginner in cryptography). go on this wiki page http://en.wikipedia.org/wiki/Optimal_asymmetric_encryption_padding scroll down to the 2 numbered points: "...
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Opinion on my idea for storing credit cards securely

I've been thinking of ways to store credit cards securely, I thought of this: Take the users credit card info Put the card info in a standard format "Full Name/Card Num/Security Num/Expiry Date" ...
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825 views

Mutual authentication with Public Key and session Key

I am trying to understand two protocols for mutual authentication and if they are secure or not. $K$ is the session key, and it's calculated $k=H(TimeStamp)$. Are the following both cases secure? ...
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1-1 trapdoor function mapping the set of $n$-bit numbers to themselves

I am looking for a trapdoor one-to-one function $f : \{0,1\}^n \rightarrow \{0,1\}^n$ (that is, mapping the set of $n$ bit numbers 1-1 onto itself [any $n$ is OK]). I was considering the use of ...
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inverse of scalar multiplier in ECC

I am learning to use ECC. i got into situation where i have $Q=abG$, where $G$ is the generator of the finite field formed on EC using a prime $p$ modulus and $a$ , $b$ are random numbers. now suppose ...
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Are there any bi-bidirectionally indistinguishable Asymmetric Encryption Algorithms

I have been using Asymmetric Encryption for a while, and I have come across an interesting concept, and it would be cool if it could be done. Are there any Asymmetric Encryption Algorithms where the ...
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can permutation matrix be found in parallel processing technique?

Let us say there exists a permutation matrix $n \times n$ for some large $n$. Then, there are $n!$ possible permutations. If one to use brute-force to find the secret permutation among $n!$ ...
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Getting the Encryption Function From the Decryption Function + Decryption Key + Encrypted Item

Is it mathematically possible to always be able to get the encryption algorithm used to encrypt a certain item (file, number, text, ...etc.) by knowing the decryption algorithm that will be used to ...
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Is inverse polynomial in a finite field NP hard?

In ECC we have: if we know $G$ and $P=kG$, it is very difficult to find $k$. I wonder whether or not in NTRUEncrypt: if we know $h$ and $P=rh$, it is difficult to find $r$?
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How does one associate the actual identity of a person or organization with a decentralized id?

In SSI(Self-Sovereign Identity), anyone can generate their own DID(Decentralized ID). No authority or authorization is needed to create one. Since a public key pair is associated with DID, the person ...
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Zero knowledge proof of symmetric keys and encrypted texts resulting in the same text, if the symmetric keys are encrypted with asymmetric ones

Suppose I have: text T, symmetric keys X, Y encrypted text T with symmetric keys X, Y = TX, TY accordingly asymmetric key Z, used to encrypt X, Y to transmit them to a person. Let the encrypted ...
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Key and Message generated on Client, and validated by Server

(Sorry in advance for my blurry thinking on this: I'm a programmer, not a cryptography expert.) I have a Client/Server web application. The Client needs to be able to alter the local state in ways ...