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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 ...

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In PKEET, OW-CCA definition, I can not understand their OW-CCA security model?

Specifically in "Probabilistic Public Key Encryption with Equality Test" article? In the article, OW-CCA definition author shown two decryption queries in random oracle model. On first Queries, ...
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Is K=1 a valid random integer in ElGamal signature?

In the ElGamal signature scheme, in addition to the public/private keypair, a random integer $K$ such that $\operatorname{gcd}(K,p-1)=1$ is chosen in the range $[1,p-1]$. This clearly excludes $K=p-1$...
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Encoding Public Keys

We would like to encode ECDSA Public Key specifically keys generated using the ed25519 for storage . What is the best and less error prone method , for now we think about using Hex strings or Base64 ...
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Where do the PKs come from in Bluetooth device?

I am studying the Elliptic Curve Diffie-Hellman (ECDH) on Bluetooth 4.2. There are some questions about the PK.. Where do these public and private keys come from? Who defines them? and Will it ...
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124 views

Is this RSA / SRA cipher modification secure?

I have modified SRA algorithm to suit my problem and I'm wondering if it is still safe to use. Main question is if RSA Encryption key that contains even number is a safe one way function? In RSA ...
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46 views

JWK vs. raw for key wrapping

Context (TLDR below) So I’m developing an application that uses a high-iteration-count PBKDF2 algorithm to derive a symmetric AES-GCM key from a user-provided (enforced to be reasonably strong) ...
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456 views

Elliptic curve and “vanity” public keys

I want to find an algorithm to get a private/public key pair where one coordinate of the public key has some specific prefix (for example: 20 leading zeroes). In the secp256k1 case (the Bitcoin curve),...
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489 views

Recovery public key from secp256k1 signature and message [closed]

Regarding this article about a signature recovery However, with the signature and the message that was signed, and the knowledge of the curve, it is possible to generate two public keys So we can ...
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67 views

Comparing stronger vs. weaker assumptions

If I have to argue that an assumption A is stronger than B, should I argue this way:- An adversary breaking the security of A does not translate to breaking the security of B. But, if an adversary ...
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1answer
29 views

Are there any “cumulative signatures” for decentralized networks?

Lets assume that there is a decentralized network $N$ with participants $A,B,C, D$ and that there was a message $m$ that all of $A,B,C,D$ agreed to. An outsider $X$ wants to know via signatures that $...
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Why is recipient hashed in this Sign/Encrypt/Sign proposal?

Own research In my journey into trying to understand PGP, and public key singing and encryption as a whole, I came across this answer on CE. It is an answer to a question with the title: Should we ...
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113 views

Why ISO/IEC 9796 (signature with message recovery) instead of just encrypt the short message with private key?

I've had a look at “Practical Cryptanalysis of ISO/IEC 9796-2 and EMV Signatures” and read the very good answer https://crypto.stackexchange.com/a/17846/59673 and I understand that signature and ...
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111 views

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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28 views

Proof of work using any computational puzzles

if we have a system in which any user can send arbitrary messages of his choice, and any one can receive that message. So a malicious user can send any messages which may lead to DOS attacks. Any ...
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1answer
140 views

Half of any bitcoin (crypto) public key - (public key half) is possible

I found a topic on bitcointalk Public key x and y == Double(Half of the Public key x and y) half any public key is possible how that possible , in crypto there is subtraction and multiplication ...
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39 views

Is it possible to manage an encrypted dataset for face recognition?

Im in my final year of PhD in computer vision and my supervisor has given me a task that I am not very familiar with. So I am teaching myself homomorphic encryption everyday. This question is mostly ...
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105 views

Calculating distance between two vectors using Paillier homomorphic encryption [closed]

I am basically trying to perform euclidean distance calculation in the encrypted domain (Paillier encryption). Using the homomorphic properties of Paillier, the squared euclidean distance formula can ...
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164 views

Ed25519 PKCS8 private key example from IETF draft seems malformed

Malformed PKCS8 Key Algorithm Identifiers for Ed25519, Ed448, X25519 and X448 for use in the Internet X.509 Public Key Infrastructure § 10.3. Examples of Ed25519 Private Key states the following: <...
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Can a PKE scheme whose plaintext space is infinte also be regarded as a 1-bit PKE scheme?

Let $\Pi = (G,E,D)$ be a 1-bit PKE scheme, now I consturct a PKE scheme $\Pi' = (G', E', D')$ as follow $$(pk',sk') \leftarrow G'(k): (pk,sk) \leftarrow G(k);~ u,v \leftarrow \{0,1\}^k;~ pk' \...
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253 views

ECDSA vulnerability related to recovering private key using same r

I'm considering this for bitcoin transaction as it uses ECDSA so if the signer generates two signatures suppose s1 and s2. where: I get it that any attacker who have s1 and s2 can recover its private ...
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52 views

How to distinguish between private key and public which are visible in text editors?

I would like to know how to understand which one is private key and public key while seeing them in raw text format?
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How to assert that n distinct users have generate an aggregate signature?

If We have n users, each one generate message m1 and signs it to generate (σ1). then by using aggregate signature scheme, we get the aggregate signature of all messages m from n users. Is there a ...
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After ECDH with Curve25519, is it pointless to use anything stronger than AES128?

Is the following reasoning correct: After ECDH with Curve25519, the resulting shared secret will be an EC public key with a bit strength of 128 bits. This public key would then be hashed (let's say ...
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262 views

Generating secure short activation code for offline applications

My application is as follows User has a hardware system (with an unique ID) that does not have connectivity but has a keypad for input. To make the hardware operational, the user has to go to central ...
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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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1answer
48 views

Signing different types of messages with the same asymmetric key

I want to be able to sign different types of messages with the same asymmetric key. (For completeness, I am using Ed25519 for my signatures). Why do I want to do this? The same key is used to sign ...
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1answer
35 views

Key derivation with implicit certificates

The big advantage of implicit certificate is their small size and fast processing. This article presents a way how to compute implicit certificates. In the end Alice is able to derive both her ...
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2answers
123 views

Information theoretical lower limit on the size of public and private keys

When we consider public key algorithms, those usually require keys that are much longer than their security level. According to the Crypto++ Security Level page, for example, integer factorisation ...
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5answers
10k views

How come Public key cryptography wasn't discovered earlier?

I became interested in crypto lately and read about symmetric and public key crypto algorithms. I understand how crucial the discoveries of the 1970s like RSA, DES and DH were in advancing the ...
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1answer
69 views

derive child keys from a private key

My problem is the following: I have an organization with many members. When someone from the outside communicates with this organization, I want any member to be able to decrypt the communication. ...
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63 views

P2P Website/Database Encryption Process

Sorry if this doesn't fit the guidelines, but I believe it is a conceptual issue that is not opinion-based and can be reasonably answered in a single authoritative answer (I'm also struggling to find ...
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1answer
64 views

Paillier subtraction for negative result

I am trying to figure out subtraction on Paillier. From what I read so far, given $m_1$ smaller than $m_2$ ($m_1<m_2$) I can compute $E(m_2-m_1)$ as $E(m_2)\cdot E(m_1)^{-1}$ where $E(m_1)^{-1}$ ...
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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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251 views

Why is RSA preferred over Diffie-Hellman if they're both used to establish shared key?

I've read that the RSA algorithm is preferred over Diffie-Hellman key exchange as it makes key management easier. In the context of online banking, before the RSA algorithm they would have to maintain ...
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1answer
48 views

Is Paillier secure from known plaintext attack for single character message?

Assuming I have three messages m1,m2,m3 where m1=m2=m3=1 and I compute c1,c2 and c3. Does that mean that c1=c2=c3 in cipher-text from ? If not, how many times can I encrypt a message m=1 and still ...
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Thought experiment: how might a publisher who has no “safe” website go about publishing a key hash online?

The security scenario is as follows. Say Mary wants to make an RSA key pair and then publish the fingerprint of the public key (once), followed by a sequence of regular online messages each of which ...
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1answer
115 views

RSA Timing Attack and Prevention through blinding

I am kind of confused regarding timing attacks on RSA. I do understand that the attack exploits the fact that the modular exponentiation (square and multiply) has key dependent branching. That is, if ...
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1answer
114 views

On Program Verification Through zk-SNARKs

Can you provide an example use case of program verification using zk-SNARKs that explains: What it actually means to verify the execution; What are the implication of this new technology; How does it ...
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139 views

What is the advantage of a symmetric encryption system over an asymmetric encryption system?

What are the reasons why somebody would choose a symmetric system over an asymmetric system considering its disadvantage such as a key management and a key transmission? Some people say a symmetric ...
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1answer
90 views

Explanation of Proof-of-Encryption

Regarding the question Provable Encryption, I'm trying to understand how a 'proof of encryption' might actually work. What I can deduce from the answers is this: we need a cryptographic scheme that ...
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36 views

How much information of the length of a plaintext can an adversary get from its ciphertext?

Let $\Pi$ be a public-key encryption scheme. For every palintext $x \in \{0,1\}^{*}$, is there a PPT adversary $A$ such that $$\Pr \left[ 1^{|x|} \leftarrow A\left( pk, \mathrm{Enc}_{pk} (x) \right) \...
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49 views

What public-key encryption protocol can use the same key pair as ECDSA?

Assume we wanted to use the same ECDSA public/private key pair (drawn for standard ECC parameters, perhaps P-256) for both its intended use (public-key signature), and for public-key encryption; this ...
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44 views

Asymmetric encryption property required in an authentication protocol

We want to choose an asymmetric encryption scheme for use as follows: A device holds its private key, with the corresponding public key known and trusted by all. The device also holds a small $b$-bit ...
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2answers
613 views

Are ECDSA keys and RSA keys interchangeable?

Is it possible to use an ES512 key pair for RS512 signatures? Is it possible to use an RS512 key pair for ES512 signatures? I've also posted an issue in the NodeJS jwa package. I created a key pair ...
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37 views

Can NTRUPrime public keys be identified from ciphertext?

Is it possible to distinguish which NTRU public key a ciphertext/encrypted message is for? Assume the attacker has no plaintext or access to secret keys. I suppose this would be a form of key ...
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1answer
113 views

how hashing algorithm is shared in public key

I am reading about public key working at following linkenter link description here Here picture is provided My question is how hashing algorithm is shared between sender and receiver?
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1answer
51 views

I'm getting a non-integer (float) private key in Paillier encryption

I'm trying to implement the Paillier cryptosystem in Matlab using the key generation guidance available here: https://en.wikipedia.org/wiki/Paillier_cryptosystem#Key_generation, but the problem is ...
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104 views

Is there a computational security of public-key encryption which is similar to the one of symmetric key encryption

We say a symmetric key encryption scheme $\Pi_{1} = (\mathrm{Gen}, \mathrm{Enc}, \mathrm{Dec})$ is computational security if for every PPT algorithm $A$ and every $x_{0}, x_{1}$ ($|x_{0}| = |x_{1}|$), ...
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1k views

How do malware rely safely on ECDH algorithm to maintain secrecy of keys?

In traditional malware (especially ransomware) using RSA approach, the public key may be hard-coded in the malware binary and is used to encrypt a symmetric key generated on the system. The symmetric ...
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1answer
33 views

Does some method exists to decrypt using some encryption keys (not all)

I'm searching for a method/algorithm that is able to manage different encryption keys and guarantee that some subset of that keys is needed to perform the decryption (not all). For example: $$D_{K1, ...