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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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SSL - encrypt with private key and then with public key?

Say there are 2 sides that wish to communicate: side A and side B. Let's say we are looking at side ...
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29 views

The goal, the method, and the interface of the signcrypt primitive.

Some time ago, I proposed making the site more educational by teaching correct cryptographic programming. The proposal had had somewhat good reception, but was met with cold ice as there had been ...
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42 views

RSA engine with inaccessible private keys - susceptible to any attacks?

We are going to integrate some hardware accelerator for RSA into our next system on chip. This chip can accelerate the core RSA operation, i.e. modular exponentiation $y=A^x \mod(N)$. The private key (...
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Format of hybrid crypto envelope structure?

From posts including the accepted answer to How to encrypt file with RSA and AES that anyone with RSA key can decrypt them? hybrid crypto (AKA envelope encryption) a GPG-encrypted file has an ...
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Why does DH-EKE require that public keys be indistinguishable from random?

The introduction to SPAKE pre-authentication states: Diffie-Hellman Encrypted Key Exchange (DH-EKE) is the earliest widely deployed PAKE. It works by encrypting the public keys of a Diffie-Hellman ...
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41 views

Send content to owner of gpg public key, nested content symmetric encryption

If I want to encrypt a text content file using a symmetric algorithm like AES, is there a standard format gpg will expect, where it can detect a symmetric key (encrypted with recipient gpg public key ...
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116 views

Performing a dictionary attack on RSA/ECB with no padding

I have the exponent $e=2^{16}+1$ and modulus $n$ (154 digit number) of an RSA public key along with the ciphertext (64 bytes) encrypted using the same key with RSA/ECB and no padding. I am required ...
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23 views

Patterns flaw to sign a counter with public key encryption protocol

In modern asymmetric encryption protocol, like secp256k1, are there any flaws if you want to sign a counter? i.e: use a private key to sign from 1-n is that any chance make n+1 easier to guess?
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How does the process of creating a new secure Elliptic Curve look like?

I'm especially curious about the technique djb would have used to come up with his Curve 25519. Say I have already written down my goals, such as - Twist Secure, Speed, Side Channel resistance, etc. ...
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3answers
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For elliptic-curve cryptography, does a 256-bit key imply that $x$ and $y$ are each 256-bits or 128-bits?

In the wikipedia article, the claim is made that "256-bit elliptic curve public key should provide comparable security to a 3072-bit RSA public key". Since, in ECC, the public-key consists of a point $...
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Difference between Secure Boot and Attestation [migrated]

What's the exact difference between secure boot and device attestation. Nowadays with secure devices both are used, even at the same time, when in the core they do similar things, which is ...
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2answers
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A private key with multiple public keys?

I'm trying to design a wallet, where any number of public keys can be handed out. Say Alice hands out the public keys to receive messages. She doesn't want others to be able to link all of the public ...
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38 views

Why does the Node crypto library do Diffie Hellman this way?

I was sifting through the Node Crytpo library and I came across their Diffie Hellman utility class. Their class implements a generateKeys function that, in their ...
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44 views

Size of group for Elliptic curves vs RSA for equal security

For my research, I would like to compare the efficiency of a scheme when instantiated with Elliptic curves and RSA. So, I would like to know a "latest" comparison (as of 2018) on what group sizes of ...
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31 views

MTI authenticated key exchange protocol and their vulnerabilities?

Can someone please explain the different MTI key exchange protocols (A0, B0, C0, C1) and their vulnerabilities. I've been trying to read about them but couldn't get much information.
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1answer
63 views

Detect MITM with hashed session-key — Is my protocol secure?

I have the following setup: An app ("client") wants to communicate securely with a device I created ("server"). The client has the public key of the server (and a hashed password) preinstalled. I use ...
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1answer
58 views

RSA How to select a value K such that $e d = 1 + k \varphi(N)$ holds

I am learning RSA cryptography. The part I am stuck on is understanding how k and the public exponent $e$ is selected. Given the formulas; Decrypting: $c^d \bmod N = (m^e)^d \bmod N$ Which is equal ...
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Do standalone Oblivious Transfer (OT) Protocols exist?

Are there any Oblivious Transfer (OT) protocols that don’t rely on asymmetrical encryption, public-key encryption or key-exchange? I’m starting to wonder, as all the OT protocols I know of (and can ...
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1answer
44 views

Is the only use for the private key of a root certificate signing certificates issued by it?

A root certificate can be used to issue intermediate certificates. The private key of the root certificate is needed in order to sign any intermediate certificates. However, after that, we only need ...
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125 views

What is the relationship between attribute based encryption (ABE) and access control?

So if possible could someone tell me or at least recommend a book.
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42 views

What are the different use cases between an HMAC and digital signature? [duplicate]

I understand that both an HMAC and digital signature are used to check the integrity and authenticity of a message. Further, I understand that a digital signature is non-repudiatible. What I do not ...
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22 views

Existence of a NIZK proof demonstrating that a ciphertext does not encrypt some specified plaintexts

Given a (El Gamal, for instance) ciphertext, can I (efficiently) prove that the ciphertext does not decrypt to plaintexts in a small set? For instance, given ciphertext $c = Enc(pk,2; r)$, can I (...
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1answer
54 views

Is a digital signature of use if you don't also encrypt the message containing it?

I'm sure this has been asked before. Its just too blindingly obvious. from wikipedia "Digital signatures, in which a message is signed with the sender's private key and can be verified by anyone who ...
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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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1answer
64 views

Does the public key and private key for WhatsApp only remain within a WhatsApp account

The world of cryptography is starting to really intrigue me admittedly. I initially hated it because it looked too hard Mathematically but now it looks cool :) Got a good question for the experts and ...
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1answer
62 views

How to exchange a secret through untrusted server in two steps?

I have a web application where I control the server, however, it should not have any knowledge of secrets that are exchanged between its users. This server holds RSA public keys of each registered ...
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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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How is public-key cryptography secure?

Quite strange question, but here goes: I don't quite understand how asymmetric encryption works. Take SSH for an example: The server will always be listening for commands, so anyone who has the ...
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2answers
63 views

How to ensure confidentiality of an encrypted but public message given that computation power increases?

Say I encrypt a message with the public key of a party whom I want to contact with and then send the ciphertext over an insecure channel. Naturally, an adversary who listens to this channel can ...
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1answer
111 views

RSA encryption/decryption process is not working correctly

I'm trying to apply the RSA cryptosystem to encrypt a byte M=72, using predefined modulus n, public key exponent ...
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1answer
46 views

How to encrypt sensitive files in a business application? Is it needed?

I'm currently working on a business Java application, and we store sensitive files related to our users. What is the appropriate approach to store them securely? Is it viable to encrypt/decrypt all ...
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1answer
78 views

Newbie question: one-way functions in cryptography

I'm reading this article on the basics of cryptography and it says that the main principle is about taking such an algorithm that knowing the end result and the algorithm, an eavesdropper wouldn't be ...
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Asymmetrical encryption with multiple sufficient key-pairs [duplicate]

I have the following requirement: There are N public/private RSA key pairs. The encrypted data must be decryptable by any of the private keys alone, but not by any other key. For encryption, the ...
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1answer
56 views

Applicability of physical unclonable functions for public-key cryptography

Can physical unclonable functions (PUFs) be used to protect secrets against physical tampering in the context of public-key cryptography? Some solutions (i.e. ChipDNA or QuiddiKey) apparently use ...
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2answers
106 views

Cryptographic scheme where a single message cannot be decrypted but if combined with other it can be

i'm wondering if this type of cryptographic scheme does exists. I know about homomorphic encryption but if one has the private key, he can decrypt every single message. I would like to know if there ...
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1answer
73 views

Does this scheme break under a DHP adversary?

Consider the following cryptography scheme: We are given a prime $p$. Alice wants to send the plaintext $m \pmod p$ to Bob. Alice chooses $a$ s.t. $\text{gcd}(a,p-1)=1$, and sends Bob, $u = m^a \...
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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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3answers
118 views

Could ANY cipher serve as the foundation for a public key cryptosystem?

My reasoning goes like this: In principle, any trapdoor function can serve as the foundation for an asymmetric encryption scheme. All ciphers are trapdoor functions, since it's easier to encrypt ...
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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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How to use public/private keys in elliptic curve cryptography to encrypt/decrypt information

I'm reading a bit about elliptical curve cryptography. The basic idea is to define a dot-operator on the points of an elliptic curve. Given a starting point $P$, and applying this dot-operation $n$ ...
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5answers
76 views

Encrypt a file in a way that decryption requires every recipient's cooperation

The best related concept I can think of is the two-man rule. https://en.wikipedia.org/wiki/Two-man_rule. To put it simply, n people are required to give their authorization before a system / secret ...
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94 views

What is it known about the hardness of the factorization search problem in non-commutative crypto?

The factorization search is an interesting problem in non-commutative crypto that can be defined as: Given an element $c$ of a group $G$, two subgroups $A,B \leqslant G$. Find two elements $a\in A$ ...
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1answer
83 views

Random Masking of Padded RSA Ciphertext through homomorphism

I had asked a question related to this before: Oblivious Decryption: Decrypting with a private key, without knowing the message @rikhavshah has an answer, which I would like to discuss the security ...
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1answer
97 views

Restoring a point on an elliptic curve

I received a representation of a point on an elliptic curve $GF(2^m)$ (with curve coefficient A, B) in specific format and some description how to decode it but not all is clear to me. I would be ...
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2answers
88 views

How to calculate Trace function for a point on an elliptic curve

I encountered trouble with calculating Tr (trace function) for points on an elliptic curve in polynomial basis ( $GF(2^m), m = 431$). Maybe there are any assumptions that can simplify and allow ...
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1answer
97 views

Finite Automata and Application to Cryptography

The automated inverse theory in cryptography, points to autonomous finite automata, which is relative to the canonical form for one-key cryptosystems based on finite automata, the public key ...
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1answer
184 views

If the Riemann hypothesis solved

"Sir Michael Atiyah claims to have demonstrated a simple solution to the Riemann hypothesis". If solved, what results we will have in Cryptography?
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88 views

Oblivious Decryption: Decrypting with a private key, without knowing the message

I’m trying to devise a protocol, complimentary to a private-set-intersection, involving three parties, namely Alice, Bob and Charlie. Alice has a public and a private key. And receives website logs ...
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1answer
65 views

Could one make an asymmetric encryption scheme based on Sudoku?

I was reading about a Polly Cracker encryption scheme based on the graph 3-coloring problem. Aren't Latin squares just a form of the same problem? If so, does this mean Sudoku can be used for public/...
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2answers
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Can a digital signature scheme also be an encryption scheme?

Using Schnorr signatures, one could devise a system where a single public key can represent multiple signers. Do signature schemes like that represent crypto systems usable for encryption? In that ...