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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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Given a 'good' basis for a lattice, how can we solve the CVP?

I'm doing a little bit of reading about lattices. I read that if we can find a 'short' basis for our given lattice, we can solve CVP and SVP very efficiently. However, the paper didn't describe an ...
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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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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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Why is this scheme not IND-CCA2 secure

I know that many lattice cryptosystems cannot be made $\text{IND-CCA2}$ or even $\text{IND-CCA}$ secure without substantial overhead. However, it seems that (when used as a KEM) that any $\text{IND-...
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In NTRU, if $N$ is not prime, prove that one can recover the private key by solving a lattice problem in dimension lower than $2N$

In the NTRU cryptosystem, it is suggested to take $N$ prime. I want to understand why. In Jeffrey Hoffstein, Jill Pipher and H. Silverman An Introduction to Mathematical Cryptography, they suggest (...
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Cloneability of AES-128

I would like to implement an anti-counterfeiting scheme for tools my company manufactures. This would ideally be done via RFID/NFC tags. However, the environment in which these tags operate would ...
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222 views

How did G.H. Hardy's work contribute to today's public-key cryptography?

I know that Hardy's work in number theory was used by Clifford Cocks in 1973 to develop the basis for public-key cryptography. What specifically was this work, and how is it used today in ...
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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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Public key encryption from (1,2)-oblivious transfer

Prove that any two rounds of (1,2)-oblivious transfer, that is semi honestly secure, imply public key encryption. My ideas so far: Let's say Alice samples two $n$ random strings $(x_1, x_2)$, and ...
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Montgomery modular multiplication – confusion with subtraction of modulus

I'm reading the paper “COMPARISON OF SCALABLE MONTGOMERY MODULAR MULTIPLICATION IMPLEMENTATIONS EMBEDDED IN RECONFIGURABLE HARDWARE” (PDF) on hardware algorithms for montgomery multiplication for ...
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Chosen Plaintext Attack and Chosen Multiple-Plaintext Attack

The original CPA game: The adversary gives two arbitrary messages $m_0$ and $m_1$ to a challenger; The challenger encrypts an arbitrary message $m_u$, $u∈\{0,1\}$ , and sends the ciphertext to the ...
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RSA - factorizing N to get p&q

I need to decrypt a message encrypted using RSA. I only know the public keys n and e. I need to get the private key p and q in order to get the decryption exponent d. Now to do so, I know I have to ...
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David Chaum's anonymous credential

I am a newbie in cryptography (I know the basic RSA, AES stuffs) and am interested in anonymous authentication systems. Looks like David Chaum is the godly figure in the field. I see lots of people ...
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Relations between RSA and DLOG, factoring and DLOG

Definition: (The generalized Diffie-Hellman problem) Let $n=pq$ for two large primes $p,q$. Given $x, x^a, x^b,n$, find $x^{ab}\pmod{n}$. (1) Is there a known reduction from the GDH problem to ...
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GPG Sub Key Renewal Questions

Last year, I followed this guide to create two GnuPG Smart Cards; one card with the Primary Key and the other card with the Sub-keys. I noticed that the sub keys were close to expiring so I renewed ...
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What standards of ECC point compression exist?

The method that I used before to decode EC point from public key led me in a dead end. So I just want to know what yet I could try. I've got a public key that I don't know how to decode and I am ...
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General Private/Public key generation

I wanted to get an idea on how the whole cold-storage private/public key generation works for different cryptocurrencies. So I was playing around with BIP32 deriviation path on: https://iancoleman.io/...
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268 views

Curve25519 / Ed25519 - Generate a private key from this term

I have 2 key pairs $(x_1, y_1)$, $(x_2, y_2)$. I also have $a = $random 256-bit array and $b = $256-bit of defined values from me. I know the values for $(x_1, y_1)$, $x_2$ and $b$. But I miss the ...
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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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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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Can proofs be relayed to derived keys?

I am aiming to find out if this problem/puzzle can be solved with cryptography at all. Say there are these two parties: Subject S which has a master private/public key pair (MPriv, MPub) and a set of ...
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Encryption design for user data with service access

I'm looking to provide users with a way to give a service sensitive information, which the service can freely use up until the user decides otherwise. I want to encrypt the data at rest (and of course,...
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Symmetric (in the execution of the protocol by the two parties) version of the Station-To-Station protocol?

The original Station-To-Station (STS) protocol is as following: Alice : Generate $x$ Alice → Bob : $g^x$ Bob : Generate $y$, compute $g^y$ Bob : Compute $K = (g^x)^y$ Bob : Sign-then-Encrypt $(g^y, g^...
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show how LWE errors can have a greater impact on result

Hi weve been given the following question in one of our classes but have not been taught anything about it and is worded strangely. It is to show how the LWE problem works by showing how small errors ...
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Are the first 4 bytes of a Ed25519 public key random?

We are using the Ed25519 signature scheme (which uses Curve25519). A key pair is generated by generating the secret key from random data and then computing the 32-byte (256-bit) public key from said ...
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Is public-key cryptography the correct choice?

I'm working on a project which requires encryption of sensitive data, with communication of said data between a mobile app and a website (via an API). I'm new to encryption and security, but my ...
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Can “PrivateKey+MagicValue” decode pre-encoded data without intermediate key?

Let's say I want to build a public repository of encrypted files. EncA(FileA) EncB(FileB) ...
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159 views

How to safely double-encrypt a secret?

Imagine two persons: Alice and Bob. We have a generated secret value that is valuable and has to be encrypted in a way that both can't reveal the value on their own but only when they both confirm. ...
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363 views

Feasible attacks on ECRSA cryptosystem

In ECRSA cryptosystem, I want to know the feasible attacks. For illustrations we have two prime $p$ and $q$ such that $p \equiv 2 \pmod 3$, $q \equiv 2 \pmod 3$ and generate key pair as follows: $$n = ...
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MITM Attack on Key Exchange Protocols

I was doing research on this attack and I am wondering, why is Diffie-Hellman always associated with such an attack? ​ Aren't other public key cryptography schemes vulnerable to the same kind of ...
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How do I prove that a bit by bit PKE scheme (that is IND-CPA secure) for an n-bit message is not IND-CCA-2 secure?

Gen generates Pk and Sk (l bits each), Enc encrypts m (length l) but by bit using each bit of Pk respectively, Dec decrypts ciphertext bit by bit using each bit of Sk respectively. How do I prove this ...
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Signing integers and UUIDs and restoring them from a third party server without tampering

I'm educating myself about cryptography. I know this is a long one, but please, bear with me. :) Now I have a scenario in my mind and I'd like to ask if what I've thought is sound (enough), what more ...
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257 views

Ciphertext size of any CPA-secure public-key encryption scheme

I know that, for any CPA-secure public-key encryption scheme, the size of the ciphertext after encrypting a single bit is superlogarithmic in the security parameter. That is, for $(pk,sk) \leftarrow ...
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Challenge-response based on public-key decryption, why send public key

Quoting the handbook of applied cryptography, chapter 10.3.3 (i): Identification based on PK decryption and witness. Consider the following protocol: $A \leftarrow B: h(r), B, P_A(r,B)$ $...
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How can I make a message into a blocks for NTRU?

I have more bits than the degree of the NTRU polynomial. For example: $x^{11}-1$ message: Hello (I am using ascii, 8 bits for 1 symbol) got: ...
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Threshold signatures vs. certificate authority+voting verification

Perhaps a silly question, but I am wondering what the advantages are of threshold signatures. Let's consider the following two signature schemes: $(t,n)$-threshold signature with a trusted dealer, i....
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282 views

Diffie-Hellman exchange

So for a Diffie-Hellman problem, I am given the prime $p$ for the Diffie-Hellman exchange. I am also given $g$, secret number for machine as $A$, secret number for station as $B$, a Diffie-Hellman ...
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Prevent/minimize replay attacks in public message board

Assume we have a public message board where anyone can send a message to. If plain messages are used, anyone can impersonate anyone. The goal is to disallow impersonations. We can use public key ...
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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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Where does one store 3rd-party Public Keys

So, I've just started looking at the subject of Cryptography and am working through Stephen Haunt's Practical Cryptography course on PluralSight but have a question that doesn't appear to be covered. ...
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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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60 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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Where shoul I store private/public keys and how should I share it?

I'm new in terms of encryption and I have to encrypt the data between two Java Spring applications, one have serves as MVC framework and other as Web Service, I'm implementing an asymmetric encryption ...
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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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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 ...