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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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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RSA 1024 bit forge a new matching signature from a chosen message

I have an RSA signature scheme with 1024-bit key where I know the following: Public modulus $N$ Public exponent $e=3$ A lot of signatures Summary: To compute a signature, an MD5 hash is calculated ...
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Construct Schnorr Protocol can only verify by designated verifier

Currently I have a DLP as following, $y = g^x \bmod p$, I can easily construct a proof of knowledge by using Schnorr Protocol. But I would like to put it a a system of 2 parties with public key and ...
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Do I need to use a MAC with asymmetric encryption?

The internet has drilled into me that when I delivery any symmetrically encrypted data, I should also deliver a MAC to authenticate it before any decryption occurs. Do I also need to do this if I use ...
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Reason for difference in assumptions for practical private-key and public-key crypto

Theoretical cryptography tells us that everything in the world of private-key cryptography (CCA-secure symmetric encryption, message authentication codes, etc.) can be built from one-way functions and ...
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What use is the signature without the message under RSA?

Using RSA for signing & verification, is there a way to take a valid signature for an unknown message, and for someone else to generate a valid signature using a different key against the valid ...
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Why does FIPS 186-4 require specific sizes for keys?

In FIPS 186-4, page 32, about FFC crypto it is required that the length of $p$ will be exactly 1024 bit and the length of $q$ will be exactly 160 bit. Why is the requirement not stated in terms of ...
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Feasibility of finding public key when private key is known

We all know that in a public key cryptosystem, given a public key it is extremely hard to compute private key from it. Is it the same case in reverse? Given a private key, how easy is it to compute ...
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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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Manually creating a GPG Public Key

I want to manually create a GPG public key that can be imported into GPG, i.e. I want to create a file with a Public-Key Packet, a User ID Packet and a Signature Packet (for an example see here). I ...
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RSA public key exponent generation confusion

Quote from Wiki: $e$ having a short bit-length and small Hamming weight results in more efficient encryption — most commonly $2^{16} + 1 = 65537$. However, much smaller values of $e$ (such as $3$) ...
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Does rsa-oaep provide or not plaintext integrity in addition to confidentiality?

My own understanding (possibly wrong of course) of RSA-OAEP encryption scheme is that it provides plaintext integrity (in addition to confidentiality) due to MGF function which for encryption ...
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Implementing symmetric encryption algorithms with whole words

Scenario I have some unique requirements to encrypt text: symmetric encryption; the encrypted text will be a valid text (that means that humans could read it and not just “gibberish”); I can not ...
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Determining message given cipher-text and public key [duplicate]

Consider the following scenario: Suppose A and B have set up their RSA public keys, namely $(e_a, n)$ and $(e_b, n)$, where the n-value is the same. Also, it happens that the $\gcd (e_a, e_b) = ...
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Why is encryption slower than decryption in elliptic curve cryptography (ECC)?

While performing encryption using public key and decryption using the private key, I am always finding that encryption takes more time than decryption in elliptic curve cryptography (ECC). It's the ...
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Maximum length in bits of the product n=pq

If p and q are two 1024-bit prime numbers, would the maximum length in bits of product $n=pq$ be ${1024}^2$ or $2^{1024}$? I think it is ${1048576}={1024}^2$? Also, would the least significant bit ...
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Quadratic residue problem on composite integers

Its believed that the quadratic residue modulo $n=p·q$ for large primes $p$ and $q$ is intractable, which forms the basis of some cryptosystems. However, it is solvable if the factors of $n$ are know,...
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Schnorr Pubkey Recovery

As per How does recovering the public key from an ECDSA signature work?, it's possible to recover public keys from ECDSA signatures. Is this possible for EC-Schnorr signatures as well? I'm looking ...
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using Post-quantum asymmetric ciphers instead of RSA

We can't trust RSA to encrypt our Emails so what is best post-quantum cryptography system as alternative for RSA which provide good security and don't be breakable? because McEliece cryptosystem looks ...
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How does the sender obtain the receiver's public key?

Cryptography process includes encryption and decryption process. In public key cryptography public key of receiver is being used for encryption. I want to know how public key of receiver is sent to ...
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NTRU key size (confused)

I'm evaluating the performance of NTRU; and I got confused. the key size is said to be smaller than RSA but larger than ECC. Using both the reference implementation when I choose APR2011_439 setting ...
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If RSA Signature is not Decryption, why is it not advisable to use same keys for enc/dec and sig/ver? [duplicate]

If RSA Signature is not Decryption, why is it not advisable to use same keys for enc/dec and sig/ver? What is the proof where you may be exposing your private key when you use the same one for ...
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What is the correct value for “certainty” in RSA key pair generation?

I'm creating an RSA key pair in Bouncy Castle and need to specify an int value for certainty. This Stack Overflow answer says it is a relative test for how prime the values are. There is another ...
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Need help understanding this exercise's solution

We were given this exercise, which asks us to identify the types of keys used on this diagram: The solution was Kxa -> A's private key Kya -> A's public key KxB -> B's private key My question is, ...
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implications of SSH server key compromission when authenticating users against a public key

Friday we had a disagreement with a colleague of mine about the implications of SSH server key compromission The question was stated as this : What could a hacker do while provided with the SSH ...
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Attack RSA knowing the public key and brute forcing all possible message

Alice want to send a message $m$ to Bob, and encrypt it with Bob public key $K_B$. $A \rightarrow B : \{m\}K_B$ Lets assume I have intercepted $\{m\}K_B$, I know $K_B$ and I know that $m \in D$ (...
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How do we guarantee plaintext is coprime in RSA?

The specifications for RSA state: $P^{\phi(N)} \equiv 1 ~mod~N$ if and only if $P$ and $N$ are coprime. Here $P$ is the plaintext and $N$ is the product of two suitable primes $x_1, x_2$. My question ...
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Explaining RSA to non-scientists

I am to give a small lecture on quantum computing in a months' time and I want to shortly give intuition to the fact that Shor's algorithm shows that quantum computers will break RSA. Ideally, I would ...
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Can private key be specified on key pair creation?

Without regards to any specific implementation of asymmetric cryptography, I am wondering if it is feasible to come up with a value of private key I want to use, and calculate the corresponding public ...
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Verification of identity by certification authority

I have question about how a user's identity is verified by a Certification Authority. As I understand it, the process works as follows: User generates his private key and (with the help of private ...
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What is the more accurate way of stating the correctness of a PK encryption scheme?

Is it more accurate to state that a public key encryption scheme is correct if for all $m \in M$ and $(pk, sk) \in \operatorname{Gen}(1^k)$ a. $\operatorname{Dec}_{sk}(\operatorname{Enc}_{pk}(m))=m\;$ ...
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Does RSA-OEAP have integrity and authenticity properties?

RSA-OAEP is IND-CCA2 secure (indistinguishable under an adaptive chosen ciphertext attack). Does it also have the INT-CTXT (integrity of ciphertext) and INT-PTXT (integrity of plaintext) properties? ...
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Can an altered RSA private key still work as the original?

I am interested in understanding public-key encryption using RSA. On the Khan Academy website, I noticed an anomaly when testing out the tutorial. I created the following public/private keys: ...
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How to generate 1024-bit RSA key

I have generated a prime number with a 1024-bit size. Now, when I create an RSA key - how many bits does the key have?
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Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate]

Possible Duplicate: Two untrusted party want to exchange data: how to insure each one gets the data it needs? I am trying to come up with what could maybe be a novel algorithm for an application ...
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Any algorithm with a master key for decrypting private key encrypted messages?

Are there any algorithm out there that implements following scenario? Create a master private key Create a private/public key #1 based on the master key Create a private/public key #2 based on the ...
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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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Is it possible to compute the y-coordinate of a point on SECP256K1, given only the x-coordinate

Given an x-coordiante of a point on the SECP256K1 curve, is it possible to calculate the corresponding y-coorindate? (Assuming the point is a verifying public key that complies with the Bitcoin ...
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ECIES for encrypting ECDH key exchange

I started studying Elliptic Curve Cryptography, and I do not know if I understand the difference between ECDH and ECIES (even with the other posts here on stackexchange). I'm wondering if ECIES can be ...
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How can i check if a public key match with a private key

Is there a way to check, (with openssl command for example), if a given public key match with a private key ? Thanks
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Is it Possible to Generate a Duplicate DH Session Key from 2 Pairs of DH Keys?

This might sound pointless at first, but I want to know if it's computationally feasible to generate the same resulting session key in 2 different DH key exchanges. The purpose would be for a man-in-...
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Will publishing two or more public keys of the same RSA private key cause a security risk?

I want to make an end-to-end messaging platform where everyone is identified with a unique random private key. Everyone uses other peers' public keys to identify and send encrypted messages and verify ...
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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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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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Message exchange with textbook RSA

I am working on this exercise but can't work out the answer to the question b. I have solved the question (a) by decrypting the ciphertext $C = 2$ using the formula: $$ M = C^d \bmod n = 2^{17} \bmod ...
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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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Negotiate a secure connection without certificates?

I would like to have a simple experience for a user for setting up a secure connection between two computers against a MITM attack. Something like the following: A number (possibly base64) appears ...
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Time complexity to solve Discrete log problem

What is the time to complexity to solve Discrete log problem now in $Z_p$? Initially for $n$ bit prime $p$, it was $Exp(n^{1/3})$.
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What is the simplest digital signature algorithm known?

The hardest part about this question is explaining what I mean by simple. I'm measuring simplicity as, simply, the amount of lines of code it takes to implement that algorithm in a simple programming ...
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Can a Cramer-Shoup public key have two different private keys?

Since I am new to the Cramer-Shoup algorithm, I would like to know: Is it possible to have two different private keys for a public key due the key pair generation algorithm that Cramer-Shoup uses? I ...

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