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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4answers
151 views

Does larger key size mean larger data size in asymmetric encryption?

I'm new to cryptography. I know the larger the key size (like 128-bit vs 1024-bit) the harder the ciphertext is to crack, generally. But assuming everything else being equal, does a larger key size ...
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Why is the NIST recommendation for the private key exponent so much smaller than the modulus?

NIST recommends a 256-bit private key exponent for DLP with a 3072-bit modulus. This question answered how the modulus was chosen/calculated, however, why isn't the private key size closer to the ...
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167 views

What does it imply if in RSA pow(m, e, n) is same as the m

So, Let's assume we have n which is made up of 2 strong primes which cannot be factored & e which is textbook value of e ...
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1answer
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What is the actual result of a Logjam's DH attack?

Does a Logjam attack calculate a group of probable Diffie-Hellman private keys for a user and then try them one at a time to see if it can decrypt the message - or does it directly calculate the one ...
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Why does RSA need p and q to be prime numbers?

Despite having read What makes RSA secure by using prime numbers?, I seek a clarification because I am still struggling to really grasp the underlying concepts of RSA. Specifically, why can't we ...
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1answer
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Can a public key be same as private key?

As I understand, we choose the public and private keys to be mutual inverses. However, it is possible that, in a group, there can be numbers which are their own inverses. E.g. Consider p = 7, q = 3. n ...
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I need to send 16 bytes using ECC keys on a resource-constrained device

I have a system where a resource-constrained device has to send 16 bytes. It has its ECC key pair, and a peer's Public ECC Key. We're using the p256 curve. The device also has an AES-128 hardware ...
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How can I prove that the plaintext of an elgamal ciphertext is the discrete log of an element?

Is there any (efficient) method to prove that the plaintext of an ElGamal ciphertext is the discrete log of an element? In the scenario I concerned, I have an El Gamal key pair $(pk, sk) = (g^y, y)$....
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How many KDF rounds for an SSH key?

What is the best practice on choosing how many key derivation function (KDF) rounds/iterations when generating an SSH key pair with ssh-keygen? Am I correct in saying that it is unnecessary if the ...
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1answer
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Post-quantum candidates for asymmetric cryptography with small key sizes

One of the things that I have come to like about elliptic curve cryptography is that the key only needs to be twice as long as the desired security level. That's a very small expansion (I also like it ...
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Are there any asymmetric key encryption/decryption algorithms?

When it comes to encrypting some data (where data being something of a large size), symmetric key cryptosystem is predominant. Symmetric key algorithms like AES, DES, Blowfish, IDEA etc. are ...
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Off-Chain Channel With Multi Participants That Have Different View/Write Access

I'm looking to expand my blockchain ability to have off-chain channels between different participants (let's say more than 2 participants). The requirements: Only the participants of the channel ...
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7answers
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How big an RSA key is considered secure today?

I think 1024 bit RSA keys were considered secure ~5 years ago, but I assume that's not true anymore. Can 2048 or 4096 keys still be relied upon, or have we gained too much computing power in the ...
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Post-quantum alternative to ElGamal? (public key verifiability)

Are there any alternatives to ElGamal that would be resistant/annoying to quantum machines? I would like to preserve public key derivability/verifiability -- ability to ensure existence of ...
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1answer
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Does anyone know an easily creatable asymmetric cryptosystem for usage in VDF?

I've read multiple papers about VDFs (1, 2, etc.). I look for a lighter alternative to El-Gamal regarding cryptosystem creation. It can be anything exotic too, but it would be nice to have at least ...
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In theory, are there algorithms where everybody can read a message but only one person can write it?

I know that there are a lot of asymmetric algorithms out there that use the public key to encrypt and the private key to decrypt. I was thinking about having exactly the opposite. I do also know that ...
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How are public keys securely and reliably obtained across the internet?

I've just decided to start learning all about PKIs, and I have come across what seems like a paradox. When fetching a public key from either a server or a CA, how can we be sure that the public key ...
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1answer
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How hard is to figure out the ENCRYPTION key given message and clear text?

How feasible is to brute force the ENCRYPTION key if you have the clear-text message the encrypted-version of the same message you know that Rijandel is the encryption algorithm you know that the ...
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1answer
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What's the difference between symmetric and asymmetic multilinear map?

In pairing-based cryptography, we have 3 types, namely Type-I, where $\mathbb{G}_1 = \mathbb{G}_2$, and in Type-II and Type-III we have that $\mathbb{G}_1 \neq \mathbb{G}_2$, however in Type-II we ...
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In which public key encryption algorithms are the private and public key not reversible?

The RSA public key encryption system has the characteristic that the public key and the private key can be reversed. That is, information encrypted with the public key can be decrypted with the ...
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Alternate to distributing master key to every user in circle of trust

I am designing an end-to-end encrypted file storage system where only the user should be able to access their own data. The best I could come up with is a system designed around a master key that is ...
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How to get a random point of a specific EC group with cofactor Not-Equal 1?

We got a EC group generated with point G, and the cofactor of E(G) is with the similar size of the Order. Now we need a random point of E(G) and not revealing the "logarithm" of the random point, so ...
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How are old encrypted messages recovered for the sender?

Take ProtonMail as an example. It encrypts all emails with some kind of asymmetric keys. But obviously, they can't store my private so the key must be obtained when I log in. This means, they must be ...
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1answer
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Can the original data be extracted from an RSA private key signed message

I'm working on a system that the main objective is to verify the message was written by the right person, but it would also be desirable if the message can't be understood by anyone sniffing it. It ...
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1answer
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Should I PGP encrypt using a publickey intended only for Certify?

I'm working with a publickey that does not include EncryptStorage or EncryptCommunication flags (see RFC4880 for flag reference). My question is, is it safe/appropriate to encrypt using this key? <...
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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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Digital signature that is only verifiable by one specific person

I would like to digitally sign a message in such a way that the signature can only be verified by one specific person. Simply encrypting the signature will not work, because that person could then ...
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What is the difference between these pairings classifications?

I know the basic definitions of bilinear groups. For example, there is a bilinear pairing that uses elliptic curves and has the following properties: For $G_1$, and $G_2$ are cyclic groups of prime ...
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1answer
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Question regarding of the ECC test vector format

I am trying to find some ECC test vector for using. I just find some post (like this) and github resource (like this ) They are good reference to my C test code but I'd like to get some more advice... ...
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Why does the recommended key size between symmetric and asymmetric encryption differ greatly?

In various articles it is mentioned that for secure communications, the recommended key sizes are 128-bit key size for symmetric encryption (which makes it $2^{128}$ possible keys?) and 2048-bit key ...
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question about RSA [duplicate]

I am very new in cryptography field, what I want to ask but I cannot find an answer is this: In public key cryptography, such as in RSA, does it matter if the adversary knows/can detect the public key?...
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Asymmetric keys (e.g. RSA) must be so much longer than symmetric keys (e.g. AES). Why? [duplicate]

I have been reading that RSA has to do with math (prime numbers), while symmetric key encryption deals with blocks of data and modifying the blocks with replacements and remappings, but I still don't ...
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Key Value Based Key Derivation

For a system that is using public key cryptography to authenticate users and their actions I'm trying to solve (ease) UI/UX problem so that users will be able to use login/passwords they're accustomed ...
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Difference between RSA & ECC [duplicate]

My question is regarding Asymmetric-key encryption, in which situation is better to use RSA? What are the advantages of RSA comparison with ECC but from a security point of view? Thank you
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Looking for commutative asymmetric cipher for data matching

I need some crypto operation for matching data privately between two peers (let say Alice and Bob). Alice should be able to encrypt her data with Alice and Bob public keys and pass the cipher text to ...
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0answers
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Security of an Elliptic Curve Public Key with a “Small” x-coordinate

Consider an elliptic curve over a finite field $F_p$ with $p$ prime and order $n$. Let $Q$ be a generator for the field. Given a public key point $P = aQ$, suppose we have an algorithm that finds an ...
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Is there a public-key system that can chain?

Does there exist any asymmetric cryptosystem that has the following properties: If I know somebody's public key PBK_1 and my own key pair (PVK_2,PBK_2), I can construct a new public key PBK_3 such ...
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1answer
135 views

Private key can't be traced (GPG)?

I am very new to cryptography. I was reading about GPG/PGP Basics when a doubt arose: As per my understanding, everyone knows the algorithm (from GPG) with which I generated my key pair. If I show my ...
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3answers
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Why is the P-521 elliptic curve not in Suite B if AES-256 is?

In the NSA's document, "The Case for Elliptic Curve Cryptography" (archived), we have ...
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1answer
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What are the benefits of lattice based cryptography?

Previously we visited the benefits of elliptic curves for cryptography. Lattice based cryptography is starting to become quite popular in academia. The primary benefit of lattice based crypto is the ...
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RSA How to find the exponent ($e$) of the Public key with the values $p$ $q$ and an example are given

I'm wondering if it's possible to find the public exponent ($e$) with an example and the (rather small) values of $p$ and $q$ given. Currently the only option I found is bruteforcing this value, but ...
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EC Key Compression

Using the secp256k1 curve, will the below yield the same result? Generate private key -> compress private key -> generate public key Generate private key -> generate public key -> compress public key ...
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3answers
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Why is it impossible to find the private key from the public key?

From what I understand, based on the article A Beginner’s Guide: Private and Public Key Cryptography Deciphered, the public key is generated by performing $n$ tangent plus mirroring operations from ...
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3answers
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In public key cryptography, how many keys are required for secure communication between n parties?

In public key cryptography, how many keys are required for secure communication between n parties? In my view the answer should be $n^2$. Reason: There are ‘$n$’ Parties. Every Party has One (1) ...
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How exactly are GPG keys (and prime numbers inside of GPG) mathematically related?

I know that the keys are somehow mathematically related, and I know that they're somehow generated via prime numbers, but how exactly are they related? I realize that it'd probably be best for me to ...
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1answer
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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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2answers
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How does RSA public and private key structure look like?

So I was reading this wiki about the RSA algorithm and I read this article to understand it better. My goal was to create a simple program that would generate private and public keys. I got to the ...
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1answer
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DH prime size required to force an attack of $2^N$ steps

Why the size of a DH prime $p$ should be about 6800 bits long to force an attacker to perform $2^{128}$ steps to attack the system? How is this relationship 6800-128 established?
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PKI Multiple Samples start to expose Private Keys?

My understanding is that using a PKI, public/private key pair is generally secure to send message to people. That is, encrypt a message using the recipient's public key so they use their private key ...
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1answer
798 views

Private and Public Keys

I have a very basic understanding of encryption and the encapsulation process, but for the life of me I can't grasp how public keys and private keys work, how they're made, and how they're exchanged. ...