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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Are My Answers for This RSA Question Correct?

I am very new to cryptography and so I am looking for feedback on this question on RSA. Please let me know if I have made any mistakes, Thank you! (a). RSA Algorithm: -choose two primes p,q -...
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Proving a user's identity after the user has forgotten his private key and password

First some background. I am building an application where people send each other emails with messages inside that need their sign-off. Once the participants receive the email they're also given a ...
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Could a private key recovery via modulus fault attacks be optimised by being able to choose the faulty moduli?

The paper 'Why One Should Also Secure RSA Public Key Elements' describes an attack where an adversary can fully recover a private key by injecting faults into the modulus before exponentiation takes ...
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Is the password based key exchange secure even if the public key is known to adversary?

I am assuming the answer for part 1 to be a "NO" as the adversary knows the public key he can get the password by offline attack IN part 2 : the answer is "yes" as the public key is freshly generated ...
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Multiparty dataset intersection count

Typically, Private Set Intersection (PSI) protocols let you learn the subset of items on each party's dataset that are in the intersection. The problem in this case is a relaxation of these kind of ...
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E2EE encrypted chat where messages are only readable by participants and admin users

As the title suggests, is there a way to have an E2EE chat between two users, and have them be visible later by an admin user. I know this defeats the point of E2EE, but i want to have the messages ...
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Proof ownership of private key for blinded public key

so i want to prove to a server that i have the private key to a public key for which i want to retrieve the server's signature. But the server is not allowed to learn either public nor private key. ...
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What is the PGP Web of Trust Strongset?

I understand that it is a system that "establishes the authenticity of the binding between public keys and their owners", but how does one join this web of trust? Do you have to physically meet one of ...
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Secure asymmetric encryption with 32byte ciphertext

I need securely asymmetrically encrypt the up to 16 bytes plaintext and receive up to 32 bytes ciphertext. I found that ElGamal produces ciphertext that is 2 times keysize. So I would need to use ...
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What is the key length of shared secret by Curve 25519 ECDH

Both parties uses Curve 25519 key pairs for ECDH key exchange. What is the key length of shared secret after ECDH?
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As an analogy to asymmetric key encryption, does the following work? If not why not?

public key... a padlock (anyone can lock it) private key... the key to the padlock (only key owner can open it) Alice and Bob each have their own padlock and key Anyone can get a replica of any ...
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Are all public-key encryption protocols based on one-way functions? [duplicate]

Are there any public-key cryptography protocols which don't rely on one-way (or trapdoor) functions? RSA and Diffie-Hellman cryptographic protocols both rely on one-way functions (prime factorization ...
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Breaking ciphertext using a quantum computer when the public key is not available

As we know about Shor's algorithm on quantum computers it is possible to crack RSA / ECC easily if we have enough qubits. Is it possible to crack RSA / ECC on a quantum computer if we only have ...
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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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Does signing multiple messages with the same RSA key weaken the encryption?

Here is the scenario, I am signing roughly 1000 messages, which consist of 16 byte hashes, with 1024 bit RSA. The private key is only used to sign the hashes, and there is no padding scheme. The ...
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Diffie-Hellman + Asymetric encryption kept simple, or alternatives to TLS

I am working on a system that includes our dear friends Alice, Bob, and a server that is only partially trusted. I have spent the majority of the day reading up on various cryptography methods, but I ...
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Is it possible to decrypt an ECDSA private key if the same nonce is used across different private keys?

If the same nonce is used across different messages under the same private key, the private key can be easily revealed. However, let's consider another scenario. Two private keys, x1 and x2, are ...
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Converting raw ECC private key into ASN.1 DER encoded key

I created a random integer array of 32 bytes to use as my private key for secp256k1 curve. ...
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RSA encryption secure mode, plaintext length limit vs. key length

I have two questions about RSA encryption to confirm: Assume use RSA 2048-bit key pair, what is the secure encryption mode? Are ECB / OAEPWithSHA-256AndMGF1Padding and ECB / OAEPWithSHA-...
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Can I switch out a private RSA Key, so that when decrypting a message, it is decrypted to a different message?

Here's a task I've been struggling with: Say I have an encrypted message $c$, and a desired plaintext $m$. How can I define a valid private RSA Key $(d,N)$, so that $c^d \bmod N = m$ Note that the ...
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Looking for feedback on the cryptographic design of my open source project: Bloom [closed]

I'm about to release the new version of my open source project: Bloom (encrypted Notes, Calendar, Contacts, Files…) which will feature end-to-end encryption. I've published the cryptographic details ...
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Standard for asymmetric encryption based on elliptic curves

Most parts of public key cryptography has established standards which are in turn used in a large amount of real world applications. There is PKCS#1 for RSA based encryption and signatures and there ...
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How is it possible to trust a public key that can confirm a message's signature?

Let's assume I am able to confirm a certain message's signature with a public key that seems to be from Alice. So I should be sure that the sender of that message is really Alice. But what if I have a ...
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Knowledge of discrete log is needed in the proof of Cramer-Shoup public key scheme?

In the proof of the Cramer-Shoup public key scheme [1], I understand that the adversary's view can be seen as equations such as $\log c = x_1 + w x_2, \log d = y_1 + w y_2$ and so on (equation 1 and 2 ...
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Is there a possibility to create a public key block cipher?

Why there is no public key-based block cipher? It is known that the block ciphers are symmetric-key encryption. However, what is the motivation to not design a public key encryption that encrypts ...
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Current situation of bilinear pairing protocols

The bilinear pairings are considered as the key enabler for many novel cryptographic protocols, such as three-party one round DH[1], shorter signatures and certificateless (ID-based) crypto[3] , which ...
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Using RSA encryption to encrypt large files

The following post discusses the use of RSA for file encryption: https://medium.com/@ismailakkila/black-hat-python-encrypt-and-decrypt-with-rsa-cryptography-bd6df84d65bc The file encrypted is a JPEG ...
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Why is a public key insufficient to decrypt a message?

I'm curious about how E2EE encryption works, but the high-level descriptions I've been able to find aren't quite as clear as I'd like them to be. My current understanding is as follows: Suppose one ...
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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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How can I make sure non-open source programs are really using end-to-end encryption?

Without going deep into math, is there a way to make sure that non-open source programs like WhatsApp, FaceTime, Zoom, etc. are really using end-to-end encryption instead of just 'regular encryption' (...
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Compared with plain RSA , what is the advantage of randomised public key encryption scheme such as EIGamal encryption?

I am new to cryptography, I am very interested in cryptography, thank you for your answer.
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How to require two PRIVATE keyholders to decrypt a document?

Consider 3 entities A,B and C. I want A to be able to encrypt a document that can be decrypted only when keys of both B and C are combined. This question talks about a similar problem, but it uses AES....
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Why is the server's public key always used in SSL encryption and never the client's public key?

I spent a lot of time looking for an answer to this question, but the majority of answers never explicitly explain why the client's public key is never used; it's always the server's public key that's ...
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Unable to determine plaintext from ciphertext

Given the letter-number cipher: a=00, b=01, c=02, etc., encrypt the word 'hi' and decrypt its ciphertext using RSA. The public key is (5,35) and the private key is (29,35). I know that 'hi' is ...
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Testing speed of symmetric vs asymmetric encryption and decryption using gpg

I'm aware that symmetric is faster than asymmetric. I want to test this, but my (obviously incorrect) tests show the reverse. Symmetric test: ...
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Encrypt symmetric session key with asymmetric or symmetric master key?

Every day, I must backup my server's files, encrypt the backup, and upload it to untrusted cloud storage (dropbox, s3, etc.) I've spent time on security.stackexchange where I discovered the typical ...
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Computationally expensive key derivation whose difficulty is asymmetric

I am looking for a primitive or a construction that meets the following requirements. Is such a construction (a) theoretically possible, and (b) in existence right now? Given are: a long secret $X$ ...
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How is asymmetric cryptography safe if one of the keys is public?

Let's suppose $A$ is sending a message $m$ to $B$ using asymmetric cryptography. To guarantee the authenticity of a message, $A$ encrypts $m$ with $A$'s private key: $E(m, k_A) = m_A$. Then, $A$ ...
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Is there a digital equivalent to the Great Seal of the United States?

Since antiquity (and, for ceremonial purposes, up to the present day), physical documents have had seals affixed. In principle, these seals enable anyone, if he knows what he's looking for, to judge ...
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Why is Multiplicative group used in RSA or Euler's theorem but not additive?

I am on the verge to understanding RSA, but suddenly a question popped into mind. When we are calculating $U(N)$ i.e $U(PQ)$, we are taking invertible elements that are co-prime to $N$. For example, $...
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Research topics related to cryptography and Hamiltonian cycles

I am very interested in pursuing a research where I can show an application of Hamiltonian cycles in Cayley graphs of some group such as reflection groups to the field of cryptography. But currently ...
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is using secp256k1 curve for ECIES considered safe?

I read SafeCurves it indicates Secp256k1 is not SafeCurve by their standards but bitcoin and ETH use it in their blockchain. I researched more and figured out that using Secp256k1 ECDSA(singing ...
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How to find the inverse of a polynomial in NTRU-PKCS

I am coding a java based implementation of the NTRU public-key cryptosystem. I can comprehend the majority of the algorithms involved in the encryption and decryption process well enough, but the key ...
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Storing public key in cookie

I am encrypting my password before sending to my server with a public that i have stored as a cookie. Is there any security risks storing my public key in the cookie? Are there any better ...
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Classification of attacks against lattices

I'm interested about the cryptanalysis side of lattice-based cryptography, and was wondering whether there is a survey paper or something that gives some classification of attacks against lattices, ...
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Relationship between $N$ and $\phi(N)$ in the RSA algorithm

Recently I started learning how the RSA algorithm works and there is one single part of the computation which really confuses me and can't get over it. Let's say I chose 2 prime numbers, namely $P ...
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Are the signcryption and the authenticated encryption same?

The signcryption and the authenticated encryption are both the combine of encryption and authentication with three natural composition (i.e., EtS, StE, E&S). I am not sure that if they are the ...
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Is it secure to use ECDSA for any arbitrary point on the Elliptic Curve as the Generator point?

My question concerns the elliptic curve $E$ over a prime field $\mathbb F_p$. To the best of my understanding, ECDSA requires a Generator point $G$ of prime order $n$, and the $r$ and $s$ values of ...
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What is the use of a nonce in public-key encryption if it's meant to be shared?

I'm using PHP. The guys over at paragonie have made encryption easy for the PHP eco-system. Now, on my computer, Alice, when I ...
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Why encrypt symmetric keys first with RSA and then the private-key with a PW?

In for example the Microsoft Encrypting File System, the SYM-Key is first encrypted with a RSA-Pub-key and its corresponding private-key is then encrypted using a users password. Why not encrypt the ...

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