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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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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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Using HKDF to derive symmetric keys from a hybrid public-key encryption scheme

RFC 5869 describes HMAC-based Extract-and-Expand Key Derivation Function (HKDF). In section 4, entitled "Applications of HKDF", it states that one of the intended uses is: derivation of symmetric ...
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decoding a Ed25519 key per RFC8032

RFC8032 Edwards-Curve Digital Signature Algorithm (EdDSA) 5.1.3 Decoding states the following: Decoding a point, given as a 32-octet string, is a little more complicated. First, interpret ...
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Group for which computing inverse is hard

Is there any group in which not only discrete logarithm and finding square root are believed to be hard, but also finding the inverse of a given element? Thank you.
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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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137 views

Comparison of different asymmetric signatures

Please forgive me, because I suspect I don't even know enough to ask this correctly: Can someone speak to the pro's and con's of the various asymmetric signatures? I have a use-case in which I put ...
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236 views

Does secp256r1 or secp256k1 use a=-3?

I saw a post here which I think states that for P256, a is equal to -3. Why is elliptic curve parameter $a=-3$ somehow special I am not sure if this is correct, or maybe I am misunderstanding ...
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102 views

ElGamal with weak public key

Assuming this setup: A prime $p$, a generator $\alpha$ in $\mathbb{Z}_p^\ast$. Alice chooses her private exponent $d$ from $[2, p-2]$ and calculates her public key $\beta$ = $\alpha^d$. Bob then ...
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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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27 views

Secure scheme to share symmetric key using asymmetric keys and certificates with N parties

I need to distribute symmetric AES key into number of end points which will use it to decrypt data. The AES key will be the same on all end points, it is not possible to generate unique on every end ...
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What's the difference between rsa_pss_pss_* and rsa_pss_rsae_* schemes?

I'm trying to understand the difference between rsa_pss_pss_ and rsa_pss_rsae_. The picture shows the extension of TLS1.3's ...
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What threat do quantum simulators pose?

I recently saw an article at phys org that did some sort of "quantum simulation" on a conventional computer to calculate prime probabilities, the article (and paper associated) does mention shor's as ...
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Why is prime factorisation computationally intensive compared to normal factorisation?

Why do we use prime factors in asymmetric algorithms compared to other factors? For example: lets say we use two prime numbers p = 53 and q = 59 our public key in RSA algorithm would be p * q =...
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What are the applications of dual receiver encryption (DRE)?

In contrast to standard public-key encryption, in which only two parties communicate, dual receiver encryption (DRE) allows sending the same message $m$ to two different receivers at once. The ...
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203 views

Allow everyone to decrypt a message, but don't allow anyone to encrypt it

I would like to create a software that will be installed on multiple clients. I would like to broadcast an encrypted message to all of those clients. Each client should be able to decrypt the message ...
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Why is the lite version of Cramer-Shoup not IND-CCA2 secure?

In the lite version of Cramer-Shoup we have a group $G$ with generators $g_1$ and $g_2$, private key $a_1, a_2, b_1, b_2$, and public key $A = g_1^{a_1} g_2^{a_2}$, $B = g_1^{b_1} g_2^{b_2}$. ...
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Is there a feasible way to generate an RSA key manually the same way as it is for an ECC one?

In elliptic curves, a private key is just a random number, and one relatively small compared to other crypto systems (256 bits for ECC vs 4096 bits for RSA for example). Suppose I don't trust ...
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Benefits of signing RSA-encrypted data?

I recently came across this (PDF) journal article, which describes what it calls "A New Design Of A Hybrid Encryption Algorithm" (which I must say, doesn't sound very novel, even in 2014!): An AES ...
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Quantum algorithm encrypting classical data

Are there schemes for encrypting classical ciphertext using quantum algorithms? Specifically, if a public key system exists for classical data, and classical ciphertexts, can this scheme be ...
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Zencash uses your passphrase to identify AND unlock a wallet - how is this secure?

When looking into Zencash I stumbled into myzenwallet.io (by the Zencash creators), which gives you the option to enter a passphrase to generate a wallet (seems normal), but then after creating your ...
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Is the private key of a private/public key pair also a symmetric key?

I think I've got a fairly good (practical, not mathematical) understanding of symmetric versus asymmetric cryptorgraphy, so the difference between those is not the question. In a local discussion ...
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428 views

How is public key cryptography used for digital signature?

In public key cryptography, there are two different keys used for the encryption and decryption of data . I am wondering how it is used for digital signature
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What's the difference between single key-pair public key encryption and proxy re-encryption?

Proxy Re-Encryption provides the ability to transform a ciphertext encrypted under some key to the one under another key. This seems interesting. But, something seems strange. Suppose Alice has a key ...
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Does public-key + hashing create a security vulnerability?

The title says it all really...let's say I have a packet of data that one of my applications needs to store encrypted with a public key (RSA, say, with the private key kept elsewhere). Let's say the ...
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What is the difference DET-ABE Vs CP-ABE and KP-ABE?

I can't understand what's does it mean DET-ABE (digital envelope technique ) exactly , and is there a difference between it and the the cipher or key policy attribute based encryption, could someone ...
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Randomized public-key encryption as binding commitment / “collision-resistance”?

I am looking to use randomized public-key encryption in a context where it should also serve as a sort of "binding commitment". That is, I want to encrypt a value $x$ with some randomness $rnd$ under ...
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How can we encrypt a file to be just readable (and not writable) after decryption?

Is it possible to encrypt a file (e.g., a text document) such that when a user decrypts it, he/she be able to just read the file and not be able to change the content of the file? I mean, the result ...
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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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308 views

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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473 views

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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Looking for a specific cryptosystem (encryption two times with two different keys and then decryption with another different key )

I am looking for a specific cryptosystem with the following properties: Suppose a User (Say $User_1$) encrypts a message $M$ with the key $K_1$ (the resulted ciphertext is $C_1$). Another user, say $...
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105 views

EL gamal cryptosystem

I have this question which gives me q=71(my prime number) , a=7(generator), Yb=3(public key), m=30(message), c1=59(first cipher text) and he wants me to find c2 (second cipher text) I know that c2 = ...
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Any downside to encrypting original signed message with the private key?

Is there any downside to encrypting the original message for signing purposes. I understand this does not provide actual protection, and any one with the public key (any one in the world if the public ...
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235 views

Integrity or Confidentiality or Authenticity

If a sender creates a hash H of message M and encrypts it using receiver's public key, what do we ensure of the above three at the receiver's end. PS : I know this is not the right way to send ...
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Benefits of using SSL certificate over a raw key pair for non-browser use?

For applications not involving CA signed certificates – or web browsers for that matter – it would seem to be easier to use a raw key pair if possible, rather than deal with potential formatting ...
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Keyed reversible hash function?

Is there such thing as a keyed reversible hash function? This would be a hash function where computing H(x) is easy and requires no key, but computing x from H(x) is only feasible with the key. Is ...
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Theoretical cost of Paillier cryptosystem

How can we estimate the theoretical cost of Paillier cryptosystem? Examples can be found here https://en.wikipedia.org/wiki/Paillier_cryptosystem ? Can any please discuss the cost in terms of big O ...
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With public-key crytography, is private-key crytography still useful?

It seems that, with public-key cryptography, there is no need to use private-key cryptography. But obviously, both public-key cryptography and private-key are taught in cryptography classes. Can ...
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263 views

Exploit RSA , given some information about n

Every week Bob updates his public RSA modulus $n=p*q$ and encryption exponent $e$ by picking a new pair of primes $p$ and $q$ and a new exponent $e$. After several weeks, bob becomes lazy and ...
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How does the authd protocol work?

So far, I have been able to research on what it is: authentication; authorization; using resource authd. I still have not come across a definitive answer or ...
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Recovering private key from Secp256k1 signatures

I've seen many answers here and many articles that says we can recover the private key from reused R signatures. But, what if the r,s signatures are different in transaction of bitcoin then is there a ...
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165 views

How trivial is it to derive a private key from two public keys?

It turns out that what I was attempting to do was create a form of ECDSA threshold signature protocol by just giving away multiple public keys and then having the two parties solve for the private. ...
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Secondary private key that produces limited certificates

I want some notion of a secondary key that behaves like this: Given a public/private key pair, it is not the private key but rather it is once-removed from it. Like the original private key, it is ...
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298 views

Verification using recovered public key from ECDSA signature and normal verification: what are the differences?

For ECDSA, a given signature and its message can be used to recover the public key used to sign it (produce 2 public keys). By making comparison of these recovered public keys against the known public ...
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62 views

Is there a way to double the size of ciphertexts of a public-key scheme which is IND-CCA2

Let $\Pi = \left( \mathrm{Gen}, \mathrm{Enc}, \mathrm{Dec} \right)$ a public-key scheme which is secure in the sense of IND-CCA2. Assume the ciphertexts space is $\mathcal{C} \subset \{0,1\}^{n}$. Can ...
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Public Key Encryption, how do you handle not trusting the middle man?

With public/private key encryption you must trust the central authority correct? What can you do if you don't want to trust the centeral authority? Are there any ways around that? for example in a ...
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Emulate multisignature wallet

I have a blockchain wallet with a single signature wallet, is there a way of making this wallet "multi-signature"? F.e can we use some secret sharing scheme to distribute the single private key among ...
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UOV signature scheme, how does the affine transformation work? What does the composition of the core map and the affine map yield?

I am having trouble understanding part of the UOV scheme, i get how it works except for when it comes to composing the core map F with an affine transformation say T, which i understand to be an ...
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Understanding how to use RSA and AES in S/MIME

I'm sorry if the question is dense, my understanding of this topic is not thorough. I have to send an email adhering to: Encrypting the email message via AES-256 Encrypting the email with their ...
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616 views

Understanding WannaCrypt's hybrid encryption scheme

I'm confused about how WannaCrypt's hybrid encryption scheme works after watching Computerphile's "How WannaCrypt Encrypt's Your Files" video a number times. Below is my thought process to make it ...