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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Given $e$ and $d$, find $\phi(n)$

Let's say we have just RSA public and private exponents $e$ and $d$ but not the corresponding modulus $n$. Is there a method to find $\phi(n)$? This is for a CTF challenge. I am not concerned about ...
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Code used for McEliece cryptosystem

In the McEliece cryptosystem, is choice of the code known to the attacker? And if a structural attack succeeded and the attacker found the generator matrix of the code, how did the attacker decode the ...
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RSA encryption key conditions

I recently read the RSA cryptosystem but now I confused in key generation phase. According to the Euler's Theorem, we have just one condition: e.d = k.ϕ(N) + 1 where: "e" is encryption ...
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Breaking RSA with Factor in Range of $\sqrt{N}$

Suppose on of the RSA prime factors $p$ is the range of $\sqrt{N}$, in particular it holds that $|p-\sqrt{N}|<\sqrt[4]{N}$ I want to show that RSA can be broken in time poly(log N) Given hint: $N = ...
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How to devise cryptographic system with data-sharing ability and password reset

I originally posted this in the security.stackexchange forums but then I was directed to this one which seems more befitting for my question. I am writing a C# .NET application. For my application the ...
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Why aren't public-private keys sufficient to build a block chain? Why do we need proof of work/stake?

Taking the simple case of Bitcoin here: If all nodes can validate published transactions by checking the signature (created using the private key of the sender) of the transaction against the public ...
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How to assert identity in a secure and non-copyable way?

Say I have the Mona Lisa, and I want to stick an RFID tag or similar mechanism on a back corner of the painting to verify this is the real Mona Lisa and any others are forgeries. What mechanism would ...
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What exactly is asymmetric about 'asymmetric cryptography'?

What exactly is asymmetric about 'asymmetric cryptography'? https://www.sysadmins.lv/blog-en/digital-signatures.aspx says: "In other words, anything that is encrypted by a public key can be ...
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Should we sign-then-encrypt, or encrypt-then-sign?

Frequently, we want to send messages that are (a) encrypted, so passive attackers can't discover the plaintext of the message, and (b) signed with a private-key digital signature, so active attackers ...
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What is the difference between openssl functions - d2i_PublicKey & d2i_PUBKEY and what scenarios decide which should be used?

What is the difference between openssl functions - d2i_PublicKey & d2i_PUBKEY and what scenarios decide which should be used?...
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How about, when using public key cryptography, one encrypts, signs, and encrypts again?

I suppose one reason for prepending the name would be that a malicious Bob could pose as Alice by encrypting the exact same message + Alice's signature using Charlie's public key, and trick Charlie ...
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Factoring an RSA modulus given high bits of a factor

I have {e,N,C} and part of p; can I get q from this example : ...
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TLS 1.3 Handshake - Usage of MAC and Digital Signature for CertificateVerify and Finished Message

I was wondering, why the TLS 1.3 handshake employs two different 'messages' that compute an authentication code over the whole handshake. As far as I understand, the CertificateVerify "message&...
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How does the key agreement process take place in Virgil E3Kit SDK for end to end encryption?

I'm using Virgil E3Kit SDK to implement end-to-end encryption in my App. Their E3Kit SDK is very effective and not too hard to understand, but I still don't understand how does the key agreement ...
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Proving the security of the public key BGV scheme

The security proof basically comes down to the following based on this paper. We want to show that two distributions are statistically indistinguishable. Say we have that $a,a′,x,x′$ are drawn from an ...
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Hashing Public Key of Lamport or Winternitz OTS

For the Lamport or Winternitz public keys, couldn't one just hash down the large public key to 256 bits in order to greatly reduce the public key size while still having basically the same security? ...
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Complete taxonomy of public-key cryptosystem primitives

This question is similar to “What primitives are needed to generically implement public-key cryptography?”, but with a more applied/contingent focus: That question asked about what's theoretically ...
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How does a forward search attack work? [duplicate]

I just came across this term “forward search attack” while reading about Interchange key and Session key. The book mentioned that using session key helps to prevent attacks such as forward search ...
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What does $\text{PK}=\text{pk}\oplus\text{H}(\text{opk})$ represent in this paper?

In Lu, Au and Zhang's 2019 paper (Linkable) Ring Signature from Hash-Then-One-Way Signature, they …extend [M. Abe, M. Ohkubo, and K. Suzuki's 2019 1-out-of-n signatures from a variety of keys] ...
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How can I enhance the security level of my RSA code?

I am trying to enhance the security level of my RSA code that I implemented in Python. I tried to add blind operation, randomized algorithm to my RSA code (separately, not together), but I am not sure ...
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What is the name of this public key encryption cryptosystem?

I have been trying to find the name of a public key encryption cryptosystem that I learnt as an introduction to cryptography some years ago but the only scheme I could find was something similar but ...
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Why does key generation take an input $1^k$, and how do I represent it in practice?

In my lecture, the lecturer said: Let $K$ be the key generation algorithm. Given a security parameter represented in unary, $1^k$, $K(1^k)$ will output a keypair $(pk; sk)$, known as the public ...
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Is cypher.js secure for sensitive data? [closed]

Is this library secure? Link to github repo Here's his explanation: Cypher does not encrypt through allocation based on mapping patterns. Cypher encryption process is completely mathematical and ...
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What is the SSL private key file format?

I was researching about how to encrypt with RSA. I understood everything but not the format of the private keys. In the phpseclib (RSA in PHP), you can import your private key (private.key format) ...
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Is this protocol secure?

Before anyone freaks out, this is purely speculative and I am not developing a cryptosystem! I can't see anything wrong with this protocol, but my knowledge of cryptography is rather superficial: ...
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Do certificates need to be stored as encrypted?

The titles says most of what we're confused with. Here's some details: On an embedded device, we have a microcontroller and external flash memory. This memory can be easily read and written to in ...
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What is the simplest post-quantum asymmetric cryptographic algorithm for key exchange?

This question has been burning in the back of my head for the past few days, and a quick Google search doesn't yield any usable results. As the title suggests: What is the easiest-to-understand post-...
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Are zero knowledge proofs alternative private key encryption? [closed]

Are they the alternative to private keys. If I understand correctly, because of the increasing computational power in today's world, zero knowledge proofs are more safe than private keys ? Are these ...
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RSA algorithm implementation

$$m^{ed} \equiv m \bmod n$$ $n =pq$, so by Chinese Remainder Theorem it is equivalent to $$m^{ed} \equiv m \bmod 𝑝, m^{ed} \equiv m \bmod q$$ where $n=p\cdot q$ So how did 2 come from 1 by the ...
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Is it possible to create a “digital seal” to tell if a document has been opened?

So, in real life we have a handful of ways to leave a physical mark on a packet to know if it has been opened without authorization (eg. you can use 'opened' security tapes, or you can put a signature ...
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RSA public key identification

Consider a multi party system where public keys of all receivers are known. Server wants to send message to one of them using (textbook?) RSA. Adversary is given ciphertext and even Message to be send,...
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How many points in RSA, such that $m^e = m \bmod n$

For every RSA-cryptosystem, there exist some messages $m$, for which it holds that $m^e \equiv m \pmod n$ As to the question, how many such messages exist, this question has already been asked and ...
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Derive one public key from ECDH when the other and and the shared secret is known

Suppose we have an elliptic curve Diffie-Hellman key exchange protocol, where Bob and Alice have public keys $pk_{Alice}= [sk_{Alice}]G$ and $pk_{Bob}= [sk_{Bob}]G$ ($[.]$ elliptic curve "...
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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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Difficult to guess the targeted receiver

The protocol is defined as : Bob want to send message to one of his friends say $k$ friends , he does not want his others friends (except one whom he want to send message ) to tell who is targeted ...
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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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Calculate private key from public key and r [closed]

I watched this video where somebody finds bitcoin wallet private keys using only the "sigR" value and the public key using a python script named "formula". How does this work and ...
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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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How do I encrypt a bunch of messages by different authors, shared with that group of people?

I'm still getting my head around public/private key cryptography, and I can't quite work out how to ask the right question to get an answer for this problem, but here goes! Alice, Bob, Carol, and ...
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Zero knowledge proof for Paillier addition under multiple keys

Suppose $m_0, m_1, m_2 \in \mathbb{N}$ such that $m_0 = m_1 + m_2$, $m_i > 0$ (none of them can be 0 or lower) Under a Paillier cryptosystem, set $e_0 = E(m_0, r_0)$ for a public key $(g_0, n_0)$ ...
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How can a public-key encryption scheme be used to construct a commitment scheme in the CRS model?

For a PKE scheme $(Gen, Enc, Dec)$, the most 'obvious' idea is to commit to an encryption of a bit and in the reveal phase maybe send $r_g$, $r_e$ where $r_g$ is the randomness of $Gen$ and $r_e$ is ...
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Should I encrypt the signature along with the message? [duplicate]

Given that A wants to send a message M to B, I have 2 scenarios as shown: The difference between the 2 is that for case 1, the digital signature is appended to the message before being encrypted ...
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Verbatim of early work on public-key cryptography?

In late 1997, the history of public-key cryptography was turned around with the announcement (then extended) that public-key cryptography was theorized in a 1970 note [1] by James Henry Ellis: The ...
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Hash of a ciphertext

Would hashing a ciphertext (so $H(Enc(pk,m))$) compromise it in any way if both schemes are secure by themselves? This doesn't seem to be the case but I couldn't find a definitive answer.
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Does there exist a provably correct and recipient hiding encryption scheme?

I am looking for an encryption scheme $E$ and a commitment scheme $C$ which allow encrypting the message $m$ for the public key $y$ as $e = E_y(m)$, so that the ciphertext $e$ does not reveal any ...
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Why is the market for cryptographic primitives non-commercialized?

There are not many successful companies in cryptographic primitives market. Certicom holds many patents attached to the ECC. RSA Security probably made some profits from the patent. Are there more ...
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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 clarification because I am still struggling to really grasp the underlying concepts of RSA. Specifically, why can't we choose ...
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Can Big Data together with deep neural networks attack RSA by affording the vast calculation of prime multiplications in advance?

This is a spin-off from Can Big Data attack RSA by just calculating many prime multiplications in advance? [duplicate]. Intro I am somewhat new to cryptography. Repeating the basics of RSA from How ...
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BIKE: Bit Flipping Key Encapsulation - Inverse encryption / decryption

I'm trying to understand white paper about BIKE Asymmetric crypt. And actually read about the inverse matrix that needs to be produced for decryption. My concern is: Can I actually encrypt data with ...
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Public key derivation for Ed448

Another potentially silly question here, but I seem to have developed tunnel vision and I am missing something very basic. In RFC 8032 one can find a number of test vectors for Ed488 - for example: <...

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