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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Is there a relation between the private keys of secp256k1 public keys of opposite parities?

From observation, 32 bit public key values of opposite parities are either both valid, or both invalid. ...
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Is public key ever used to encrypt data directly?

In TLS, asymmetric encryption is used to agree on a symmetric key, which is used to encrypt/decrypt the data. I want to ask if there is any scenario or system where the public / private key is ...
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Would asymmetric cryptography be feasible in World War II?

Assuming people in the forties would have known asymmetric cryptographic methods like RSA, would they have been able to make sensible use of them? There were no real electronic computers at the time, ...
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How can two parties offline generate a sequence of corresponding key pairs that are still sufficiently random

I'm looking to design a protocol between two parties A and B to generate sequence of RSA private keys $p_{a_0}, p_{a_1}, ... p_{a_k}$ and a sequence of corresponding RSA public keys $P_{b_0}, P_{b_1} ...
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Choosing UWP encryption algorithms

I've just come across the large variety of encryption ciphers available in the UWP WinRT API, both symmetric and asymmetric. I'm trying to figure out which are commonly seen as the most favourable ...
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Smart's attack for secp256k1 does not work

This is the Sage code that I use, and the results I get: ...
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Find Consecutive X-Coordinate algorithm

The question is as follows: Is there an algorithm to calculate a $(x,y)$ pair which is consecutive to an existing $x$-Coordinate on an elliptic curve? Background Information for the curve: Known ...
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Does selectively generating keypairs with particular public-key hash prefix weaken the security?

I'd like to embed 8-bits of information by selecting only keypairs where a hash of the public key begins with those 8-bits. (The expected number of keypairs that will need to be generated is 256, so ...
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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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Are the asymmetric roles of the two keys in the elliptical curves the same (as for RSA)? Can they be interchanged indifferently?

More precisely, and as for RSA, is it really true that it is not feasible to recirculate one of the keys knowing ONLY the other with the Elliptic Curves, as for RSA? Or does ECs work differently on ...
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DES decryption of the homomorphic encryption ciphertext

I implemented an application using partial homomorphic encryption for outsourced computations. To get an efficient bandwidth, I am thinking to apply (DES) symmetric algorithm to encrypt the message ...
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How to compute $m$ value from RSA if $phi(n)$ is not relative prime with the $e$?

Here is some information we got : We know the value of $n$, with size $1043$. We know the value of $p$ (size $20$) and $q$ (size $1023$) as the factors. $e = 65537.$ $\varphi(n)$ = $(q-1)(p-1)$ When I ...
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How to recover RSA messages if they are padded with spaces?

I have a message m="hunter". Let's say we pad it with 2 spaces from the left making the final message as ...
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How exactly is signature verification done in SSH v2 authentication?

One of the authentication methods in SSH involves the client signing a message with its private key and sending it to the server for verification. RFC 4252 (page 9) says: ...
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Any gotchas when deriving a symmetric key from two seeds?

Consider a connection protocol where, after jumping through several other hoops, Alice and Bob know each others' public keys; and they now want to do a RSA-handshake-kind-of-thing to come up with a ...
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Signing a GPG Public Key

I am trying to manually create a GPG Public Key (see here). I am able to generate a GPG Public Key with a correct hash, but fail to RSA-sign that hash in a way that is accepted by the GPG CLI. For the ...
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MQV protocol and man-in-middle attack

Why MQV is said to be an “authenticated Diffie-Hellman” protocol? The process in the picture shows nothing about authentication. Besides, a man-in-middle can impersonate B to negotiate with A, because ...
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How would I get started in auditing and finding vulnerabilities in encryption algorithms?

I know, it sounds dumb. Very dumb in fact. But regardless, I want to actually begin doing security research on cryptographic algorithms (SHA, RSA, ECDSA, etc.). I would prefer that this question be ...
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Proof by reduction for for digital signature scheme $S_2((sk_0,sk_1), m):=(S(sk_0,m), S(sk_1,m))$

Let $(Gen,S,V)$ be a secure signature scheme (existentially unforgeable under a chosen message attack) with message space${\{0,1\}}^n$. Generate two signing/verification key ...
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Adversary for attack on one variant of ElGamal

I came by the following question: Consider the following variant of ElGamal encryption. Let $p= 2q+ 1$, let $G$ be the group of squares modulo $p$ so $G$ is a subgroup of $Z_p^*$ of order $q$, and ...
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Same private key for signing and decryption

I am designing a service which identifies records with public keys. All other fields are encrypted with that public key and protected by a HMAC. For authentication, I am thinking about signing ...
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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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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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Key strength comparison: symmetric key vs RSA/DH key

I came across different reputable sources quoting different equivalent symmetric key strengths for RSA/DH keys. This NIST paper (page 67) states the following offer corresponding security strenghts (...
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RSA encryption/decryption values not working as expected [duplicate]

I'm faced with an issue I can't seem to understand when it comes to RSA. Below are my values for all of the parameters, unfortunately I can't seem to get the expected decrypted values from my ...
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Generating a recovery phrase for a RSA key-pair

What is an optimal way to associate a RSA key-pair with a recovery phrase/seed for access recovery purposes? I've seen a lot of cryptocurrency wallets provide this feature, however, I'm not looking to ...
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Is choosing $1$ as a public exponent valid in RSA?

I know it will not encrypt anything. But is $1$ valid as a public exponent in an RSA public key?
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Is it fair to say that MACs use a signing algorithm?

The Wikipedia page on MAC calls the algorithm that is used to generate the MAC as a signing algorithm. Is that a fair use of that term? Can we then say that HMAC-SHA-1 uses SHA-1 as the signing ...
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How does CL signature work?

I'm studying the CL signature that how can it works. However, I cannot understand how equation (42) is calculated. What is the last three factors? The value T is as follows: $$T \leftarrow(A')^{\...
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Calculating RSA Public Modulus from Private Exponent and Public Exponent

If I know the private and public exponents ($d$ and $e$) of an RSA key pair, is it possible to (efficiently) calculate the public modulus $n$?
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Sensible amateur usage of web crypto API

I want to know if my usage of the web crypto API is sensible. I want to use it for symmetric and public-key encryption and decryption, and signatures, but as a non-expert I am scared by the warning on ...
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Can we defends against RSA Timing attack when we use java.math.BigInteger.modPow?

I think that Montgomery and sliding window techniques are applied within java.math.BigInteger.modPow (and more specifically ...
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How to generate Multiple Encryption Keys for use in RSA polymorphic multiplication

I am a long time scroller, first time poster in the crypto stack. I've recently been finding myself leaving the realm of mainstream/standard crypto (imo that consists of symmetric/asymmetric ...
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Could someone please explain the implementation of public-private key encryption for storing passwords?

As someone new to cryptography,I have a question about how logins work on websites. I understand mathematically how asymmetric encryption works and how https web requests work to securely send ...
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Which public-key cryptosystems are used the most?

Does anybody know if there is some kind of measure on how often public-key cryptosystems like El Gamal, RSA,... are implemented. Which ones are most common?
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How do NTLMv2 hashed passwords work?

We have an application which embeds NTLMv2 password hashes into its configuration. In attempting to assess the security of this practice, I'm not finding much straightforward information about how an ...
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How to derive a private/public keypair from a random seed?

For RSA, my understanding is that large primes are found randomly to build a private/public keypair. If a static seed can be used in that random search process, it should be possible to derive the ...
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Authentication using a nonce

For an authentication problem imagine the following scenario with two devices: 1 server 1 client. The client starts a conversation with the server and sends him his public key. All public keys in ...
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What if the CSR is intercepted in transit while sending it to CA?

I was studying PKI the other day and I had a serious thinking about the following question. What is CSR? - It is a block of encoded text that is given to the CA when applying for an SSL certificate ...
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Why does Encrypt-Then-Sign not yield a CCA-secure public-key encryption scheme?

In symmetric cryptography, combining an IND-CPA secure symmetric encryption scheme with a secure MAC with the encrypt-then-MAC method yields a IND-CCA secure symmetric encryption scheme. I am trying ...
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What's happening with IEEE 1363?

IEEE 1363 (or more precisely, IEEE 1363-2000) - the IEEE Standard Specifications for Public-Key Cryptography - has been inactive for so long, that it is now with status Inactive-Reserved by IEEE, and ...
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What is the exact meaning of the public key cryptosystem properties in New Directions In Cryptography by Diffie and Hellman

I'm quite new to cryptography and don't have much mathematical knowledge. I'm studying cryptography, especially public key algorithms. I have some basic knowledge of public key algorithms so I know ...
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What is the code when looking at the LPN problem?

We are given the problem in this question. We know that we have to use the algorithm $A_D$ in order to get $e_i$. Our idea is that we construct a vector $l$ of $l_i$'s by getting $n$ samples from the $...
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Can libsodium's X25519 encryption construction be generalized?

It is my understanding that libsodium's sealed_box is based on X25519, a Diffie-Hellman function: By combining the X25519 key agreement with a symmetric cipher and having a recipient derive the ...
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Can I still use insecure curves/ciphers for time relevant encryption?

Can Ciphers that are known to be insecure because their keysize is considered too small still be used in appliances that have a tight decryption timeframe? In particular I am looking at ECC2K-130. ecc-...
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TLS 1.2 AES-GCM decryption problem

I'm trying to decrypt a PCAP encrypted with TLS 1.2. I have the private key and Wireshark is able to decrypt the data so what I am doing should work but there is obviously something wrong. The ...
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Solving LPN using algorithm for syndrome decoding

Given an algorithm $A_D$ which solves an instance of the decoding problem $e \in \mathbb{F}_2^n$ in time $T_D$ given a parity check matrix $H \in \mathbb{F}_2^{(n-k)\times n}$ and a syndrome $s \in \...
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How to get fixed m from different pairs of n, e and c in RSA?

In RSA cryptosystem, if I have two (or more) pairs of public key and also the corresponding ciphertexts, can I get the fixed message from them? I cannot think up any good idea for now.
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Can we use HMQV in an asynchronous setting?

Following the HMQV paper, to perform a key-exchange, Alice ($\hat{A}$) and Bob ($\hat{B}$) perform the following: $\hat{A}$ generates the long-term key pair ($sk_A= a$, $pk_A =g^a$) and the ephemeral ...
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Does Cramer-Shoup allow re-randomization?

Is it possible to re-randomize a ciphertext with the Cramer-Shoup System? I have some Cramer-Shoup ciphertexts and i want to re-randomize them, so they look different and are unlinkable to there ...

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