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 any encryption system that changes keys for each session “forward secure”? [duplicate]

As far as i understand, a encryption system is forward secure if new session keys are generated for each session, which is also part of what wikipedia says about forward secrecy: By generating a ...
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Chaining signatures of different parties

My question might be quite beginner, so please pardon my ignorance :) So, assume there are 10 parties, each with their own keypairs. There is a message $M$ that is passed from one party to the next. ...
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Can I use ECC for encryption/decryption, just like RSA? [duplicate]

I'm familiar with RSA for asymmetric encryption. I also understand it's only supposed to encrypt small amounts of data (smaller than the key) so for encrypting arbitrary data I would typically ...
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Public key decryption?

In the article How Does the Blockchain Work? the writer makes the following statements: Since only you should be able to spend your bitcoins, each wallet is protected by a special cryptographic ...
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Why would you want to keep the Initialization Vectors Public?

So I was researching Initialization Vectors (IV) and even took a look at this thread... What is the main difference between a key, an IV and a nonce? ,but I was hoping that I could get some clarity. ...
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Safety of a private key when knowing the full content of an encrypted message in case of fixed initialization vector

When knowing the full content of the original message, will I be able to derive the private key from the encrypted message when the underlying encryption uses a fixed initialization vector? Meaning if ...
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Is it safe to use RSA multiple times

Assuming I have multiple symmetric keys on specific machine(more than 10000 probably), can I use the same rsa key to encrypt all of those keys? I'm a bit concerned from a situation where multiple ...
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Is there a cryptographic scheme that achieves both confidentiality and integrity?

Suppose that Alice wants to send a relatively long message M to Bob. Also, suppose that both Alice and Bob have a set of {PK, SK} for public key cryptography. Alice proceeds to encrypt the message M ...
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How Does Prime Factorization Break ECDSA?

I have heard that ECDSA will be broken in the not-to-distant future (roughly 15-25 years) by Quantum Computers running Shor's Algorithm. However, to my understanding, the only purpose of Shor's ...
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Has anyone implemented a public-key encryption scheme using a universal one-way function?

There exists a function $f$ such that if one-way functions exist then $f$ is a one-way function. Such a function is called a universal one-way function. Now the public-key encryption schemes that I’...
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Can I use the same key pair for authentication and Diffie-Hellman? [duplicate]

Assume Alice has a key pair $(A, a)$ and Bob has a key pair $(B, b)$, where $A = Ga$ and $B = Gb$. In general, the basic rule of crypto says that we should not use the same key for different ...
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May an adversary be fooled by a random-looking input that in reality is fixed?

I want to prove the EUF-CMA-security of a signature scheme. It is a variation on an established scheme, therefore I would ideally like to reduce the new-scheme-security to the old-scheme-security. the ...
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Implementation of a decryption mixnet, and problems with the size of the key

I've been studying decryption mixnets, in the context of e-voting and stealth networks. Let's describe it in a very simplified way. The concept is pretty simple. A message M is forwarded through ...
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Is it possible to have perfectly secure public-key cryptography with oracles?

It is a basic theorem of cryptography that it is impossible to have a perfectly secure public-key encryption scheme. That’s because the adversary can search through all possible private keys. But I’m ...
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Difference and relation between ed25519, x25519 and XEd25519 [duplicate]

In my Rust implementation of a messaging system, I'm using currently two cryptographic primitives: ed25519_dalek and x25519_dalek. I use ed25519_dalek for DSA, while x25519_dalek for encryption of the ...
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Why should I export my private key instead of well known asymmetric crypto mechanism on openkeychain?

I'm trying to use password-store as password manager under linux. I created a private github repo with my gpg files in order to use it with other devices. I installed android-password-store app for ...
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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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Privacy preserving aggregation of encrypted data

I have the following problem: I have $t$ servers $S_1, S_2, S_3, \ldots, S_t$, each of them storing some $key : value$ list. They have to upload this data into a big dropbox server $D$, but in such a ...
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ECIES for encrypting ECDH key exchange

I started studying Elliptic Curve Cryptography, and I do not know if I understand the difference between ECDH and ECIES (even with the other posts here on stackexchange). I'm wondering if ECIES can be ...
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Using first, say, 50 letters from a public key as user identifier?

I am making a messaging system where users are identified by their public keys. It doesn't matter which friendly username they have, so I'm not going to prompt them to choose one. Each user will ...
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What are the smallest possible RSA private and public keys?

I'm trying to understand what the smallest possible RSA public and private keys are. When using $p = 2, q = 3$, the encryption function doesn't encrypt. So I have to shift one prime to get $p = 3, q = ...
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Significance of y-coordinates in ECDH public key exchange

In the research paper Breaking the Bluetooth Pairing – The Fixed Coordinate Invalid Curve Attack? by Biham and Neumann, 2019, they talk about attacks in Bluetooth pairing, they state that in the ...
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Have time-release servers been implemented?

Conceivably, Alice could release a public encryption key and promise to release the private decryption key on a certain date. That way anyone could use that encryption key, combined with others from ...
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Which is the simplest cryptographic algorithm which is close to commercial-level security?

An algorithm is simpler than another if It is easier to explain to a noob with basic high-school math knowledge. It is easier to securely self-implement by an intermediate programmer (Yes I know one ...
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Why are ed25519 keys not recommended for encryption?

Was wondering why there is no straightforward way of using ed25519 keys for encryption. Then I found this: https://github.com/indutny/elliptic/issues/108 There it is stated that it's unlike RSA not ...
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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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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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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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