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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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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Encrypt encryted message vs DS
In digital signature The encrypted message is signed by the sender private key and verify using sender public key. The encrypted message is encrypted with another public private key pair which the ...
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Interchangeability of hash outputs
I'm looking at tweetnacl, its crypto_sign_keypair, crypto_sign, and crypto_sign_open ...
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is it possible to achieve authenticated key agreement without using PKI or pre-shared secret?
After reading different techniques to achieve authenticated key-agreement (X3DH, HMQV, Asynchronous Ratcheting tree, An efficient protocol for authenticated key agreement, I understood that all these ...
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Forging a new secret key in RLWE
In a RLWE setting where you are given a secret key $s$ and an associated public key $pk = (p_0,p_1) = (-(p_1s+e),p_1)$, is it possible/easy to forge a new secret key $s'$ such that $p_0+p_1s'$ has a ...
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Signing a secret key with ECDSA
Assume Alice and Bob both separately come into possession of the same randomly generated 256 bit secret key.
Alice has Bob's public ECDSA key.
Alice wants to verify that Bob has possession of the ...
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Fixed point in RSA encryption
Some papers count the number of the fixed points in the RSA encryption algorithm. They're a minimum of 9 and the real number depends on the smoothness of primes $p$ and $q$.
It very unlikely that a ...
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Asymmetric Cryptography decryption
I am new to cryptography, i know essential part of asymmetric cryptography but is it possible to decrypt 617 decimal digits (2,048 bits) with RSA ? How it can be factored?
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Can I use the secret part of a asymmetric encryption keypair as a symmetric encryption key?
Background
I'm working on a framework for crypto-based authentication and authorization that is largely inspired by the way Keybase's Teams product works.
Keybase uses the same process to generate ...
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Bruteforce attack on a 64bit computer [duplicate]
How would I attempt to brute force a RSA encrypted message with a 64bit computer if it the memory can't put up with calculations bigger than 64bit? Without going that far to attempting to crack it, ...
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Implementing BFV Relinearization
I'm currently working on a Python implementation of the BFV[12] cryptosystem.
I got to a point where key generation, encryption, addition and decryption works as expected. Where I'm struggling with ...
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Is MAC process different for symmetric and asymmetric?
Message Authentication Code as far as I know works on the shared secret key. Do they work in the same way. Is there no difference between symmetric and asymmetric processes. Can anyone please explain ...
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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 ...
