Tagged Questions

An asymmetric cipher is an encryption scheme using a pair of keys, one to encrypt and a second to decrypt a message. A special class of asymmetric ciphers are public-key ciphers, in which the encrypting key need not be kept secret to ensure a private communication.

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Bilinear Map vs Inner Product

What is the difference between a Bilinear Map and a Inner Product?
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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 by the CESG (April 2000 archive) that public-key cryptography was theorized in a 1970 note [1] by James ...
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66 views

DHE key exchange. Is it really secure?

Context I recently came across a video on the net showing the process of key exchange in Diffie Hellmann. Alice and Bob want to communicate. Eve is the (wo)man in the middle. This video is the ...
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1answer
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special public keys and modulo n

I just picked up cryptography and have some questions on RSA cryptosystem: Say there are two public keys (n, e1), (n, e2), e1 is coprime to e2. They share the same n. Is it possible to find the ...
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Opinion on my idea for storing credit cards securely

I've been thinking of ways to store credit cards securely, I thought of this: Take the users credit card info Put the card info in a standard format "Full Name/Card Num/Security Num/Expiry ...
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How can I prove CPA secure by using a new scheme gen,enc,dec from GEN,ENC,DEC?

Given public key encryption scheme $(gen; enc; dec)$, we now construct a new scheme $(Gen; Enc; Dec)$ as follows: The key generation algorithm $Gen$ is the same as $gen$. Each ciphertext for a ...
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1answer
80 views

Determining message given cipher-text and public key [duplicate]

Consider the following scenario: Suppose A and B have set up their RSA public keys, namely $(e_a, n)$ and $(e_b, n)$, where the n-value is the same. Also, it happens that the $\gcd (e_a, e_b) ...
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47 views

File format of an $2048$ bits RSA public key

From here, there are $14$ bytes specifying the file format of the key. I am still quite confused about the format bytes. For example, the following public key 30 82 01 0a 02 82 01 01 00 8e a3 d1 c7 ...
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Is Paillier cryptosystem commutative?

Is Paillier cryptosystem commutative? If not, how can we construct an oblivious decryption protocol based on Paillier?
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1answer
53 views

Can public key be recovered from chipher text & encrypted private key?

I'd like to implement something like a write-once public/private encrypted shared secret (no better quick description for the lack of terminology knowledge). I guess, i'm trying to implement HSM. The ...
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1answer
149 views

Security of RSA with $\gcd(pq, (p-1)(q-1))\ne 1$

The Congress of ThéOùÇa enacted that civilian use of any public-key encryption system is authorized on the territory of ThéOùÇa, subject to meeting certain security requirements published by the ...
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2answers
80 views

what is contained in a public key certificate

Public key certificate is a digitally signed document which verifies the sender is indeed the person. May I know how can the receiver tell the sender is indeed the person solely based on information ...
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signed message susceptible to block re-ordering , block deletion , block replication

We would implement a Public Key Cryptography (PKC) based digital signature by breaking the message into blocks and signing each block independently. One of the issues associated with digital ...
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43 views

Public key encryption without ciphertext expansion

Say I have a database column that is defined as VARCHAR(255) that stores names. I can assume that names can be up to 255 chars. I need a public key encryption so that I can replace names with their ...
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61 views

public key certificate on TLS/SSL

Currently I am working on a public key certificate. I got a question: Why is a public key certificate needed for TLS/SSL? Wouldn't TLS/SSL itself is enough? What is the role of the certificate?
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1answer
61 views

rsa public and private keys

I have a question about RSA key generation: this is a simple rsa algorithm: Choose p = 3 and q = 11 Compute n = p * q = 3 * 11 = 33 Compute ?(n) = (p - 1) * (q - 1) = 2 * 10 = 20 Choose e such that 1 ...
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1answer
47 views

Efficiently show/prove knowledge of third party secret without leaking information

Say Alice publishes (i.e. all parties in the universe) a key or certificate $x$ and sends a secret $s$ to Bob. Bob then publishes some data $d$ (his identity or a message or smt.) and an ...
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1answer
65 views

What can be learned from the ciphertext of LibSodium's crypto_box_detached()?

LibSodium, (https://github.com/jedisct1/libsodium), has a function crypto_box_detached() which does authenticated encryption using the public key of the recipient ...
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1answer
64 views

How can convert affine to Jacobian coordinates?

I have a point in affine coordinates: $(x,y)$. What should I do when I want to convert to $(X,Y,Z)$ in Jacobian coordinates? I need it for calculating ECC in a prime field.
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Alternative to NSA encryption algorithm

I am looking for a strong alternative to elliptic curve cryptography. It should be something that could face quantum computing attacks, but nothing created by the NSA. I heard about isogeny key ...
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Possible Digital Signature Hack?

I am starting to learn more about cryptography and I just read more about how asymmetric keys can make a digital certificate, and I would like if someone could explain me why the following case can't ...
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48 views

Protocol for establishing physical ownership of a connected/IoT device?

If I'm connected to a device e.g. using BLE are there rules/protocols for establishing that I'm also in physical possession of that device (at least for the first time I connect to it)? Crypto is in ...
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1answer
100 views

Modes of operation for Public Key Encryption schemes

Symmetric key encryption schemes have well defined modes of operations for achieving deterministic (ECB) or Randomized (CBC, OFB, CTR ) etc. and other applications of the same. But are they defined ...
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1answer
130 views

Is it feasible to use combination of ABE schemes for encrypting the data?

I have a peculiar requirement for preserving the shared log files. For example I have 1000 records which belong to different organizations as listed below and all the logs are present in a single CSV ...
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3answers
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Feasibility of finding public key when private key is known

We all know that in a public key cryptosystem, given a public key it is extremely hard to compute private key from it. Is it the same case in reverse? Given a private key, how easy is it to compute ...
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2answers
151 views

Why would an RSA library tell me that the public key must be at least 512 bits in size?

I'm trying to interoperate with a web service by reverse-engineering it. Currently, when sending a POST request, it encrypts the form data one-by-one with a 'RSA' function. But it's rather weird as ...
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1answer
133 views

Can I remove new lines in a public key?

Can I remove new lines from the rsa public key file to get a one line string? So the question is if the key looks like this AAA BBB CCC or ...
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1answer
107 views

Why does FIPS 186-4 require specific sizes for keys?

In FIPS 186-4, page 32, about FFC crypto it is required that the length of $p$ will be exactly 1024 bit and the length of $q$ will be exactly 160 bit. Why is the requirement not stated in terms of ...
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1answer
103 views

Which public key encryption scheme is re-randomizable? How can I re-randomize an encryption scheme?

Which public key encryption scheme is re-randomizable? Is there any library for re-randomizable encryption scheme? If not, how can I re-randomize a given public key encryption scheme? I cannot find ...
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2answers
158 views

Are SSL/TLS used for maintaining data confidentiality?

In SSL/TLS, we use symmetric and asymmetric keys to encrypt the data. Does that mean that the keys are used to encrypt the data (preserve the integrity) or provide a secure channel for the data to be ...
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0answers
55 views

Managing data permissions/access through asymmetric cryptography

I want to manage authorization, as 3rd-party permissions, through asymmetric cryptography. I'm concerned about how is it possible to share access of encrypted data with N entities, and be able to ...
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3answers
151 views

Asymmetric algorithm for one time signing of small cleartext

I want to generate a key pair such that the private key can be used once to sign a small message (1024 bytes) at some indeterminate point in the future and the public key can be used to verify that ...
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2answers
140 views

Homomorphic Encryption: how does the equality test on ciphertexts work?

Let's suppose we have a asymmetric crypto-system $H$ which is homomorphic with respect to some function $F$. Alice encrypts a message $m$ with her private key $e$ in the crypto-system $H$ and ...
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1answer
209 views

RSA was rejected by which journal?

Is it true that first time RSA algorithm was rejected by a journal?
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1answer
242 views

Can all asymmetric key pairs be reversed?

After reading about public/private key cryptography, there are still a few points I don't really understand. Based on the way (I understand) challenges work, the public key is used to encrypt a ...
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1answer
146 views

Proof of Communication

I desire an algorithm in which Alice sends a block of data $X$ to Bob, with proof that the data was both sent and received. Ideally this would take the form of a public-key signature of the block $X$ ...
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1answer
71 views

public key delivery without third party

I am currently working on an anonymous P2P file sharing application and I am elaborating some already existing solutions. Some of them allegedly provide point-to-point encryption using RSA ...
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1answer
84 views

Is encryption mainly using Diffie-Hellman Key Exchange?

I know how Diffie-Hellman Key Exchange works. Is this the main way of encrypting with PGP, ssh, ssl (https), DKIM, ...? I wonder if Diffie-Hellman is the clue to understand how encryption with ...
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1answer
93 views

Multi-key decryption

Let's assume I want to send a secret message to $N$ recipients in an asymmetric way. My message could be encrypted with $N$ different public keys $p_i$ one after another and send to each user ...
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1answer
192 views

Is it possible to find plaintext from ciphertext if (n) and (a) are known for RSA?

I have a couple of questions pertaining to a RSA problem. I need to decipher some ciphertext and find out what the original plaintext was. Modulus: $n = 2537$ and exponent: $a = 11$ Encrypting ...
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1answer
115 views

Discovering private exponent from public key

I'm going to assume this isn't possible, but I have to ask because I'm trying to fundamentally understand what I've thus far been trying to implement by following an RFC. SRP-6a starts off with ...
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Given a 'good' basis for a lattice, how can we solve the CVP?

I'm doing a little bit of reading about lattices. I read that if we can find a 'short' basis for our given lattice, we can solve CVP and SVP very efficiently. However, the paper didn't describe an ...
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0answers
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Challenge-response based on public-key decryption, why send public key

Quoting the handbook of applied cryptography, chapter 10.3.3 (i): Identification based on PK decryption and witness. Consider the following protocol: $A \leftarrow B: h(r), B, P_A(r,B)$ ...
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Public key Issue - same key pair as existing one? [duplicate]

My question is a bit naive, but what if someone generates the same RSA key pair as someone else? This person would have the same private key and so would be able to decrypt messages not intended to ...
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1answer
66 views

PGP message integrity : How can receiver of an email check the integrity using the sender's public key?

PGP message integrity: Basically, only private key can decrypt message encrypted with public key. But in the message integrity service in PGP does the reverse, where the Hash of the message if ...
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2answers
661 views

The modulus of RSA public key

I am studying the RSA cryptosystem. The public key consists of $(n, e)$, the modulus (product of two large primes), and the encryption exponent. I want to separate the modulus $n$ and exponent $e$. A ...
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1answer
669 views

RSA example-calculation: Public Key = Private Key (e = d)

I am a bit confused. I just calculated manually the single steps of RSA for an implementation with small numbers and suddenly $d$ was equal $e$. Please help me understand what I am doing wrong. ...
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1answer
73 views

Exchanging session keys over symmetric-key channel?

I know session keys are exchanged (in SSL e.g.) over public-key cryptography channels but I was wondering if there are already known algorithms/methods for exchanging session keys over a symmetric-key ...
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2answers
362 views

In public key cryptography, how many keys are required for secure communication between n parties?

In public key cryptography, how many keys are required for secure communication between n parties? In my view the answer should be $n^2$. Reason: There are ‘$n$’ Parties. Every Party has One (1) ...
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1answer
89 views

Is email an example of public-key cryptography?

It seems like email is at least analogous to public-key cryptography, the public portion of the key being your email address, and the private portion of the key being the password to the email ...