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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If I send a signed email, how does the end user get the public key?

I am sending a signed email using Python and smtplib. I have successfully signed the email using this example: http://proj.badc.rl.ac.uk/svn/ndg-security/branches/Dependencies/m2crypto/doc/howto.smime....
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Which public key cryptosystems are not based on number theory?

Are there any public key cryptographic systems whose hardness assumptions don't involve number theoretic problems?
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RSA: special parameters construction

I have to show that the following construction of $q$ allows to factorize $N$ : $p \in \mathbb{P}$, the set of primes $q \gets p \cdot \left((p - 1)^{-1} \bmod e\right) \bmod e$ $k=1$ while $q \not \...
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1answer
21 views

In Paillier homomorphism, how do you deal with bit length? [on hold]

I'm trying to figure out homomorphic encryption and would like to multiply two paillier encrypted numbers. Like so: [a].[b]=[a+b] To try this I got this Paillier.java and tried the following: <...
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1answer
119 views

Could this “symmetric RSA” scheme provide key compromise resistant communications?

This question, and fkraiem's answer to it, made me wonder about the security and practicality of using "symmetric RSA" to provide a partially compromise-resistant secure channel. Specifically, assume ...
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1answer
29 views

In Paillier homomorphism how do you substract?

I'm trying to learn homomorphism so the problem may also be in my code (which I will include). I want to compute $a - b$ where $a$ is bigger then $b$. In order to do this I tried to compute $\frac{a}...
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1answer
282 views

Simple digital signature example that one could compute without a computer?

I am working on a document to explain Bitcoin to students. But I am having a hard time translating the principle described in §2 of the Bitcoin whitepaper in layman's terms. There is a great question ...
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39 views

Feasible attacks on ECRSA cryptosystem

In ECRSA cryptosystem, I want to know the feasible attacks. For illustrations we have two prime $p$ and $q$ such that $p \equiv 2 \pmod 3$, $q \equiv 2 \pmod 3$ and generate key pair as follows: $$n = ...
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131 views

Where and how to store private keys in web applications for private messaging with web browsers

I am working on a web application enabling users to communicate over private messages which is just one part of the whole system. The main focus during my development process is to protect the privacy ...
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2answers
75 views

Initializing PGP keys by one side

I am using a PGP method to encrypt and decrypt messages shared between users A and B. Upon the start of a message exchange is the initialization of the public and secret keys by both Users. Lets say ...
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1answer
30 views

Do RSA keys contain a checksum mechanism? [duplicate]

I'm new to cryptography, and I was making an experiment a few minutes ago, but I want to have some deeper knowledge about RSA public and private keys. I have a set of keys One begins with ...
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56 views

Explanation of cryptographic terminology for newbies [on hold]

I feel like I'm making a mountain out of a molehill here, but I have (what should be) a relatively simple project, but the terminology used all over the Internet is either too simple or too difficult ...
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Public-key Cryptography: I need a technical answer [closed]

So, I already understand the point of Public-key cryptography, and how it's supposed to work. I understand the basics, and I've seen way to many diagrams. What I haven't seen enough of, however, is ...
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1answer
86 views

Salting Hash stored on RFID tag?

In my application, I am trying to prevent counterfeit widgets from being used on our gadgets; think HP ink-cartridges. I will be doing such with UHF RFID tags embedded in the widgets. Unfortunately, ...
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0answers
31 views

Are public key and private key exchangeable? [duplicate]

If I get a key pair from RSA algorithm, can I make Private-Key public, and keep Public-Key secret without breaking the security of encryption and signature?
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1answer
65 views

Key Hierarchy and key Encryption

If i have two 56-bit DES keys, and I use these two key to encrypt a 256-bit AES key. Like this $K_{AT}$ encrypts $K_{BT}$ and $K_{BT}$ encrypts $K$ What is the effective security of key $K$? Is it $...
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1answer
58 views

Does encryption of data/information take place in peer to peer networks like Gnutella, Bittorrent?

Do peer to peer networks like Gnutella, Bittorrent have any encryption system to secure the users privacy or encrypt the file/data being shared? Elaborate please.
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1answer
65 views

Why is Diffie-Hellman used instead of just RSA in key-exchange (TLS, IKE)?

Why should a key exchange protocol (such as in TLS or IKE) use Diffie Hellman? Why not just use RSA? For example: Alice picks a random session key, signs it, encrypts it with Bob's public key, and ...
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3answers
65 views

Is PGP's way of maintaining email security optimal? [duplicate]

I read a book called "computer networking: A top-down approach". It talked about how PGP creates an email message between Alice and Bob to maintain confidentiality, integrity, and authenticity. Let me ...
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1answer
88 views

Is this a proper key-exchange implementation?

I've been trying to implement Diffie Hellman key exchange so far from my own understandings (I know I could just stick with SSL/TLS, but I want to understand it in depth more), so I created this basic ...
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1answer
55 views

How to verify a sever's ECDSA fingerprint during SSH

I have read somewhere that Servers which have SSH access for users in the public can have their public key posted publicly (e.g., on a website), so that people who access such a server using SSH can ...
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0answers
25 views

Why SSH does not use a certificate authority in the same way as SSL [closed]

SSL requires the use of a trusted third party -- the certificate authority to verify a public key presented by a server to a client. SSH on the other hand relies on the client having the server's ...
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1answer
36 views

Is there a way to turn a PGP key into its semi-prime counterpart?

From my understanding of PGP keys they use the RSA algorithms to encrypt/decrypt messages. So, I know that the RSA algorithms use a semi-prime number to encrypt/decrypt messages. So, what I was ...
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24 views

To utilize asymmetric cryptography in symmetric manner - demand-of-security-definition?

Cryptography can largely be divided into two classes: asymmetric and symmetric. Like homomorphic encryption now greatly restricted in the asymmetric cryptography, the difference of asymmetric and ...
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1answer
69 views

What's is the simplest possible example of using cryptography to sign a message?

I am interested in explaining to a total layman the basics of how a network can know that you are authorized without having to compromise your private key. Using an example consisting of simple ...
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71 views

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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126 views

Why does choosing the first coprime e greater than half of φ(n) result in the same d (private exponent)

While reading on RSA's algorithm, I attempted a simplified implementation and noticed the following: When choosing the public exponent $e$, if the value chosen is the first coprime after $φ(n)/2$ ...
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1answer
761 views

How to build an electro-mechanical public key cipher machine?

It is generally assumed that asymmetric encryption schemes were invented in 1973 at GCHQ in Britain and, independently, in 1976 at the MIT. Imagine, if the abstract idea of having a public key and a ...
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147 views

How does SSL work on the browser

I recently bought an SSL certificate from a website and was able to make it work on my Apache server. As far as I know, it uses asymmetric keys and the private key is stored on the server while the ...
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1answer
47 views

How to use the hardcoded server's public key to register a client application?

I'm designing the security for a smartphone app that can be used to make car reservations. Clients have to register them with their driver's licence through the application and can then book a car. ...
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1answer
36 views

How does this solution guarantee authentication of B and privacy?

The exercise is: What could be changed on the second message " Kya(Kxb(Ra,Ks)) " to guarantee B's authenthicity and also privacy? My teacher's solution was "add a destination" , so it would be ...
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1answer
117 views

ECDSA non random k - Retrieve private key [closed]

At the moment I'm playing around with ECDSA. I know that I can retrieve the private key if the same K is used to sign two messages. I tried to use this script: Ruby Script to crack the private key. ...
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1answer
52 views

Need help understanding this exercise's solution

We were given this exercise, which asks us to identify the types of keys used on this diagram: The solution was Kxa -> A's private key Kya -> A's public key KxB -> B's private key My question ...
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225 views

ECDSA key recovery - floating point values

I'm currently attempting to recover an ECDSA key. I have $m$, $m'$ and signatures $(r, s)$, $(r', s')$, and I know that $k$ is constant, the curve is NIST P-192 and the hash function of the. As such,...
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1answer
252 views

Is there a administrator key that can decrypt all ciphertexts encrypted with different keys by different persons in a group?

here is the scenario: $A, B, C, \ldots, Z$ are in a group with a administrator $Admin$, each of the users in the group has his own key $Key_A, Key_B$, and so on... everyone encrypt his own ...
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50 views

What are the most appropriate PKI based cryptographic protocols for peer to peer communicaton?

I've been trying to find out which is the most appropriate PKI based cryptographic protocol for peer to peer communication. I do understand that they vary with respect to the peer to peer architecture ...
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39 views

Key Distribution Center Key Protocol Analysis

As shown in the image, why is Circle 1 to be B and Circle 2 to be A? Why is not the opposite, that is, Circle 1 to be A and Circle 2 to be B? like this picture From my understanding, Notation B in ...
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Different kind of PGP keys or IDs, how to interpret them?

When people say "Here's my PGP key", they tend to come up with all sorts of different stuff. Sometimes they provide an 8-digit hexadecimal number, which seems to be a key ID (although I'm not sure). ...
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Are any of the major asymmetric ciphers distinguishable (EG, RSA, ECC)?

Related to "Is it possible to derive the encryption method from encrypted text?". Given ciphertexts generated by any of the major asymmetric ciphers (RSA, ElGamal, ECC, etc..) can these ciphertexts ...
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How does asymmetric encryption work?

I've always been interested in encryption but I have never found a good explanation (beginners explanation) of how encryption with public key and decryption with private key works. How does it ...
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3answers
479 views

Is there an algorithm to find the number of intersections of two sets?

Suppose both I and my friend have a set of integer numbers. We want to know the number of common elements in our two sets but without knowing elements of the sets of each other. So I don't want my ...
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1answer
27 views

Use MDC to provide origin authentication for public key encryption?

Why can't we use an MDC (“Manipulation Detection Code”, as also handled in this Q&A) to provide origin authentication when using public-key encryption?
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Why is a-symmetric so much harder to compute and why does it need such big keys? [duplicate]

I read that a symmetric encryption requires a way bigger key size to have the same security as symmetric encryption with smaller keys. But why is this, and why is it so much harder to compute?
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1answer
67 views

Can I change an encryption key used without decrypting first

I'm looking to solve for a little challenge I have in regards to changing the encryption on a message with asymmetric keys. I'd love to be able to swap the encryption to a different key in memory and ...
9
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2answers
743 views

Are there any signature schemes for underpowered devices (8-bit microcontroller)?

I am currently researching into a small scale home automation system, aiming for cost. The system architecture is basically one master and several slaves which are connected in parallel. Recently i'...
4
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1answer
47 views

Padding schemes for asymmetric encryption with provable security in the standard model

Most padding schemes for asymmetric encryption (OAEP, OAEP+) are only proven secure in the random oracle model. Although no attacks are known, it would be nice to find a padding scheme with provable ...
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1answer
49 views

How to convert roots of Weber polynomial to Hilbert class polynomial over modulo prime?

Using any non square root discriminant $D$, we should be able to find the Weber class polynomial. How can I convert the roots of a Weber polynomial to a Hilbert class polynomial over modulo prime?
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RSA with small exponents?

Just to establish notation with respect to the RSA protocol, let $n = pq$ be the product of two large primes and let $e$ and $d$ be the public and private exponents, respectively ($e$ is the inverse ...
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Are there asymmetric cryptographic algorithms that are not based on integer factorization and discrete logarithm?

In the computer security class (in which cryptography is a big chapter) that I took, I remembered the professor said about current asymmetric cryptography algorithms are based on integer factorization ...