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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Signing the hash of a key with the same key

Given a private signature key sk and a public signature key SK, does revealing sk(H(SK)) (in ...
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Public-Key Deterministic Encryption : Why does not provide perfect security?

I've got a question about an assignment . The question is "Why a Public-Key Deterministic Encryption Algorithm does not provide perfect security ?" . I suppose it means according to Shannon . Any ...
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1answer
132 views

Reason for difference in assumptions for practical private-key and public-key crypto

Theoretical cryptography tells us that everything in the world of private-key cryptography (CCA-secure symmetric encryption, message authentication codes, etc.) can be built from one-way functions and ...
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2answers
141 views

Encryption of a number with RSA bigger than $n$

I'm having trouble understanding why encrypting a number $m$, which is larger than $n=p\cdot q$. I've looked into the following threads: Why RSA can't handle numbers above 76? Why does plain RSA ...
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2answers
130 views

Is there a metric (term) for work required to decrypt a public key?

Any public key decryption can be decrypted given enough time and computing power. Is there a metric or term for this? Something like it would require on average 2^43 1024 bit hashes to find private ...
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1answer
68 views

Why are security against eavesdropping and security against CPA equivalent in the setting of public-key cryptography?

Why are security against eavesdropping and security against CPA equivalent in the setting of public-key cryptography?
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86 views

ElGamal encryption with private key [closed]

Does the encryption with a private key and decryption with a public key works in ElGamal likewise what is done when we use RSA for sender authentication?
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130 views

Symmetric encryption is no longer necessary?

Here is it: Symmetric encryption is no longer necessary, because all security services can be implemented with public-key cryptography. Moreover, in public key cryptography the operations for ...
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3answers
904 views

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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1answer
99 views

How to protect against ephemeral key reuse in some signature schemes?

Given that some signature schemes (for instance Elgamal) use an ephemeral key that cannot be reused ever. How do people usually protect against this? I'll elaborate more: if you reuse the ephemeral ...
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0answers
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inverse of scalar multiplier in ECC

I am learning to use ECC. i got into situation where i have $Q=abG$, where $G$ is the generator of the finite field formed on EC using a prime $p$ modulus and $a$ , $b$ are random numbers. now suppose ...
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1answer
1k views

Low Public Exponent Attack for RSA

I'm having trouble understanding the algorithm for finding the original message $m$, when there is a small public exponent. Here is the example I'm trying to follow (you can also read it in the 'Low ...
2
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1answer
133 views

what's the advantages of identity-based systems over certificate-based ones?

Actually, I'm not familiar to how identity-based and certificate-based systems work, so ,can anyone give me a detail and comprehensive answer to this question? Moreover, in what environments the ...
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3answers
353 views

How to perform authentication without central server in P2P?

How you be sure that the man who you're talking with is the one who you think he is? I.e. how to perform authentication in P2P network without central trust server or Certificate Authority? I'm just ...
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3answers
174 views

EC equivalent for RSA-OAEP

I have some questions regarding aforementioned subject: Is there a EC equivalent of RSA-OAEP key transport/encryption algorithm ? Is ECIES-KEM sufficient ?
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2answers
196 views

Encrypt and decrypt data accessible by multiple users within a team

I'm currently working on web services which allows to send and retrieve data. The data belong to a team. A team is composed of users. Each authenticated user can send and retrieve data to/from their ...
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1answer
162 views

how do you calculate the private exponent in asymmetric key encryption [duplicate]

Here is an excellent paper on the math of asymmetric key encryption: http://www.mathaware.org/mam/06/Kaliski.pdf‎ See the example on Page 6. The public key = $55$ Primes used to calculate public ...
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1answer
199 views

Is it possible to decrypt double-key crypted file knowing public key and a having one or more original files?

I have some encrypted files with double-key. I know public key and don't know private key. Can I obtain the private key (and decrypt all files) using two version of one file - crypted and decrypted? ...
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1answer
97 views

Time complexity to solve Discrete log problem

What is the time to complexity to solve Discrete log problem now in $Z_p$? Initially for $n$ bit prime $p$, it was $Exp(n^{1/3})$.
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1answer
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ECDSA vs ECIES vs ECDH

Recently I started studying ECC and I just loved it. I want to transfer some big data (like 3KB), What is the best method, ECDSA, ECIES, or ECDH (and why)? I am confused, how should I choose between ...
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2answers
374 views

How does Clifford Cocks 'Non-Secret Encryption' work?

I have read Clifford Cocks "A Note on 'Non-secret Encryption'" and thought I would try to implement this, but I don't seem to be able to get it to work. I'm obviously missing something. From the ...
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6answers
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Types of Cryptography for a 4-8 bit microcontroller

This is more of a research question. I was wondering what types of crypto algorithms would work best on a small 4-8 bit micro controller. I recently read a paper called Security Considerations for ...
6
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2answers
621 views

Knowing pre-encryption data, can we find the private key CryptoLocker used?

One of our users seems to have been hit by CryptoLocker. As a result, he has a hard drive full of encrypted files. The ransom-ware claims to have used public key encryption on the files. If we know ...
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1answer
289 views

Can you explain Bleichenbacher's CCA attack on PKCS#1 v1.5?

I've studied that the Bleichenbacher's CCA attack on PKCS#1 v1.5. is a base to many versions of attacks in the area. I'm trying to understand that attack, but every explanation I saw starts with the ...
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1answer
192 views

Verification of identity by certification authority

I have question about how a user's identity is verified by a Certification Authority. As I understand it, the process works as follows: User generates his private key and (with the help of private ...
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2answers
319 views

Where is my private key stored when I communicate to a website that uses SSL/TLS?

If I communicate with a website that uses SSL/TLS, my browser will generate a private key. Would the browser store that key on the hard disk or would store just it in the RAM?
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297 views

Can an RSA public key be generated without ever knowing the factors? [duplicate]

Context: http://blog.cryptographyengineering.com/2013/12/a-few-more-notes-on-nsa-random-number.html Assume I wanted to use RSA as the basis for a hash function or DRBG. Also assume that my construct ...
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3answers
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Why is public-key encryption so much less efficient than secret-key encryption?

I'm currently reading Cryptography Engineering. After giving a high level explanation of the difference between secret-key encryption and public-key encryption, the book says: So why do we bother ...
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1answer
127 views

Hierarchical Encryption

Is there a way to setup a hierarchical encryption using public key encryption? Let's say a higher level user can decrypt messages encrypted by lower level users. Is that possible? I guess it is only ...
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1answer
201 views

Single Party Encryption, Multi Party Decryption

I am looking for an adequate protocol for public key decryption, which would allow $n$ parties to jointly decrypt a cipher text. The usage scenario for such a protocol would be a mixnet that wouldn't ...
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2answers
108 views

What's the alternative should PKI collapse?

Premises - please check it and critique if necessary: If factoring the products of large numbers suddenly becomes simple, PKI goes up in smoke. Is this correct? If it is correct, it seems to me ...
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2answers
163 views

Can we say that if $P=NP$ there is no CPA secure public key encryption?

I've learned that public key encryption is based on the problem of Discrete Log (as regard to group theory) which believed to be hard. But, can we say that it doesn't matter on which problem our ...
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1answer
171 views

What exactly is inside a private key?

May sound stupid to many, but I would like to have some pointers on what exactly is contained inside a private key. I have decent understanding of public/private keys/certificates (have created them ...
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1answer
127 views

In S/MIME, are the same certificates always used to sign and encrypt messages?

My assumption is that S/MIME almost always utilizes certificates as follows: My certificate can be used to allow people to encrypt messages and send them to me. My certificate (the same ...
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1answer
501 views

Multi-party encryption algorithm

To give some foreground information: I acknowledge that I am a cryptography newb and not by any means an expert (and probably never will be). In a recent CS class we had several assignments writing ...
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1answer
311 views

Should new applications still use RSA? Is it worth going down the ECDH route for protocols?

I am currently designing an application for communication between two and more users. At the moment I am trying to figure out what methods to use for the asymmetric cryptology. With the recent ...
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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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2answers
398 views

Implement deniable encryption with AES/RSA

I'm on a crypto app using OpenSSL (I'm more an implementer/cryptographer than a cryptologist), mainly as a hobby, for now. My app will be able to encrypt a file (not a container) with symmetric or ...
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3answers
161 views

Why use a timestamp and how can someone know it's the correct one?

Let's say A wants to send a message, so everyone who gets the message, can be assured that it's from A. A then sends a message ...
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1answer
97 views

Generate random in secure message transfer

I’m doing a school assignment about secure communications between a Server and a Client. Basically, messages are exchanged between the clients and the server and these communications must implement ...
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27 views

Different between Shared Key and Common Key in DLP Application

What is the different between Shared Key and Common Key? Are they the same? Shared Key = Common Key?
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184 views

Public-key cryptosystems without poly-time quantum attacks

It's well-known that Shor's algorithm can solve integer factorization, discrete logarithm and discrete log over elliptic curves in cubic time. This implies that cryptosystems like RSA, ElGamal, and ...
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Is there a public key semantically secure cryptosystem for which one can prove in zero knowledge the equivalence of two plaintexts?

If Alice encrypts two messages $a$ and $b$, such that $x=E(a)$, $y=E(b)$. Can Alice prove (without revealing $a$, $b$ or the private key) that $a = b$? Obviously the proof must not be too long and it ...
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660 views

Applications of Group Ciphers

I've been reading a paper [1], and I've ran across something called a "Group Cipher", which is similar to homomorphic encryption, with an important difference. In homomorphic encryption we have an ...
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1answer
399 views

What's the main difference between Pohlig-Hellman and RSA?

Both Pohlig-Hellman and RSA perform encryption and decryption by exponentiation modulo some integer ($p$ prime for PH, $n$ composite for RSA). They both use a key $e$ as the exponent to encrypt a ...
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4answers
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Is it possible to create an open-source SecurID?

As far as I understand it, the hardware key-fob two-factor systems such as RSA SecurID depend on secret algorithms, and employ tamper-resistant hardware to prevent reverse engineering. Is there some ...
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1answer
156 views

How should I manage Diffie-Hellman parameters on a Web Server?

Is there a best practice for Diffie-Hellman parameters (p, g, and q) used on a web server? The server is using ephemeral keys, but should the parameters be rotated on a regular basis? Is it OK for ...
3
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1answer
91 views

Asymmetric Cryptography Confusion - 'Sign' a file to guarantee its source

What I want to do is use asymmetric crypto to guarantee that a file comes from a source. I have software that runs on lots of wireless devices, and each of those has a license file with an encrypted ...
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243 views

RSA performance

I was wondering what is the performance bottleneck in RSA algorithm? Is it the size of message, calculating the modular inverse, exponentiation? Say I have a fixed value of n to encrypt and decrypt ...
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125 views

If H(m) = 0 for some m, how can a DSA signature be forged?

If we know for some message $m$ that $H(m) = 0$, how can we forge a DSA signature with only the public key? I got that $g^s*r = (g^x)^r$ where $x$ is the private key, but that's one equation with 2 ...