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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How can a message encrypted with the public key be decrypted with the private key? [duplicate]

I've been reading about encryption and have a basic understanding of the concept. What I don't understand, however, is how a calculation with one key can result in a number that, through calculation ...
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133 views

history of non secret cryptograph

Prior to the discovery of any specific public-key schemes, such as RSA, an existence proof was developed whose purpose was to demonstrate that public-key encryption is possible in theory. Consider ...
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102 views

How to attack RSA-CRT with large public exponent?

Suppose we have $(n,e)$ and the ciphertext $c$ where the public exponent $e$ is of the same length, 1023-bit, as the modulus $n$. It is also assumed that the factors of $n$ are balanced. The message ...
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2answers
120 views

How can comparision like (>=,==) be done using homomorphic encryption?

Since we know that Homomorphic encryption allow computation on encrypted data. Let two n-bit integers $(x,y)$ are encrypted using some LWE public key cryptography. For example - if $x'= HEnc(x,pk)$ ...
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Is there any more information on this RSA backdoor?

Someone posted this on reddit a few days ago, and I haven't found much about it except for links back to the same page. Here's the article ...
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1answer
176 views

Finding the subgroup in isogeny-based cryptography

Isogeny-based cryptography is one of the newest post-quantum cryptography. Hardness of this system is based on finding isogeny between two elliptic curves. Also this is theorem: Elliptic curves ...
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1answer
152 views

Understanding ransomware – What makes plain-text-attacks or brute-forcing so hard?

Say I have four files. Two are completely unencrypted, while the other two are the exact same files other than that they have been encrypted with (apparently) the same public key (via a ransomware ...
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2answers
139 views

The difficulty of computing discrete logs

I understand that in Diffie-Hellman it should be hard to compute $a$ given $g$ and $g^a$. In computational Diffie-Hellman, it appears to be hard to compute $(g^{ab})$ from $g^a$ and $g^b$. As for ...
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1answer
134 views

Encryption scheme like RSA where encryption is the inverse of decryption

In RSA, it is basically equivalent to use the private key $d$ to encrypt as it is to use the public key $e$ to encrypt. They are exactly inverses: $e=d^{-1}$. I need to know, are there other public ...
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61 views

Diffie-Hellman, RSA and the types of public key cryptography

Are these schemes fundamentally different? Are other schemes fundamentally different in the sense that you can do different operations with them (or the same operations, but needing different ...
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0answers
91 views

splitting the plaintext and ciphertext into blocks

Say I was to use RSA with a given value of n. I choose to split the plaintext and ciphertext written in a 27 letter alphabet into blocks with k and m characters resp. How would I find the largest ...
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1answer
122 views

Limitations of Elliptic Curve Cryptography?

Simple question, what are the limitations of ECC, both in terms of application and how secure it is? I heard that the NSA were able to read emails a few years back due to a backdoor they had ...
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1answer
106 views

Why gcd(r,(p-1)/r) needs to be 1 in benaloh cryptosystem

I recently discovered the benaloh cryptosystem. I am working with the system as it is discribed in the following link: https://en.wikipedia.org/wiki/Benaloh_cryptosystem However I need some help in ...
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3answers
60 views

Defining Symmetric vs Asymmetric cryptosystems

I'm writing a project on the advantages and disadvantages of symmetric vs asymmetric cryptosystems. At the moment I am trying to define both systems using mathematical notation. Under the heading ...
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1answer
59 views

Does a “commutative” asymmetric system exist?

Completely crypto noob here. I'm looking for a cryptosystem made of a func f + key1 + key2 such that they satisfy: g(f(msg, key1),key2)=msg g(f(msg, key2),key1)=msg key1 != key2 Does such a ...
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1answer
3k views

Why does my SSH private key still work after changing some bytes in the file?

I (for a test) just randomly altered a private RSA key by opening it up in Vim and changing a few bytes. It is the private part of an SSH key pair used for logging in on a remote system. Puzzlingly, ...
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0answers
58 views

Convert messages to elliptic curve points [duplicate]

Let $E$ be an elliptic curve; $\alpha,\beta$ two points of $E$; and $a$ a private key such that $\beta=a\cdot\alpha$. We choose random integer $k$ and plain text $x\in E$. Encryption and decryption ...
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1answer
98 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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2answers
126 views

Is there an asymmetric encryption algorithm where the public key cannot be derived from the private key

Is there an encryption algorithm that will produce a public key and a private key such that the public key cannot be generated using the private key. For example, if the private key is compromised ...
2
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1answer
117 views

end-to-end encrypted chat app with symmetric + public key encryption, TLS and cert pinning

A big drawback of end-to-end encrypted messaging services is that, as soon as you lose your device, you lose all your messages. Your private key is gone after all. I was wondering though, wouldn't it ...
4
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1answer
87 views

Does rsa-oaep provide or not plaintext integrity in addition to confidentiality?

My own understanding (possibly wrong of course) of RSA-OAEP encryption scheme is that it provides plaintext integrity (in addition to confidentiality) due to MGF function which for encryption ...
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1answer
214 views

How is El Gamal different from Diffie Hellman Key Exchange [duplicate]

I am Reading RSA and Public-Key Cryptography by Mollin and I can't make out how El Gamal is different from Diffie Hellman Key Exchange. Any thoughts?
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1answer
106 views

How does encryption work in elliptic curve cryptography?

So I think I understand a good amount of the theory behind elliptic curve cryptography, however I am slightly unclear on how exactly a message in encrypted and then how is it decrypted. So my ...
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1answer
160 views

When/why is RSA (hybrid) encryption used rather than alternatives?

I've read that RSA is not meant for encrypting large plaintext because: (Are these also true for other public-key encryptions like ElGamal?) It is slow. Padding makes the ciphertext blocks much ...
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1answer
210 views

Modular exponentiation on calculator for textbook RSA

How do you encrypt $51$ with public key $(n,e) = (91,23)$ I understand that $c = 51^{23} \bmod 91$. How can I calculate the result on a calculator?
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1answer
93 views

Would it be better to use HKDF or SCrypt for deriving a child key?

Okay so I'm trying to derive a child public key from an EC public key. I've come up with a couple ideas and now I'd like to know which is more secure. Mp: The master key pair, this includes a ...
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1answer
109 views

How long can a RSA public key be?

If I create an RSA of 4096 bits, what would be the range of the length in bytes of the public key in DER format? Also, will the private key always be exactly 4096 bits (512 bytes)? Does the public ...
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1answer
217 views

Why $e>n^{3/2}$ prevents Wiener's attack

Here's the Wiener's attack as I understand it. Suppose $n=pq$ with $q < p < 2q$, and $d < n^{1/4}/3$ where $ed=k\phi(n)+1$ and $e < \phi(n)$. $$\begin{align*} n-\phi(n) ...
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1answer
93 views

Contrasting Key Rotation Requirements : Asymmetric vs. Symmetric Ciphers

I'm trying to contrast key rotation requirements for asymmetric and symmetric ciphers. In the case of symmetric ciphers, we have the results such as the so called "CBC Theorem" (stated on pg. 24 of ...
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225 views

How do I get the equivalent strength of an ECC key?

I know how to calculate the comparable symmetric strength of an RSA modulus: calculate the running time for a field sieve. This is how NIST gives approximate symmetric sizes for asymmetric algos in ...
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2answers
122 views

Why is Paillier Cryptosystem called probabilistic?

The definition of Paillier Cryptosystem says that it is a probabilistic asymmetric key algorithm for public key cryptography. Can some body explain why it is called "probabilistic"?
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1answer
199 views

Secure, patent-free alternative to NTRU

I'm working on a P2P communications and chat framework, and am looking for a quantum-secure asymmetric key exchange algorithm which I can use to perform a key exchange of an AES-256 bit key. This is ...
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1answer
51 views

Can the original message be retrieved from a public/private key signature?

When I sign a message (which has potentialy low entropy) using a private key and I send it without the original message, can the original message be retrieved from the signature(s)? I want to prove – ...
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1answer
64 views

Compromise between HMAC and Digital Signature, by encrypting and sending secret key?

For achieving stateless authentication tokens (like JWT), is there a compromise between the performance of HMAC, and public key distribution of Digital Signature? Scenario: Sender is a centralized ...
6
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1answer
122 views

What is the difference between RCCA and CCA2?

Well, I know it's easy to tell CCA1 from CCA2, but I failed to find the difference between RCCA and CCA2. What is the difference?
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2answers
85 views

What is the purpose of Pseudorandom Function Families (PRFs)?

I'm currently in a course in Cryptography, and was wondering why pseudorandom function families exist at all. If there existed one pseudorandom function f(x), based on its definition, could that not ...
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2answers
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Alice answering Bob without knowing the question

I'm a student and I don't know how to solve the following problem : Alice is proposing a 10 questions list to Bob. Bob choose only 1 question and wants to know the answer without Alice knowing the ...
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2answers
227 views

Lightweight Asymmetric encryption algorithm

I'm an embedded systems researcher, and new in the crypto field. Actually, I need to know if there are any lightweight asymmetric encryption algorithm especially considering the time needed for key ...
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0answers
24 views

Generating keys in RSA [duplicate]

I'm trying to learn how RSA works. From what I found online, I'm supposed to generate private key using Extended Euclidean algorithm. I've managed to generate the public key, but don't know how to ...
3
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1answer
131 views

How to determine if padding has been used while encrypting a message with RSA?

I am trying to decrypt a RSA encrypted text file. I have a 2048 bit public key. Analyzing the public key with openssl reveals the exponent used is 3. ...
2
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2answers
390 views

Why is hybrid encryption more effective than other encryption scheme?

Currently I am learning about Hybrid Encryption but I was not able to find any good study material. Below is my understanding: One of the reason why we use ...
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4answers
309 views

Message exchange with textbook RSA

I am working on this exercise but can't work out the answer to the question b. I have solved the question (a) by decrypting the ciphertext $C = 2$ using the formula: $$ M = C^d \bmod n = 2^{17} \bmod ...
0
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1answer
229 views

Help with RSA-2048 crypto ransom virus [closed]

The RSA-2048 Crypto Ransom Virus has devastated me, I tried the backup method, the previous version, the Shadow Explorer, it deleted all my restore points, Its took out 5 HDs and my USB pen that ...
0
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0answers
32 views

Is it possible to re-generate ECPublic key from raw private key and curve params?

As per my understanding, in Elliptical curve cryptography, the EC PrivateKey is nothing but a bigInteger value. If you know the curve specs and you have this private BigInteger value (which I am ...
2
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0answers
63 views

MITM Attack on Key Exchange Protocols

I was doing research on this attack and I am wondering, why is Diffie-Hellman always associated with such an attack? ​ Aren't other public key cryptography schemes vulnerable to the same kind of ...
4
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1answer
90 views

Usefulness of Damgård–Jurik

I am trying to understand what are the benefits of using Damgård–Jurik over Paillier. I understand that expansion factor decreases as s increases. But isn't it the ...
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2answers
130 views

Random Coin Flip

Quoting an old question: Consider the following protocol for two parties A and B to flip a fair coin (more complicated versions of this might be used for Internet gambling): A trusted ...
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0answers
43 views

How do I prove that a bit by bit PKE scheme (that is IND-CPA secure) for an n-bit message is not IND-CCA-2 secure?

Gen generates Pk and Sk (l bits each), Enc encrypts m (length l) but by bit using each bit of Pk respectively, Dec decrypts ciphertext bit by bit using each bit of Sk respectively. How do I prove this ...
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83 views

What type of encryption scheme can prevent cheating in this coin flip protocol? [duplicate]

Consider the following protocol for two parties to flip a fair coin: Trusted party $T$ publishes her public key $p_k$ A chooses a random bit $b_A$, encrypts it under $p_k$, and announces the ...
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1answer
62 views

RSA Optimal Asymmetric Encryption Padding Beginner

I'm new to the OAEP scheme. I learn it from the Wikipedia page. Link The page does not explain a proper setup for of the system. So I'm not sure if the output of the padding scheme which contains ...