# Tagged Questions

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 ...

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### 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 ...
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### 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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### 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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### 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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### 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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### 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 ...
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### 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. ...
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### 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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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 ... 1answer 246 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 ... 0answers 36 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 ... 0answers 71 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 ... 1answer 95 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 ... 2answers 157 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 ... 0answers 45 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 ... 0answers 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 ... 1answer 82 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 ... 0answers 23 views ### Does OEAP padding limit the size of my modulous to the size fo the hash function? im looking at wiki at the moment as how to use oeap padding and it appears, help me out if im wrong as G(r) - expands r to the size of the padded message, I am then limited by the size of my hash ... 1answer 61 views ### Perfect Forward Secrecy in PGP/asynchronous email Looking at the RFC for PGP email/asynchronous chat with PFS here https://tools.ietf.org/html/draft-brown-pgp-pfs-03 can anyone tell me why the following scheme is no good? Alice and Bob retrieve each ... 1answer 137 views ### Cryptography of numbers Is there any algorithm capable of encrypt securely (symmetric) N numeric digits in a numeric message of M digits (N < M)? I am especially interested in a specific case in which N = 10 and M = N + 3.... 1answer 124 views ### Are there comprehensive alternatives to RSA? If we wished to, is there a comprehensive alternative to RSA? I say comprehensive as I wonder if there is one which does both encryption and digital signature like RSA? If not, simply what ... 1answer 103 views ### RSA: must d be an integer? I am only taking baby steps in RSA. If p=11, q=7 and e=3,$$\phi(n) = 10*6 = 60$$Then:$$d = (2 (\phi(n)) + 1 ) / 3 = 121/3 Should $d$ be kept as a non-integer or is such a $d$ invalid?
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Suppose I want to keep a client's password database secure (not in plaintext), while still having access to the plaintext password. Now I generates a public/private keypair. Then I send the public ...
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### Why is PuTTYgen-created RSA public exponent(e) not in {3,17,65537}?

As far as I know, RSA public exponent(e) should be one of {3,17,65537}. However, I found PuTTYgen-created RSA public exponent(e) is 0x25(37) by default,as follows, (PuTTYgen version: 0.66) I am ...
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### Confused about how chosen ciphertext attacks work?

When performing a CCA, the adversary gets the public key. At some point, he will send a message m to the challenger, and the challenger will send back either $E_{pk}(m)$ or $E_{pk}(r)$, where r is ...
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### David Chaum's anonymous credential

I am a newbie in cryptography (I know the basic RSA, AES stuffs) and am interested in anonymous authentication systems. Looks like David Chaum is the godly figure in the field. I see lots of people ...
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### Exactly how slow is asymmetric encryption?

I'm currently doing a project on RSA, and have just come across this website. https://www.namecheap.com/support/knowledgebase/article.aspx/798/67/what-is-an-rsa-key-used-for On here, it says that ...
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### Is there a way to do single key-pair asymmetric encryption?

All of the information on asymmetric encryption I can find uses key-exchanging to get a mutual symmetric key. What I am trying to do is encrypt a message with a public key and have it only readable ...
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### State of the art techniques for Anonymous Authentication?

What are the state of the art techniques for Anonymous Authentication? What are the most popular ones? The problem domain I am considering is with respect to different users accessing cloud content; ...
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### How to generate a bilinear group of prime order p for key generation

I am trying to implement an IEEE Paper In Cryptography. I read many reference regarding an RSA key generation. But i am confused with above statement. Please someone explain me What it says with ...
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### How to generate a bilinear group of prime order p [duplicate]

I am trying to implement an IEEE Paper In Cryptography. I read many reference regarding an RSA key generation. But i am confused with above statement. Please someone explain me What it says with ...
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### What part of an RSA key is referred to by the number of bits? [duplicate]

When we speak about 4096- or 2048-bit RSA keys, what part of the key is this number of bits? The public key comprises both the modulus and the public exponent, and the strength of the key can also be ...
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### Securely generating auth tokens

(Disclaimer: I'm an experienced server-side Java programmer, but with little crypto experience.) Objective: I've got a login server which, given a login+password pair, should issue a unique auth ...
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### Is this ECC based messaging method secure?

I developing an encrypted messaging for ZeroNet (aP2P file-based network, website: zeronet.io) and would like to have some guidelines if any of this could work. My first idea: In ZeroNet every user ...
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### Leading 00 in RSA public/private key file

I found these following values ALWAYS have the leading 00 in public/private key, public key: modulus private key: modulus, p,q, d mod (p-1), d mod (q-1), coefficient e.g., modulus ...
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### Strength of a cryptography algorithm [duplicate]

I'm just read this article from Atmel corporation in comparing RSA with ECC cryptography algorithms. First of all please read these two paragraphs quoted from the article: P1: Strength of an ...
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### Relationship between exponent and modulus in RSA (as RSA properties as listed in X.509)

In one of my assignments, I had the following question (Please read on. Not a homework assignment :) ): X.509 (1998 version) lists properties that RSA keys must satisfy to be secure. One such ...
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### Prevent replay attack without storage

I am designing a set of low-power sensing motes. Each mote will communicate to a central base over RF. I want the mote to be able to authenticate itself with the base, and send its data without being ...
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### Private and public keys, how do they relate mathematically? [closed]

Assuming everyone here knows the basics of a public private key, then you know the keys are mathematically related. My question is, what is the math? I really would like an in detail algorithm of the ...
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### Private and Public Keys

I have a very basic understanding of encryption and the encapsulation process, but for the life of me I can't grasp how public keys and private keys work, how they're made, and how they're exchanged. ...
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### Are private and public key sizes of Elliptic curve related?

I'm new to elliptic curve cryptography. I just want to know in the case where I take a random number (private key) and find its associated public key, does the size of the public key depends upon ...
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