an asymmetric (e.g. public-key) cryptosystem, based on modular exponentiation with big exponents and modulus. RSA can be used both for signature and encryption.

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how to let other people respond to emails only decrypt-able with my private key

First of all I have to say it's a homework question but since I have no one to consult with, I ended up here :) Suppose a case in which you are the manager of a company and all employees encrypt ...
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29 views

Program implementation and flaws [on hold]

I had written an email encryption program in Java almost an year ago. I want to improve upon it and need your help in determining any obvious flaws in implementation and functionality. About program ...
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1answer
65 views

For which RSA moduli, precisely, is $e=d$ for all $e$?

This question shows that there are at least two valid RSA moduli $n$, namely $35$ and $91$, such that for any $e$ coprime to $\lambda(n)$, $$e^2\equiv1\mod\lambda(n)\text.$$ Reading the linked ...
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1answer
70 views

Find private exponent in RSA

The other answers for this confuse me, I know the principle of d in terms of the equation it has to satisfy. However I'm not sure how I would go about finding the private exponent without trial and ...
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0answers
641 views

Ransomware RSA-1024 encrypted files [closed]

Sorry if this is not the right place to ask this question, but it seemed most relevant to the Cryptography topic. One of the users on our domain was infected with a ransomware virus that caused all ...
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2answers
144 views

Does RSA operate over a Finite Field (Galois Field)?

Is it correct to say that RSA operates over a Finite Field (Galois Field)? In this case GF(p)? I do understant that the modulo in RSA is not itself a prime number, but all the operations ...
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1answer
52 views

RSA Protocol behind Yaksha Security System

So I'm reading over the Yaksha Security System and see it is based on the RSA cryptosystem and a centralized server, easy enough. What I'm slightly confused on is the math behind the related keys. It ...
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0answers
72 views

How do I find a random BigInteger smaller than another random BigInteger? [migrated]

How do I Select a random element α ∈ Z∗p? P is a random 1024 bit prime BigInteger. Here is how I find BigInteger p: ...
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1answer
50 views

RSA-blind signatures vs. DSA-blind signatures

I see that the RSA blind signature scheme tends to be implemented more often than others, e.g., DSA blind signatures. Isn't the RSA blind signature scheme a 'lesser' scheme, if you may, compared to ...
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0answers
65 views

Crack RSA with imaginary algorithm [duplicate]

I was given a cryptography question during an interview the other day and I couldn't come up with a valid answer. Imagine you are given an efficient algorithm which for a given RSA public key (n,e) is ...
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1answer
129 views

Decrypt all RSA ciphertexts if you can break 1% of them

I was given a cryptography question during an interview the other day. Imagine you are given an efficient algorithm which for a given RSA public key (n,e) is able to decrypt 1% of the messages ...
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1answer
91 views

What are the potential (major) flaws in this security scheme?

It’s been a few years since I read anything involving crypto. I’ve come across this scheme and I wonder how secure it is: Alice generates an RSA keypair (we assume Alice is using proper random ...
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1answer
59 views

Is xgcd faster than Fermat for calculating $d$ in RSA?

I want to calculate $d$ from $e$ when generating RSA keys. What is faster? Calculating $\operatorname{xgcd}(e,p)$ and $\operatorname{xgcd}(e,q)$ and CRT. Or calculating $e^{p-2}\bmod p$ and ...
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0answers
51 views

RSA or Paillier is good? [closed]

I want to implement file storage in cloud using homomorphic encryption. I want to use paillier encryption. Can you suggest the drawback of RSA to store and retrieving the files. Then only i can use ...
2
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1answer
153 views

2048-bit RSA Decryption

Im in need of help with this study question. I heard that there was some relation between small a's and b's and being able to do a trick but I cant find where I read it in my book. Could someone help ...
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1answer
80 views

Probability of factoring keys as a function of bit length

kinda new here, I had a question pertaining to someone being able to factor one's RSA keys through the GCD. Anyways the question goes that there are two people: A and B. A makes his/her private key as ...
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1answer
62 views

Does it necessary the public key is prime number in RSA algorithm?

I read some books talk about RSA cryptography but I did not understand something when choosing a public key $e$ Sometimes the condition is $1<e<$$\phi(n)$ Where $\phi(n) = p-1 * q-1$ also ...
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1answer
87 views

Timelock puzzle improvment

I came across this question with this answer about a cryptographic timelock-puzzle that needs approximately 30 years to be solved. There is also an explanation with source code for that puzzle ...
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0answers
45 views

Existential Forgery on textbook RSA signatures

Can an adversary who haven't seen the message before forge the signature of that message? The adversary has seen $σ_1 = (m_1)^d \bmod N$ and $σ_2 = (m_2)^d \bmod N$ He forges $m' = m_1\cdot m_2$ $σ' ...
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0answers
21 views

How to compare security parameters of different schemes (Sign-Encrypt, Encrypt-Sign, etc)? [duplicate]

How can one compare the security parameters (confidentiality, integrity, non repudiation, etc.) for different schemes (Sign-Encrypt, Encrypt-Sign, Sign-Encrypt-Sign, Encrypt-Sign-Encrypt)? Are there ...
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1answer
62 views

RSA Cryptosytsem, choosing $e$ [duplicate]

I am using the RSA crytposytem. I have $p$, $q$ and hence $n$ and $\phi$ however I don't understand how to get $e$ such that $gcd(e,\phi)=1$ Many thanks
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68 views

Generation of strong primes

It seems that this is pretty difficult to find large (above 1024 bits) strong primes, or at least such primes p where (p-1) has a very large prime factor. Is there any information regarding the ...
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3answers
127 views

Maximum length in bits of the product n=pq

If p and q are two 1024-bit prime numbers, would the maximum length in bits of product $n=pq$ be ${1024}^2$ or $2^{1024}$? I think it is ${1048576}={1024}^2$? Also, would the least significant bit ...
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47 views

RSA OAEP: prevention of partial decryption of ciphertexts

I'm trying to understand RSA encryption (as a beginner in cryptography). go on this wiki page http://en.wikipedia.org/wiki/Optimal_asymmetric_encryption_padding scroll down to the 2 numbered points: ...
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135 views

Cracking RSA with Small exponent 5

I have read following questions - Cracking an RSA with no padding and very small e Small Encryption Exponent where in first it says to run out all the possible m options and second says factor ...
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1answer
80 views

Cracking plain RSA by factoring the modulus n

This is the setup: I have both public and private keys of one "instance" of RSA. And I have only the public key of another RSA cryptosystem, but this system has the same modulus as the first one. I ...
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1answer
98 views

Python. RSA common modulus attack problem

I have: N = /*500 decimal numbers*/ E1 = 3740453 E2 = 4226171 M^E1 = /*500 decimal numbers*/ M^E2 = /*500 decimal numbers*/ I must use RSA common modulus ...
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2answers
195 views

Is there a way to systematically calculate the public exponent $e$ in RSA?

I'm learning RSA in one of my classes and we were given a problem: $p = 5$, $q = 11$ I have done the following steps: $n = 5 \cdot 11 = 55$ $\phi = (5-1)\cdot(11-1) = 40$ I know that to ...
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1answer
54 views

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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1answer
49 views

what does rsaSha512Sign do?

I have the following function: ...
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1answer
51 views

OpenSSL RSA same plaintext but different ciphertext

how OpenSSL RSA work ? I generate public (n,e) and private key (n,d) then I encypted a file by : ...
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2answers
226 views

Can RSA signing be implemented on top of RSA encryption/decryption?

I need to use RSA-SHA256 signing. Unfortunately not all Microsoft CryptoAPI providers support that. It's possible that I might get a handle to a CryptoAPI provider that can just encrypt/decrypt with ...
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1answer
80 views

Storing AES encrypted RSA private keys on a server

I'm thinking about creating an encrypted messaging web application where users create RSA key pairs, they store the public key on the server for others to see and also store an AES encrypted private ...
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1answer
91 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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1answer
90 views

RSA: Fermat-Euler Theorem - coprimality of message and modulus [duplicate]

I understand the implication of the Fermat-Euler theorem and how it applies to RSA and the detailed explanation by user Ninefingers at What is the relation between RSA & Fermat's little ...
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2answers
279 views

Which attacks are possible against raw/textbook RSA?

The PKCS#1 standard defines multiple padding schemes for signature generation/verification (EMSA-PSS and EMSA-PKCS1-v1_5), and encryption/decryption (EME-OAEP and the less safe EME-PKCS1-v1_5). ...
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56 views

Franklin-Reiter related message attack m2 = a(m1)+b

As shown in their paper, https://www.cs.unc.edu/~reiter/papers/1996/Eurocrypt.pdf, if one is given an equation relating the two messages m1 and m2 as well as other information one can crack both the ...
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1answer
73 views

In RSA, why does Alice's $N$ need to be relatively prime to Bob's $N$?

I was asked this by my professor and I didn't understand the reasoning behind it. If Alice has a the key pair $(p_a, n_a)$ and Bob has the key pair $(p_b, n_b)$, why do $n_a$ and $n_b$ have to be ...
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1answer
53 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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80 views

Is a RSA 2048 bits public key secure [duplicate]

I realize servers such as Google, Yahoo, which use RSA has 2048 bits public key. After comparing those keys, I realize that the public keys share a common property, that is first 9 bytes and last 5 ...
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1answer
93 views

Crypto libary with Commutative Encryption

I want to implement Mental Poker in JavaScript as a toy program and lead in to a larger serious project so I did my research and found Massey-Omura cryptosystem and the Shamir three-pass protocol ...
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1answer
92 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
156 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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1answer
46 views

When homomorphic encryption goes wrong?

Consider I have two ciphertext $c_1$ and $c_2$ encrypted using RSA encryption. By definition if I multiply them I'd get $c_1.c_2 \ modN$. My question is what would happen if $c_1.c_2 >N$. Can we ...
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2answers
168 views

RSA Decryption given n, e, and phi(n)

my cryptography professor gave us this problem for extra credit a while back and I attempted it but I didn't get it correct. I have gone back to it, but I'm even more lost now than I was the first ...
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1answer
29 views

RSA signature scheme

In RSA signature scheme, it is a common practice to 'sign' the hash value of the message so that the length can be fit. Question: If we have $s=m^d \bmod n$ where $d$ satisfies $ed \equiv 1 ...
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42 views

Low exponent attack against RSA

According to this: http://www.cims.nyu.edu/~regev/teaching/lattices_fall_2004/ln/rsa.pdf One can calculate the message m, if there was no padding scheme involved. My question: is it possible to find ...
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1answer
124 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 ...
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2answers
99 views

RSA prove $a^{\varphi(n)/g} \equiv 1 \pmod{n}$

I should prove that $a^{\varphi(n)/g} \equiv 1 \pmod{n}$, so I thought I would prove it with primitive roots but I got stuck. Here is the assignment: Let $p, q$ be primes such that $p \ne q$. ...
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1answer
84 views

RSA CRT modulo reduction

I am working on RSA CRT and there is a point that I don't understand : So we have $n=pq$ and $c = m^e \bmod n$ an encrypted message. To decrypt $c$ with RSA CRT, we have to compute : $d_p = d \bmod ...