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Questions tagged [rsa]

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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3answers
408 views

Why are in asymmetric cryptography as many keys as people involved needed?

The question: "10 friends wish to establish secure communications between themselves using asymmetric-key cryptography. How many keys need to be known by each user?" was posed by my teacher. He says ...
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1answer
39 views

Generate private key from public key RSA

I am doing a tutorial where my lecturer (PhD) gave me an optional question to do relating to RSA. He said: write a python function that takes as input the server’s public key and then uses that to ...
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What is the likely cause the RSA algorithm gives back plain text in this case?

Text book question of Chapter 9 of "Crypto and Network Security" by William Stallings: When using the RSA Algorithm — if a small number of repeated encodings give back the plain text, what is the ...
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1answer
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RSA decrypt message with low public exponent (n = 187, e = 3 and C = 185)

n = 187 e = 3 C = 185 How to decrypt message? I know there is some way using cryptogram exponentiation. Can you give me a hint?
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2answers
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RSA exercises example

I have doubts about this question Consider the following textbook RSA example. Let be p = 7, q = 11 and e = 3. Give a general algorithm for calculating d and run such algorithm with the above ...
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Should I proceed with this for my project? Is it correct?

We have: Select five Prime numbers $p$, $q$, $r$, $s$ and $t$ Compute $n=p*q*r*s*t$ Calculate $Φ(n)=(p-1)(q-1)(r-1)(s-1)(t-1)$ Collect $e$ such that $p < e < Φ(n) … Φ(n)$ and $n$ are co-prime ...
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41 views

Problem on RSA modification [on hold]

I'm working on the security of the cloud using RSA encryption algorithm. I need help with the simulation of the RSA algorithm against the modified RSA algorithm. Instead of the two prime number , I ...
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42 views

RSA attack using chinese remainder theorem [on hold]

After encryption same message for 3 different people using their public key (187, 3), (35, 3), (247, 3) there are cryptograms (109, 15, 208). What is that message? Use chinese remainder theorem. ...
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1answer
32 views

How to calculate base value in modular exponentiation

If you have $a^b \bmod n = c$, and $b,n,$ and $c$ values are given, is it possible to find a value for $a$ within a given range? So is it possible to find $a$ in $a^{2051} \bmod 3149=636$ knowing a ...
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Asymmetric algorithm with indefinite number of public keys

So RSA algorithm uses pre-generated set of public and private key, and public key is usually included in private key. So public key stays always the same. Is it theoretically possible to have some ...
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1answer
7k views

Can an RSA private key have several public keys?

Ok, so my cryptography lecturer in University posed this question at the end of the RSA key generation lecture as a brain teaser. I have been thinking about this and I think I have come up with a way ...
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1answer
31 views

Forgery against RSA signature [closed]

Is there a way we can forge a RSA signature for a message given that the message starts with 10 leading zeroes?
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1answer
313 views

Is padding of the digest needed in SHA256 with RSA-2048 scheme?

For a signing scheme involving generating a $256$ bit digest using SHA256 followed by RSA with $2048$ bit modulus, the signature would always be 256 bit without padding even though signatures of up to ...
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5answers
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Why is it important that phi(n) is kept a secret, in RSA?

Why is it important that $\phi(n)$ is kept a secret, in RSA?
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1answer
71 views

Attacks on code misusing RSA_public_decrypt

I've encountered some code that I'm reviewing that is misusing RSA_public_decrypt to "authenticate" a variable-length response without using any hash. The code ...
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1answer
55 views

I am new to digital certificate 509V3 concept. can some one please clarify the below points [closed]

I am using RSA 2048 with SHA 256 primitive in certificate: How to verify the user certificate n + 1 with Root certificate n? why it is required to perform Certificate chain verification? How to ...
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275 views

Usability of padding scheme in blinded RSA signature?

In Wikipedia's article on Blind signature, in the section Dangers of blind signing which describes RSA blinding attack one reads the following This attack works because in this blind signature ...
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1answer
3k views

Certificate signature with SHA-1 and RSA: where do 1888 bits come from?

Plenty of X.509 Certificates use "PKCS#1 SHA1 with RSA encryption" as the Certificate Signature Algorithm for generating a 2048-bit signature. The SHA-1 hash function generates a hash value of 160 ...
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1answer
5k views

Is RSA with SHA1 broken?

I am using CryptSignMessage to sign a string/file. Is using RSASha1 insecure? I know Sha1 is broken as a hashing algorithm, but does that also mean that using it for signing with RSA is broken?
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How is message length involved in public/private-key encryption?

I've just read this question regarding why to sign only the hash of a message. I kind of understood the answer, but the question arisen is now: Why can I encrypt any text messages with the same ...
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1answer
700 views

1024 RSA Hash Signature attack. Forge a valid signature

I have an RSA signature of 1024 bit where i know the following: Public modulus N Public exponent (0x03) Cypher message Summary: An MD5 hash is calculated from a collection of byte and is used as ...
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6answers
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Why MACs are so important despite digital signatures doing everything a MAC can do and more

When an entity A wants to send a message to entity B, he can attach a MAC to the message. Entity B on receiving the message can use the pre-shared key to compute the same MAC and confirm if the ...
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2answers
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Should signature verification work using two different RSA libraries?

I am new to the forum, so forgive me if this question is out of place or lacks adequate detail. I am working on a project that involves allowing discreet clients to upload content to a central host. ...
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3answers
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What can I do if I get private key of signing algorithm in Digital signiture

I am confused in digital signature. what is use of encryption with private key and decryption with public key. Using public key we can decrypt the signature then what is use of private key privacy. ...
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Determining Secret text [closed]

Bob has observed a ciphertext $C$ which was sent to Alice, encrypted with RSA. As usual, Alice’s public modulus is n, her public exponent is e, and her private exponent is $d$; so if the secret ...
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PKCS1 v 1.5 Signature questions

I'm crash studying the public key cryptography topic and I have a few questions about how signatures are created. So are digital signatures just encrypted hashes? If that's the case then I can hash ...
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1answer
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Is this Bleichenbacher '06 style signature forgery possible? (Or more like, why isn't it?)

I assume that most of you know this, but just for the sake of context; Bleichenbacher's signature forgery (https://www.ietf.org/mail-archive/web/openpgp/current/msg00999.html) basically abuses ...
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Does RSASSAPSS use RSA signature

I just need to know is it correct to classify the RSASSAPSS scheme and sha[256 | 512 | 1]WithRSAEncryption all under RSA ...
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153 views

Signature Generation with RSA PKCS#1 v.15

I am trying to validate my RSA implementation for digital signatures with the test vectors provided by NIST. For now, I am focusing on the tests for signature generation (SigGen15) with the PKCS#1 v....
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1answer
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Forging RSA1024 signature with e=3 where hash is right justified

I am trying to understand (in the frame of exponent 3) how to calculate a "forgery" in the case where the desired result is: xxxxxxxxxxx[...]xxxxxxxxxxxxxxxxxxxxHHHHHHHHHHH[...]HHHHHHHH where HH = a ...
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47 views

Manually (mathematically) signing and verifiying a file using RSA [Solved] [closed]

It is only recently that I entered cyber security field.. and one of the main foundations is nothing but Cryptography. Something which always fascinated me was the 'Chain of Trust' which is holding on ...
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3answers
914 views

Is using RSA with SHA-1 considered as secure as HMAC-SHA-1?

I know SHA-1 hashing is regarded insecure. HMAC-SHA-1 is still regarded secure as this is an encryption process with symmetric key of the hash produced by SHA-1. So signing using RSA with a key size ...
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1answer
36 views

Combine signature with encryption

I have some embedded device for which I want to sign and encrypt firmware files. Firmware updates are generated by me and may be installed by the customer. The encryption is supposed to protect the ...
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1answer
423 views

RSA-OAEP Padding scheme

Honestly I'm really confused about padding in RSA scheme. I don't study computer science, and I'm a beginner learning cryptography (self-taught). Can anyone give me suggestions?
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Decryption of RSA with e that has no inverse

I'm studying the RSA protocol and I was wondering if there was any way of decrypting a message if the $e$ doesn't have an inverse $\mod (p-1)(q-1)$. Usually, you have to choose a value of $e$ that is ...
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2answers
121 views

Efficient function/algorithm/method to do modular exponentiation

I was working on this project where I needed an RSA key, and I wondered if there was and more efficient way of doing $g^a \bmod n$ other than calculating $g^a$ and then finding the remainder when you ...
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What is the state of the art in fast implementation techniques for modular exponentiation?

I want to calculate ($m^{e} \pmod{N}$) in C or C++. I want to use 2048 bits long modulus $N$ and thus the above process of ...
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1answer
87 views

Is there another group structure that is suitable for RSA other than $U_{pq}$?

I know that calculating the cardinality of $U_{pq}$ is infeasible and therefore it is extremely hard to break a code using Lagrange's theorem. But later on my studies i realized main principle of RSA ...
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Question about RSA timing attack and a Chosen Ciphertext Attack on RSA

I am quite new to the RSA and I have a couple of questions that confuse me. Q1: A Timing attack on RSA can be prevented _____________________________ A. By performing the “square and multiply” ...
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How does DHE-RSA work and why is PFS guaranteed?

How does it work and why is forward secrecy guaranteed? I understood that it is not susceptible to a man-in-the-middle attack by using certificates in the beginning.
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1answer
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RSA - Calculating $d$ given $\varphi (N)$ and $N$

From this discussion, I know that if I know $\varphi (N)$ and $N$ (where $N=pq$, $p$ and $q$ prime), then I can very easily get $p$ and $q$. Suppose I have the encrypted message $c$. I want to get ...
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1answer
214 views

Is there a feasible way to generate an RSA key manually the same way as it is for an ECC one?

In elliptic curves, a private key is just a random number, and one relatively small compared to other crypto systems (256 bits for ECC vs 4096 bits for RSA for example). Suppose I don't trust ...
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1answer
75 views

RSA: Decrypting message with public key and private key

I am trying to decrypt a message which its ciphertext in Hex A3 BB 05 00. The original plain text is 8 bits and it is encrypted by a 32 bits RSA key. I have successfully found the public key is $(e=...
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1answer
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What changed in PKCS#1 v2.2, and why?

PKCS#1 is one of the most used (de-facto) standard for real-world use of RSA. That's for good reasons: PKCS#1 is well thought, versatile, understandable, has been relatively stable for over two ...
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1answer
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Which elements of private RSA file are really constitutive of private key?

I have used openssl rsa to generate a RSA key of 2048 bits and as expected output belongs to a file beginning with ...
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3answers
3k views

Method to calculating e in RSA

For simplicity I choose two small primes for p and q. p=3 q=11 n=33 Φ(n)=20 Now we need ...
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RSA factorization [closed]

I'm trying to factor the given modulus, to find $p$ and $q$ so I can calculate the totient and then use that to decipher a message, but so far most of my attempts have fallen flat. I did notice that ...
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RSA Accumulator construction - how to pick the initial state?

I read about RSA Accumulators and I wish to construct one using a programming language of my choice. For selecting modulus N, I see various implementations picking the RSA-2048 number. Also, as the ...
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OAEP padding for OpenSSL [migrated]

I'm trying to decrypt a file using a private RSA key using OpenSSL. It keeps giving me the same 3 errors that I believe can be solved by adding oaep padding to it. What is the syntax for adding the ...
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1answer
637 views

What is the number RSA 2048 used for?

The RSA factoring challenge lists this RSA 2048 value: ...