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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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 ...
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54 views

help understanding part of Wiener's attack on RSA w/ small d

In this paper, the author writes: Now $k\phi(N) = ed - 1 < ed$. Since $e < \phi(N)$, we see that $k <d < \frac{1}{3}N^{\frac{1}{4}}$. Hence, we obtain: $\mid \frac{e}{N} - ...
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142 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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139 views

How many bits to flip in an RSA public key to do signature forgery?

Scenario: Alice wants to verify a signature from Bob. Alice knows Bob's RSA public key (e, n). However, Alice is getting the data, the signature of the data and the public key from an attacker Eve. ...
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84 views

In what cases will RSA not work? [duplicate]

I know that there are cases when RSA will not work like when the number to feed into the system is greater than the modulus. I was wondering if there were any other cases when RSA won't work I looked ...
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55 views

How to determine the exponent when using RSA

Can someone please explain to me how, when using RSA, to determine the exponent to be used in encryption and decryption? I have attempted a worked example on using RSA (shown below) but I can't ever ...
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108 views

RSA: How effective is this keypair-trash attack [duplicate]

A question that could very well be part of xkcd's "what if?": Let's say Monica made a piece of software that sends all RSA keypairs to a central database after they're not used anymore. Something ...
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392 views

Practical Attack on RSA

Currently I am designing an RSA based application, and I am thinking of how long should the key be in order to be secure against attacks. I know that RSA 4096 bit key can be recovered using Sound ...
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610 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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507 views

Find private exponent in RSA [duplicate]

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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145 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 ...
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788 views

RSA decrypt long messages (javascript)

I am attempting to encrypty/decrypt a long message in RSA using javascript (with crypto-js and jsbn libraries). I posted this on stackoverflow too but I figured someone here on crypto might be able ...
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154 views

Physical Level Encryption

What types of algorithms that are capable of signing a message are out there that run on a physical level, e.g. lacking the infrastructure of a standard PC, no memory, processor or motherboard in the ...
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148 views

Certificate == signed public key

For primes p and q used to create a keypair, I understand that the following operation is used to create a signature: $M^d (\bmod\ N)$ where d and N have their usual meanings and M is the message. ...
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89 views

inverse of 985 mod(φ60131)

Alright Ive been working on this one for a while I found φ(60131) to be 97294 ½(60131+60131(5)^.5) = 97294 then I worked through the GCD ...
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49 views

Stripping off message authentication or signature

If attackers can strip off RSA / EC / -DSA digital signature and conduct CCA on AES-CTR or CBC payload, why can't they do the same for AES-GCM?
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Is ssl_sign safe as it is using OPENSSL_PKCS1_PADDING

I've been hearing a lot of scare talk about PKCS1 padding attacks. Is PKCS1 v1.5 safe in signatures as it is practically transporting only message digest? I'm using it in one of my applications so ...
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71 views

Inverting RSA using an oracle

Say you are given an efficient deterministic algorithm 'I' that can invert the RSA function on 1% of the points in $Z^*_{N}$. That is to say that if y $ \in $ $Z^*_{N}$ is a "good" point for 'I', ...
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51 views

Is webkey a reasonably secure authentication system?

I just created Webkey in the last couple days. This should allow any website to do single-password auth with a much higher level of auth security and convenience for users (single password with ...
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In case M is small is it possible to recover the message

In the plain RSA encryption, suppose $N$ is 1024 bits and the public key $e = 17$. Is it secure to use this setting to encrypt very small message, say $3 \leq m \leq 9$? In other words, is it possible ...
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109 views

Algebraic structures in RSA

Why do we need a field for RSA and what are the two operations in this field? Why can't we have a ring or group for example? Because in a group you also have inverse elements.
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How to encrypt incomplete block with RSA as a block cipher?

I have a question about an RSA academic example. If we are using block-RSA with a block-size of 3 and we have this message: "android". It is broken into 'and', 'roi', 'd'. How to encrypt the last ...
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RSA numerical questions

Let $n$ be the modular arithmetic, $p$ and $q$ the two large primes such that $n=p*q$ and $e$ the public exponent. Here they are two "simple" numerical questions: If $p = 13$ and $q = 17$, what is ...
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61 views

RSA-OAEP: How does it work?

I was looking at this image about OAEP: ..and was wondering what was happening here. We have a data block DB which consists of: ...
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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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121 views

Is it possible to correct the exponent of an RSA public key if it has been altered?

Is it possible to change the exponent of an RSA public key?
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How to deliver an encrypted message to multiple recipients without revealing keys

Let's say I have generated a private and a public key. I create a message and encrypt it with the public key. I deliver this encrypted message and a private key to multiple recipients. Why would I do ...
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179 views

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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1k views

PGP public RSA key format

I have been trying to use Go (I could post the code, but I think I posted enough already...) to generate a PGP RSA key. However every time I try to encrypt something with it, something fails. However, ...
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220 views

How to calculate RSA CRT parameters from public key and private exponent

Given the public key (n, e) and private exponent (d), how to calculate CRT parameters (p, q, dP, dQ, and qInv) of this RSA key pair?
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4k views

How to decrypt a '.enc' file that has been encrypted with RSA using a public key? [closed]

While solving a CTF challenge online, I came across a situation where I needed to decrypt a '.enc' file that has been encrypted using someone's public key. The ...
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38 views

Identification by RSA

Suppose we have identification scheme as such: Bob takes random $r$, and encrypts it with Alices public RSA key $(n,e)$, sends $r^e$ to Alice. Alice decrypts $r$ and sends it back to Bob, becomes ...
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109 views

RSA generation of private key using public key

In RSA private key generation e*d ≡ 1 mod φ e is public, also n is public. How to prove mathematically, generation of ...
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Proof that $gcd(e, \lambda(N)) = 1 \hspace{1mm} \Longleftrightarrow \hspace{1mm} gcd(e, \varphi(N)) = 1$

What is the proof for the fact that $gcd(e, \lambda(N)) = 1 \hspace{1mm} \Longleftrightarrow \hspace{1mm} gcd(e, \varphi(N)) = 1$ Where: $N = P * Q$ where $P$ and $Q$ are both primes. $\varphi(N)$ ...
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287 views

How does RSA padding work exactly?

I've read everywhere online and people say plain text RSA is very unsafe. To make it safe you pad it but no examples are shown anywhere on how to do it. It's explained that random data is added to the ...
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128 views

RSA signing security

I'm curious about the security of RSA signing with the same public private key pair when the same message is sent multiple times. It's my understanding that once you generate the hash of the message ...
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107 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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128 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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118 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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169 views

Is there any probabilistic version of RSA?

I have now studying the RSA, but I think that is it possible to have some probabilistic version like a random bit string "r" XORed with the key? Is there any probabilistic version of RSA? Thak you ...
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327 views

RSA Proof - Is Z(n) closed under multiplication

In RSA proof it can be proved that $\mathbb{Z}^*_n$ is closed under multiplication. Can it be also proved that $\mathbb{Z}_n$ is closed under multiplication? If yes, then how?
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655 views

Decrypting a small Message using RSA with a Private Key [closed]

If I have a private key of (43, 341). What would be the steps I need to take to decrypt a small message using RSA? I have looked ...
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409 views

Digital signatures under plain RSA

Show that digital signatures under plain RSA are insecure (Plain RSA means that signing is done by calculating $m^d\bmod n$, with $0\le m<n$, and no padding or hashing of $m$). Write an algorithm ...
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161 views

Is it possible to decrypt an RSA ciphertext with only $N$ and $e$?

Is it possible to perform RSA decryption if one only knows $N$ and $e$? Failing that, what is the maximum key length where brute-force is still practically feasible?
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129 views

What is the difference between exhaustive search and factorization in relationship to determining a key?

It seems to me an exhaustive search would simply try to use all the possible bit combinations of a key, while factorization is some mathematical formula for determining the key? When discussing the ...
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441 views

Key space: Dense and sparse

I'm taking a cryptography class and I come across these terms dense and sparse key space allt he time. What do they mean? As far as I can I understand, dense key space means that there are more ...
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94 views

How to choose the appropriate public (i, m) and private (j, m) keys?

I studied some encryption and decryption and I have found some very interesting problem to solve on the internet. I hope I am writing to right site - there are so many in StackExchange otherwise I ...
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353 views

Solving congruences using PARI

I'm having trouble finding info in the docs about how to solve a system of congruences. The closest I can find is 'matsolvemod' in here: ...
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352 views

How can we find Public key have only 8 or 16bits? How many messages does Eve need to know the Public key in RSA?

Suppose Alice sends messages to Bob by encrypting the messages with Bob's public key. Eve knows that the data is encrypted using RSA, but does not know the public key. Can Eve figure out the public ...
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Where is the mistake in my RSA by-hand calculation?

Like several previous askers, I seem to have made a mistake in my RSA calculation, but despite going back over it three times, I cannot spot it. I picked 1000003 and 6000011 as my primes, ...