Public key cryptography describes all cryptographic algorithms which have a pair of keys, one key that performs encryption and one key that performs decryption. One of these keys is made available publicly, allowing anyone to send messages that only the holder of the private key can read. You should ...
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282 views
Why the following attack in common modulus RSA works?
Suppose that i share a common modulus $N$ with two users $u_1$ and $u_2$ with public, secret keys ($e_a,d_a$), ($e_b,d_b$).
Why then $gcd(V,e_b)=1$ where $V=d_a*e_a-1/$W and $W=gcd(e_b,d_a*e_a-1)$ ...
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4answers
412 views
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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362 views
Why is asymmetric cryptography bad for huge data?
I've been told that asymmetric cryptography requires that the message to be encrypted be smaller than its key length.
Why is this?
I know about hybrid encryption, which uses symmetric encryption to ...
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1answer
81 views
How to generate a public key from a private ECDSA key?
Having some specific ECDSA curve and a private key, how does one calculate the public key? I am having a hard time finding the algorithm and equations for it.
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3answers
115 views
Public keys and their protocols
I'm having difficulties understanding exactly what this protocol means:
$S \to D : \{N_S , S\}K_D$
$D \to S : \{N_S , N_D \}K_S$
$S \to D : \{N_D \}K_D$
"where $S$ represents the supervisor’s ...
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2answers
139 views
Can one have an authentic, but repudiable, message without a previously shared secret?
Bob wants to send a message to Alice, such that Alice can be sure that the message came from Bob, but can't prove it to anyone else.
If I understand right, this means that the same message could have ...
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2answers
90 views
Polynomials and efficient computability
In public key crypto, the popular definitions of security (CPA, CCA1,2) depend on PPT adversaries. I'm trying to understand why adversaries should be PPT.
It's clear that adversaries should be at ...
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1answer
144 views
What are the benefits of lattice based cryptography?
Previously we visited the benefits of elliptic curves for cryptography. Lattice based cryptography is starting to become quite popular in academia. The primary benefit of lattice based crypto is the ...
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1answer
223 views
How much extra information is in an RSA public key?
I'm trying to calculate the size of an RSA public key in Ruby. I've retrieved the key in PEM format, and once I've decoded the base64 part from the PEM format, I get the size in bytes. What I find is ...
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1answer
102 views
RSA Key generation Public exponent too big
I'm currently writing a paper about RSA (a self-chosen subject).
I'm writing about the key-generation in RSA, and I have problem finding the public exponent e.
I have chosen p = 61 and q = 53.
Then ...
2
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2answers
121 views
Public key cryptography - public key encrypts and cannot decrypt?
I understand the basics behind public key cryptography, in that each party has two keys - the public one encrypts, and the private one decrypts. What I cannot figure out is, How does the public key ...
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1answer
131 views
using Post-quantum asymmetric ciphers instead of RSA
We can't trust RSA to encrypt our Emails so what is best post-quantum cryptography system as alternative for RSA which provide good security and don't be breakable? because McEliece cryptosystem looks ...
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1answer
245 views
Get RSA PlainText without Knowing Private Key
If I have an algorithm,RSA-Crack(), that, for a given RSA public key (n,e), is able to decrypt 1% of the messages encrypted with that key (without knowledge of the corresponding private key).Can there ...
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1answer
95 views
Does RSA-OEAP have integrity and authenticity properties?
RSA-OAEP is IND-CCA2 secure (indistinguishable under an adaptive chosen ciphertext attack). Does it also have the INT-CTXT (integrity of ciphertext) and INT-PTXT (integrity of plaintext) properties?
...
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1answer
141 views
In RSA encryption, does the value of e need to be random?
I am a novice programmer and am just finishing up an RSA encryption program that I am writing for practice. Currently I have the program generate a relatively small random value for the public key e. ...
2
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3answers
132 views
Safety of DSA key parameters sharing
I'm looking for a solution to use in a context where I need to be able to generate new asymmetric key pairs quickly (using a widely recognized algorithm, and EC-DSA is not applicable). It sounds like ...
3
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6answers
309 views
Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?
With a standard authenticated encryption scheme (or MAC), Alice and Bob share a symmetric key. When Alice sends something to Bob, Bob can check that it is authentic. At that point, Bob can deduce ...
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0answers
99 views
Ring Signature - paper/code difference in trying to solve inverse trap door function?
there is a paper on ring signatures and a python implementation of it here.
The Step 4 in the paper describes $y_s = v =C_k,_v(y_1, y_2, ... y_r)$ for all $1 \leq i \leq r$ where $i \neq s$. The ...
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0answers
68 views
Cryptograpy library for Python [closed]
I was searching for libraries/modules for encryption of data and found a few such as M2Crypto and GNUTLS but both of them don't support CMAC which is what I wanted to use for authentication. Anyone ...
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1answer
139 views
What is a trapdoor permutation?
Can anyone explain to me what a trapdoor one-way permutation is? Is RSA a trapdoor one-way permutation?
Context: I was reading about ring signatures. On page 560, it describes steps to ...
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2answers
118 views
Breaking RSA, given a special kind of oracle that decrypts related ciphertexts for us
Let $c=E^{RSA}_{e}(w)$ be the ciphertext belonging to the plaintext $w$ if an $RSA$ system is used. Assume that the public exponent $e$ satisfies $e \le 10$. Furthermore, assume there is an oracle ...
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156 views
How does a client verify a server certificate?
As far as I know,
when I request a certificate from Verisign (for example), and after they approved that me is me, they create a certificate (for me) which contains the digital signature and public ...
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1answer
137 views
How can I prove in zero knowldege that an ElGamal shuffle is correct for a special setting? [closed]
In a special ElGamal encryption scheme, every user has an ElGamal encryption key-pair using the same cyclic group $G$ and generator $g$.
The system has a special function :
$$ ...
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1answer
191 views
Can ElGamal encryption and ElGamal signatures be used together sharing the same key-pairs?
I'm working on a encryption system where each party can store exactly a single ElGamal private key in a device. This is a hardware limit. The system must be expanded to support signatures and ...
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2answers
142 views
Can I save space for short messages by using encryption with private key instead of a signature?
Let's say I have a message, a Private Key and a Public Key.
Normally if you want to see if the message is unaltered and is from the sender you would have the message part + signature part, which you ...
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0answers
190 views
How do I encrypt with the private key? [duplicate]
Possible Duplicate:
RSA encryption with private key and decryption with a public key
This wording is creeping everywhere (e.g. there): "I encrypt with the private key" and even sometimes, ...
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3answers
209 views
Is there a public key semantically secure cryptosystem for which one can prove in zero knowledge the equivalence of two plaintexts?
If Alice encrypts two messages $a$ and $b$, such that $x=E(a)$, $y=E(b)$. Can Alice prove (without revealing $a$, $b$ or the private key) that $a = b$?
Obviously the proof must not be too long and it ...
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1answer
167 views
What's the main difference between Pohlig-Hellman and RSA?
Both Pohlig-Hellman and RSA perform encryption and decryption by exponentiation modulo some integer ($p$ prime for PH, $n$ composite for RSA). They both use a key $e$ as the exponent to encrypt a ...
4
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1answer
101 views
Correct method to encrypt data so that it can be decrypted only by Alice and Bob
I need to build a system that stores encrypted transactions. Transaction involves always two parties. Payer and payee. Both must be able to download encrypted transaction from server and decrypt it ...
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2answers
88 views
When is each key used when encrypting an email using OpenPGP?
When you send an email using PGP to encrypt emails, is the recipients public key used to encrypt the email, or is your private key used? Are they both used?
At what points do each of the four keys ...
2
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1answer
152 views
What is the strength of unpadded RSA?
I would like to use unpadded RSA for homomorphic encryption in a toy P2P game, for things like fair coin flips and shuffling.
How many bits of security does unpadded RSA have, in relation to its key ...
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3answers
219 views
How to avoid a chicken and egg scenario with encrypting passwords?
I am working on application that allows users to upload files containing company data and then share those files with a list of other users that have specific roles within the system.
I want to ...
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1answer
189 views
implications of SSH server key compromission when authenticating users against a public key
Friday we had a disagreement with a colleague of mine about the implications of SSH server key compromission
The question was stated as this :
What could a hacker do while provided with the SSH ...
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3answers
327 views
Is it possible to pick your Ed25519 public key?
Is it possible to generate an Ed25519 keypair that has a very similar public key as another keypair (fooling a casual visual comparison) or is this as hard as solving one of SHA-512 or the discrete ...
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1answer
238 views
How to jusify {e,n} is a valid RSA public key?
I have a two set of key {36,77} and {50,117},
How can validate if it is a valid RSA public keys?
Is there any simple method?
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2answers
216 views
Additive ElGamal cryptosystem using a finite field
I'm trying to implement a modified version of the ElGamal cryptosystem as specified by Cramer et al. in "A secure and optimally efficient multi-authority election scheme", which possesses additive ...
2
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1answer
184 views
Is truncating a hashed private key with SHA-1 safe to use as the symmetric key for AES for data at rest?
I realize this is mixing the purposes between asymmetric and symmetric crypto, but I was wondering if it is safe to use a hashed, truncated private key (asymmetric) as the symmetric key for encrypting ...
2
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2answers
489 views
Why should the RSA private exponent have the same size as the modulus?
Consider the generation of an RSA key pair with a given modulus size $n$ and a known, small public exponent $e$ (typically $e = 3$ or $e = 65537$). A common method is to generate two random primes ...
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3answers
109 views
Is it possible to ensure security with zero pre-shared information?
Is it possible to secure a communications channel against both passive (sniffing) and active (injecting / MitM) attackers without either legitimate party knowing any pre-shared information?
I know ...
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2answers
316 views
Is this a correctly formatted PGP session key packet?
RFC 4880 may be full of information, but it can be incredibly vague at times, so im looking for someone who actually knows the answer to this.
Given this public key:
...
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2answers
172 views
Encryption with private key?
we normally always encrypt by public key and decrypt with private key.
If i encrypt with private key, then its still secure as normal PKI ?
i mean known-plain-text will not take private key on the ...
2
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1answer
409 views
Is this design of client side encryption secure?
I want to build a secure file storage web application. Users should be sure that server doesn't know how to decrypt files so encryption should take place at client side (i.e. in Javascript) and TLS ...
2
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2answers
116 views
Does a high exponent compensate for a low degree of certainty?
If a RSA certificate is created with a low degree of certainty, does the value of the exponent compensate for this?
I'm asking because certain implementations of key generation software hide the ...
2
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2answers
198 views
How to decrypt this RSA-like cipher
Suppose we have a RSA-type Modulus $n = pq$ with $p,q$ prime. We also pick a random public exponent $e$ with $\gcd(e,\varphi(n)) = 1$ and compute the private exponent $d$ with $de \equiv 1 ...
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1answer
218 views
What is the correct value for “certainty” in RSA key pair generation?
I'm creating an RSA key pair in Bouncy Castle and need to specify an int value for certainty. This Stack Overflow answer says it is a relative test for how prime the values are.
There is another ...
6
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2answers
999 views
Impacts of not using RSA exponent of 65537
This RFC says the RSA Exponent should be 65537. Why is that number recommended and what are the theoretical and practical impacts & risks of making that number higher or lower?
What are the ...
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2answers
934 views
How much computing resource is required to brute-force RSA?
It's been over 30 years since Rivest, Shamir and Adleman first publicly described their algorithm for public-key cryptography; and the intelligence community is thought to have known about it for ...
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2answers
225 views
Is it possible to use the RSA algorithm, or a variant, for software licensing?
I'm almost a newbie about RSA encryption, so my question could it be banal.
I'm beginning to create a licensing system for my software.
I need to distribute a crypted license file to many customers.
I ...
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2answers
100 views
How can the Schmidt–Samoa cryptosystem uniquely decrypt large messages?
Suppose I choose $p=7$ and $q=11$.
This gives a public key of $p^2·q = 539$.
However, decryption occurs using a modulus of $p·q=77$.
If a person chooses to encrypt $500$ using my public key, how ...
5
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1answer
266 views
GPG/PGP Verification of Revocation
How does one verify a key revocation?
After revoking a key and sending the revocation to MIT's keyserver, I noticed that the key is listed as such:
...
