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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241 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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1answer
182 views
ECIES protocol - what does the || operation mean?
I am studying elliptic curves problems, which also includes study of related protocols such as ECIES. A there is a problem I don't understand operation $||$. What this operation mean?
Some stuff is ...
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682 views
Symmetric vs. Asymmetric cryptographic approaches to data security
Ok. So, I now know the basic differences between them. But I'd love to know the deeper things, like:
Exactly why is the asymmetric approach slower than the symmetric?
Why does it make use of ...
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2answers
80 views
standard way to authenticate parties with public keys without certificates
Is there some standard protocol for mutual authentication of two parties when there is possibility to use public key cryptography? The problem is that two parties can use public key cryptography but ...
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3answers
106 views
Requiring a “supervisor” key pair and a “user” key pair to decrypt multiple-recipient messages
I've been toying with some encryption scenarios recently. One of the hard ones I came across is a multi-party system.
So we have
Bob -- The person who sends the message (and knows it's recipients)
...
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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
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 ...
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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
84 views
How can I protect against the failure of a block or symmetric cipher?
Can I protect against the failure of a block or symmetric cipher by chaining different techniques together? If so what implementation details should I be aware of?
Are some combination of ciphers ...
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2answers
99 views
When to prefer exchanging cryptographic certificates over exchanging only public keys?
Let's think of the following case:
A group of peers want to exchange messages with each other. They use public-key cryptography to sign and encrypt messages. Anyone with any name can join the ...
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75 views
How can a key pair be derived from an arbitrary hash?
If I correctly understand the concept of a "brain wallet" in BitCoin, you start with a passphrase, generate the hash of the passphrase, then somehow derive a public / private key from that to use as ...
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133 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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192 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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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 ...
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1answer
148 views
Public Key Encryption with forward secrecy
Is there a known non-trivial system with plausibly secure public key encryption where:
1. $\;\;$ the $\:$ time $\:$ function is efficiently computable
2. $\;\;$ [pubkey,privkey] $\:$ pairs are ...
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136 views
How are the primes used to generate RSA keys?
I am confused about how keys in RSA asymmetric encryption are generated and what the implications for open communications are. Textbooks say the one-way function is merely two primes (with some ...
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1answer
98 views
Proof of batch RSA security
Suppose we have two encrypted messages with two different public key issued from the one server. There is a client who wants to send these to messages to the server.
In the middle there is an ...
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1answer
2k views
Calculating private keys in the RSA cryptosystem
The number $43733$ was chosen as base for an implementation of the RSA system.
$M=19985$ is the message, that was encrypted with help of a public key $K=53$.
What is the plaintext text?
What is the ...
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1answer
42 views
Adversary Two Stages
I am read this paragraph and I have a doubt.
"An adversary to PKC $\Pi$ is given by two probabilistic polynomial
time algorithms, $A = (A1; A2)$. In the first stage, the "find"
stage, the ...
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1answer
74 views
Which public key was used. PGP
Is it possible to find out which public key was used to generate the message?
Scenario is like this :
I got data which is encrypted with a public key. Now a "bad guy" hast the encrypted data, and ...
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1answer
118 views
Generate an insecure public / private key pair
I am looking for a way to generate an "insecure" public key pair. and by insecure I actually mean a pair that is breakable using brute-force (or other encryption) methods.
As far as I know PGP ...
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1answer
56 views
Is sharing the modulus for multiple RSA key pairs secure?
In the public-key system RSA scheme, each user holds beyond a public modulus $m$ a public exponent, $e$, and a private exponent, $d$.
Suppose that Bob gives his private exponent to other users. ...
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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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138 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
147 views
Which encodings have |encoding key| >> |decoding key|?
I'm looking for an encoding scheme that requires a very large encoding key E (>10MB) and suffices with a relatively small decoding key ...
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53 views
Prevent/minimize replay attacks in public message board
Assume we have a public message board where anyone can send a message to. If plain messages are used, anyone can impersonate anyone. The goal is to disallow impersonations. We can use public key ...
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84 views
Determining the algorithm used to generate a digital signature
I have a string "abcd pqrs". This string is digitally signed with an X.509 certificate (with its private key) and it produces a signature.
From the signed string, is it possible to find out what ...
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64 views
In S/MIME, are the same certificates always used to sign and encrypt messages?
My assumption is that S/MIME almost always utilizes certificates as follows:
My certificate can be used to allow people to encrypt messages and send them to me.
My certificate (the same ...
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0answers
76 views
Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate]
Possible Duplicate:
Two untrusted party want to exchange data: how to insure each one gets the data it needs?
I am trying to come up with what could maybe be a novel algorithm for an ...
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2answers
92 views
risk of attacker decrypting RSA ciphertext without public or private key
As I describe in my previous question I am trying to decide if it's worth it for me to use the Offline Private Key Protocol in creating some long term private archives, instead of just going with a ...
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1answer
96 views
Why are RSA keys encoded with ASN.1 for TLS?
Browser vendors use ASN.1 encoding for RSA certificates in the TLS protocol. RSA public keys are just a number, so why do we need encode them to something else? That increases the risk of security ...
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2answers
119 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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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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1answer
104 views
RSA/DSA: Wouldn't it make sense to sign using decoding the data hash?
Why is encoding using the private key used for signing? Wouldn't it make sense to keep the premise, that private is for decoding and public is for encoding? i.e. create a hash and threat it as a ...
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1answer
54 views
Efficient algorithm for remainder calculation over prime field for ECC implementation?
I am working on 224-bit elliptic curve cryptography. In this 224-bit * 224-bit multiplication results 448-bit output. I am reducing 448-bit into prime field range( prime number $2^{224}-2^{96}+1$) ...
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1answer
219 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 ...
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1answer
46 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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1answer
66 views
Why is Blum-Goldwasser not IND-CCA-2 secure?
Consider the Blum-Goldwasser encryption scheme as described on Wikipedia. I was told that it was not IND-CCA-2 secure.
I heard there was malleabilty, probably it has to do with XOR-ing. But I do not ...
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3answers
131 views
File encryption with one keypair?
I'm working on a program that uses an ECC keypair in a (password protected) PKCS12 file (.pfx) to encrypt files. I like this method because I think it will be higher security (using ECDH to negotiate ...
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1answer
49 views
EC equivalent for RSA-OAEP
I have some questions regarding aforementioned subject:
Is there a EC equivalent of RSA-OAEP key transport/encryption algorithm ?
Is ECIES-KEM sufficient ?
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1answer
63 views
GPG vs PGP vs OpenSSH and management of them
What is the main difference of the three?
Can I use only one of them for everything (e.g. GPG for SSH authentication)
If I encrypt my private key with a pass-phrase, is it strong enough so that if ...
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1answer
65 views
Tell me about non-MD5/SHA1 key fingerprints
I understand there are specifications for public-key fingerprints that use modern hash algorithms like SHA2. What are they?
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1answer
120 views
What would the Internet be like without public-key cryptography?
The functioning of the Internet as we know it nowadays depends very heavily on public-key cryptography, including several key root systems that depend on its asymmetric properties.
But what would it ...
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1answer
287 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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1answer
140 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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1answer
157 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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0answers
53 views
how many bit flips current computers can carry per second? When brute force is hard?
How many bit flips the fastest current computers can accomplish per time unit? i.e per second. I am trying to find when brute force attacks are considered infeasible. The reason I chose bit flips is ...
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47 views
How compute encrypt and decrypt runtime for agorithm [closed]
I programming RSA algorithm is the following two function in java language in my thesis
...
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0answers
154 views
Cryptographic Protocol using NaCL
Why?
I wanted to add some security and privacy to a chat-type server for playing various games (with a few things that are done on the server to limit cheating). Going by the "Don't implement ...
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69 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 ...
