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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106 views
Do public/private pairs work both ways?
Public/private key algorithms such as RSA encrypt a message with a private key but only decrypted with another (mathematically related) key.
Can the public key decrypt the messages encrypted with ...
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219 views
X.509 CSR: Why does CA remove signature?
I just read this article on Wikipedia: Certificate Signing Request
I'm not a PKI or Crypto expert. As I understand, a CSR (certification request) is always signed by the PKCS#10-Request creator.
...
4
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2answers
214 views
What is the appropriate public key encryption for secure coin flipping?
I quote Bobby's question here since I encountered the same one...
Random Coin Flip using ElGamal and a Trusted Party
Consider the following protocol for two parties to flip a fair coin.
Trusted ...
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2answers
431 views
Is a RSA-signature of some identifying data a safe way to implement a license key?
I have this idea of implementing a license key:
After the user downloads the program, he connects to a website and sends his Windows product ID.
The website, then, sends this back to him with a ...
4
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2answers
355 views
Random Coin Flip using ElGamal and a Trusted Party
An old exam question I am trying to figure out:
Consider the following protocol for two parties to flip a fair coin.
Trusted party T publishes her public key pk
A chooses a random bit ...
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2answers
421 views
How do I solve this RSA instance for m?
How we can solve this equation and get the value of M?
$$8 = M^{13} \mod 33$$
not a computer program, but a mathematical operation.
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3answers
572 views
ElGamal: Multiplicative cyclic group and key generation
Here on the ElGamal wikipedia page http://en.wikipedia.org/wiki/ElGamal_encryption
Alice generates an efficient description of a multiplicative cyclic group G, of order q, with generator g.
How ...
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257 views
Why is Diffie-Hellman considered in the context of public key cryptography?
In all textbooks I used the Diffie-Hellman key exchange is under "public key cryptography".
As far as I can see it is a method to exchange a key to be used with a symmetric cryptographic algorithm, ...
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190 views
Why does RSA give better security on longer messages?
I am trying to understand the notion of RSA security.
Choosing a public exponent where $e = 3$ facilitates the calculations, considering that it is secure if the plaintext or message is long.
If the ...
4
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2answers
3k views
When to use RSA and when ElGamal asymmetric encryption
If i am not wrong in cryptography there are 2 basic cryptographic schemes for public key cryptography. RSA encryption whose security is based on the infeasibility of solving the factoring of big ...
4
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1answer
105 views
Client and server using same SSL certificate - any issues?
I'm working on software where multiple components will communicate with each other using SSL.
There would be one central component acting as a server, which would also require the clients to present ...
4
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1answer
103 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 ...
4
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1answer
148 views
Question about why RSA is hard to attack
I think I understand why RSA is hard to attack but I'd like to get clarification if I actually do.
Assume there are two people, Alice and Bob, who are attempting to communicate privately but that we ...
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1answer
260 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 ...
4
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1answer
197 views
How are trapdoor functions developed/found and where can I find existing ones?
Trapdoor functions are a fundamental part of public key cryptography. An example of the most common trapdoor is
Prime Factorization, used in cryptosystems such as RSA
How are these trapdoor ...
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327 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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3answers
265 views
Preventing message replay with RSA
I am using RSA to encrypt some data but I would like to eliminate the possibility of message replay. By message replay I mean sending a valid message multiple times to the original recipient. It is ...
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3answers
5k views
RSA encryption with private key and decryption with a public key
Does the encryption with a private key and decryption with a public key works in RSA? Is it done when we use RSA for sender authentication ?
Thanks.
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Can a computationally unbounded adversary break any public-key encryption scheme?
Assume there is a public-key encryption scheme $(KeyGen, Enc, Dec)$ with perfect correctness (i.e., for all messages M and valid key-pairs (PK,SK), we have $Dec_{SK}(Enc_{PK}(M))=M$).
Will there ...
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3answers
625 views
What is the importance of Modular arithmetic in cryptography?
Why do we use modular arithmetic so often in Cryptography?
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2answers
234 views
If Bob steals Alice's private key, how exactly would he read her encrypted documents?
So Bob grabs Alice's secret key when she isn't looking and her encrypted files, doesn't he need to know her passphrase to read her files?
What I am reading is that no he does not need it but as far ...
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6answers
317 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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2answers
306 views
Can RSA encryption produce collisions?
In RSA, a message is encrypted by $m^e \pmod N$. $N$ is the modulus, $m$ is the message and $e$ is the public exponent. (I know that $m$ should not be greater than $N$.)
My question is, can $m^e$ be ...
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2answers
149 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 ...
3
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2answers
342 views
Difference between symmetric and asymmetric hash function?
The Linux kernel supports symmetric and asymmetric hash functions. E.g. sha1, sha256, ...
See tcrypt.c and search for test_hash_speed and ...
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3answers
228 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 ...
3
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1answer
172 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 ...
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249 views
Key space size when either of two public keys are valid for authentication?
If for authentication a user can own either A OR B public key instead of just one specific key is that equivalent to halving the key space. i.e. it it theoretically twice as easy to brute force and ...
3
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4answers
955 views
How are timestamps verified?
You put an input and the hash value comes as an output then when someone puts the input the hash function it is applied to see if it is the same hash original value is stored in some database , that ...
3
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1answer
276 views
What happens if an RSA key pair has identical public and private exponents?
Rather, is it possible for big prime numbers?
Classroom examples usually involve smaller primes, so for example if you are given a prime number pair $p = 3$, $q = 13$ you would get $n = 39$ and $e = ...
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2answers
499 views
Difficulty of breaking RSA for a given key size
Is it true that breaking a 1024-bit RSA key is as difficult as breaking a 128 bit symmetric key (e.g. AES)? I know that breaking a RSA key is equivalent to factoring the modulus $N$. To factor it, you ...
3
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1answer
638 views
RSA: If n=35, show that e will equal d
Show that if $n = 35$ is used as an RSA modulus then the encryption exponent $e$
always equals the decryption exponent $d$?
What I have so far:
$n = 35$
Therefore $p = 5$ and $q = 7$ or vice versa, ...
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3answers
446 views
public key cryptography and digital signature
I read the following from Understanding Public Key Cryptography on Microsoft TechNet:
Using a private key to establish identity shows that the full
encryption and decryption operation was ...
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1answer
133 views
When is an asymmetric scheme considered broken?
Does the following quote imply that valid encrypted data can be created and decrypted by someone other than the owner of a private key:
An asymmetric encryption scheme is considered to be broken ...
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3answers
60 views
What are some good references for the implementation weaknesses in RSA
I'm pretty sure I understand textbook RSA.
Choose p and q, large primes, and compute n=pq.
Choose e such that $gcd(\phi(n),e)=1.$
Publish n and e.
Compute d such that $de=1$ (mod $\phi(n)$).
To ...
3
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1answer
281 views
Is a known plaintext, ciphertext, and public-key a viable attack on RSA?
Assume Alice and Bob are using RSA to create a common session key and Cindy is listening, attempting to obtain the session key.
Alice and Bob each have their public- and private-key pairs ...
3
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247 views
What is the computational cost of a public key certificate signature verification?
What is the computational cost of a certificate signature verification in terms of exponentiation, multiplication and other computation operations?
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159 views
What is the property of RSA where N=e?
In RSA, suppose we know that $e=N$ and we are given the value of $e$.
($N = p\cdot q$ for some large primes $p$ and $q$; $\gcd(e, \varphi(N) = 1)$
Can we calculate $d$ ($d = e^{-1} \mod ...
3
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2answers
101 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 ...
3
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1answer
136 views
Signature scheme with two private keys, neither derivable from the other
Is there any scheme, ideally one widely used or at least widely available, where you can treat both the signing and verifying keys as secret?
Basically, the functionality I'm looking for is this:
...
3
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1answer
120 views
Combining AEAD with RSA
'Hybrid' encryption, where we combine symmetric encryption with public-key cryptography, is pretty 'tried and tested'.
To summarise, we generate a symmetric key and encrypt it using RSA. We would ...
3
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1answer
61 views
In a lattice, how can one define a good basis and a bad basis?
When it comes to lattice based cryptographic systems, all the literature talks about, good bases and bad bases.
How does one define what a good basis is and what a bad basis is?
3
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3answers
175 views
Are asymptotic lower bounds relevant to cryptography?
An asymptotic lower bound such as exponential-hardness is generally thought to imply that a problem is "inherently difficult". Encryption that is "inherently difficult" to break is thought to be ...
3
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1answer
166 views
Secure encrypt-then-sign with RSA
I understand that when you want to encrypt and sign data with RSA the generally recommended approach is sign-then-encrypt.
However, I have encrypted data that I need to sign, to prove the author of ...
3
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1answer
128 views
DGK Cryptosystem Key Generation and Decryption Issues
I detailed here the DGK (Ivan Damgård, Martin Geisler and Mikkel Krøigaard) cryptosystem, and I managed to get it to work, most of the time...
The BIG problem that I am facing at the moment is that ...
2
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2answers
387 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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2answers
1k 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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3answers
235 views
How can one sign with NTRU?
I am looking at implementing NTRU, but I noticed that while the encryption/decryption algorithm seems to be mature and well-documented, there is comparatively little information about how to sign ...
2
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2answers
521 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 ...
2
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2answers
120 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 ...
