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Results tagged with public-key
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user 452
An asymmetric cipher is an encryption scheme using a pair of keys, one to encrypt and a second to decrypt a message. This way the encrypting key need not be kept secret to ensure a private communication. Similarly in public key authentication, the verification key can be public and the signing key private.
1
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A secure public-key cryptosystem
Is there any public-key cryptosystem that is (possibly) secure against $NP\cap coNP$ adversary?
Hash based signatures come to mind; essentially, to break them, you need to find a (second) preimage o …
- 151k
4
votes
Accepted
Public Key Encryption with forward secrecy
One approach can be found in this paper by Canetti, Halevi and Katz. To summarize the approach:
This generate a tree of private keys; from a node, you can generate private keys downwards (to child …
- 151k
3
votes
Accepted
Is the product of two primes only factorisable by those two primes?
Yes, that is true (unless you count the trivial factors of 391, namely 1 and 391). The fundamental theorem of arithmetic states that any postive integer is a product of a unique multiset of primes, a …
- 151k
12
votes
Which public key cryptosystems are not based on number theory?
In addition to McEliece (already mentioned by Mike), there's also Hash Based Signatures (such as this one); these are signature algorithms that is based only on some security assumptions of a hash fun …
- 151k
1
vote
What threat do quantum simulators pose?
What threat does this model pose to current cryptography?
Do you mean "what threat does their algorithm run on a quantum simulator pose to cryptography"?
If so, the answer is "none". Yes, there …
- 151k
2
votes
Accepted
Is there a library that implements the "Mickey Mouse Version" of asymmetric cryptography?
You are asking about a cryptosystem that is similar to a public key encryption system, except that the "private key" (or decryption key) cannot be used to encrypt.
One way to get this sort of functio …
- 151k
13
votes
Accepted
Do public/private pairs work both ways?
Well, first of all, the answer to your question depends quite a lot on whether your asking about RSA specifically, or public key algorithms in general (of which RSA is one example).
For raw RSA, the c …
- 151k
18
votes
Accepted
Why is a 2048-bit public RSA key represented by 540 hexadecimal characters in X.509 Certific...
That's because the public key in DER format (which is a way of expressing X.509 objects as a sequence of bytes) includes more than just the modulus. Specifically, it consists of:
This is a collecti …
- 151k
4
votes
Accepted
I don't understand Digital Signature
bob hashes his message and encrypt it with alice public key
No, Bob would sign it with his own private key. For some signature methods, this is roughly similar to "encrypting with the private key", …
- 151k
4
votes
Applications of Group Ciphers
One thing I would like to add: a "Group Cipher" comes fairly close to the properties you need from a public key cipher. In particular, if the group is abelian (or has an abelian subgroup for which th …
- 151k
1
vote
Is there an algorithm to find the number of intersections of two sets?
How about this idea:
We'll assume that the integers in the sets are all in the range $[2, N]$ for some agreed-upon $N$.
(why is the start of the range $2$? Because the below protocol doesn't work w …
- 151k
3
votes
Why is public-key encryption so much less efficient than secret-key encryption?
When, the problem is that for public key cryptography, you have to have a lot a mathematical structure than you need for symmetric key cryptography.
For symmetric operations, we can pick our algorith …
- 151k
9
votes
What is Identity-Based Encryption (IBE) and why is it "better"?
Well, the quick answer to what is IBE is "it's public key encryption except that someone's public key can be an arbitrary string, rather than something picked by a key generation process".
The first …
- 151k
4
votes
Accepted
Signature scheme with two private keys, neither derivable from the other
Well, one obvious way to do this would be using RSA with a large 'public' exponent. That is, it is the traditional RSA sign/verify operation except that, instead of the usual optimization of having a …
- 151k
10
votes
Does RSA work for any message M?
Yes, RSA works for every M. Remember Fermat's Little Theorem:
$x ^ p = x \mod p$ (for all $x$, and all prime $p$).
A bit of induction gives this simple extension:
$a = 1 \mod p-1$ implies $x ^ a = …
- 151k