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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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.
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2answers
237 views
How do public key rings work in cryptographic applications?
I am wondering if there are any links to articles or resources available online, or explanations that you can give, that would help me to understand the concept of a public key ring, and why I might ...
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237 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?
3
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1answer
58 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?
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Exposing RSA private-key data… bad?
We know that exposing $p$, or $q$ or $\phi(n)$ results in trivial attacks on RSA since they allow us to factor $n$ and to compute the private exponent $d$.
In OpenSSL (and most RSA implementations) ...
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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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2answers
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How to distribute session keys in public key cryptography?
In public key cryptography we can also use session keys which are symmetric. How do the sender (say a server) provides this session key information to its clients?
If the sender (here server) ...
2
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1answer
898 views
Secure way to transfer data over NFC?
I am currently writing a payment system to accept payment details from an NFC enabled smartphone (BlackBerry 9900) to a Windows client (C#.NET)
I am currently having two issues relating to security:
...
6
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5answers
2k views
Why do we need asymmetric algorithms for key exchange?
In SSL protocols, both symmetric and asymmetric algorithms are used. Why is it so? The symmetric algorithms are more secure and easier to implement. Why are asymmetric algorithms usually preferred in ...
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1answer
178 views
ECC Cryptography
I want to know th basic understanding of ECC algorithm for cryptography.But I am not aware of the algorithm so please any one give me the basic understanding of the algorithm.
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Why does the PKCS1 RSA private key structure contain more than just exponent and modulus?
The ASN.1 spec for the PKCS1 RSA private key format is as follows:
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1answer
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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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2answers
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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 ...
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2answers
243 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 ...
5
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3answers
584 views
Is it possible to validate a Public Key in RSA?
If I have a 1024-bit number, and someone is telling me that it is in fact a valid RSA public key, is there any way I can quickly validate that it is indeed so (without cracking RSA)?
(I suppose I am ...
6
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1answer
273 views
Compressing EC private keys
For reasonable security, EC private keys are typically 256-bits. Shorter EC private keys are not sufficiently secure. However, shorter symmetric keys (128-bits, for example) are comparably secure.
I ...
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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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How can I use asymmetric encryption, such as RSA, to encrypt an arbitrary length of plaintext?
RSA is not designed to be used on long blocks of plaintext like a block cipher, but I need to use it to send a large message.
How can I do this?
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3answers
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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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542 views
Cycle attack on RSA
I originally posted this question in the mathematics section, you can see it here.
Let $p$ and $q$ be large primes, $n=pq$ and $e : 0<e<\phi(n), \space gcd(e, \phi(n))=1$ the public encyption ...
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3answers
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What other one-way functions are used in cryptosystems?
For RSA and El Gamal (and most other public key cryptosystems), one of the key ideas is that factoring and finding discrete logarithms are hard. There are other systems that rely on certain properties ...
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1answer
561 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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2answers
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Definition of Textbook RSA
What is the definition of Textbook RSA?
What are some of the properties of textbook RSA?
How does it differ from other RSAs?
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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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1answer
179 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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3answers
612 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
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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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1answer
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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 ...
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2answers
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Protocol to generate Client Certificates at the start of a SSL session automatically?
A more secure form of 'cookie' could be created for SSL communications through the following method.
The client generates and requests the server to sign a certificate.
Then the client authenticates ...
4
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2answers
411 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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3answers
436 views
What is Identity-Based Encryption (IBE) and why is it “better”?
Most CS/Math undergrads run into the well-known RSA cryptosystem at some point. But about 10 years ago Boneh and Franklin introduced a practical Identity-Based Encryption system (IBE) that has ...
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346 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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Are there practical upper limits of RSA key lengths?
Suppose one wanted to use RSA encryption for the sole purpose of sending key bits for use in symmetric crypto systems, a dedicated key exchange system so to speak.
And say you didn't think that the ...
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For public-key encryption, why does COA resistance imply CPA resistance?
My professor told me:
If a public-key crypto-system is secure against ciphertext-only attacks,
then it is also secure against a chosen-plaintext attack.
Why is this true? Is there a proof that ...
6
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Is key size the only barrier to the adoption of the McEliece cryptosystem, or is it considered broken/potentially vulnerable?
A recent paper showed that the McEliece cryptosystem is not, unlike RSA and other cryptosystems, weakened as drastically by quantum computing because strong Fourier sampling cannot solve the hidden ...
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3answers
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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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In RSA, do I calculate d from e or e from d?
In the original paper introducing RSA, it is implied that one should first choose $d$ and then calulate $e$ from $p$, $q$, and $d$. However, I have found in other places (such as the wikipedia article ...
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Asymmetric cryptographic algorithms that are not based on integer factorization and discrete logarithm
In the computer security class (in which cryptography is a big chapter) that I took, I remembered the professor said about current asymmetric cryptography algorithms are based on integer factorization ...
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1answer
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How do other, non-RSA algorithms, compare to the PKCS #1 standard?
Arguably the PKCS suite of standards have a profit-oriented bias as they are promoted by RSA and promote their algorithms over others in the form of RFCs and other means.
I'm considering the ...
3
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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 ...
3
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1answer
135 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:
...
2
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1answer
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A set of key pairs and one hash to secure them
I have a simple problem: I have a set of users' ECDSA key pairs, and say I want to encrypt them with a simple algorithm. I have access to one variable that uniquely identifies the user, so I hash it ...
3
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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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Is it possible to create an asymmetric cryptosystem where the private keys are not easily verifiable as such?
Plaintext that consists of an RSA key is easily recognizable as such, because it satisfies certain mathematical properties, in particular (See the answer for Why can an encrypted private key be brute ...
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Why can't Diffie-Hellman be used for signing?
I understand that signing is often a case of hashing data and then encrypting the hash with the private key. What properties keep Diffie-Hellman from being useful for this?
4
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3answers
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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 ...
3
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2answers
514 views
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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Basic explanation of Elliptic Curve Cryptography?
I have been studying Elliptic Curve Cryptography as part of a course based on the book Cryptography and Network Security. The text for provides an excellent theoretical definition of the algorithm but ...
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1answer
341 views
Digital Signature Algorithm signature creation
I was studying DSS from "Cryptography and Network Security" by William Stallings. What puzzled me was the DSS approach figure described in the text. It says it uses Public and Private Keys for ...
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Why is public-key encryption so much less efficient than secret-key encryption?
I'm currently reading Cryptography Engineering. After giving a high level explanation of the difference between secret-key encryption and public-key encryption, the book says:
So why do we bother ...
