All Questions
3
votes
2answers
160 views
What crypto system allows for 3 parties: Party 1 who makes an assertion, Party 2 mutates the assertion, Party 3 validates it
I'm looking for the cryptographic equivalent of a Drivers license where the issuer can be verified, the issuer doesn't need to know who you showed the drivers license to, but also allows ...
1
vote
1answer
65 views
How to obtain a one-value share in Shamir's secret sharing
This is a trivial question, but I had to ask:
since each generated share in a Shamir's secret sharing scheme initially consists of a pair of values (representing the coordinates of a point on the ...
2
votes
1answer
153 views
Encrypting many small messages (log-lines)
What would be the best way of encrypting small mesasages to be stored in encrypted form? (This sounds like somthing a textbook would cover, but I haven't found any references).
Let's say I have many ...
1
vote
2answers
212 views
Would a “Triple AES” (in the sense of how Triple Des works) serve for a dramatic increase in safety?
The system requires to be as paranoid as possible regarding security. One of the few contemplated changes to the current design is to use multiple encryption. First proposal was to use Serpent on top ...
1
vote
1answer
66 views
Isn't the structure of a potential plaintext of a ciphertext generated by a one-time pad dispositive, cryptanalysis-wise?
That is, if I generate every possible result, and analyze the structure against, for example, a dictionary, won't that identify which of the solutions in the domain is most likely the correct one?
I ...
0
votes
0answers
60 views
Method and explanation for calculating difference in speed between DES and RSA
Our assignment asks us to convert an RSA speed in bytes per second to a DES speed in bytes per second. Our professor's treatment of this ("RSA is 100 times slower than DES") seems insufficient. Could ...
1
vote
2answers
181 views
Diffie-Hellman key agreement with both Server Authentication and Perfect Forward Secrecy
I am trying to find the protocol with the least overhead, which still meets the following requirements:
Server Authentication of server identity to client. The client has an authentic copy of the ...
0
votes
1answer
96 views
Is there an efficient way to hide the encrypted plaintext length with a block cipher?
In block cipher modes of operation for encryption on input of a plaintext of $N$ blocks (We assume that the input size is always a multiple of the blockcipher mode: $N·16$ bytes) the size of the ...
0
votes
0answers
76 views
computing inverses in truncated polynomial rings manually for NTRU encryption
Can someone explain how to find inverses in truncated polynomial rings manually (i.e. on pen and paper)?
As an example from the tutorial:
Example. Take $N=7$, $q=11$, $a=3+2X^2-3X^4+X^6$. The ...
-2
votes
2answers
147 views
Where to store the private key and the public key in a communication protocol
I want to create a simple secured connection protocol over TCP/IP.
I just want to connect from my mobile device to a server securely.
Firstly I thought to use an SSL connection, but I changed my ...
3
votes
2answers
71 views
Current Status of mixnets for voting
I am currently doing some research on universally verifiable mixnets, but it seems to me that there are too few papers about them after 2006 or so and most of them come from the team of Douglas ...
0
votes
1answer
80 views
Can one detect if two pairs of elements in Zp have the same exponential relation?
Suppose that $p$ is a safe prime of 2048 bits ($p = 2q + 1$, and $q$ is prime).
Suppose that one is given two pairs $(x_1, y_1)$ and $(x_2, y_2)$ such that:
$y_1 = x_1^{r_1} \pmod p$
$y_2 = ...
1
vote
1answer
85 views
Is this method for exchanging private key using RSA sound?
Bob know's Alice's public key, and he wants to make sure he's connecting to the one which has that key. Furthermore, Alice wants to verify when she gets a connection from Bob who'll give his public ...
1
vote
1answer
81 views
Zero-knowledge proof that a group element is a quadratic residue?
In a paper it says: "To convince a verifier that a group element is a quadratic residue, the prover executes the following proof with the verifier":
$PK \left\{ (\alpha) : y = \pm g^\alpha \right\}$
...
3
votes
1answer
161 views
Understanding Feldman's VSS with a simple example
I'm trying to understand Feldman's VSS Scheme. The basic idea of that scheme is that one uses Shamir secret sharing to share a secret and commitments of the coefficients of the polynomial to allow the ...
1
vote
1answer
63 views
What is the usual block cipher mode that goes with CTS
I am just wondering what is the most common, or most used, block cipher mode used to goes with CTS?
ECB or CBC?
0
votes
0answers
37 views
Is it possible to determine the group order by knowing the “public” and “private” key exponents in an RSA group?
I have an RSA group with modulus $n = p \cdot q$, two safe primes $p=2p'+1$ and $q=2q'+1$ and the "public" and "private" key exponents $d$ and $e$. $\phi(n) = 4p'q'$ is the order of the RSA group. If ...
1
vote
1answer
78 views
How difficult is it to check if a group element is in a sub group?
I am just curious. We have a group $G$ and its subgroup $H$ with a generator element $h \in H$. How difficult is it to check for $x \in G$ that $x \in \langle h \rangle$? Is there a better way than ...
2
votes
3answers
135 views
Is there a way to use Shamir Secret Sharing with updatable data?
I want to divide a system that maintains these properties, based on Shamir's Secret Sharing:
A secret key is split up to N pieces, where T of them are enough to reconstruct the key.
The original key ...
8
votes
0answers
135 views
What changed in PKCS#1 v2.2, and why?
PKCS#1 is one of the most used (de-facto) standard for real-world use of RSA.
That's for good reasons: PKCS#1 is well thought, versatile, understandable, has been relatively stable for over two ...
5
votes
2answers
127 views
Security of tokenization of plain text conversations - cryptanalysis
I came across a marketing video here. They claim to perform AES encryption and tokenization of sensitive data, at the corporate gateway, before it leaves the company firewall destined for the public ...
2
votes
1answer
253 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 ...
0
votes
0answers
54 views
Strength of Combining Hash functions [duplicate]
If I combine two hash functions, what will the impact on the strength of the resulting function.
If I combine in following way:
H1*H2 (multiply)
H1 + H2 (concat)
H1 Xor H2
H1 (H2)
EDIT:
Lets say H1 ...
2
votes
1answer
46 views
Equivalents to a physical hat+shaking?
I would like a multiparty protocol, secure in the honest-but-curious model at least, but hopefully other situations as well, that can do the following: every party among $\{P_1, P_2, \ldots P_n\}$ ...
4
votes
2answers
134 views
ChaCha cipher + Poly1305
The Poly1305-AES paper summarizes the MAC as
$$ Poly1305(m, AES_k(n)) = {H_r(m) + AES_k(n)} \mod 2^{128} $$
Can I presume that $+$ here is just meant as a form of 16-byte mixing $H_r(m)$ and ...
2
votes
1answer
204 views
XOR cipher for encrypting compiled C code
I'm exploring ways of encrypting Intel hex files we send to customers for flashing onto an embedded device. The embedded processor itself has a built-in mechanism that prevents anyone from reading the ...
0
votes
0answers
65 views
Use curve25519 for ElGamal crypto
DJB described curve25519 in his paper which can be found here: http://cr.yp.to/ecdh/curve25519-20060209.pdf. It seems that the main purpose was for Diffie-Hellman key exchange. I think this means that ...
0
votes
1answer
55 views
Exponentiation In PBC library
I need to compute a function $h^l$, where h is an element of G2 and l is a rational number. How can this be done using the PBC library?
I have converted the h to ...
6
votes
3answers
449 views
Is this encryption algorithm build from MD5 secure?
I'm being asked to use an encryption algorithm in my code, and besides the fact that I'm sure there will be implementation faults that lead to vulnerabilities, I also have concerns about the algorithm ...
2
votes
1answer
57 views
How are Elliptic Curve Cryptography and Pairing Based Cryptography related?
I have been doing a project that uses the PBC library developed by Ben Lynn. But I am still not clear on how PBC is related to ECC.
I know that this is a site for complex crypto QA, but I did not know ...
1
vote
1answer
59 views
RC4-52 by hand / pen-and-paper?
I've played a lot with VIC and enjoy its complexity and effectiveness as a field cipher . However RC4 has caught my attention lately and I've read there is a RC4-52 variant that can be done by hand.
...
1
vote
0answers
81 views
One-time pad and perfect secrecy properties
I have a homework problem:
Explain how to find $m_{0}$ and $c$ such that $P[c=c': k \leftarrow K, c' \leftarrow E(k, m_{0})] > 0$
where P is probability and k is chosen uniformly.
I do not know ...
1
vote
2answers
187 views
What data is saved in RSA private key?
What data is saved in RSA private key in openssl? How to view it?
Wikpedia says these variables are saved.
2
votes
1answer
124 views
What should I be aware of when implementing algorithms myself?
I plan to build my own crypto library. The project will be primarily for me to learn (and if useful for no other purpose, that is fine). In the past I have implemented a few hashes, and AES quite a ...
3
votes
1answer
122 views
Should the secret key of Shamir's secret-sharing algorithm be interpreted byte by byte?
Should the secret message of Shamir's secret-sharing algorithm be interpreted and processed byte by byte?
Interpreting it byte by byte makes it easier to process, but in case one of the shareholders ...
0
votes
1answer
129 views
Possibility of factorisation of rsa modulus due to vulnerability in java implementation code
Below is my implementation of the RSA algorithm. Actually I'm choosing the private key (d) instead of public key (e) and computing the public key.It is working fine but
I want to know if this is a ...
0
votes
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 ...
1
vote
2answers
197 views
is AES secure for java application licensing
I have to license a java application and want to code a quick implementation, the scheme I came up with is:
1) The Application calculates a string X which we assume to be the md5 sum of the ...
1
vote
1answer
70 views
Security relevance of random factor in Paillier
In the Paillier cryptosystem [1] the encryption of $m \in \mathbb{Z}_N$ with randomness $r \in \mathbb{Z}_n^*$ is $c = g^m r^n \bmod{n^2}$.
The additive-homomorphic property of the system shows that
...
1
vote
2answers
135 views
Zero-Knowledge Challenge-Responce Protocol
Good day to everyone.
I am trying to implement an e voting system (just for reference -it is not important though-it is described at the Internet Voting Protocol Based on Improved Implicit Security ...
1
vote
1answer
67 views
How to secure a mental poker protocol?
I would like to implement a mental poker protocol in a secure fashion. How should I go about that without (preferably) infringing on the Mental Poker Framework patent?
2
votes
0answers
78 views
Are there any secure commutative ciphers?
This answer lists two commutative cipher algorithms - Pohlig-Hellman and SRA. However, they don't appear to be too secure.
My question is, here there any commutative ciphers out there that are secure ...
3
votes
2answers
115 views
Simple RC4 key generation scheme
I would like to ask you about your opinion on the following scheme of combining a master key and a nonce and stretching the result to the full 256-bytes RC4 key.
Master key $K_m$ is a pre-shared ...
1
vote
1answer
80 views
Why is Bcrypt called a Key Derivation Function?
I am trying to understand why is bcrypt called a Key Derivation Function?
I looked up the details of Ekfblowfish on Usenix article here:
...
1
vote
3answers
147 views
What goals is homomorphic encryption aiming to solve?
As I understand from this article about homomorphic encryption, it
mainly aims to enhance the security of cloud computing. We should be able to encrypt data and send it to the cloud. After it is send, ...
2
votes
1answer
94 views
Security of Pohlig-Hellman exponentation cipher?
I am looking into implementing Pohlig-Hellman exponentation cipher and I would like to know how secure that algorithm is? I am guessing it's security relates greatly to the prime number used in it. ...
0
votes
1answer
38 views
What information to include is the 'info' input for HKDF?
The RFC states the following:
3.2. The 'info' Input to HKDF
While the 'info' value is optional in the definition of HKDF, it is often of great importance in applications. Its main ...
4
votes
1answer
86 views
In RSA, how to make sure that $p-1$ and $q-1$ are still hard to factorize?
See this question. The comment by Brett Hale stated:
On the other hand, ensuring $(p - 1)$ has a large prime factor requires very little extra effort.
What's actually the 'little extra effort'?
0
votes
2answers
87 views
Is solving a modular linear equation a hard problem when the coefficient is not an invertible element?
Assume that we have a linear equation like this:
$$ax=b \pmod n$$
when $x$ is the unknown, and $a$ is not an invertible element in $n$.
is finding $x$ a hard problem?
(by solving I mean finding an ...
1
vote
2answers
60 views
Is it safe for the ChaCha8 nonce to be deterministic?
ChaCha8 takes a 8 byte nonce (or IV) that should not be the same twice for the same key. Generating this nonce randomly makes me very very nervous for collisions.
Is it safe to generate this nonce ...
