All Questions
3
votes
1answer
501 views
Common Modulus Attack in a Lucas Group
I'm trying to decrypt a message that is encrypted using a LUC encryption scheme and running into roadblocks. I know that with RSA if Alice and Bob use the same public modulus but different encryption ...
1
vote
0answers
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 ...
1
vote
0answers
48 views
P-Complete hashes, hashing to a larger set
Historically hashes have been from a large set (say 256 characters) to a smaller set (256 bits).
Also, hash functions that are P-complete have no known parallel algorithm; they must be computed ...
1
vote
0answers
27 views
Generating Polynomials for the MPQS
I'm going to try and eventually factor RSA-100, but my current QS needs a lot of improvement, so I'm going to try and switch over to the MPQS.
I'm a bit confused as to how the MPQS works, which is ...
1
vote
0answers
99 views
Sigma-protocol for 3SAT problem
I have some questions from previous years exams, I hope you could help me with them. :)
Let $g,h$ denote generators of a group $G$ of large prime order $n$ such that $\log_g h$ is unknown to anyone. ...
1
vote
0answers
83 views
Quadratic Sieve Bottleneck, Multiple Polynomials an option?
After my failed attempt at trying to implement the ECM, I started working on the quadratic sieve. It works, but the bottleneck is finding smooth values over the factor base.
The way I implemented it ...
1
vote
0answers
100 views
Computer appliance protocol
I build the computer appliance system that consist of software server and multiple controllers. The system I want to build must be pluggable in the sense that when I connect a controller C to the ...
1
vote
0answers
98 views
Structure of encrypted office files
I try to find out the structure of encrypted office files (I'd like to implement something like a carving tool for finding certain encrypted file types). I try to understand the Office Document ...
1
vote
0answers
109 views
Is TOTP or a timestamp encryption a better timestamp-based authentication token system?
Are there advantages to using TOTP over encrypting a timestamp with a shared secret, in cases where the readability or ease of typing the token are not important?
1
vote
0answers
88 views
Efficient zero knowledge proof of least significant bits either RSA or Rabin?
I need to reveal the log(n) least significant bits of $x^2 mod\ N$ or $x^3 mod\ N$ without revealing x.
So far the best I have involves a Boudot range proof and is not a very nice construction
1
vote
0answers
150 views
Proper formatting of symmetric algorithm secret key
Given this description from RFC 4880 sec 5.1:
The value "m" in the above formulas is derived from the session key as
follows. First, the session key is prefixed with a one-octet algorithm
...
1
vote
0answers
92 views
Setting protocol parameters to achieve concrete security
Background
One issue with modern security proofs is that they are usually asymptotic. In other words, such proofs are usually formulated as follows: For any polynomial-time adversary $\mathcal A$, we ...
1
vote
0answers
65 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 ...
1
vote
0answers
140 views
Most frequently used digital signature schemes in the recent years
I am looking to understand if there are any hard figures on which digital signature schemes are most commonly in use today.
I'm only really interested in what is employed recently (ie. last couple ...
1
vote
0answers
101 views
Security of stream cipher based on Matrix multiplication GF(256) with randomized padding
The actual question is stated at the end of the text. Suppose you have a (grossly inefficient) confidentiality stream cipher with the following components:
The keyed function ...
0
votes
0answers
55 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 ...
0
votes
0answers
85 views
Adding and multiplication in jacobian coordinates
How can I derive formulas for adding and multiplication of 2 points in Jacobian coordinates $(x,y) = (\frac{X}{Z^2},\frac{Y}{Z^3})$ over an elliptic curve?
0
votes
0answers
55 views
How do I generate decryption keys for the IDEA algorithm from the 128 bit key?
I am trying to implement IDEA algorithm in C#, just to learn how it works. I have taken a 128 bit binary key and generated the 52 encryption keys using the following code:
...
0
votes
0answers
54 views
How fast can a wrong decryption key be detected using ECC?
When can a decryption function detect that the ECC key I use for decryption is incorrect? Is it possible to do that during initialization, or does the complete message have to be decrypted to do that?
...
0
votes
0answers
81 views
How to choose between AES-CCM and AES-GCM for storage volume encryption
We are using the encryption built into Solaris 11 ZFS, which offers the choice between CCM (CBC counter mode) and GCM (Galois counter mode). What are the pros and cons of choosing each of these cipher ...
0
votes
0answers
80 views
Secure modulus length for Diffie-Hellman
What is secure modulus length for modular exponentiation so that finding discrete log is computationaly impossible?
0
votes
0answers
54 views
What is the significance of i^Q mod P = 1 and are there any special properties to be aware of?
I'm studying UProve, and one of the fundamental components of this technology is based upon the relationship between
i^Q mod P = 1
Lacking a specific name I can call this mathematical ...
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 ...
0
votes
0answers
78 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 ...
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 ...
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
0answers
78 views
Why do we need to hash both the message and the $h$ value in ElGamal signature?
The professor left us a question on ElGamal signatures:
Given the hash function $H$ and message $M$, choose a random $r$ and compute $h=g^r$ and $H(M||h)$. Show that, if $H(M)$ is used instead of ...
0
votes
0answers
71 views
Strong RSA problem in $\mathbb Z^*_{n^2}$
Comparing to this question, assume $C, M \in \mathbb Z^*_{n^2}$, $e \ge 3$, is it hard to compute $M$ that satisfies $C=M^e \mod n^2$ when $C$ and $(n, e)$ are given?
0
votes
0answers
33 views
How hard is a known prefix hash preimage attack?
Suppose the attacker knows X, Z such that
H(X || Y) = Z
If bit-length(Y) < 60 then a brute force attack is possible.
What if
bit-length(Z) = 256 (such as in SHA-256)
bit-length(X) = 128
...
0
votes
0answers
23 views
How can I validate generated session keys in SRP-6a protocol
I have genereted two equal session keys on client and server successfully. But I couldn't understand how each other should validate that they have same session keys.
On the client I generated a SHA1 ...
0
votes
0answers
40 views
SRP6a client server exchanged message order
In SRP6a, the public key of server is send after receiving the public key of client A. Its that okay that B send along together with s right after client send the username, and then later on client ...
0
votes
0answers
37 views
ElGamal signature: Forging a signature of a specific form
I have a question I can't solve from one of the courses I'm currently taking:
Show that given a legitimate ElGamal signature $(S,R)$ on a given message $m$, an attacker
can compute a signature ...
0
votes
0answers
19 views
Kryptos : K3. What is the accepted transposition for a solution?
I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4.
It's understood that K3 is solved via transposition, but I have seen several solutions. Which is the best/accepted one?
0
votes
0answers
39 views
Padding in PMAC
How does padding in PMAC work? I have been told two stories: Firstly, I have been told that it works similar to CMAC padding, and secondly, I have been told that it does not need padding.
I find the ...
0
votes
0answers
32 views
Security of .net AES implementation and security of a hash MAC
Hello I wanted to ask if there is any review about the security of the AES implementation of the .net Framework?
I found nothing concrete to that question, searching the Internet.
And, but this is a ...
0
votes
0answers
82 views
RSA and One Time Password (OTP) service
What is the expert cryptographic opinion on the following?
Assume that there is a web server and a client on web page.
User on the Client calls an OTP web service on the server which
a) creates a ...
0
votes
0answers
30 views
How to create a public-key certificate for RSA Web of trust?
How to create a public-key certificate for RSA Web of trust?
I have (for exemple) two public / private key pair (obviously).
They all need to sign each other certificate.
How to create the ...
0
votes
0answers
48 views
How compared encryption algorithm in terms of efficiency
I doing to compare two algorithm cryptography. first algorithm is RSA cryptography and second algorithm is El Gamal elliptic curve cryptography. now I want a way to compare between two algorithm by ...
0
votes
0answers
40 views
elgamal based decryption mixnet
Can anybody help me to understand elgamal based decryption mixnet? Pure elgamal can be used in mixnet (re-encryption mixnet) and its very easy, and I have implemented decryption mixnet using RSA also.
...
0
votes
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 ...
0
votes
0answers
77 views
Factorize RSA knowing several N and E
I did a CRT challenge yesterday and there`s one problem I was unable to solve, probably due to my lack of understanding advanced crypto math.
It`s about RSA. There are ten given pairs of N and E ...
0
votes
0answers
60 views
Is this a valid real-time authentication scheme?
The scenario in Alice/Bob/Cindy terms:
Alice approaches someone she doesn't know, but thinks is Bob, and asks for some secret information. Bob doesn't know and doesn't trust Alice, but Alice says she ...
0
votes
0answers
52 views
Timestamping services authorities, utilizing Linked, hybrid and other than PKI schemes
What are well respected Cryptographic Timestamping authorities utilizing more sophisticated than just PKI (RFC 3161) schemes, like Linked, Linked and signed, distributed hash trees (maybe P2P?), ...
0
votes
0answers
47 views
What happens when you use Windows credentials to sign a message?
I'm trying to dig into the messages that are exchanged when you sign a message using Windows credentials. I've modified the default service that is provided when you create a WCF service to use the ...
0
votes
0answers
73 views
Is this a secure multiparty protocol?
I am facing the following situation and i am trying to break down the problem into some specific cryptogrphic primitives.
There is a function F that takes as input a bit string and produces a ...
-1
votes
0answers
57 views
Perfect secrecy Proof
A symmetric cryptosystem have perfect secrecy $\iff$ for all
distribution over the messages space, $M$, and for all $m0$, $m1$ (messages) and any ciphertext $c$,
$$P(c|m0) = P(c|m1).$$
I got ...
-1
votes
0answers
36 views
Adaptative chosen ciphertext security McEliece
I am read the paper and I found the follow Lemma2 (pp. 13)
Suposse that there exists, for any $Hash_z$ and any $Gen$, an algorithm $A$ ...
My question is Why "for any $Hash_z$ and any $Gen$"? Are ...
-2
votes
0answers
34 views
sir,please suggest me an algorithm or method how can i improve the prediction based encryption method using randomization?
I am doing research on security for data migration in cloud computing. I have gone through many encryption algorithms to secure data for migration, but I want to create my own algorithm that could be ...
-2
votes
0answers
42 views
Is the likelihood of a birthday collision linear (evenly distributed) for all ciphers? When are they not?
When discussing the Birthday Principal, in combination with the pigeon hole principal, it was argued that an uneven distribution of birthdays (bias for September and any Tuesday of the year) made ...
-2
votes
0answers
58 views
One time Pad Adversary
I like know Why $Pr[\mathsf{PRIV_{EAV}}(\Pi,A,n)=1] = 1/2$, when $\Pi$ is a One Time Pad. I trying:
$$Pr[\mathsf{PRIV_{EAV}}(\Pi,A,n)=1] = Pr[b'=0|b=0]Pr[b=0] + ...
