0
votes
1answer
67 views

is this possible to use asymmetric encryption schemes as order preserving encryption

Are we able to use order preserving encryption in asymmetric schemes, is this work efficiently. is this secure at any one of the situations
0
votes
3answers
113 views

How can complexity be increased or decreased in AES?

I have been studying data compression for a while. For educational purposes, after a lot of reading, I managed to create a software that performs encryption and authentication using AES256-GCM. ...
1
vote
0answers
31 views

Voting protocol - How many dishonest tallying centres can the protocol cope with?

We have the voting protocol that is described here. I am looking at the following exercise: Determine how many dishonest tallying centres the protocol can cope with before the following properties ...
2
votes
1answer
51 views

Establish Trust By Signing Random Seed

I'm trying to get my server to establish trust with a client. Neither is on the Internet, so there are no certificate authorities. The typical way to establish trust in my domain is for a client to "...
0
votes
1answer
88 views

What does the acronym “CRT” stand for in the PKCS #1 specification?

What does the acronym "CRT" stand for in the PKCS #1 specification? Does it stand for "Chinese Remainder Theorem"? Thanks, Pete
0
votes
1answer
876 views

What's the structure of server-key-exchange message during TLS handshake

Here is a relevant question: With OpenSSL and ECDHE, how to show the actual curve being used? Using ...
3
votes
1answer
127 views

Proof that two parties can communicate

Suppose we have three parties, Alice, Bob, and Carol. Alice can receive messages from Bob and Carol individually, but can only send messages to both simultaneously. Additionally, Alice cannot tell if ...
2
votes
1answer
142 views

Can I use an ECDH Shared Secret from the same Private / Public Key Pair?

I'd like to know if using the ECDH shared secret of a static EC Private Key with it's own corresponding static EC Public Key causes a problem / weakness. (edit) not asking if it's ok to re-use the ...
0
votes
1answer
324 views

How HMAC.Update function works?

I know how standard HMAC(key,msg) function works, and I want to write a Delphi port of HMAC class that implements Update function. The problem is that I don't understand how this Update function works ...
19
votes
3answers
9k views

SHA512 faster than SHA256?

I'm getting this strange result that SHA512 is around 50% faster than SHA256. I'm using .net's SHA512Managed and SHA256Managed ...
1
vote
1answer
188 views

What is difference between Cryptographic Transformation, Encryption and Hash? [duplicate]

I read in a book that: let $f(K,R)$ is cryptographic transformation of $R$ using $K$, $K\{R\}$ means $R$ is encrypted using $K$ and $h\{R\}$ is the hash of $R$ and then the example follows. I want to ...
5
votes
1answer
214 views

How to generate own secure elliptic curves?

I know that the algorithm used to generate the Brainpool curves and the NIST curves is published. The algorithm should be this one (RFC5639 Appendix A). From what it looks like it's rather slow to ...
5
votes
1answer
127 views

EC: Why does $h>200$ need to hold?

From BSI-TR-03111 (PDF), on page 15: The class number of the principal order belonging to the endomorphism ring of E SHOULD be at least 200. This value commonly is referred to as $h$ in that ...
3
votes
1answer
184 views

What are the differences between the elliptic curve equations?

I think we're all aware of the "classical" Weierstrass (short?) elliptic curve equation: $y^2\equiv x^3 + ax +b \pmod p$. Well known examples of these curves include the NIST's and Brainpool ones. ...
1
vote
1answer
82 views

Period of pseudo random sequence generated from (5, 2, 0) LFSR

I was reading about the Linear Feedback Shift Registers and I am confused about the technique to find the period of a primitive polynomial. Consider the polynomial $x^5 + x^2 + 1$. As this is a ...
4
votes
2answers
107 views

Brute-force attack given multiple hash prefixes

(Context: I'm auditing some code which I suspect to be insecure, but I'd like to be able to quantify this.) Suppose you have a 56-bit secret key ($secret), and ...
0
votes
2answers
46 views

Securely start a client server connection without ssl/tls [closed]

NOTE: Pardon my ignorance of encryption, I learned about these concepts today Going to rephrase this question, but I think I already have fine answers provided. I need to have a block of data ...
2
votes
1answer
62 views

Compression in Symmetric-Encryption?

When using symmetric encryption is it important to compress the data first? I think that compression will make data look "more random" and this might help the ciphertext be harder to crack but I am ...
1
vote
0answers
47 views

Digital signature in a group chat scenario?

I understand that RSA is great for 1-to-1 digital signature. In the group chat of N people, other than storing and maintaining N public keys, is there a simpler way of authenticating each and everyone ...
0
votes
2answers
63 views

Get AES key from client request

I get a request from a client who encrypts the message with the wrong AES key. Is there a way for me to know what AES key the client actually used? I understand I may get the decrypted msg which is ...
1
vote
3answers
308 views

How to quickly detect incorrect password in encrypted file without compromising security?

I am developing a software to encrypt/decrypt files/streams using symmetrical encryption algorithm. During encryption phase data wil be compressed and encrypted. When decrypting data, I want to be ...
0
votes
1answer
293 views

Why does rsyncrypto require a public key during decryption?

I recently came across a project called rsyncrypto that sacrifices some security so that you can have rsync-friendly files. My understanding is that it works by generating a symmetric key for each ...
3
votes
1answer
134 views

Doubling a point on an elliptic curve

I'm working with the elliptic curve $\mathcal{E} : y^2 = x^3 + 11x^2 + 17x + 25$ over $(\mathbb{Z}_{31},+,\cdot)$ and am trying to double $P=[2,7]$. Following the instructions here, I'm doing the ...
5
votes
2answers
341 views

An electronic voting system

This semester I am taking the course Cryptography. I will have a presentation about the topic "Voting Scheme". I am preparing myself by reading from the book “Cryptography : an Introduction” by N....
2
votes
1answer
448 views

Supersingular Isogeny Key Exchange Software [closed]

Are there any optimised implementations of the Supersingular Isogeny Key Exchange by Defeo, Jao, and Plut. It seems like this would be a great drop-in replacement for Diffie-Hellman in both OpenSSL ...
3
votes
2answers
191 views

Meaning of entropy of a bitstring in NIST SP 800 - 90A

From NIST SP 800 - 90A from January 2012 (see http://csrc.nist.gov/publications/nistpubs/800-90A/SP800-90A.pdf), page 6: For the purposes of this Recommendation, an n-bit string is said to have ...
1
vote
1answer
62 views

Why does UMAC encrypt the output of universal hash function?

UMAC uses a key to choose a random hash function from a family of universal hash functions. The value of the hash function is always encrypted using yet another key, and the resulting ciphertext ...
-1
votes
1answer
87 views

Safe way to generate different encrypted output from the “same” plaintext

Imagine I want to send imaginary defcon levels to another party over the internet. I know there are good protocols for this like SSL, but lets say I only have a blackbox tool where I can input an AES ...
1
vote
1answer
83 views

Distinguishing between two probabilities and the uniform probability

Say I have a polynomial adversary $A$ that can distinguish with a non-negligible adventage between $x$ generated from a probability $X$ and $y$ generated from a probability $Y$. Obviously, this ...
1
vote
1answer
133 views

On countermeasures for replay attacks. Does this one require plaint text password storage?

I was reading this wiki section on the countermeasures against replay attacks and it basically suggests that: If Bob wants to confirm Alice's identity he can send a one-time token (I think it should ...
2
votes
0answers
67 views

Convolution and catastrophic codes

i'm reading the article of Massey and Sain (here) and i cannot unserstand - what is "foreforward inversion"? I mean There is a description of circles in convolutional codes and a little bit ...
3
votes
1answer
188 views

Is there a scheme that allows to use RSA based challenge response protocol limited to signing only 8 bytes to create a secure signature of any data?

I have a tiny device that has a challenge-response authentication mechanism where the device signs 8 bytes of any data with it's internal 2048 bit RSA key. I would like to be able to certify any data ...
1
vote
2answers
55 views

Definition of indistinguishable schemes

Let $\mathsf{Exp}_{A,\Pi}(\lambda)$ be some indistinguishability experiment that finally outputs 1 if A outputs $b'$ that satisfies $b' = b$, otherwise 0. Then the textbooks often define the security ...
3
votes
1answer
143 views

Can we reduce Diffie-Hellman problem to “Discrete-log inversion” problem?

Let $G$ be a cyclic multiplicative group of order $n$. Let $g$ be a (public) generator of $G$. The Diffie-Hellman (DH) problem asks: Given $g^x, g^y\in G$ for $x, y\in \mathbb{Z}^*_n$, to compute $g^{...
1
vote
1answer
212 views

Encryption of exe file

I recently started learning cryptography. I have learned some basic stuff. I'm also started learning about pc security, so I was wondering how do hackers use cryptography for bypassing antivirus ...
2
votes
2answers
223 views

RSA private key d knowing e,n

I need to find RSA private key $(d, N)$ knowing $(e, N)$. It's "own" RSA implementation. As i know $p$ is random 70 bit number, then $q$ is $p-2^{10} < q < p+2^{10}$ $d$ is max 16 bit long with ...
1
vote
1answer
119 views

Deriving 2 shared secrets from one private key and 2 different public keys

I have a key pair, say $(d, Q)$. I send my public key $Q$ to 2 different people. I also get their public keys $Q_1$ and $Q_2$. Now I can derive 2 shared secrets, $d*Q_1$ and $d*Q_2$. The 2 other ...
2
votes
2answers
3k views

Why are RSA ciphertexts different for the same plaintext?

I am using SpongyCastle for a project in android. I have used RSA to encrypt the data and then decrypt it in another activity, the keys are stored in the shared preferences. I discovered a thing I ...
0
votes
0answers
45 views

Cryptanalysis and Copying encrypted volumes

I just recently concerned myself with cryptography due to Snowden's revelations and there are a few things I cannot really wrap my head around but maybe you can help me with that. I am not a ...
0
votes
0answers
41 views

Join Datasets While Protecting Anonymity

I've run into this issue a couple of times in my career. I'll see if I can explain with an example (please ignore the fact that this is implausible in the real-world). Suppose I sell computers, and I ...
3
votes
1answer
84 views

How to prove the hardness of Rabin's function?

I am unable to prove the following theorem: If for a $1/(\log(n))$ fraction of the quadratic residues $q\pmod n$ one could find a square root of $q$, then one could factor $n$ in random polynomial ...
0
votes
0answers
76 views

Can a combination of encryption algorithms weaken the overall encryption?

Are there any instances where a combination of industry standard encryption algorithms can weaken the overall encryption of the data? As a Naive example using non-standard encryption algorithms, ...
1
vote
0answers
56 views

How is an epsilon of 1/1000 non-negligible? [duplicate]

Lately I've been studying cryptography and in the current course I'm taking we're reviewing statistical tests and how they can be used to determine if a pseudo-random generator is secure or not. ...
2
votes
3answers
1k views

Is DES slow in hardware or only in software?

I have been reading that DES is slow. Is it only slow in software or slow overall? Also, as far as Triple DES being slow is concerned, is double AES with two 128 bit keys slower than single AES with ...
1
vote
2answers
4k views

simple algorithm to encrypt/decrypt a text file

I need to write a first program in one language that saves data in a text file, and write a second program in a second language to decrypt that file. The two languages in question don't include any ...
2
votes
1answer
112 views

What's the principle to design the functionality under UC framework?

Though I can get the basic idea of UC Framework, namely let the environment cannot distinguish the real protocol with the real adversary and the functionality with the simulator, I am still puzzled in ...
1
vote
4answers
131 views

How is an epsilon of 1/1000 non-negligible?

Lately I've been studying cryptography and in the current course I'm taking we're reviewing statistical tests and how they can be used to determine if a pseudo-random generator is secure or not. ...
0
votes
1answer
26 views

Blinding value of particular form

I'm working with an implementation that creates a blinding value for RW signatures with the following C++ code: ...
2
votes
2answers
98 views

SHA256_HMAC for deriving session keys using a counter

I need to generate some session keys from a master key that was generated from an ECDH key exchange. The master key is 256 bits and I need 256 bit sessions keys. Is it safe to use SHA256_HMAC with ...
2
votes
1answer
308 views

Why isn't Rabin-Williams cryptosystem widely used?

I think we all know RSA. And of course we also know DJB (a.k.a. Daniel J. Bernstein). Now some already have noticed that he has an opinion towards cryptographic questions. In his 2008 paper ("RSA ...

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