1
vote
0answers
43 views

In symmetric searchable encryption are the algorithms public? [duplicate]

If a user (other than the data owner) possesses the secret key in symmetric searchable encryption scheme are they able to run the trapdoor algorithm, or is this not publicly available?
5
votes
1answer
225 views

Is SHA256 good enough to shrink a key?

I have a key that is the combination of two shorter keys generated by PBKDF2, which together are long more or less 64 bytes. Now I need to shrink it down to 32 bytes and I'm not sure what to use to do ...
3
votes
0answers
44 views

Feasible way to check n-dimensional equidistribution of PRNGs

I am currently gathering some test methods and test suites for random number generator qualities, and am a bit stuck at finding something feasible to test for n-dimensional equidistribution. As input ...
4
votes
3answers
148 views

Algorithm for computing square roots in $GF(2^n)$

Short question: is there an algorithm for efficiently computing square roots in $\mathbb{F}_{2^n}$?
1
vote
0answers
115 views

Public and Private key encryption in simple math

Can anybody show me (or point me to resource) how to generate public key and private key with simple math? Steps which can be reproduced in a simple calculator – so the message, keys all can be ...
4
votes
1answer
168 views

Can a homomorphic encryption scheme be made CCA2 Secure?

Is it possible to modify a homomorphic encryption scheme so that it can be CCA2 secure? From the definition of a homomorphic scheme, it seems that it is malleable, which would result in lack of CCA2 ...
3
votes
1answer
129 views

Pseudorandom permutations on domains of arbitrary (i.e. not a power of 2) size

The Feistel cipher algorithm produces a pseudorandom permutation with domain size equal to $2^{2m}$ (for some $m \in \mathbb{Z}^+$). That is, a one-to-one function $\pi$ of the set $\{0, 1, 2, \dots, ...
6
votes
1answer
669 views

Are there any specific requirements for the function $F$ in a Feistel cipher?

In a Feistel cipher (as shown below), it seems that the security of the cipher would be entirely dependent upon the function $F$. What requirements on $F$ are necessary for a secure Feistel cipher? Is ...
3
votes
1answer
130 views

Math to replace s-boxes - Good or bad idea?

The following was going through my brain for the past week. If my thoughts are generally known to the cryptographic community would someone provide a link or two. Even if I’m making a classic newbie ...
2
votes
1answer
79 views

Is a keyed PRF a MAC?

I remember I read that a MAC can be considered as a PRF. Can a variable-length input keyed-PRF be considered as a MAC?
0
votes
1answer
219 views

Problem with Python Implementation of Key Exchange part OTR Protocol

Being new to software development and crypto in general, I thought I would write a simple p2p encrypted chat app using the otr protocol detailed here: https://otr.cypherpunks.ca/Protocol-v3-4.0.0.html ...
5
votes
1answer
464 views

Does collision resistance imply (or not) second-preimage resistance?

I've seen contradictory results. Sometimes hash functions are collision-resistant but not necessarily second-preimage resistant. I've seen this kind of things in papers from Bart Preneel: “Security ...
5
votes
1answer
187 views

Determine LFSR phase quickly?

I know it's possible with work backwards from the output bits of an LFSR to determine its feedback polynomial in a O(n) fashion. I'm also curious if, given an LFSR state and polynomial, is it ...
3
votes
1answer
93 views

Indistinguishable encryptions in the presence of an eavesdropper equivalence

I'm trying to prove that definition 5 and definition 6 in this document are equivalent. This is what I've done at the moment: Asume that the scheme has Indistinguishable encryptions in the presence of ...
3
votes
1answer
208 views

Attacks on AES-128 (ECB) based on some knowledge of plaintext

I'm working with a third party protocol which employs AES-128 in ECB mode of operation to encrypt a packet composed of 16-byte blocks (it encrypts each block independently). I'm trying to determine if ...
2
votes
1answer
293 views

RSA 896 vs 1024 vs 2048 in Javascript?

I am currently working on a secure messaging website and I had been using RSA 2048 for encryption, decryption and signing of messages but I found it to be EXTREMELY LAGGY so i've moved to 1024. I did ...
4
votes
2answers
396 views

Exactly two of the four roots must be greater than N/2

Theorem: Let $y$ be a quadratic residue in $\mathbb{Z}_N$* where $N=pq$. There are exactly four integers $x_1, x_2, x_3, x_4$ where $0 < x_1 < x_2 < \frac{N}{2} < x_3 < x_4 < N$ ...
1
vote
0answers
78 views

Types of cryptography

We have cryptography based on hard problems from number theory, like DDH. When we speak about symmetric cryptography with AES, a mode of encryption (CBC, ...), what is the type of problem ? What is ...
0
votes
2answers
193 views

Pi Message Encryption [duplicate]

I created a simple yet efficient message encrypting page that will encrypt messages using Pi. Though not being an expert in this area, I am nowhere near sure how secure this is and how easy it would ...
1
vote
1answer
145 views

Combining Random Hashes - avoiding collisions and ensuring randomness

I have a series of integers which I want to convert to random integer (64 bit). The idea here is to produce random numbers very quickly. The issues that good quality random numbers are required with a ...
4
votes
2answers
310 views

Is there a standard way to use a nonce with HMAC?

Many protocols use HMAC on messages that include a nonce, but they don't seem to do it in a consistent way. For example, in OAuth the nonce is in the middle of an URL-encoded key-value string, like ...
3
votes
2answers
111 views

Associative standard cryptographic hash function

I am looking for a standard hash function which satisfies the following property: A hash function $H(a,b) = F(h(a),h(b))$ with $h$ (within $F$) any standard cryptographic hash function and $F$ an ...
-2
votes
1answer
183 views

How to find out the method used to encrypt [closed]

How to find out the method used to encrypt the string 123456 which results in the value: 6g9SkDLIKa8l2VhafFnHvg==?
3
votes
1answer
262 views

How to calculate inverse affine transform in AES from forward affine transform?

In AES the forward affine tranformation matrix is defined as: $$ \begin{bmatrix} 1& 0& 0& 0& 1& 1& 1& 1 \\ 1& 1& 0& 0& 0& 1& 1& 1 \\ 1& ...
2
votes
0answers
190 views

Elliptic Curve based blind signature implementation

I want to use Elliptic Curve based blind signature scheme for my research. There is no proper implementation of ECC-based blind signatures. Can someone describe to me which things I need to follow ...
5
votes
1answer
191 views

Is HMAC needed for a SHA-3 based MAC?

HMAC does nested hashing in order to prevent Length Extension Attacks. Given that you use the SHA-3 hash (which is resistant against length extension attacks), would you still need to go through that ...
2
votes
1answer
1k views

When NIST disallows the use of 1024-bit keys, what effect will that have on SHA-3 (with max. 512 bits)?

Quoting the article Gone in 60 Months or Less: The National Institute of Standards and Technology (NIST) has disallowed the use of 1024-bit keys after 31 December 2013 because they are insecure. ...
2
votes
3answers
143 views

Do sites store login password with hash? If so, can people can use hash collision to log in?

I was researching about hash, and I thought, If sites store passwords with hash algorithms, then can't this happen: User A has the password 'hello' User B finds out the hash code of the password of ...
5
votes
1answer
113 views

Condensed ElGamal + AES

In normal ElGamal encryption, the encrypted message is a pair (gb, gabM) - that is, the actual "encryption" is simply multiplication by the shared secret ...
4
votes
1answer
270 views

Description of signatures with message recovery (as in ISO/IEC 9796-2 and EMV Signatures)

I'd like to get an overview of how the signatures with message recovery work, especially in case EMV and other smart card systems. Is there a nice overview available without being required to read the ...
1
vote
1answer
118 views

How to convert projective to jacobian co-ordinate in ECC?

I am doing a small project using elliptic curve in cryptography. My doubt is, can I directly convert a projective to a Jacobian coordinate system without using the affine conversion in elliptic curve ...
1
vote
1answer
75 views

Public Key Cryptography: Diffie-Hellman Key Exchange

Please watch this video it's very short. If you already know cryptography and really good at it please start from 3:51. I didn't understand the step at 4:39, can someone here to explain? Why is ...
-2
votes
2answers
221 views

How to decrypt 3DES in ECB mode (using a wordlist)? [closed]

I have some encrypted texts (encrypted with 3DES in ECB mode without salt). My question: How can I decrypt them using a wordlist? (or without one) Example: Encrypted text: ...
2
votes
1answer
95 views

Empty message Hash length

I am learning Hash Algorithms and in a presentation (PDF) about these algorithms I read that: Length of $h(m)$ much shorter then length of $m$. Now my question is: What if we talk about an ...
1
vote
1answer
107 views

Large text file encryption per line

Some background: I receive data in text files of over 16 million records (lines). I need to be able to encrypt the first column in that file so that it cannot be deciphered. This process will be ...
-2
votes
1answer
57 views

moduli in SSL certificates [closed]

this is normally seen in a typical SSL certificate. For the modulus, I know that it is represented in hexadecimal form, but why is there a semicolon (:) after every group of 2 digits? ...
2
votes
1answer
117 views

Is it possible to get better randomness by using multiple PRNGs?

I don't know if this question even makes sense, but: Is there be any benefit or impact to some sort of hierarchical (e.g. a PRNG drives the decision for which PRN to pull from a set of PRNGs) or ...
8
votes
2answers
541 views

What are the methods to construct a primitive binary nonlinear feedback shift register (NLFSR)?

Given a binary shift register of $n$ bits, a primitive binary nonlinear feedback shift register will generate a sequence with a period of $2^n - 1$. While I am unable to find a paper which directly ...
3
votes
1answer
206 views

Convert m-Sequence into a de Bruijn Sequence

In his paper Alternating Step Generator Controlled by de Bruijn Sequence, C.G. Günther states on page three that a de Bruijn sequence (..) can easily be obtained from an m-sequence (maximal length ...
2
votes
1answer
199 views

SSL-like protocol with public-key hard-coded in the client

Imagine a SSL-like protocol that instead of using certificates signed by a trusted CA, has the server's public key hard-coded in the client. My question is: what happens if the server's private key is ...
4
votes
3answers
621 views

Malleability of ElGamal and Hashed ElGamal

Question: Suppose A encrypts a number $x$ which indicates her bid on a contract, using ElGamal encryption. Say that the encryption of $x$ produces a ciphertext $c$. Explain how E can modify $c$ to ...
2
votes
1answer
114 views

LFSR Output Sampling for Berlekamp-Massey

Looking at the use of Linear Feedback Shift Registers in cryptographic algorithms, I have learned that the Berlekamp-Massey algorithm can be used to find the (shortest) LFSR that generates a given ...
2
votes
3answers
150 views

Encrypt-then-MAC: full random keys or keys derived from master key?

I have this scenario where I use Encrypt-then-MAC (AES256-CBC and HMAC-SHA256) with keys generated by a CSPRNG (specifically, SecureRandom in Java). I'd like to know which is better: Use the CSPRNG ...
3
votes
1answer
130 views

Is it a good idea to use Lagrange/Newtonian interpolation for encryption?

I see that Lagrange interpolation is commonly used for secret sharing, but could it be used for encryption? The goal is to reduce database I/O and compute new values on the fly. Suppose the use case ...
8
votes
5answers
348 views

Choose a random number that is different from a bunch of other secret numbers

I'm looking for an algorithm where n participants each have a different secret number between $[0..x]$ (and where $x$ is known) and where the participants then select randomly another, non-secret, ...
6
votes
2answers
112 views

Is there a way to compress multiple signatures of the same data?

So, I'm working with a system that allows individual users to each have their own private-public key pair. I would like to allow multiple users to use their private key to sign the same piece of ...
3
votes
2answers
202 views

Using PBKDF2 twice with different argument order

I'm pretty sure this is a really bad approach (in theory), but one of my clients is doing this and I was wondering… How bad it is to perform pbkdf-2 in this way (with 2000 iterations)? ...
1
vote
1answer
291 views

Solving a discrete logarithm using GDlog

I am trying to calculate an $x$, such that $t = g^x \pmod p$ in order to crack a weak ElGamal encryption for university. I found GDlog, but I cant figure out how I can use the input to calculate my ...
5
votes
1answer
147 views

How come Shamir Secret Sharing uses Lagrange interpolation?

I've read that Newton polynomials have better computational complexity, but Shamir's uses Lagrange polynomials instead. Does anyone know if there are particular reason why Newton polynomials aren't ...
2
votes
1answer
78 views

Exchanging session keys over symmetric-key channel?

I know session keys are exchanged (in SSL e.g.) over public-key cryptography channels but I was wondering if there are already known algorithms/methods for exchanging session keys over a symmetric-key ...

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