2
votes
1answer
76 views

Generation of N bit prime numbers -> what is the actual range?

Short version: When generating a prime number of N bits, should I draw random numbers from the range $[0 , 2^n]$, or $[2^{(n-1)} , 2^n]$? Context: I'm trying to implement a toy-version of RSA as a ...
0
votes
1answer
25 views

Most efficient conceivable padding mode, and with no padding oracle

When plaintext padding is required, there are various commonly-used padding techniques. It seems the two most used approaches are : Always add at least one byte of padding, and have every byte of ...
1
vote
2answers
121 views

Key management for military GPS receivers

I wonder what encryption scheme is used in high-precision encrypted GPS streams (the so-called “P(Y) code”). If there's a master key needed, then it has to be in every device. Yet the master key ...
1
vote
0answers
55 views

Forward pseudorandom permutation [closed]

Please consider the following scenario: The user A and B use their keys, K1 and K2 respectively. Each client have a vector of elements. Each client separately permutes his vector using his key and ...
0
votes
1answer
69 views

Is it possible to hand-negotiate an SSL/TLS session?

I'm interested in trying to hand-negotiate an SSL/TLS session. Similar to how one would use telnet to port 80 and type GET / HTTP/1.1. I know there's a lot of steps ...
2
votes
1answer
101 views

Using modulus in one time pad?

I would like to know what is the real purpose of using a modulus in the equivalent of a Vernam cipher: Data $d$, large number $M$ Assume the key length is λ bits. Then M could be 2^λ. k is picked ...
0
votes
0answers
28 views

Perform general computation using a crypto algorithm as a building block

I have a somewhat special question. In our software we use a existing dongle which got cracked by our customers. The protection offered by the dongle isn't very sophisticated. For the moment I can't ...
1
vote
2answers
85 views

Random vs. Fixed Paddings

Is there any consensus (i.e. are there any research results) on the benefits and drawbacks of various padding schemes? Generally there seem to be two kinds of them: random paddings, like ISO10126 ...
0
votes
1answer
73 views

AES Affine Transformation in $GF(2^4)$

in $GF(2^8)$ the AES affine transformation is defined as \begin{equation*} b( x ) = ( x^7 + x^6 + x^2 + x ) + a ( x )( x^7 + x^6 + x^5 + x^4 + 1) mod (x^8 + 1) \end{equation*} where the polynom $( x^7 ...
4
votes
3answers
188 views

Cryptographic data structure: sparse array without membership test

I would like a data structure supporting two operations: $\mathsf{set}(k,v)$ and $\mathsf{get}(k)$, with the following properties: $k$ can be any number between $0$ and something impressively large, ...
0
votes
1answer
46 views

For calculating the index of coincidence for each sequence

I was learning about the finding the key length reading the following web site... http://practicalcryptography.com/cryptanalysis/stochastic-searching/cryptanalysis-vigenere-cipher/ and I really don't ...
0
votes
1answer
42 views

Checking the share membership in secret sharing schemes

I was thinking of this since yesterday. Imagine, a secret is split into its respective shares (using any secret sharing scheme) with threshold $t$ and total $n$. Can we find out given any random ...
0
votes
1answer
53 views

Is elliptic curve point multiplication semantically secure?

Is elliptic curve point multiplication semantically secure? I'd like to know if there are some sets of elliptic curve parameters (e.g. NIST curves) that are proved to be semantically secure or that ...
1
vote
2answers
91 views

How do disk encryption programs solve the “IV problem”?

I was reading a paper on the "elephant diffuser" used in BitLocker and it got me wondering how other systems (e.g. TrueCrypt before it shutdown) solved the problem the elephant diffuser was meant to ...
-1
votes
1answer
51 views

Bouncy Castle elliptic curve from explicit parameters (E-521)

I'd like to use a curve that's not included in the Bouncy Castle EC named curves spec, specifically E-521. According to the BC javadocs, you need a few values in order to do this: q, a, and b for the ...
1
vote
1answer
84 views

DES Encryption Algorithm all 64 bits for key instead of 56 bits

Would a DES algorithm that uses all 64 bits for the key instead of just the 56 bits be more secure? I have been thinking about it but those 8 bits used for parity are very useful and but including ...
0
votes
1answer
29 views

Security properties and Cryptography objectives applied in algorithms

We all know there are five properties of Security. They are: Confidentiality Availability Authorization Integrity and Provenance As Security and Cryptography are co-related these properties ...
2
votes
1answer
26 views

Committing Bilinear equation in Groth-Sahai framework

Groth-Sahai framework enables us to commit to QE, MSME, PP equations. Now, is the equation below committable in GS framework? A bilinear map $e: G_1 \times G_2 \rightarrow G_T$. $g_1 \in G_1$ and ...
2
votes
1answer
55 views

Calculate the security of a cascade cipher

I’m reading “The Security of Multiple Encryption in the Ideal Cipher Model” and I’m having a hard time understanding something. How do I calculate the bounds of cascade cipher from the following ...
1
vote
0answers
33 views

Plaintext-aware encryption for symmetric schemes?

The notion of plaintext-awareness is well-known for asymmetric encryption, but the notion seems to make sense for symmetric encryption as well. Is this a known concept?
0
votes
0answers
21 views

Plain cascade and Xor cascade

I have seen in few places (mostly papers) talking about plain cascade and XOR cascade. I know what is cascade cipher is but I am not clear about what these are. Can anyone help to understand using ...
1
vote
1answer
76 views

AES-128 with weak key

Doing malware research (simple crypto locker) I found out that it uses AES-128 with weak key - every one of the sixteen bytes is represented by (a-z,A-Z,0-9). Thus simple brute-force attack should ...
1
vote
0answers
45 views

exchanging private key between service and iPhone app - digital signing

I need to do digital signing of my request data which will be sent to the server. My server sends distinct private keys to her clients after authentication and expects all responses to be digitally ...
-2
votes
0answers
28 views

what is the difference between existential forgery by know message attack and existential forgery by chosen message attack in digital signature?

existential forgery is the attack must create a valid signature on at least one message ,so can i know what is the differences between when they apply on chosen message and known message attack ? I ...
0
votes
1answer
48 views

How can i calculate prime of Elliptic Curve?

In many articles i have found directly the calculation of prime elliptic curve. How can i calculate this prime $p$ ? For example if I consider NIST P-256, $ p = 2^{256}-2^{224}+2^{192}+2^{96}-1$. Why ...
1
vote
1answer
84 views

Modes of operation for Public Key Encryption schemes

Symmetric key encryption schemes have well defined modes of operations for achieving deterministic (ECB) or Randomized (CBC, OFB, CTR ) etc. and other applications of the same. But are they defined ...
2
votes
1answer
142 views

Why is 224 bit ecdsa faster than 192 bit ecdsa?

I ran several benchmarks using openssl on 2 different computers and I got a surprising result. for the Nist 192 bit curve the benchmark result is ...
1
vote
0answers
41 views

Does Ciphertext policy ABE support search operation on encrypted data

Basically CP-ABE (or attribute based encryption) allows end-users to encrypt the data with desired access control structure. I was investigating the how to do keyword-search on encrypted data given ...
4
votes
1answer
232 views

reducing false positives in searchable encryption

Practical techniques for searchable encryption proposed by Song et al. [1] have a false positive rate of $l/2^m$ where $l$ is left half of encrypted bits and $m$ is right half and $l+m=n$ where $n$ is ...
4
votes
3answers
436 views

Diffie-Hellman and man-in-the-middle attacks

See here for the man-in-the-middle attack on Diffie-Hellman that I'm concerned about: What is Diffie-Hellman? How do we combat this? I have two questions: Is one solution for both Alice and Bob ...
1
vote
0answers
84 views

Is it possible (how difficult) to find MORE than one valid RSA signature?

Is it possible (how difficult) to find more than one valid RSA signatures for a given message m (after padded) and a public key ...
2
votes
1answer
109 views

SHA-1 collision resistance

I'm researching on the SHA-1 algorithm and looking for reasons why it has fallen prey to differential cryptanalysis. I have read the research papers by Merc Stevens and Wang both of which describe how ...
4
votes
1answer
59 views

Authenticating Very Short (Sub-Block) Data

If I'm encrypting very short/small data - like an int or a long (32 or 64 bits), does it make any sense to authenticate the ciphertext, when using an "online" mode of operation (like EAX)? ...
0
votes
1answer
57 views

Is there any definition for “generic attack” in context of cryptography or more specific “hash functions”?

I'm searching a definition of "generic attack" in context of cryptography or more specific in context of "hash functions". I searched some books and the web but I did not found any definition for it ...
1
vote
1answer
114 views

Is it feasible to use combination of ABE schemes for encrypting the data?

I have a peculiar requirement for preserving the shared log files. For example I have 1000 records which belong to different organizations as listed below and all the logs are present in a single CSV ...
2
votes
0answers
45 views

VKO GOST R 34.10-2001 (described in RFC4357), Key Agreement Algorithm. Looking for its implementation/detailed description/examples

VKO GOST R 34.10-2001 was described in RFC4357 Page 7 But the description is very poor. Here it is: This algorithm creates a key encryption key (KEK) using 64 bit UKM, the sender's private key, ...
-2
votes
1answer
54 views

Question about the security of Substitution-Permutation Network

In general, we execute key-mixing, substitution and permutation sequentially in a single round in a n-round SPN, but if we execute n-round key-mixing firstly, n-round substitution secondly and n-round ...
3
votes
0answers
75 views

Finding algorithm: desire RSA's uniqueness and ECDSA's space efficiency

I am asking for help in finding a signature algorithm with the following property: Given a message m and a private key prikey, ...
2
votes
1answer
125 views

Understanding Pseudo Random Generators

I've been taking a crypto course online. I have a good idea how PRG's and Stream Ciphers work, but I'd love to get some input to help visualize what is actually happening. I understand a seed is used, ...
1
vote
0answers
62 views

Encryption with data loss protection [closed]

Is there an existing format out there that not only encrypts data but also protects against loss of data much like the QR codes can lose up to 33% of it's bits and the message is still recoverable. I ...
0
votes
0answers
64 views

fuzzy commitment implemenation to make secure biometric template

I want implement some ideas from an article that is about making secure biometric templates using fuzzy commitment and fuzzy vault. I need to implement just the fuzzy commitment (fuzzy commitment is a ...
3
votes
1answer
117 views

Efficient AES - Use of T-tables

I'm really in trouble! I'm trying to understand how the T-tables in AES encryption work. But I don't know if I get the point. What I understood is that they are used to reduce the whole computation of ...
0
votes
0answers
48 views

Scalar multiplication of elliptic curve point by a fraction

I'm implementing an algorithm that works on a generic finite cyclic group written in the classic multiplicative notation: (G,*) = < g > , n = |g| At a ...
1
vote
1answer
103 views

On the privacy of perfect hash functions

I'm digging into the several algorithms for building (Minimal) Perfect Hash Functions. It seems that the recent works provide quite a few very efficient algorithms. However, I'm wondering how a ...
2
votes
1answer
85 views

GCM: Math behind update of AAD after ciphertext has been processed

In the Bouncy Castle libraries, the GCM cipher implementation has an interesting property that does not seem described in the GCM papers (neither the NIST or the original paper): Some AAD was sent ...
2
votes
2answers
227 views

salsa20 is invertible, useless in CTR mode?

I'm reading the salsa20 spec (sorry for the newbie question, i'm really a newbie here). Every paragraph ends with : "this operation is invertible", I suppose the whole salsa20 algorithm is. If I use ...
4
votes
3answers
123 views

The difference between being not strongly collision resistant, and not weakly collision resistant?

So I understand the two concepts: (Strong) collision resistance: it is infeasible to find a pair $x \neq x'$ such that $h(x) = h(x')$ Weak collision resistance / 2nd-preimage resistance: for all $x ...
1
vote
1answer
90 views

Is Rabin's cryptosystem secure against known-plaintext attacks?

I've bee learning about Rabin's cryptosystem, and I already know that Rabin's cryptosystem is vulnerable to a chosen-ciphertext attack, but I was wondering, is it also vulnerable against ...
1
vote
2answers
48 views

Are password salts equivalent to keystream?

I am new to cryptography so my apologies for asking such a basic question. I was reading up on keystream when I came upon the definition of it: A keystream is a stream of random or pseudorandom ...
3
votes
2answers
171 views

Ways to make a “doomsday” cryptocurrency which becomes untradable

As a social experiment (not a money-making scheme), I'm interested in developing a crazy cryptocurrency which, by its very design, will become worthless and untradable after a certain point. Ideally, ...

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