0
votes
0answers
14 views

Checking my crypto — encryption of file contents using AES-256 in CBC mode w/HMAC authentication

I'm trying to ensure that contents of files that are uploaded to my web server are properly encrypted. I came up with the following encryption scheme and I'm asking to check my crypto. PS. I cannot ...
0
votes
1answer
33 views

Non-repudiation and digital signature of a dishonest participant

Let's assume a dishonest Alice who sends, encrypts & digital signs a message to Bob. Bob stores the decrypted message and the digital signature in a database. However Alice is a bad girl and ...
0
votes
2answers
18 views

Generation of a cyclic group of prime order

I am trying to implement a cyclic group generator in Java, but I am running into some issues. In many cryptosystems, the following phrase is expressed during the key generation stage. Let G be ...
0
votes
3answers
688 views

Kryptos : K1. What is the origin of the “palimpsest” keyword?

I'm studying the Kryptos sculpture with its cryptographic puzzles K1 to K4. I understand that the keyword "palimpsest" was reverse-engineered using the tableau (and brute-force computer processing), ...
4
votes
1answer
94 views

How hard is it to find plaintexts whose hashes satisfy $h(a)\oplus h(b)=h(c)$?

Given a cryptographic hash function $h$, for example SHA256, how hard is it to find plaintexts $a,b,c$ such that $$h(a)\oplus h(b)=h(c) \text?$$
0
votes
0answers
6 views

Kryptos K2 keyword derivation

So I've been doing some reading on Kryptos, and to be honest the keyword for K2, ABSCISSA, has a pretty weak derivation. (The method using the eee's). Isn't there a better way to come to that? I dont ...
4
votes
0answers
23 views

Parallel Pollard's Rho: Number of distinguished points

When using the parallel version of Pollard's Rho algorithm for discrete logs, each processor performs its own random walk to find distinguished points, and reports the starting point and the ...
1
vote
1answer
157 views

Can public key be recovered from ciphertext & encrypted private key?

I'd like to implement something like a write-once public/private encrypted shared secret (no better quick description for the lack of terminology knowledge). I guess, I'm trying to implement HSM. The ...
0
votes
0answers
26 views

Local UC(LUC) : About the impossibility of any simulations which consists hybrid protocols

In LUC framework, if a protocol has access to an ideal functionality(hybrid model), is it impossible to simulate this protocol? Just because, each of simulators has its own view of the protocol, so, ...
0
votes
1answer
20 views

XOR cipher with three different ciphertexts and repeated key, key length known. How do I find the plaintexts?

Let us say we have three different plaintexts (all alphabets, A-Z): $x$, $y$ and $z$, each of length $21$. Let the key, $a$, be also of length $21$. Now, what we have is $x \oplus a$, $y \oplus a$ ...
-1
votes
0answers
14 views

ECDSA: By using non-random k twice, is absolutely or occasionally leak the private key? [on hold]

In this blog: http://www.nilsschneider.net/2013/01/28/recovering-bitcoin-private-keys.html the author showed a case that using same k twice will leak private key. Many people know this method. But I ...
0
votes
2answers
81 views

The perfect way of using IV in CTR mode

I understand that it is necessary to use the same IV for both encryption and decryption in the CTR mode. I'm thinking about the case when I concatenate the secret ...
0
votes
1answer
43 views

Asymmetric sign in public enviroment

I have RTS game, where all players run game and server just relays messages. Game can generate and store text file on player pc. I want to allow some players to be moderators, so I need to sign or ...
0
votes
1answer
27 views

Why is it a quadratic equation?

In Groth-Sahai NIZK proof system, they have defined something called Quadratic Equation in $\mathbb{Z}_n$ as shown below. But, my idea of quadratic equation was a second order polynomial equation in a ...
0
votes
1answer
43 views

Proof that $gcd(e, \lambda(N)) = 1 \hspace{1mm} \Longleftrightarrow \hspace{1mm} gcd(e, \varphi(N)) = 1$

What is the proof for the fact that $gcd(e, \lambda(N)) = 1 \hspace{1mm} \Longleftrightarrow \hspace{1mm} gcd(e, \varphi(N)) = 1$ Where: $N = P * Q$ where $P$ and $Q$ are both primes. $\varphi(N)$ ...
-1
votes
0answers
4 views

Is it possible to do audio steganography using DWT(Discrete Wavelet Transformation) in java?

Audio Steganography in java using lsb is possible but using dwt is possible or not??? and also using spread spectrum is possible or not??
2
votes
2answers
24 views

One-way function definition

I cannot understand why a one-way function $f$ is defined in this way $\text{Pr}(f(A(f(x))) = f(x)) < \frac{1}{p(n)}$ and not $\text{Pr}(A(f(x)) = x) < \frac{1}{p(n)}$ where $A$ is a ...
0
votes
2answers
53 views

One time pad probability

I'm trying to solve a question about one time pads but I'm not sure if my assumptions are correct. I am to assume that I have a one time pad with perfect secrecy. This one time pad is used to ...
3
votes
2answers
75 views

Power analysis and exponentiation by squaring

I am trying to understand how one can retrieve the secret exponent via a simple power analysis. Lets suppose that the exponentiation by squaring algorithm is implemented in its simplest form : ...
1
vote
1answer
21 views

Do any stream ciphers with aperiodic keystreams exist?

Exactly what it says on the tin. I can imagine constructing such keystreams from: The binary expansions of irrational numbers Chaotic systems like the logistic map or the Lorenz attractor. The ...
0
votes
2answers
4k views

Decrypt files with original file CTB-Locker

I have problem called CTB-Locker. It encrypted all of my files on computer and since I have lot of documents that are very important I am in problems! As I read online CTB-Locker uses "elliptical ...
1
vote
1answer
140 views

Creating serial key generator using ECDSA, how to get signature short enough?

I've written some questions in this stackoverflow and got great responses but now I'm trying to wrap it all together. I have for the last couple of weeks been building a serial key generator project ...
1
vote
1answer
92 views

Merkle hash tree updates

It seems that merkle hash tree (MHT) traversals have been discussed somewhat in the literature, but there does not appear to be much written on inserting, deleting, and updating leaves. Is this lack ...
-1
votes
0answers
33 views

Methods for “chained authentication”

I am currently looking at different methods which can be used to perform what I would call "chained authentication". By chained authentication I mean authentication between two systems that cannot be ...
0
votes
0answers
16 views

Reducing key shares in Damgård-Dupont threshold RSA

I'm working on understanding and implementing Damgård, I., & Dupont, K. (2005). Efficient Threshold RSA Signatures with General Moduli and No Extra Assumptions. Public Key Cryptography-PKC ...
1
vote
2answers
57 views

Usage of GF(p^m) fields, where p != 2

$GF(2^m)$ Galois fields are widely used in different cryptographic algorithms, for example, in Rijndael. However, $GF(p^m)$ fields are possible with any prime $p$, not only 2, but $GF(2^m)$ fields ...
2
votes
1answer
207 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 ...
3
votes
1answer
152 views

Is there a flaw in this ECC blind signature scheme?

Recently I've found the following work on the internet: An ECC-Based Blind Signature Scheme The paper claims to be an ECDSA blind signature however it seems that their scheme has a flaw in it. The ...
2
votes
2answers
127 views

Can AES in CCM or GCM counter mode interoperate with AES in “plain” counter mode (CTR)?

I am exploring the use of Windows CNG to replace some OpenSSL-based code that takes advantage of AES in counter mode. From the outside, everything should look the same after the switch. The section ...
0
votes
0answers
26 views

Proving the complement property of DES? [duplicate]

I'm trying to show that for a given plaintext (P), key (K), and cipher (C) in the DES algorithm: ...
2
votes
2answers
221 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 ...
5
votes
1answer
2k views

What is Attribute Based Encryption?

Can someone explain what attribute based encryption is? I was searching for a book or something that can help me in this regard but so far I have found none. Google also returns practically nothing ...
0
votes
2answers
72 views

How secure is it to use password as AES key?

I am developing a steganography app where user encrypt any file into an audio file. The user can enter a password to protect the hidden data. The same password is converted as a 256 bit key and the ...
0
votes
1answer
27 views

Is there a reference that prove that the AES Key Schedule generate random looking round keys?

Starting from uniformly random generated AES master key, is there a reference that prove that an specific roundkey can be considered as uniformly random generated as well ?
9
votes
2answers
9k views

Many time pad attack [duplicate]

I've already sent my correct solution to a homework exercise from Dan Boneh's Introduction to Cryptography class on Coursera: "Let us see what goes wrong when a stream cipher key is used more than ...
0
votes
0answers
23 views

Pairing Based Cryptography API [on hold]

What are some of the good Pairing Based Cryptography support in python? I want to design Android based UI and test my pairing security scheme.
3
votes
2answers
75 views

Achieving 32-bit verification code with 16-bit CRC? [on hold]

I am programming an embedded chip that has a hardware 16-bit CRC module. I have to protect some data bytes $d_0,d_1,...,d_{n-1}$ against corruption caused by sudden loss of power; a 32-bit CRC would ...
4
votes
3answers
338 views

State of the art RSA key generation

I would like to know if there is an algorithm to generate a RSA key at the state of the art of the present cryptanalysis. Beside the key lenght I know there are some weakness in the choice of prime ...
6
votes
2answers
1k views

A timestamping authority (digital notary)

Does there currently exist a free online service that accepts a file, hashes it, takes an authoritatively chosen timestamp (from one or more time services), signs these and sends this signed message ...
1
vote
2answers
107 views

Is there any existing cipher capable of scaling from a 1 bit key up to a one-time-pad?

We have ciphers that handle small amounts of entropy, such as a 256 bit key for AES; and we have one time pads for enciphering 1:1 entropy, such as a 1GB key for a 1GB file if you could ever harvest ...
0
votes
1answer
57 views

Negative exponents in Shoup's threshold RSA?

I'm trying to implement threshold RSA operations, starting with decryption based on Peeters, R., Nikova, S., & Preneel, B. (2008). Practical RSA Threshold Decryption for Things That Think. ...
1
vote
2answers
105 views

1 Billion Bit Encryption?

So, browsing through YouTube, I stumbled on this video interview of John Draper (Captain Crunch), one of the first "hackers". He talks for about 3 minutes (until 27:48) about his home rolled ...
5
votes
3answers
1k views

Why should the RSA private exponent have the same size as the modulus?

Consider the generation of an RSA key pair with a given modulus size $n$ and a known, small public exponent $e$ (typically $e = 3$ or $e = 65537$). A common method is to generate two random primes ...
2
votes
1answer
36 views

Definition of the Decryption oracle

In the context of public-key encryption, what would be a formal definition of the decryption oracle? I know the informal definition (i.e., a function that is available to the adversary and that ...
3
votes
2answers
118 views

PGP String to Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
1
vote
0answers
20 views

Any ideas on login using Digital Signature PKCS

I am curious to know about possibility to login into web application just by identifying the user based on digital signature in usb token. any reference in this direction?
0
votes
0answers
37 views

Difference between Ascii85 and Base85? [on hold]

I have a python script that encrypts using Ascii85, but when I encrypt using base85, the output is different. What is the difference? Is it just a different alphabet? ...
2
votes
3answers
268 views

In RSA, why does $p$ have to be bigger than $q$ where $n=p \times q$?

In openSSL – during RSA key generation – if $q$ is bigger than $p$, they exchange them. Why is that?
2
votes
1answer
210 views

2048-bit RSA Decryption

If a message is encoded with 2048 bit RSA. The ciphertext is $M^e mod N$. In some cases, the message is short, $ M \approx 10^{20} $. With a high probability, $M$ can be written as $M = ab$ with $a, b ...
0
votes
1answer
43 views

RSA: How effective is this keypair-trash attack [duplicate]

A question that could very well be part of xkcd's "what if?": Let's say Monica made a piece of software that sends all RSA keypairs to a central database after they're not used anymore. Something ...

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