All Questions

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22 views

Should I use a key store to keep my symmetric keys

I'm maintaining an application which handles several keys to encrypt/decrypt information. Some keys are used to encrypt text (user passwords, some sensitive data in the db, etc). Some other keys are ...
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1answer
39 views

Java: How to handle authenticated encryption for big files

First I need to mention that I can't use BouncyCastle to implement this solution. I have to encrypt files into the file system. Those files are not going to be tranfered over the wire to any other ...
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0answers
19 views

if using cbc+hmac dealing with small size of data(less than 128bit) , will it cause any problem?

if use AES-cbc,HMAC-SHA256, and there is some txt needed to be enc, and I divide this txt into small packages with variable length, then enc them. some of these package can be less than 128bit. Is ...
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0answers
28 views

Elliptic curve trapdoor function without modular arithmetic?

From what I understand, an elliptic contains a set points satisfying the equation $y^2=x^3 + ax + b$ together with the point at infity. It seems clear how multiplication with a scalar and a point ...
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0answers
31 views

How many characters per block in an El Gamal ECC cryptosystem?

While I look for how many characters that can be encrypted using the The elliptic curve ElGamal cryptosystem. of each block found for these lines. But I can not understand Actually in our case we ...
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0answers
27 views

Find the encryption method from the cipher and plaintext [on hold]

I have been given iogdaybDfD which is a cipher of the word narcolepsy. I need to find the type of encryption that has been applied to narcolepsy to encrypt it to iogdaybDfD. Could anyone advise on how ...
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0answers
16 views

CP-ABE: structure of the secret key SK

I am working on Ciphertext-Policy Attribute based Encryption (CP-ABE) and I need to understand how a secret key looks like. For example, assume that the universe of attributes is defined to be ...
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0answers
38 views

Interactive assumptions not falsifiable?

Can someone explain why an interactive assumption is not falsifiable? Maybe I'm misunderstanding what the statement means, but isn't even a non-interactive assumption interactive, but just with a zero ...
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0answers
21 views

Java RSA/ECB/PKCS1Padding encryption with .NET [on hold]

I need to encrypt a password on a web site developped in .NET using a public key. The public key is delivered through a Java web service with the information: The key is a RSA key to be used with ...
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0answers
28 views

proving the security of 1 out of 2 oblivious transfer using AND function

Hello ladies & gentlemen, I need to improve the security of 1-out of 2 oblivious transfer using AND function method with a given info. use one-out-of-two oblivious transfer as building block, ...
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0answers
24 views

number theory and cryptographic hardness assumptions [on hold]

Let p be a prime and e>=1 an integer. Show that the totient(p^e)=p^(e-1)*(p-1). Let p,q be relatively prime. Show that the totient(pq)=totient(p)*totient(q). (Dont use chinese remainder).
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0answers
47 views

Key generation in Digital Signature Algorithm

In DSA, one needs to generate two primes $p$ and $q$ such that $q$ is $256$-bit and $p$ is $3072$-bit and $p-1$ is a multiple of $q$. Question: How to generate such $p$ and $q$. Attempt: First, use ...
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1answer
76 views

Collision resistant hash functions

Let (Gen1,H1) and (Gen2,H2) be two hash functions. Define (Gen,H) so that Gen runs Gen1 and Gen2 to obtain keys s1 and s2, respectively. Then define Hs1,s2(x)=Hs1(x)||Hs2(x). a) Prove that if at ...
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1answer
39 views

Show CBC-MAC construction isn't secure [on hold]

Show that the basic CBC-MAC construction is not secure when used to authenticate messages of different lengths.
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0answers
48 views

RSA with PKCS#7 and DES-EDE3-CBC (and padding)

I have this smime file ...
0
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1answer
54 views

fully homomorphic encryption (FHE)

Please, I would like to find some hints or solution to my following problem, I would appreciate your assistance to walk with me throughout the solution Given fully homomorphic encryption (FHE) ...
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0answers
30 views

Importance of ShiftRows in AES

If ShiftRows is excluded from AES, then an attacker can attack the modified AES by simply treating $128$-bit input as $4$ $32$-bits blocks. The attacker can attack these $4$ blocks separately. ...
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0answers
25 views

Secure symmetric encryption algorithm for any-size base62 data

I am searching for a secure algorithm to encrypt base62 (or any other base) data for ids in urls. It should feature: No blocksize etc, limiting the length of the message to a factor of n If you ...
0
votes
1answer
62 views

Decrypting A Cipher Text without knowing the key or plaintext

i'm new to cryptography and i am doing a research based on cryptanalysis of vigenere cipher. If i have a ciphertext which is encrypted using vigenere cipher, is it possible for me to decrypt the ...
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0answers
49 views

How does chosen ciphertext attack on Elgamal work?

Can it be proven that attacker can obtain the full message if he knows some plain-ciphertext pairs?
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0answers
59 views

Complexity to find an preimage of a hash function

Suppose a hash function based on Merkle-Damguard construction. Its compression function is given as $H_i=E_{m_i}(H_{i-1})$, where $E_{m_i}()$ denotes the encryption of an ideal block cipher with ...
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0answers
67 views

CCA security of a system that splits messages and encrypts each packet

Propose a symmetric key based crypto-system for implementing a secure email system. This system is based on AES and CCA secure. Suppose that you have to encrypt a large message and that this message ...
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0answers
29 views

The Inhomogeneous Short Integer Solution (ISIS) problem with a clue

The Inhomogeneous Short Integer Solution (ISIS) problem is as follows: given an integer $q$, a matrix $A \in \mathbb Z^{n\times m}_q$, a vector $b\in \mathbb Z^n_q$, and a real $\beta$, find an ...
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0answers
25 views

Where can I get a security audit for a crypto app storing files on the cloud? [closed]

We are completing a new app the encrypts files (AES 26-bit) prior to sending them to cloud storage services (ex. OneDrive, Google Drive, DropBox, etc.). We want to find a consultant who can do a ...
0
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1answer
70 views

Client encrypts AES key and send it to other clients using public key (RSA) and server?

i have implemented AES and RSA methods myself. The server generates the AES secret key and encrypts it with every new client's (public key, modulus) then it is sent to that client, the client then ...
0
votes
1answer
36 views

Blowfish ECB mode: Tools for known-plaintext attack?

I'm currently dealing with multiple blowfish-encrypted files that share the same key. All are encrypted using ECB mode judging from their appearance. I don't know what the key is but I know 64 byte ...
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0answers
18 views

Hokkaido (proof-of-Work system) and pseudo-random permutation table

This question is regarding a proof-of-work system suggested in this article "Cryptology ePrint Archive: Report 2005/356". The outset goal of the Hokkaido algorithm is to provide a task to somebody's ...
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0answers
39 views

ASP.NET MembershipProvider uses passwordSalt when encrypting [migrated]

I've a question about the ASP.NET Membership (from .NET 2.0), and more specifically the way it encrypts passwords (when you choose to encrypt them, and not hash then), and the way it verifies them. I ...
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0answers
36 views

Permutation parity after cycle-walking

Let $E$ be a random even permutation of the set $\{0\dots n-1\}$. We construct a permutation $P$ of the set $\{0\dots m-1\}$, for some $m\le n$, using cycle-walking; that is, computing $P(x)$ is as ...
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0answers
14 views

openssl - Recommended way to encrypt and sign S/MIME messages using openssl

OpenSSL has two command line tools, cms and smime, that can encrypt and sign S/MIME messages. Both can specify ciphers and ...
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0answers
9 views

java.security.spec.InvalidKeySpecException and Inappropriate key specification error in java program [migrated]

As a part of project implementation,I have done: 1. Generete DSA keys 2. Encrypt the private key using AES 3. Save into the file 4. Open the file and read the encrypted private key 5. I tried to ...
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0answers
17 views

Validity of ElGamal signature variation

I'm trying to solve excersise 7.6 from Hoffstein - Introduction to Mathematical Cryptography page 459 (http://goo.gl/oRyInT) Let $p$ be a prime and let $i$ and $j$ be integers with $gcd(j, p − 1) = ...
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0answers
30 views

Test framework for hash functions for collision resistance?

I have two questions about the assessment of collision resistance in hash functions. Given a hash-function what would be the next step to inquiry about it's collision resistance / probability of ...
0
votes
1answer
45 views

Storing AES encrypted RSA private keys on a server

I'm thinking about creating an encrypted messaging web application where users create RSA key pairs, they store the public key on the server for others to see and also store an AES encrypted private ...
0
votes
1answer
62 views

Handbook of Applied Cryptography as an entry point - is it ok book?

I recently chose to make an entry to Cryptography and encryption by starting to read the book Handbook of Applied Cryptography. I come from computer science background. To be honest, I have forgot ...
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0answers
37 views

How can I calculate the size of an encryption key?

I have encryption algorithm that has two variables are used as encryption key. How can I calculate the size of the encryption key. I will show an example of what the variables can be: ...
0
votes
1answer
35 views

Storing salts and iteration number?

I have a function that derives two sub-keys from one passphrase using PBKDF2 one which is used as a encryption key the other for HMAC generation, because these two sub-keys will need to be regenerated ...
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0answers
75 views

How can I prove CPA secure by using a new scheme gen,enc,dec from GEN,ENC,DEC?

Given public key encryption scheme $(gen; enc; dec)$, we now construct a new scheme $(Gen; Enc; Dec)$ as follows: The key generation algorithm $Gen$ is the same as $gen$. Each ciphertext for a ...
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0answers
24 views

Do OpenPGP SmartCards have the same or better security than an air-gapped machine?

Are OpenPGP SmartCards, such as the OpenPGP SmartCard V2, suitable enough to have secure communications? Meaning, if I connect my smart card to my Mac which is connected to the internet and always ...
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0answers
18 views

The number of surviving key after “Meet in the middle stage” in 3-subset MITM attack

In 3-subset Meet in the middle attack, how can we calculate the number of surviving key after meet in the middle stage? and how can we calculate the complexity of Key testing stage? I have read about ...
0
votes
1answer
36 views

Why is g is less than p in Diffie-Hellman?

In non-authenticated DH, p and g are made as public record. p needs to be a large prime number and g should be smaller than p. Why does g need to be smaller than p?
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0answers
26 views

recommendation to see documentaries about history of cryptography

Can anybody recommend any good documentaries which go into some history about cryptography and state of cryptography as of date ? I am not asking for favorites or subjective good documentaries but ...
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0answers
42 views

Franklin-Reiter related message attack m2 = a(m1)+b

As shown in their paper, https://www.cs.unc.edu/~reiter/papers/1996/Eurocrypt.pdf, if one is given an equation relating the two messages m1 and m2 as well as other information one can crack both the ...
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0answers
29 views

Is it possible to add OpenSSL engine for a block algorithm with different input and output block size?

I need to add a new symmetric cryptography algorithm to OpenSSL, and I thought that the best way to do it is via its engine API. This algorithm will later be used by an application via the OpenSSL ...
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0answers
22 views

Multi-round Transposition/Playfair as a secure hand cipher in the computer age

Given that computers can be easily compromised, there is a need for a hand cipher that can withstand computer attack. Clearly the traditional hand ciphers fail. One time pads work. They also have ...
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0answers
26 views

How good is middle cube method with jumbled digits?

I had to make my own prng for a stream cipher for an inter school science project (I am mentioning that a lot). So I thought of cubing the seed instead of squaring it (like in the middle square ...
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0answers
30 views

Is Paillier cryptosystem commutative?

Is Paillier cryptosystem commutative? If not, how can we construct an oblivious decryption protocol based on Paillier?
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0answers
21 views

NRPAD and FPAD padding schemes (Korean Seed?)

I've got an API spec that specifies NRPAD and FPAD as possible padding schemes. I see these being used together with the Korean SEED algorithm. The SEED specification however is void of any padding ...
0
votes
1answer
43 views

Complexity of preimage resistance

Why is the complexity of pre-image resistance $2$ raised to the power of $n$? I have been looking in everything lecture about pre-image resistance, but I still didn't know the answer.
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0answers
23 views

symmetric encryption A5/1 and A5/2 algorithms

where does the key (Kc) used to generate the keystream comes from and also where does the 22bits counter comes from

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