# All Questions

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### What Java actually stores inside Keystore when generating Keys?

When we use Keytool to generate a Keystore to store Private/Public keys, what Java actually stores inside the Keystore file ? I ...
34 views

### Designing hash function in space-efficient identity based encryption

Let $n$ be an RSA-prime and we know prime factorization of $n(=pq)$. The hash function is the current context maps from a given user identity(id) to a positive integer less than $n$, whose jacobi ...
279 views

### Hash collision using the leading 40-bits of SHA-1

I am trying to implement Floyd's cycle finding algorithm for finding a leading 40-bit hash collision in the SHA-1 algorithm. However, my code will not find a repetition even with 800,000,000 hashes. ...
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### Are all binary-additive stream ciphers reciprocal?

I'm writing a thesis focused on Maurer's provably-secure stream cipher. Long story short, this cipher works by expanding a short key into a long keystream and then XORring this keystream with the ...
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### What is the difference between order of base point and curve order in EC? [duplicate]

When I was read about the elliptic curve cryptography I found some definition about domain parameter of elliptic curve like the follow. But I did not understand something $p$: prime number. $a, b$: ...
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### Verbatim of early work on public-key cryptography?

In late 1997, the history of public-key cryptography was turned around with the announcement by the CESG (April 2000 archive) that public-key cryptography was theorized in a 1970 note [1] by James ...
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### Is there a Javascript and Java implementation of a good CSPRNG [closed]

I need to use a cryptographically secure pseudo random number generator in my client running Javascript and in my server running Java. Is there a well-known implementation of a good CSPRNG in both ...
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### Proving correctness of a decryption of a homomorphically summed ciphertext?

I would like to take some additively homomorphic cryptosystem - don't care much which one for now - and encrypt a series of numbers with it. I would then like to (in public) take these numbers, add ...
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### Cryptographic Operations and Security

sign((M’, TAlice, sign(( encrypt(( encrypt(M, KpbBob), M’), K), TBob), KsBob)), KsAlice) Can you tell me six security-related facts ...
186 views

### Availability of a simple limited PRNG algorithm

I am in need of a really simple limited PRNG, that either exists or can easily be created in virtually any language on any platform. It takes only the initial seed, and is only expected to generate a ...
63 views

### Is there an “additive” proof-of-work?

I'm trying to find a proof-of-work algorithm with the following properties: If A(1) is a proof of work with Difficulty(A(1))=n (requires n basic operations on average), then one can find a proof of ...
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### To prove $r \cdot f_1 +f_2 \cdot (s+1)$ is secure

We define the polynomials $r, f_1,f_2,s \in R[x]$. Where $r$ is a random degree 1 polynomial and $s$ is a random polynomial such that: $degree(s)=degree(f_1)=degree(f_2)$, let $R$ be $\mathbb{Z}_p$ ...
107 views

### AES - Encrypting multiple blocks of files

On my site, users can download files which are stored on public hosting, so I need to encrypt them. A downloaded file is divided into blocks of 1 kB and I want encrypt them individually, using the ...
150 views

### Modes of encryption for hard drives?

What are the currently recommended modes of encryption for large disks? Basic requirements would seem to be that you can update an encrypted sector independently of others, which rules out most ...
129 views

### Where have all the cypherpunks gone?

In 1992, cypherpunks was created as a mailing list for activists advocating for cryptography. Arguably, the cypherpunks mailing list was the foundation for the movement and the centre of it all. ...
186 views

### DHE key exchange. Is it really secure?

Context I recently came across a video on the net showing the process of key exchange in Diffie Hellmann. Alice and Bob want to communicate. Eve is the (wo)man in the middle. This video is the ...
516 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 ...
2k views

### Encryption of big files in Java with AES/GCM

I have to encrypt big files. Say their size ranges from 500mb to several of gigabytes. I would like to use AES/GCM/NoPadding as provided by Java 1.8 since that gives me automatic authentication and ...
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### 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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### What happens when cbc+hmac get a replay attack?

If it use AES-CBC and HMAC-SHA256 for message send online, and someone try to replay attack on this message. Can the attack be successful? what will be happen when attacking?
185 views

### Is the output of AES-CBC + MAC the same size as the input?

I use AES-CBC and HMAC-SHA256 to encrypt a text file. Will the output be larger in size than the input or will it be the same size? Is it more secure secure if the size of the output is larger?
109 views

### Do data-dependent rotations have any advantage over fixed rotations?

There are many ARX ciphers, however most use fixed rotations. I know data-dependent compared to fixed rotations are: patented harder to implement constant time more expensive in hardware harder to ...
260 views

### Is there a way to systematically calculate the public exponent $e$ in RSA?

I'm learning RSA in one of my classes and we were given a problem: $p = 5$, $q = 11$ I have done the following steps: $n = 5 \cdot 11 = 55$ $\phi = (5-1)\cdot(11-1) = 40$ I know that to ...
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### 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 ...
107 views

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

Looking for the number of characters that can be encrypted using the The elliptic curve ElGamal cryptosystem of each block, I found these lines. But I cannot understand them: Actually in our case ...
94 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 ...
109 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 ...
161 views

### Malicious DH groups

Can an attacker construct a DH group, large enough to be considered secure (say, a modulus of 2048-bits), such that the group appears safe, but the attacker is able to solve the DLP in the group ...
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### special public keys and modulo n

I just picked up cryptography and have some questions on RSA cryptosystem: Say there are two public keys (n, e1), (n, e2), e1 is coprime to e2. They share the same n. Is it possible to find the ...
141 views

### How can I start the following crypto project? [closed]

(Cryptography: encrypting files before storage in the cloud): The project consists of a software implementation of a method to pre-process a file before storing it on a cloud storage server so that ...
86 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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### Bouncy jdk 1.51 Serpent KAT tests vs Nessie vectors

Having a little trouble getting Nessie vectors working with the Bouncy Castle SerpentEngine. Do the Nessie vectors require a mode or some pre-processing? Nessie Serpent 128, set 1, vector 0 reads: ...
57 views

### what does rsaSha512Sign do?

I have the following function: ...
110 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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### Many single-time use keys encryption scheme (not Shamir's Shared Secret)

I'm looking for encryption scheme with the following properties: There's a sequence of keys that can be used to decrypt the message Strictly only one key from the sequence is required to decrypt the ...
470 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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### Solving a quadratic equation for a variant of Rabin

My understanding of Rabin We have $p$ and $q$ which are distinct primes congruent to $3 \pmod 4$. Then we have $n = pq$. Encryption is done as $e(m) = m^2 \pmod n$, where $m$ is our message. ...
166 views

### Secure Multiparty Sum in malicious model using threshold encryption

Suppose $n$ actors each hold a plaintext $p_i$. We wish to find $\sum p_i$, without leaking any information about individual $p_i$. Any actor (or any link in the network) could be controlled by an ...
445 views

### BruteForcer XOR (bfxor.exe) to attack 64-bit keys and longer

First of all, this is not a beginner's question since I already know a good deal about encryption and brute-force attacks. This is also no question on how to code programs for brute-force attacks ...
190 views

### OpenSSL RSA same plaintext but different ciphertext

how OpenSSL RSA work ? I generate public (n,e) and private key (n,d) then I encypted a file by : ...
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### plaintext distribution ,perfect secrecy cryptosystem

I have been trying to solve the next problem: let pi be a perfect secrecy cryptosystem with specific plaintext probability distribution. How to prove pi will have perfect secrecy for all other ...
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### 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) ...
260 views

### Why sorting is needed for Meet-in-the-middle attack

The weakness of double DES, E (k1, E(k2, M)) is that Meet-in-the-middle attack is possible. When performing Meet-in-the-middle ...
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### 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. ...
205 views

### extract ciphertext from encrypted SMIME file

the main question of this message is how to get the true ciphertext from S/MIME file? I created RSA keys and encrypted a message with S/MIME as follow : ...
106 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 ...
239 views

### Block cipher to encrypt 8 bytes/64 bits - Use 64 or 128 bit cipher?

Here's the problem: I have a transport stream that I have been requested to encrypt between the transmitter and receiver. The data size is at most 8 bytes so it seems I can only use ECB as I only have ...
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### Checking both Quadratic residuosity and Jacobi symbol simultaneously and efficiently

I have to randomly generate a number $u$ such that $u \in J(N)-Q(N)$ where $J(N)$ denotes the set of elements less than $N$, whose Jacobi symbol value is equal to 1; and $Q(N)$ denotes the set of ...