# All Questions

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### Full Disk Encryption Alternative [on hold]

Since developers of TrueCrypt discontinued their software, i'm looking for a alternative. It should be pre-OS, so that just after Bios, the Password is requested. Like in TrueCrypt. I took a look ...
60 views

### Crypto Challenge.sucked [on hold]

The solution was hardened using MD5(MD2(SHA1([a-zA-Z]{6}))). Now crack this: e24b02c81cabe0d4af45f9ceaccde2c7 i couldnt crack it.
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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 ...
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### How can I start the following crypto project?

(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 ...
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, ...
35 views

### 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: ...
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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### what does rsaSha512Sign do?

I have the following function: ...
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### 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 ...
63 views

### 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 ...
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### 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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### Show CBC-MAC construction isn't secure [closed]

Show that the basic CBC-MAC construction is not secure when used to authenticate messages of different lengths.
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### Rabin Cryptosystem Problem (variant)

My understanding of Rabin We have p and q which are distinct primes congruent to 3 mod 4. ...
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+50

### 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 ...
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### 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 ...
48 views

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

I have this smime file ...
34 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 : ...
30 views

### 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) ...
39 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. ...
18 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 : ...
26 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 ...
52 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 ...
49 views

### 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 ...
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### Why is Poly1305 popular given its 'sudden death' properties?

ECDSA has the undesirable property that if a key pair reuses a nonce in a signing operation, the cryptosystem experiences catastrophic failure in the form of private key leakage. I've heard this ...
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### 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 ...
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?
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 ...
322 views

### Why we can't implement AES 512 key size?

Out of curiosity why we can't implement AES 512 key size? Please explain somehow i can understand! I'm not an expert.
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### Key derivation for AES-Encryption key and HMAC

Okay so I have two options for how I would derive two keys for AES encryption and HMAC they are as follows: Run BCrypt on a users passphrase and then use the bouncy castle implementation of HKDF in ...
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### How many of primitive point on the elliptic curve?

In elliptic curves for cryptography, I know $nG=O$, where $G$ is a base point represented by $G=(x_g,y_g)\ on\ E(F_P)$, where $n$ is Order of point $G$. For example, $P(0,6)$ is a primitive point on ...
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I am encrypting files using AES/CBC/PKCSPadding, with 256 bits long keys. So far the first 16 bytes of each encrypted file are the IV. I would like to store some more information regarding the ...
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### How can CBC-MAC be secure when message length is fixed?

I was doing some self-initiated knowledge gathering about digests, signatures and hmacs and I ran across the fact that you can use CBC as a MAC, but if the message size is not fixed; then it is not ...
62 views

### Fairness in cryptography

Two users A and B decided to share a file of same size and transfer data bit by bit. And at the end of exchange, A will have B's data and B will have A's data. Assuming, A starts to transfer the ...
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 ...
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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### What is primary security in ECC?

I read the following paragraph in a book about Elliptic Curve Cryptography, but didn't understand it: The primary security in ECC is the parameter $n$; where $n$ is Order of point $G$, that is $n$ ...
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### 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 ...
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### Consequences of AES without any one of its operations

Suppose AES-$128$. There are $4$ operations in AES's encryption, they are SubByte, Shift Row, MixColumns and AddRoundKey. Question: If I remove one of the following opearations, what will happen to ...
1k views

### Perfectly secret cipher can leak about the key?

As defined by Shannon, a cipher is perfectly secure if ciphertext leaks no information about the plain text. Under this definition, can ciphertext leak something about the key? Are there any ciphers ...
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### Condition on Vector Boolean Function to be Bijective

Suppose the vector boolean function be \begin{align} f:F^n_2 \longrightarrow F_2^n \\ (x_1,\dots ,x_n) \longrightarrow (x_2,\dots x_n,g) \\ \\ g:F^n_2 \longrightarrow F_2 \\ (x_1,\dots ,x_n) ...
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### Strange MAC algorithm

I'm working with a payment provider which uses the following algorithm for signing messages: The merchant is securely given a secret key k, known to them and the ...
259 views

### AES with weak keys

Suppose that the key generation is insecure; each key bit is independently generated, but the value of each key bit is '$1$' with probability $0.90$. These keys are used in AES. What is an efficient ...
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### Verifiable, Distributed Secret Santa Assignments

My family was planning a secret santa and I thought about how I might write a little web app to dole out these secret assignments. But the downsides to this approach are obvious: there's no way for ...
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### Different Encryption schemes i have no idea to achieve [closed]

I want to find examples for encryption schemes that: are resistant to a total break but not against universal break are resistant to universal break but not partial break are resistant to partial ...
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### What is the bilinear pairing? [closed]

I read that public key encryption with keyword search using bilinear pairing what this mean?
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### example of predicate encryption explaining what is attributes with ciphertext and what predicate with key is

I know that predicate encryption schemes are encryption schemes in which each ciphertext is associated with a binary attribute vector and keys are associated with predicated. I want to ask what is the ...