# All Questions

24 views

### Using a straight password for encryption and authentication

Assume we have a password like 3buNCh_7kaRmencrEst3. Now suppose we have two parties who know this password. We a have communication scheme that uses the password ...
21 views

### Is there a function that can be used to satisfy collision resistant property in MAC?

I am doing a project in cryptography where i need to satisfy collision resistant property in my MAC algorithm, is there any function that can be used in MAC that already satisfies collision resistance ...
64 views

### Is there any function that does not suffers birthday problem?

I am eager to know that if there is any function that does not suffer birthday problem and how to prove it formally that the function is not suffering the birthday problem.
32 views

### Can one extend the nonce of ChaCha20 by using XORing the extra bits with the key?

Can one extend the ChaCha and Sslsa nonces by XORing the extra nonce bits with the key? Both functions are considered secure against related-key attacks.
23 views

### MAC is constructed by hashing and then encrypting

Suppose the MAC is constructed by hashing and then encrypting, that is $MAC(m, k2)=E_{k2}(H(m))$ where H is a public hash function. There can be several alternatives in how the transmitted message is ...
19 views

### About BGV Scheme Batching Technique

I am reading BGV12 about BGV homomorphic scheme right now.But I am being stuck to understand Batching technique in this paper. In Pack function (page 32),this paper feeds ciphertext $c_i$ and sk ...
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### Using Openssl Libarary to convert .key encoded to .pem [migrated]

So i created a c program that takes in an encrypted (encrypted.key) file and a public key to decrypt the private encrypted encrypted.key. However, my program only works when taking in two files that ...
265 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 ...
41 views

### Key management and derivation - Allow changing of the passphrase

I'm working on a program, which allows encrypting files before storing it on a cloud service. Currently I'm trying to figure out how to derive and store the keys. First, I wanted to use a simple ...
50 views

### When to chose hardware accelerated crypto for Big Data

if you were to recommend a cipher/mode configuration that emphasizes performance for your customers, would you recommend a hardware based accelerated solution over one that isn't? For big data at ...
61 views

### Analysis of DGHV Security

I want to know how security of DGHV can be breached using oracle and Binary GCD. As I study this paper : Fully Homomorphic Encryption over the Integers But I am not able to understand Section 4.1: ...
74 views

### RSA when n= 2360221 and encryption = 5 find decryption key d, when M =1234

when n= 2360221 and encryption = 5 find decryption key d,and Cipher text C when M =1234
60 views

### Initializing PGP keys by one side

I am using a PGP method to encrypt and decrypt messages shared between users A and B. Upon the start of a message exchange is the initialization of the public and secret keys by both Users. Lets say ...
186 views

### Trapdoor and RSA (Schneier)

Disclaimer: I'm new to cryptography. Background: From Applied Cryptography (Bruce Schneier), page 30 of 2nd edition A trapdoor one-way function is a special type of one-way function, one with a ...
59 views

### What are applications of math in cryptology that can be explored by a high-school student? [on hold]

I was interested in knowing applications that would be comprehensible to a high school senior with a strong mathematical background
29 views

### Doubling or half of the private key range [on hold]

bitcoin private key range n = 1 to FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364140 and p = FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F bitcoin public key x = ...
151 views

### Modular Multiplicative Inverse and RSA?

In trying to understand this specific part of the RSA algorithm, I found this online: $$e \cdot d = 1 \pmod{(p-1)\cdot(q-1)}$$ Therefore: e \cdot d \cdot d^{-1}= d^{-1} \cdot 1 ...
35 views

### What implementation properties of a hash function prevent safe truncation? [duplicate]

Truncating a hash function's output should, in theory, not increase the likelihood of a collision more than you would expect based on the truncated output size. This makes sense when thinking about ...
53 views

### What are the time considerations with regard to security against birthday attack?

When designing security for a physical safe, one of the critical specifications is how long will the safe resist attack, this tells you how quickly you must detect and respond to an attack on the ...
106 views

### Why only one secret value with Shamir's secret sharing? [duplicate]

Shamir's Secret Sharing works by sharing data points on a curve, whereby when you have the required number of data points, you can find the function of the curve and find out the secret, which is ...
57 views

### How to detect what crypto-method is used by Filecoder.Q?

I have 2 different images, one original, and one locked by a malware detected by eset as "Win32/Filecoder.Q". How to detect the encryption method that is used and the key, that is not using any ...
14 views

### Testing the first 40 bit sequence for A5/1 if all registers initialized to 1

I have an assignment where my instructor asked to generate the first 40 bits for an A5/1 algorithm if all registers are initialized to '1' initially . I have implemented the algorithm successfully ...
45 views

### Does using a verifiable secret sharing scheme ensure robustness of a protocol if it is secure under the semi-honest adversarial model

Consider a protocol $\pi$ which uses a linear secret sharing scheme like that of Shamir secret sharing. Further assume that the protocol $\pi$ has been proven to be secure (correctness and privacy) ...
41 views

### What would be a typical value for the security parameter of the Fully Homomorphic Encryption over the Integers scheme?

The parameters of the Fully Homomorphic Encryption scheme by Dijk et.al are chosen according to the value of the security parameter ${\lambda}$, section 3 of the aforementioned article. What is the ...
32 views

### How to solve this public-key cryptography system? [on hold]

I need to solve this problem: someone know where I can find info for this? I have google'd around but can't find too much, those $N, I, J, C$ variables confuse me.
34 views

### Synchronous Stream Cipher Problem

Hello I am facing a problem trying to solve this question in the picture. Does anyone know how to produce the mentioned 32-bits of the key stream? The plaintext in this case is ...
69 views

### Trying to understand textbook exercise question regrading RSA

I am preparing for the final exam in my Data Security class so I am trying to read and understand the textbook's exercise questions. Any hint would be great. Question (Exercise 9.14 of textbook): ...
31 views

### Is Schannel supposed to use SHA1 for (EC)DHE params?

I captured a TLS 1.2 handshake on my server (WIN2012.R2/IIS 8.5) and noticed that SHA1 is being used to hash ECDHE parameters despite both the server and client(s) supporting SHA2 signatures. ...
243 views

### What is the fastest block cipher in the (Intel) world?

In AES competition,Rijndael cipher obtained first rank and become Standard and Serpent, Twofish, RC6 and MARS obtained another ranks and I know that Serpent took second rank because it was slower than ...
174 views

### Finding the subgroup in isogeny-based cryptography

Isogeny-based cryptography is one of the newest post-quantum cryptography. Hardness of this system is based on finding isogeny between two elliptic curves. Also this is theorem: Elliptic curves ...
40 views

### About ORAM initalization and running out of space

I have two questions about ORAM Since at the beginning,the server allocates unused storage for ORAM cient,there are no user's data in the storage.if now client access the storage the server will ...
167 views

### Full encryption of IDs, partial decryption with customer specific key

I am looking for a "partial" encryption/decryption algorithm. Let's say I am encrypting the following List of IDs (long values) $[1,2,3,4]$ (with a secret key) to an encrypted string $e$, I would ...
136 views

### System parameters in identity-based encryption

In IBE schemes, the system parameters are $(q, \mathbb{G}, F, \hat{e}, P, Q, T, H_1)$. I don't know $\hat{e}$. For example, in type A pairing… ...
207 views

### Are there any practical attacks that create a printable chosen prefix MD5 collision?

I would like to create two ASCII text messages with the same MD5. Is this possible? If not, is there a similar but less strict attack that could work? Or to rephrase my last question: what are the ...
26 views

### How to vary bit length of prime numbers in RSA by using MATLAB? [closed]

Please Can any one Tell me how to vary bit length of prime numbers of RSA cryptography algorithm in MATLAB.When i am considering more then 16 bit length of prime numbers Its not working. So can any ...
54 views

### what is meaning of operator “ := ” in cryptography?

I've seen := used in several cryptography papers where the this symbol has been used instead of assignment operator ($\leftarrow$ ) or equal sign (=), but never with an accompanying explanation. ...
44 views

### Are collision-resistant hash functions even possible? [see description] [duplicate]

Surely there can be no real collision resistant Hash function since hash values are of finite size which means there are finitely many of them, but there are an infinite number of messages we could ...
9k views

### What are preimage resistance and collision resistance, and how can the lack thereof be exploited?

What is "preimage resistance", and how can the lack thereof be exploited? How is this different from collision resistance, and are there any known preimage attacks that would be considered feasible?
38 views

### signature, hashing schemes

I have 20 friends. we create message(s) (1...i) and tar them up with a file messages.hashes(1..i). We sign these tars with our ...
57 views

### Is a PRF applied to a secure MAC also a secure MAC?

Suppose I apply a PRF to a secure MAC. Do I still have a secure MAC?
38 views

### Find SHA256(secret||data) using SHA256(secret) and data

I need to find the SHA256 hash of s string like this: "part1-part2". I know the SHA256(part1), length of part1 and I know part2, but I don't know what is the contents of part1. Is there any chance I ...
24 views

### What is transaction capacity of a POS using 3DES DUKPT?

I am looking for the transaction capacity of a Point-Of-Sale device using 3DES DUKPT. Once all keys derived from the future key set are exhausted (1M or 500K?), how will the POS be reloaded with a new ...
7k views

### AES encryption using a Diffie-Hellman key exchange

I have two systems which need to encrypt their communication by AES-128. The key for the AES encryption should be exchanged with the Diffie-Hellman (DH) algorithm. Now, I've read about DH and got a ...
98 views

### AES implementation to encrypt files

I'm making a small python program to encrypt an arbitrary text file. Currently I have a file to store passwords (hashed values), so nothing stored in plaintext. The user enters the command line ...
64 views

### SHA256(RsaPrivateKey) == AES key?

I have an RSA private key (more specifically, an SSH key in Putty format, 4096bit) and want to use its SHA256 hash as an AES256 key, instead of using an independent newly generated AES key. Are ...
58 views

### Is OCB the state of the art in authenticated encryption modes of operation for block ciphers?

OCB mode seems to represent the state of the art in authenticated encryption modes, largely due to its speed – it is faster than GCM even when GCM has hardware support. Its only drawbacks seem ...
64 views

### Exploiting XOR one-time-pads with dictionary length that isn't a power of 2

I realized that if the key is chosen randomly from a range that isn't a power of 2, the one-time-pad leaks information about the plaintext. For example, if the alphabet was the first 20 naturals, ...
33 views

### Why hash function are used in digital signatures? [duplicate]

In the lectures I see, hash functions are always used when we want to sign a document $d$. My question is why they are used in digital signatures? Maybe, because it is more easy and fast to calculate ...
Suppose that an $n$-bit integer $c$ has been randomly drawn from a distribution $\chi$, whose description is known. Is there a general method to check if this particular sampling helps factorize $n$? ...