# All Questions

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### Randomness in generation of Virtual Machines from pre-built Image [closed]

I am studying Multi-Tenancy vs. Virtualization, and I got thinking about randomness, true randomness, virtualization etc, and I couldn't find anything on it. From what I gather, ...
23 views

### Why the Symmetric Key algorithm requires small key compared to Asymmetric algorithm? [duplicate]

According to a book I am studying: The key lengths for symmetric and asymmetric algorithms are dramatically different. For instance, an 80-bit symmetric key provides roughly the same security as a ...
136 views

### Salsa20-GCM composition secure?

AES-GCM seems to be used by everyone but I never seen even one post about Salsa20-GCM. Is it secure? Wikipedia mentions that GCM ...
115 views

### Is it possible to combine true streaming with AEAD?

It seems there is a difference between "streaming" in cryptographic sense (as in CTR) and "streaming" in general programming sense (as in "accept a file larger than RAM from socket and save it on ...
309 views

### How multiplicative property of RSA can be exploited

It is known that RSA has the multiplicative property $E(m_1) \cdot E(m_2) = E(m_1 \cdot m_2)$ because $m_1^e \cdot m_2^e = (m_1 \cdot m_2)^e \pmod n$ But how can this property be used to break ...
77 views

### Algebraic cryptanalysis on public-key schemes

The book Algebraic Cryptanalysis (Bard, G.V.; Springer, 2009) speaks about transforming a symmetric scheme into a system of polynomial equations and solving these equations to break the scheme. But ...
192 views

### KDFs for symmetric encryption master key & serial number

Let's assume that I generate a high entropy AES master key (through /dev/random for example) and I want to derive it with a fixed-length serial number (12345 for instance). The derived key is used to ...
271 views

### CTR HMAC SHA256 implementation

After trying to invent my own AES mode, I decided to just implement something that's known to work, namely CTR with HMAC SHA256. From what I understand, I can use the IV as a counter, and the IV ...
159 views

### What use is the signature without the message under RSA?

Using RSA for signing & verification, is there a way to take a valid signature for an unknown message, and for someone else to generate a valid signature using a different key against the valid ...
444 views

### Is it possible to tweak AES-GCM so that it is satisfactory for whole-disk encryption (like XTS mode)?

Is it possible to leverage a preexisting implementation of AES-GCM to provide the key security benefits essential for full-disk encryption (similar to AES-XTS)? GCM is a popular encryption mode ...
7k views

### Differences Between White-Box Cryptography and Code Obfuscation

I have been reading the question "What is a white-box implementation of a cryptographic algorithm?" and it led to this short article / Q&A which states in question 2: Q2: What is the ...
275 views

### Creating a random password based off of a prime number

So I am making an application that basically creates strings that must be encrypted before they are stored on a user's device. If the user blindly starts running the application without creating a ...
2k views

### Any efficient text-based steganographic schemes?

While there are sophisticated and efficient steganographic schemes with images as cover available, I am yet ignorant of the existence of any fairly efficient and secure schemes with texts as cover. ...
176 views

### BER or DER X9.62 ECDSA signature

The signature format for ECDSA signatures can be encoded using ASN.1 integers according to X9.62 or it can comprise of two integers with the same size as the key size. In case the X9.62 format is ...
283 views

### Creating unique keys with md5

The project I'm working on requires me to find a way to create a unique key based on data stored in a table. The table in question consists of x columns and y rows. In order to create the key I want ...
682 views

### What do I use as the encryption key and initialization vector in AES cfb128

I'm writing a program that can encrypt a file using AES cfb128 (using Openssl and C++). The scenario of the program is this: Person A visits computer, encrypts a file they make, takes away a key ...
78 views

### Altering the message space of Paillier

Is there any obstacle if we restrict in Paillier the plaintext values to be drawn from $\mathbb{Z}_N^*$ instead of $\mathbb{Z}_N$ as the original scheme indicates.
92 views

### difference between soundness in ZKPoK and special soundness for sigma proofs

What is the difference between soundness in ZKPoK and special soundness for sigma proofs?
105 views

### Why is a Feistel network not a type of substitution-permutation network?

I understand what substitution-permutation networks look like. I understand what Feistel networks and Feistel-like networks look like. A Feistel network or a Feistel-like network features substitution ...
60 views

### Are there any noisy homomorphic encryption schemes?

Are there any Homomorphic Encryption(HE) schemes that result in noisy answers ? By noisy i mean , the answers could be approximately near the actual answers by noise factor $\epsilon$. For example , ...
136 views

### Removing “security by obscurity” from port knocking

Every article about port knocking, for instance https://wiki.archlinux.org/index.php/Port_Knocking , declares this method as security by obscurity. Is the following enough to remove that title; a ...
204 views

### Why would an Initialization Vector be supplied externally?

My software uses a 3rd party encryption appliance. One of the capabilities they allow is for the client software to supply an IV while doing CBC encryption. Why would they not generate a random ...
3k views

### How to decrypt a '.enc' file that has been encrypted with RSA using a public key? [closed]

While solving a CTF challenge online, I came across a situation where I needed to decrypt a '.enc' file that has been encrypted using someone's public key. The ...
194 views

### New to cryptology, studying Message Authentication Codes

I understand the basic operational theory behind MAC, but I'm getting tripped up on some of the finer details. Also the differences between MAC, HMAC and MIC are getting lost on me, including the ...
780 views

### Decrypted RSA 64 bit encryption using modulus and private exponent. Got gobbledygook [Verify] [closed]

As part of an experiment, I was given a .enc RSA (encrypted) file that was most likely generated using openssl. I had the public key, I factored it, obtained the private exponent, and decrypted the ...
2k views

### What is the probability of breaking the AES algorithm?

I am doing a project which requires the encryption to be done using AES. Is it really possible (technically) to crack AES? If yes, please tell me: What is the probability of breaking AES? How ...
92 views

### Common reference string in NIZK

I want to ask that does the common reference string in NIZK have to be random? Or can it be anything?
71 views

### AES inversion operation in sub byes

I was wondering why in the AES sub-bytes operation one can represent the inversion as computing $x^{254}$. What is the reason for this? Moreoever, I was wondering what the text on page 212 of ...
457 views

### Toy public/private key example open to frequency analysis?

I've been looking at an online Public Key Encryption Example (summarized below). It seems to me that choosing cyphertext = plaintext^(key) mod n would produce the ...
82 views

### Key change and key derivation

There are two ways for key change: key update, and Re-keying. Which of these methods use a KDF (Key Derivation Function) for getting new keys?
197 views

### Is the SEED blockcipher still secure?

I did found an old question which answers exactly this but it is from 2 years ago and i was wondering if there were any changes. I have not been able to find any new information on the cipher and am ...
163 views

### Hash functions to the power of two and three notation

I have found in a Wireless Sensor Networks security paper, operations where cryptographic hash functions are elevated to the power of 2 and to the power of 3 (i.e. $h^2(x)$ and $h^3(x)$). This might ...
510 views

### Computing IV for CBC from PBKDF2 + HKDF

Note that this question is somewhat similar to Can I use my random IV (for AES) as a salt for PBKDF2? My current encryption format computes two random PBKDF2 salts (encryption and HMAC, 8 bytes each) ...
99 views

### Pseudorandom Function Proof

Given a set of pseudorandom functions $F=\{f_s^i\}_i$ for each $s\leftarrow\{0,1\}^n$ generated at random; moreover each $f_s^i$ uses a specific PRG $G^i:\{0,1\}^n\to\{0,1\}^{2n}$, where: ...
238 views

### What is the difference between chosen-plaintext attack and adaptive-chosen-plaintext attack?

I've just dived in cryptography and would like to learn basics of this science. Currently I can't understand the difference between these two types of attacks. As I understood from Bruce Schneier's ...
281 views

### Elliptic Curve Crypto, is a distributed signing method possible using Shamir's Secret Sharing?

Note: A distributed signature scheme exists for RSA: Practical Threshold Signatures, Victor Shoup. Is it possible to adapt such scheme for ECC? A centralized signing machine is vulnerable to ...
37 views

### Identification by RSA

Suppose we have identification scheme as such: Bob takes random $r$, and encrypts it with Alices public RSA key $(n,e)$, sends $r^e$ to Alice. Alice decrypts $r$ and sends it back to Bob, becomes ...
395 views

### Why is diffie-hellmangroup1-sha1 used instead of diffie-hellman?

For SSH why is diffie-hellmangroup1-sha1 used instead of just diffie-hellman? In other words, why is the hash function used?
97 views

### Replay Attack in Stream Cipher

Stream ciphers are vulnerable to replay attack if the same key k is used. If E() is a stream cipher and an attacker intercepts the message m that's being transmitted at time t, how can the attacker ...
443 views

### What is the purpose of pre master secret in SSL/TLS?

I studied about SSL/TLS and learned that client and server must share keys below. common key for encryption common key for generating message authentication code Then, in SSL/TLS, a client doesn't ...
305 views

### Crack linear congruential generator knowing every other word in sequence

I need to crack one of the example of linear congruential generator. I have $X_{n+1} = (a \cdot X_n + b) \bmod m$ and I know every other word in the output sequence: ..., 3158, ..., 1888, ..., ...
87 views

### Will ANY prior knowledge assist in determining contents of a SHA1 hash?

I am working on a project testing a hash that protects some data, and I've already eliminated hash length extension attacks as a possible point of compromise, and I'm trying to educate myself on all ...
133 views

### Solve a problem, thought it was hash length extension, hours later, am I wrong?

Here is my situation. I'm working with an application for which uses hashing to authenticate data. I have a string, which is hashed. It is, like in a hash length extension attack, H(key:known_value) ...
595 views

### Find out which keying option is being used in Triple DES?

As far as I know, there are three standard options for the three keys $K_1$, $K_2$ and $K_3$ used by 3DES: Three distinct keys. The first and last key are equal: $K_1$ = $K_3$. Three equal keys: ...
105 views

### What makes this mixer function resistant to differential cryptanalysis?

I recently learned how differential cryptanalysis works, and decided to have a play around with testing various designs for resistance against attack. My testing algorithm is essentially to loop ...
219 views

### Is the keystream transmitted with the ciphertext when a stream cipher is used?

When a stream cipher is used and a keystream is generated to be XOR'ed with the plaintext, is the keystream sent with the ciphertext so that the receiver knows how to decrypt it? Or does the ...
224 views

### How to encypt/decrypt messages after ECDH key agreement

I am using Diffie-Helman key exchange to generate the shared secret. But how will can a message be encrypted using this shared key?
230 views

### Is it possible to calculate the 'skeleton key' for DUAL_EC_DRBG? What would it take?

According to Bruce Schneier the constants used in the spec of DUAL_EC_DRBG may be related to a secret set of numbers, that could function as a master key for ...