# All Questions

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### Figure out the encryption being used [closed]

There is a web API (for a game) that sends and receives data encrypted in hex format. I'm interested in accessing the api outside of the game client (mobile app). When sending a request with an ...
58 views

### Why would using a random seed with other variables be bad for ecrypting if you can't guess the key?

I asked this on stack exchange with it being code based, but someone suggested to ask here. Basically, I've done a script in python and wanted an option to encrypt the input, but I couldn't get any ...
32 views

### Worked example of McEliece Cryptosystem

I am trying to learn about the McEliece cryptosystem, unlike other more common systems, like RSA or El Gamal, educational literature such as the Handbook of applied cryptography doesn't contain worked ...
77 views

### Hash “Preimage by product” resistance

Let H() be a hash function that achieves collision resistance as well as first and second preimage resistance. Let's equip the output set of H of a multiplicative group structure, more precisely a ...
30 views

### Implications of reversing CBC encryption

What would be the security implications if we reverse CBC encyption? Here is a picture of CBC encryption: Here is a picture of CBC decryption: My guess is that the encryption would work if we ran ...
44 views

### How does double-encryption work with a client server model

With mobile applications like Accompli (now the base for the Android Outlook application), credentials are stored. Reading from the Accompli website: Each user’s credentials are double-encrypted ...
25 views

### LUKS multiple key slots - what's the intuition?

LUKS volumes have the ability to allow multiple independently usable passwords, as explained here: [https://code.google.com/p/cryptsetup/wiki/FrequentlyAskedQuestions] The intuition behind basic ...
48 views

### Full Domain hash library

I need to know if any of the well-known crypto libraries (openssl, crypto++) supports full domain hash function. If not, what library I can use?
34 views

### What is the polynomial to use in the Massey-Omura cryptosystem?

The Massey-Omura cryptosystem uses "multiplication over the finite field $GF(2^n)$. I'm just starting understand the idea of multiplying polynomials and I've searched for online calculators to use for ...
41 views

### Crypto hash function vs encryption algorithms

Why is a cryptographic hash function generally faster to execute in software than conventional encryption algorithms such as DES?
78 views

### What are the computational benefits of primes close to the power of 2?

Recently I was reading some article about the Bernstein's Curve25519. This is a particular Montgomery curve over $\mathbb{F}_q$ where $q = {2^{255}-19}$. What I missed or was unable to understand is ...
44 views

### Encryption - How to find $\sigma$?

Alice communicates with Bill using an encryption system of type Feistel. Specifically, each block has a length of 128 bits, the algorithm has 4 rounds and the common secret key of Alice and Bill is ...
41 views

### Key Length vs KeySpace

I am a newbie here, this is my first post. I have searched the forum but I haven't found a clear answer to this. In general. What is the relationship between key length and the keyspace? (if there ...
183 views

### What is the period of a cipher?

For the following explanation of RC4: It is a variable key-size stream cipher with byte-oriented operations. The algorithm is based on the use of a random permutation. Analysis shows that the ...
62 views

### Complexity of attacks on affine cipher

I am interested in the complexity of attacking affine ciphers under the following two scenarios during a Ciphertext only attack during a Chosen Plaintext attack For an alphabet of size $m$, how ...
61 views

### Find a polynomial time algorithm for the following problem

Let $p$ be a prime number and let $c \in \mathbb{Z}_p$ and $e \in (\mathbb{Z}/(p-1))^{\ast}$. Put $c \equiv_p m^e$. Find a polynomial time algorithm that given $p$, $e$, and $c$ will compute $m$. I ...
80 views

### Do all stream ciphers (and AES-128-CTR in particular) produce equal output size as the input size?

I'm particulary interested on knowing if the output of the AES-128-CTR ciphertext is always going to have the same size as the input plaintext, or it could be padded somehow. It seems so from my tests ...
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### Crack RSA with additional information [duplicate]

Suppose $N=3953$, Alice encryption key is $e_A = 337$ and bobs is $e_B=23$. Eve happens to know the corresponding decryption keys, $d_A=3385$ and $d_B=2663$. Can I use this information to find the ...
29 views

### ECIES with AES-GCM

The Elliptic Curve Integrated Encryption Scheme (ECIES) describes how to derive a "temporal" key, encrypt a message (eg. using AES) and creating a MAC. However, from my understanding using AES in GCM ...
91 views

### How many attempts does it take to crack a 32-bit password hash with this scenario?

How many attempts does it take to crack (match) a 32-bit password hash from a database of 4 million password hashes? Correct me if I'm wrong, but to crack a 32-bit password hash would take roughly ...
30 views

### Affine transformation in finite field SubBytes

Can anyone please explain how this computation was done? I picked it up from How are the AES S-Boxes calculated? The affine transformation is as follows. The input bits are multiplied against the ...
132 views

### Given infinite unencrypted and encrypted texts, can I find the algorithm?

Given an infinite amount of both unencrypted and the corresponding encrypted text, would I be able to calculate the algorithm? I am relative new to cryptography and don't know if I would be able to ...
52 views

### Is it necessary to encrypt nonce in cryptographic communication?

Server and client have a pre-shared key K. Assuming that that pre-shared key is safe, so nobody other than server/client can encrypt/decrypt. Client sends a nonce N to server, server then sends back ...
99 views

### What prime lengths are used for RSA?

Let's assume we have an RSA 2048 that was produced by two primes multiplication. What is the digit's difference in those 2 factors? For example one prime is 1024 digits and second one 1024 or, one is ...
67 views

### Equivalent key size between HMAC and AES?

I have seem comparison between AES and RSA, e.g., AES 128 bit key is equivalent to RSA modulus 3072 bits. Is there such comparison between AES key size and HMAC?
90 views

### ECC considered secure in OpenSSL?

this is my first question, please bear with me if it comes across silly. If I openssl ecparam -list_curves on my OpenSSL version (1.0.1f), it spits out the ...
61 views

### Pseudorandom number generators based on hard problems in mathematics

I know that Dual_EC_DRBG's security is based on the ellitpic curve discrete logarithm problem, Micali-Schnorr is based on the difficulty of factorization, and MQ_DRBG is based on multivariate ...
52 views

### How to store and use a Cryptographic Seed in a database [closed]

Companies such as Barclays use cryptographic seeds (for their PINsentry system), RSA do the same for RSA SecurID, but how do they safely secure the seeds in the database. With passwords you just hash ...
67 views

### Questions about updating the secret key of RSA?

I want to update the secret key of RSA. I understand there exists a common modular attack on RSA. Precisely, if adversary knows $(e_1, m^{e_1})$ and $(e_2, m^{e_2})$, where $e_1$ and $e_2$ are the ...
29 views

### Decryption of message in IBE without random oracle using bilinear pairig reg

I find the following IBE scheme from the videos posted and i don't understand the decryption algorithm, will any one please elaborate the 6th step scheme S(λ) : (G, GT , g ,P) <-- ...
70 views

### SHA-512 Length Field - What is it?

If I am using SHA-512 on a message and need to determine the padding field and length field, how do I determine the length field? I think I understand the padding, but not the length field. For ...
138 views

### Alternative sources of random numbers

Considering that algorithmic methods for generating unpredictable streams are hard to come by, I've wondered if any of these potential sources are good for making keys, seeds, and the like: stocks, ...
46 views

### How does the attacker include input before compression and encryption in CRIME?

I have read this article about the CRIME attack against TLS and SPDY. The article says that: What is not yet clear is how the attacker is including their input in the source material before it ...
39 views

### Are there any standard implementation of Goldreich–Goldwasser–Halevi in lattice cryptography?

As you may know GGH is lattice based asymmetric cryptosystem, I'm looking for an implementation of this cryptosystem in Python with details.
43 views

### Requirement for the exponent generation during DH protocol [duplicate]

The setting is classic DH protocol. Alice computes $A = g^a \bmod p$. Alice then sends $A$ to Bob. Then Bob will send $B = g^b \bmod p$ to Alice. Are there any requirements for the values $a$ and ...
40 views

### Why don't very many HTTPS websites supply ownership information in their certs? [migrated]

Why don't very many HTTPS/SSL websites supply identity information in their certs?
56 views

### Crypto++: How to re-generate pseurandom integers in Crypto++

I'm using Crypto++ to implement my protocol to mask a value $y_i$ by a seudorandom value $r_i$ such that $m_i=y_i \cdot r_i$. Since there are many $r_i$'s I want to generate them using PRG and then ...
105 views

### Evaluating Algebraic Complexity of a S-box

While studying the design and the desirable properties of an AES S-box , I came to know that Algebraic Complexity is also an important property of an S-box which is usually considered while evaluating ...
50 views

### Counter Mode (CTR) and mult-CPA

I am not sure if Counter Mode (CTR) encryption is mult-CPA (chosen-plaintext attack) secure or not.
127 views

### How to accurately calculate Unicity Distance for English?

The Unicity Distance for the DES cipher is around $8.6$ characters, and can be calculated using the $U=H(k)/D$ formula, where $D = R - r$, and where $R = 8$ is the number of bits in a byte (ASCII is 7 ...
82 views

### Factoring two RSA modulus with known $|p_1 - p_2| < \ell$

I have two 1024bit RSA modulus $N_1 = p_1q_1$ and $N_2 = p_2q_2$ such that $0 <|p_1 - p_2| < \ell$, and $\ell$ is at most 64bit integer. Can I factorise $N_1$ and $N_2$? What's the answer when ...
202 views

### Anonymous Gravatar Problem

Gravatar is a service that serves avatars for users based on md5(email_address). The hash is embedded on websites, so it's public. One of the problems with this ...