# All Questions

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### Are there any long term RC4 bias based exploits?

The RC4 cipher possibly exhibits low level bias in it's long run PRNG keystream. I'm specifically excluding short term bias attacks which I'm defining as outputs < 1024 bytes. Are there any real ...
78 views

### Checking the integrity of RSA public key

Let's say I need to verify a digital signature and the public key is stored in untrusted storage which I need to fetch before I verify the digital signature. However, I can store the cryptographic ...
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### How can I factorize a 106 digits number in two prime factors?

I have this large number: 1728098743723095094470726818328193358068864405124007684733613106475812450278961107574624070107782941006379 which is the multiplication of two unknown large prime numbers. I ...
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### Probabilistic RSA, IND CPA

Suppose we have classic RSA scheme. Let $n=pq$, $e$ public, $d$ secret. Then message(M), not empty(not 0), is encrypted by choosing random $r$ and computing $A=(r^e)^e$ and $B=(Mr)^e$ $(A,B)$ is ...
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### Comparing messages given only the ciphertext

Under RSA protocol I was wondering how a message sent could be verified under the following scenario Alice has a private (encryption key) and public key (decryption key) If Bob sends Alice ...
21 views

### How to find the secret message from the code

Intercepted the following encrypted message 1964337423618695353 RSA public key (n,e) = (7957006798137453877, 47493) When decrypted, the secret message written in base 10 can be converted into 8 ...
259 views

### How does constant-time comparison work?

libsodium has a method for comparing two byte sequences in constant time. Is the idea here to simply avoid early-out if a difference in the data is detected? When I first heard of such a thing I ...
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### Implementing AES-CBC (Matasano Crypto Challenge 10)

I am currently doing the Matasano Crypto Challenge to learn a bit about cryptography. In that specific challenge one had to implement AES in CBC mode. I did that and verified that encryption and ...
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### Continuous stream of strong randomness from limited entropy?

I need a continuous (infinite) strong random generator, but I've only got limited entropy as seed. I know there's already a contradiction there, but I'm looking for a practical approach. Suppose I ...
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### Is libsodium the best to use for two way encryption between a mobile app and an api

I'm building a mobile application that sends some personal information over a network to an API. I want to encrypt the details before sending it to the API, and also encrypt the data the API is ...
25 views

### Benchmark for new cryptographic algorithms [on hold]

I have to compute the number of cycle per bytes for some new cryptographic algorithms. The research I have done so far leads me to the fact that the only way to compute the cpb is to perform a lot of ...
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### programming a sniffer for AES GCM with gcrypt

I want to write a sniffer that can read AES-GCM communication using the gcrypt lib I can see in the manual that for encryption there is an additional 2 methods (for AEAD) but what about decryption ? ...
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### Finding collisions for the DES F-function

It's known that for a given subkey, the F-function of the DES is not injective (see Is the DES F-function injective for a given subkey?). I am interested in efficiently finding collisions for this ...
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### How much entropy is generated by 'random' human keystrokes?

I'm wondering about using human input as an entropy generator. We all know humans are terrible at making up random numbers or keys or passwords. But what if we let a user 'randomly' type in some ...
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### Why does GPG ciphertext length differ with fixed plaintext length?

We are using gpg2 and base64 commands with 2048R algorithm. Input: encrypted 36 bytes of input text data with fixed length Current problem: if I run gpg command ...
21 views

### What is the security parameter in “KAC” key generation? [duplicate]

I am trying to implement key generation from the paper Key-Aggregate Cryptosystem for Scalable Data Sharing in Cloud Storage. In the paper, the first step in key generation is a setup phase state as ...
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### How to prove secret value in Pedersen commitment is equal to secret value in Fujisaki commitment?

We have Pedersen commitment C to the secret value x, and Fujisake commitment C' to the secret value x. How can we make a zero-knowledge proof of equality for x value in the commitments?
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### What Does This Symbol Mean? (Hardcore Predicates for One-Way Functions)

I am studying Pseudorandom Number Generators and when reading the discussion on One-Way Functions and Hardcore Predicates, I came upon this equation. $$b(x,r)=\displaystyle \bigoplus_jx_jr_j$$ I ...
76 views

### Are there comprehensive alternatives to RSA?

If we wished to, is there a comprehensive alternative to RSA? I say comprehensive as I wonder if there is one which does both encryption and digital signature like RSA? If not, simply what ...
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### How do a user register his verifier at host in SRP(Secure Remote Password) protocol?

I read RFC 2945, 5054 decribed about SRP. But there is no coment about registraion... How can i know the method of registration of SRP. plz, introduce some paper, or give me some advice.
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### How to force an adversary to call a certain oracle?

Consider there is a protocol in real world, which uses a random oracle $\mathcal{H}$. In the ideal world, after the calling of $\mathcal{H}$ by some parties, intuitively I want the simulator gets some ...
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### Cryptographic operations for NISTP256 can be implemented using montgomery method?

I need to implement cryptographic operations starting with the curve NISTP256. I have been told to implement it using Montgomery method. I read a pfd from ...
33 views

### May I use Random Oracle for Inversed Look-up?

Consider there is a protocol in real world calling a random oracle $\mathcal{H}$ for a priavte input $k$. Then in the ideal world, after the calling of $r \leftarrow \mathcal{H}(k)$ by a honest party, ...
1k views

### RSA & DH at risk due to math advances, will this eventually affect elliptic curves too?

I was looking into the predictions by some researchers that RSA and Diffie-Hellman may not be secure in the next few years due to advances in math and being able to calculate the discrete logarithm ...
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### Why does the time complexity of RSA encryption and decryption depend on the size of the modulus?

I would think that the time complexity would depend on the exponent, not the number of bits in the modulus. For example, if the exponent were 5, using the "naive" method, we would perform 5 ...
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### Is the RC4 keystream random or not?

I have cause to use the PRNG half of RC4, but am seriously confused as to the randomness of its output. (Only the PRNG half.) On the one hand, there is a large body of literature finding ever ...
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### What is the difference between LCG and Affine cipher?

What is the difference between LCG and Affine cipher? More specific: What are they used for, and what are the structural differences between them?
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### Generate non-random EC private key with openssl [migrated]

I'm trying to generate a deterministic private key for the EC secp384r1using the Unix command openssl. What I mean is, instead ...
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### More rounds after AES related key attack?

In his blog Schneier discusses that there is a new related key attack on 10 rounds of AES-256 "Another attack can break a 10 round version of AES-256 in 245 time, but it uses a stronger type of ...
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### Implementation specific differences between RDRAND and RDSEED

I've read Intel's The Difference Between RDRAND and RDSEED, but I have some open questions that are specific to usage in an application. I work with Wei Dai's Crypto++, which is a C++ class library of ...
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### S boxes in Blowfish

I know how the s-boxes in blowfish are initialized, but how is the output sorted, I mean which bit from the input goes where in the box ? and what do mean they have 256 entries if they are 32-bit ...
34 views

### Big block cipher as memory-hard function

I'm wondering, if something like block cipher with big block size is memory-hard function? All memory-hard key derivation functions I've seen look more complex than that, which made me question my ...
26 views

### bank websites using AES_256_CBC vs AES_128_GCM/CBC [duplicate]

Hello i have just recently started learning about cryptography, so i was doing some little research on what kind of encryption techniques and modes that were used in bank web pages. I have noticed ...
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### Muchomor cipher

I've been given a task to research and possibly implement so called 'Muchomor' cipher. Has anybody ever heard of this cipher? I've found only one article about it and it was in Russian. I'm quite ...
82 views

### RSA: must $d$ be an integer?

I am only taking baby steps in RSA. If $p=11$, $q=7$ and $e=3$, $$\phi(n) = 10*6 = 60$$ Then: $$d = (2 (\phi(n)) + 1 ) / 3 = 121/3$$ Should $d$ be kept as a non-integer or is such a $d$ invalid? ...
35 views

### Reusing same source for single-source randomness extractor

Let $ext$ be a single-source randomness extractor which takes a $d$-bit seed and a $n$-bit source as input and produces a $m$-bit output. Suppose we have a source $X$ with min-entropy $k$. Is it ...
31 views

### Rogue CA Certificate MD5 Collision Control

Papers from Marc Stevens et al show that X509 certificates that rely on MD5 signatures can break the assumed security model, that is, it allows for a forged certificate to have the same signature as a ...
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### paradox on fully homomorphic equality checking

Imagine, a client encrypts a corpus of data (say documents of text) with the public key of a Fully Homomorphic Encryption scheme (FHE) and outsources the data to an untrusted server.Now the client ...
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### Problem reproducing AES results

First of all, I just implemented AES because I wanted to understand how it works and as a challenge to see if I could do it and I won't use to encrypt anything important, ever. The (German) Wikipedia ...
32 views

### Using HMAC as a nonce with AES-CTR encrypt-and-MAC

Suppose I use the following encrypt-and-MAC construction: $E(k_1, k_2, n, m) = E_\text{AES256-CTR}(k_1, n, m) \| \text{HMAC-SHA256}(k_2, m)$, where: $k_1$ and $k_2$ are 256-bit keys $n$ ...
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### RSA: Most significant key bit always 1?

Is it possible to say that the most significant bit of an RSA private exponent is always 1? Wouldn't that weaken the key strength by exactly that one bit? I refer to the paper "Timing Attack: What ...
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### How can there be AES-256-GCM, when GCM is defined for 128-sized blocks?

In both node.js and OpenSSL, I am seeing cipher "aes-256-gcm". However, in NIST Special Publication 800-38D, that defines GCM, I am reading: The underlying block cipher shall be approved, the ...
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### Bitlocker on windows 10 [on hold]

How much does using Bitlocker on windows 10 slows the file processing on the drive? (I am planning on activating bitlocker on my C drive where my OS is present) and is it recommended to use bitlocker ...
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### Probabilistic Disjoint Verification [on hold]

Let $r_1,...,r_n$ be routers in the same organization, and let $h_{CO}$ be the least significant 32 bits of the hash of data packet $CO$. Router $r_i$ verifies $CO$ if $h_{CO} ≡ i \bmod n$. Assuming ...
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### Fully homomorphic encryption arbitrary functions formulation

I am currently studying the interesting field of homomorphic encryption. I read that from a fully homomorphic encryption function that supports both addition and multiplication you can perform any ...
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### Unbreakable encryption [duplicate]

I am a newbie, I know that I must be wrong, but I need a good explanation. How is it possible to break a cryptographic algorithm created by me, when only I know the algorithm and the key for ...
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### Which hash function is usually used in RSA?

I know there are several available, however I can't seem to find whether there is one standard one or not. I think I understand the process of digital signatures, just wondering which has function is ...
61 views

### Cryptographic hash with ability to ignore specific bits based on a hidden pattern?

I'm looking to use password-style hashing to validate an environment, where some parts may be irrelevant. For example: ...
An NTRU public key is generated essentially by multiplying the inverse of a polynomial $f$ by a polynomial $g$. The polynomial $f$ is the private key; $g$ is discarded. My question is: Is it insecure ...