# All Questions

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### Avalanche effect sample size

With a fixed key size: how do I calculate how many different keys and texts I have to test for an statistics study? I will encrypt that samples and see how many bites has changed from the inputed ...
7 views

### Simple way to sha256 using CUDA? [on hold]

I'm trying to do some hashing acceleration, but I'm not sure where to start. there's not really any open source simple implementations of sha256 for CUDA. Could give me a step in the right direction ...
40 views

### Are there full cycle cryptographic/one-way hash primitives?

I'm looking for behavior similiar to that of LCGs, (i.e. input and output sizes are same). Full cycle of $2^{32}$ different inputs generates full cycle of $2^{32}$ different outputs, distribution of ...
20 views

### Inverting One-Way Functions

One of the conditions that a one-way function has to satisfy is the following: $$Pr[A(f(x))\in f^{-1}(f(x))] \leq negl(n)$$ Now, suppose that we have the following function that's not one way: ...
39 views

### Encrypt hash using hash of hash?

I wonder what is wrong with this scheme for authentication. Server sends random challenge, C Client returns (C, B(P)) encrypted in H(B(P)) where B(P) is high work factor salted hash of the user ...
22 views

### Hash regex for malware recognition [on hold]

I'm looking to store two types of hashes for recognizing blacklisted code. These are the FireEye "import hash" (or imphash) and the ssdeep "fuzzy hash". Is there a regex (or formal documentation) I ...
12 views

### In which ways one can prevent key substitution attack

For Diffie-Hellman two parties need to exchange their public keys. Which ways are known to prevent key substitution at this stage? Those I know of so far: Certificate Authority (single third ...
24 views

### What is the notion of an interactive assumption?

In this paper: Sequential Aggregate Signatures with Short Public Keys: Design, Analysis and Implementation Studies the authors sell the paper as the first who propose Aggregate signatures without ...
13 views

### Implementing Oblivious Transfer protocols [on hold]

I have to implement a series of Oblivious Transfer and Oblivious Transfer Extension protocols for my MSc thesis. My goal is to implement the various protocols and compare them in terms of speed and ...
13 views

I am using the javax.crypto.Cipher in Java to do AES/CBC/PKCS5Padding encryption. What I am observing is that, if you try to encrypt a Plaintext with no padding, PKCS5 adds another entire block just ...
68 views

### How to protect key in software

I need to encrypt/decrypt data from my software by AES, the problem is how to make the aes key secure, there is no HSM, should I hard code the key in my code? it seems that hacker can read the key ...
23 views

### Secret only known on concencus

Does a method exist where a secret is generated so that is is unknown until 3 or more people (predetermined) reach concencus that it should be revealed?
54 views

### Is there a cryptographic protocol that let's me prove someone has a large binary?

I'm working on a system that has a P2P component. When an individual downloads a binary and decides to mirror it, they advertise themselves in a providers set. The binaries can range from 1-1000MB. I ...
64 views

### Inverting RSA function

I am in high school and I am writing a paper on RSA. I want to show that low values of the public key exponent can make it easy to 'invert' the function so that the encrypted message can be recovered. ...
32 views

### Construct points with the same discrete logarithm

Assume we have an elliptic curve $E$ with a Tate (or Ate,...) pairing $G_1 \times G_2 \mapsto G_T$ Now the task is to find $g_1, g_1' \in G_1$ and $g_2, g_2' \in G_2$ such that the discrete logarithm ...
61 views

### How does perfect hash function works?

According to wikipedia, a perfect hash function is a hash function that uses algorithms that has a certain random aspect to their logic. It is suppose to be collision-free. However due to the pigeon ...
41 views

### The example of Wikipedia on steganography doesn't work

I was reading some stuff on steganography. There is an example on the wikipedia page : However, I tried many software to get the hidden image, but no one worked. Is there anything wrong about ...
55 views

### Creating own ciphertext after a padding oracle attack?

I've written a script that breaks a cipher text based on a padding oracle for an assignment, but was wondering how I would continue on to create my own cipher text with any plain text I desired? ...
66 views

### Hypothetical encryption technique, is it secure?

This to me, sounds like a great idea, but with all rosy-tinted ideas it needs some grounding in reality. Here are the steps of the hypothetical system (with the hypothetical part highlighted): User ...
42 views

### Is it worth hiding an AES encrypted text string in a PNG image for better security?

I need advice as to whether it is worth the extra "security" and processing of an AES encrypted text string to be hidden in a PNG image as opposed to an AES encrypted text string to be saved in a ...
30 views

### X509 certificates: Two Algorithm Identifiers?

I'm wondering why there are two Algorithm Identifiers in a X509 certificate. One is in the "to be signed" part and the other one is at the end right before the actual signature. Are they used for the ...
2k views

### What is a “freestart collision”?

In their work on SHA-1 collisions Stevens et al show that they are able to generate "freestart collisions" on SHA-1. They say: Even though freestart collisions do not directly lead to actual ...
35 views

### For hardware encryptions, is it possible to know the key by analysing the hardware?

For example, Square reader uses hardware encryptions when swiping credit cards. Is it possible to know the key that is used by the hardware encryption cipher by analysing the hardware circuitries? ...
31 views

### encrypting simple letters homemade algorithm [on hold]

I'm new to this community but wanted to ask if you guys could find any flaws in my algorith. Basically my whole algorith is based upon the following table: ...
37 views

### Computing the padding of MD5

So I'm reading this question to learn more about length extension attack, and I want to make sure I understand the basics of padding. It says in the post that given the hash and the length of the ...
35 views

### Hash functions vs. keyed hash functions in the context of private key generation

I'm designing a key distribution mechanism and have thought of using a securely generated/acquired private key as a seed for a sequence of private keys to be distributed to a number of users using a ...
56 views

### Wanted: Simple ring signature example

I spent all day trying to figure ring signature schemes out but apparently I wasted time. I read the original ring signature paper (Rivest's How to leak a secret). I'm having numerous problems. Let's ...
25 views

### For the scrypt HMAC storage format, why run the input of the hash and the hash itself into the HMAC

Generally if the body is hashed, why provide the body and the hash as input into the HMAC. Instead wouldn't the same security be achieved by hashing the body and providing only the hash as input into ...
17 views

### Security of SRP-6a against impersonating server choosing small/wrong N

I'm looking at an implementation of SRP (Secure Remote Password) that essentially follows the Stanford documentation (http://srp.stanford.edu/design.html). I'm worried about one aspect though: In the ...
46 views

### How to derive a key from an existing AES key?

Currently, the code I am staring at uses the CKM_EXTRACT_KEY_FROM_KEY mechanism. That has been disabled in our hardware module, so I need a different mechanism to ...
79 views

### How to show something is not a one-way function?

Lets say that $f:\{0,1\}^* \to \{0,1\}^*$ is a strong one way function. Let $h(x)=f(x)||x_n$ where $x_n$ is the $n$th bit of $x$. I understand that $h$ will not be a strong one-way function. However, ...
44 views

### Binary equation with encryption

I'm trying to test the ring signature scheme proposed by Rivest Shamir and Tauman in the famous paper "How to leak a secret". One of the step consist in 4) the signer solves the following ring ...
18 views

### Profile Complexity LFSR

I try to understand how Complexity of an LSFR calculated. For example I have a bit sequence 110101 and it's profile 1 1 2 2 3 3. Is there any easy way in order to produce the profile?
19 views

### MD5 SSL Collision Attack

I want to create fake certificate for test purposes. I have read about the http://marc-stevens.nl/p/hashclash/index.php project but I am unable to understand the two files that I have to put as input ...
36 views

### special class of lattices in lattice based cryptography

A special case of lattices in lattice cryptography is that of q-ary lattices. A q-ary lattice L is defined as that in which any vector which consists of multiples of some scalar q is in ...
71 views

### Are there MD5 collisions for inputs of different length?

There are many examples of MD5 collisions (some of them can be found here Are there two known strings which have the same MD5 hash value?). But as far as I know two inputs should have the same length ...
72 views

### Is Diffie-Hellman Secure or backdoored? [on hold]

I'm a noob cryptography. The Diffie-Hellman algorithm looks extremely straightforward and simple, however, is it backdoored by the NSA?
39 views

### Is there a correct way to generate a symmetric key?

Looking in some cryptographic algorithms, I've realized that: The way the plain text is encrypted/decrypted is always specified, but what about the key? Every paper I've seen describing the algorithm ...
32 views

### Best way to implement secure client/server communication in Python

For a college programming assignment I have to implement a secure communication protocol between a server and one or more clients. Upon instantiation of the server program, a file is generated, call ...
63 views

### Real-world example of AES-GCM?

I'm having a lot of trouble trying to understand how to implement AES-GCM. My usecase: Person A sent me a file with a gauranteed unique name. I want to be assured it was from person A, and that no ...
78 views

### How to find the value of a vector modulo a basis in lattice-based cryptography

In Gentry's paper on fully homomorphic encryption using ideal lattices, he finds the values of vectors modulo a certain basis. For instance: $\psi \leftarrow \psi' \mod B$ Taken from page 69 of ...
91 views

### How have MD5 constants been determined?

For instance, the per round shift amounts, ...
26 views

### ABE Attributes Based Encryption

I have a question . How the system know the attributes of the users to be after that as a public key in ABE?
36 views

### Who knows Kryptnostic? [on hold]

Does anyone know the company kryptnostic [https://www.kryptnostic.com]? They claim to have a real world fully homomorphic encrytion solution.
17 views

### assessment framework for cryptography algorithm [on hold]

One of my lecturers at the university asking me to do a research on creating a framework to evaluate any cryptography algorithm . if you have any idea what should I consider/ put inn the framework ...
16 views

### What is the proper way to delete a file which had secrets in it? [on hold]

Keep in mind that nowadays, on most UNIX systems, filesystems are journalized. So the shred command does not work, for example.
87 views

### SHA-256 “almost unique”?

I have seen numerous references on the internet of people describing SHA-256 as generating an "almost unique" hash. Exhibit A. there are more. Is there some mathematical basis to the almost ...
45 views

### How to break a columnar transposition cipher?

I'm currently studying for a cryptography exam. I've been given ciphertext that has been encrypted by a columnar transposition cipher. I've been given no shift key length or key word, the only thing I ...