# All Questions

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### ECDSA signature verifiable 1-way transformations

Alice signs a message $m$ with her private key, yielding a signature ($r$,$s$). I want to prove to someone else that I have this signature, but I don't want them to have the knowledge of what ...
85 views

### How to calculate key size of a security algorithm?

There are lots of security algorithms. One of the way to measure security of a cryptography algorithm is to find out its key size. There are many key size of a single algorithm. ECC (Elliptic ...
245 views

### Is it OK to use a data-encryption key for key wrapping, too?

Our industry (area of cheap networked devices) has a standard that defines the usage of keys for both authentication and encryption using EAX mode of AES. This standard does not define key management, ...
32 views

### Breaking the Rabin Signature system with chosen message attack

I heard that we can break the Rabin Signature system using chosen-message attack. I can't find a message to ask for its signature in order to spoof my message M. Any suggestions?
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### Questions about Scyther tool [on hold]

everyone, I want to use Scyther tool to do a project about security protocol analysis but met some problems when I wanted to get familiar with the tool. I used the codes in the Scyther website but ...
20 views

### Progrmaing Language [on hold]

I want to write encryption & decryption programs using ceaser,playfair,vigener,rail fence & monoalphabetic ciphers with c++ language. help me with sites or ideas
196 views

### Where is CFB-MAC defined?

I can find descriptions of using CFB mode to create a MAC and even implementations, but cannot find any standard or papers analyzing its security bounds. Is there a standard for CFB-MAC? Where can I ...
30 views

### Ways to identify mystery ciphers with no information but the code itself? [duplicate]

I recently offered to solve a cipher that was sent to my friend because he couldn't. I'm really having issues with the identification, I've tried a simple Caesar shift, and it came back with nothing. ...
62 views

### Diffie-Hellman key size to symmetric formula?

I've noticed that on every site I checked I kept finding the relationship between D-H key size and symmetric encryption equivalent as a table, like: 384 - 56 768 - 80 1792 - 112 2304 - 128 10753 ...
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### How to convert the 128 bit output of AES_CTR to 32 bit number? [on hold]

I want to run Dieharder test suite on the output of AES_CTR. How should I form the text file consisting of the cipher text obtained from AES_CTR, to be run directly with Dieharder package for linux? ...
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### AES128 Decryption in Objective-C just slightly off

I have been asked to integrate a home-grown CRM system with a 3rd-party data service provider (DSP). The DSP has encrypted the information they are providing. I only have their decryption ...
31 views

### Extracting key bits from linear cryptanalysis equation for SDES

From the linear cryptanalysis of SDES, we get a linear equation consisting the K[1, 3] of the round key 1 and 2. From this how will I retrieve the key bit? How do we solve the linear equation we get ...
72 views

### Convert ciphertexts of one encryption scheme to another without decryption

I want to convert ciphertexts of one encryption scheme to another without decrypting them under the first scheme and then encrypting with the second scheme. For example convert OPE encryption to ...
46 views

### Are these hash function compositions collision resistant?

If a hash function $H$ is collision resistant, are the following two hash functions collision resistant or not? ($||$ is concatenation) $H'(m) = H(H(m)) || H(m)$ $H''(m) = H(m) || H(m)$ My first ...
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### Is it safer to use timestamp in REST authentication?

I am working on a personal project to build a REST authentication system which authenticate clients via three parameters: ...
34 views

### Possible to generate a one time secret which all nodes on the distributed network can know but cannot pre compute

I have a distributed P2P network. Everyday, I want each node to have a secret which is only valid for that day, while each of the other remaining nodes on the network will be able to calculate the ...
605 views

### PRNG taking advantage of very large seed

Can anyone suggest a good (CS)PRNG algorithm that takes advantage of having a very large (ideally arbitrarily large) seed? I'd like to use several kilobytes, perhaps several hundred kilobytes, of ...
32 views

### Why is AES-128 considered secure while RSA needs a 1024-bit size to be considered secure [duplicate]

I got asked this question today and I didn't know the answer, AES-128 is considered secure, the key size is 2^128, so you would need in average 2^127 tries to break the key. Why does RSA need at least ...
369 views

### Why does WPA2-PSK use 4-way handshake instead of 2-way handshake

I don't seem to grasp why is the handshake for PTK in WPA2-PSK 4-way and not 2-way. Isn't it enough to just have these two steps: First party sends Nonce1 to the other party Second party sends to ...
54 views

### What effect does a salt have on attacks against hashes's fundamental properties?

I am interested in analyzing how adding a salt to our hashed passwords affects the three types of attacks we can use. The three types of attacks against hashes are as follows: We have the hashed ...
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### Do most TLS 1.2 implementations express curves in a canonical form when performing EC arithmetic?

Sorry if this is a silly question, but does anyone know if the cryptographic libraries which implement TLS 1.2 for Firefox, Chrome, etc. express a given curve in a canonical form (i.e. one of ...
2k views

### Webcam random number generator

I have a question about random number generators. I have read from a real random number generator, based on a webcam ("randcam"). My problem is, that I do not really understand how the generation of ...
27 views

### I have a challenge for anyone willing [on hold]

I am incredibly new to the world of cryptography, and perhaps this isn't quite the best site to post on, but I was hoping I could gain insight from some smart minds on my method. I encrypted an ...
37 views

### Caculated time One Point Multiplication with double and method

I am using double and add method for point multiplication in affine coordinates. How we compute 1PM in double and method? Di Wang said one point multiplication consists of repeated addition and ...
48 views

### How to design a deliberately weak PRNG for experimentation?

I'm looking for a PRNG that is deliberately weak, that is, follows a set of rules stochasticly. For example: Encounters a set of bits that is a multiple of X, starts exhibiting bias, or starts to ...
52 views

### How can we define division operation by using Fully homomorphic encryption

Last fews months, I'm working with homomorphic encryption. Now I am dealing with some computational problems with integers or real-numbers (like arithmetic mean, standard deviation) where division is ...
18 views

### Vulnerabilities in specifying the hash algorithm used for signature verification on a per-message basis

Let's say that I have a 4096-bit RSA key and when I sign data, I typically use SHA-512. As far as I understand it, the hash algorithm used to sign/verify a message is specified in the message. If a ...
25 views

### Gaussian distribution in lattices

In many lattice based cryptosystems, Gaussian distribution is used. Can you explain why only Gaussian distribution is preferred?
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### How are the attributes of a user authenticated in attribute-based encryption?

It seems that the papers I am reading do not talk much about this point. That is how the attributes of a user are authenticated in ABE system. To my understanding, there is an attribute authority ...
23 views

### How is the root certificate transmitted to pc?

i understand that the purpose of root certificates and CA's is to ensure that the communication parties are who they say they are. But how is the root certificate acquired? Is it not possible that ...
53 views

### Single-algorithm authenticated encryption

Are there any authenticated encryption methods that combine encryption and authentication, rather than useing a separate cipher and MAC?
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### How Diffie-Hellman authentication works? [duplicate]

There are a lot of good videos on a simple Diffie-Hellman in the internet but unfortunately that is susceptible to the MITM attack. I understand how with DH the two parties are able to calculate a ...
47 views

### Data integrity using steganographic methods

I am looking for a lightweight and fast (almost real time) data integrity checker for a very time critical application. Is it possible to provide data integrity using a steganographic method, lets say ...
79 views

### How does non-linearity (S-box) add security to AES?

I'm trying to understand how AES guarentees security. One of the named points on the web is that AES uses a non-linear step (the SubBytes step). But how exactly does the Rijndael key schedule add ...
13 views

### Attribute based access control and role based, online bookstore example

I am asked to answer a question that says: One online book-store wants to grand access to clients regarding their subscription. There are 3 types of subscriptions A , B and C. Customers get access ...
17 views

### What does the probability subscript mean in Shannon's secrecy definition?

Shannon's secrecy can be defined as: $$P_M (M=m) = P_{SK,M}(M=m|E(SK,m)=c)$$ What does $P_M$ means? (same question for $P_{SK,M}$) I know that is the probability space M, M being the messages; I do ...
130 views

### Security of a parallelizable block cipher mode

This is the scheme of a parallelizable block cipher mode of operation: $IV$ is the initialization vector. $BN$ is the zero-based index number of a block in a stream of data. $BT$ is the tweak that ...
4k views

### Why do we need Diffie Hellman?

Diffie–Hellman offers secure key exchange only if sides are authenticated. For authentication, sides are using public/private key. So if side A knows the public key of the side B, then A can simply ...
42 views

### TLS RSA Certificate with Elliptic Curve Negotiation

When I look at Google's Public Key in Firefox I get PKCS #1 SHA-256 With RSA Encryption Yet according to SSL Labs Google has EC 256 bits / SHA256withRSA and supports ...
32 views

### Fast hash for 64-bit inputs

I am looking for a fast hash (~few machine instructions) to be used for hash tables with 64-bit keys. I can't use SipHash as the hash function will be inlined in too many places and so the code size ...
23 views

### Determining collision resistance of a function?

I am having trouble trying to understand if the function is collision resistant. As I understand it, preimage resistance means that it is hard for an adversary to find two messages that produce the ...
44 views

### construction of division polynomials

I'm not sure if this is the right place for my question.... I'm trying to understand the construction of the division polynomials used in the schoof algorithm. I firstly followed the report of ...
20 views

### why OCB over AES for authentication encryption? [on hold]

why should anyone use OCB-offset code book over AES algorithm?
33 views

### What is the time requirement for pairing computation and modular exponentiation?

I want to design a cryptographic protocol for encrypted search without pairing. I have seen some papers for protocols without pairing. How would I compare pairing computation and modular operations?
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### Multi Authority Attribute Based Encryption Library

Anyone aware of a library that has MA-ABE implemented in any language preferably python? P/S - I hope this is the right place to ask this. Apologies if not, then a redirect will be appreciated
54 views

### Steganographic embedding of an RSA-encrypted message into an image

The goal is to combine the RSA encryption system with the LSB steganography system in a BMP image. Since every pixel of the image is an integer between 0 and 255, if we choose $p$ and $q$ such that \$N ...
15 views

### How do substution-permutation networks work?

I understand what's going on in higher level. But i don't understand what's really going on in page 3 and 4 of this slide. Specifically, How S0 and S1 is used? What goes in what goes out? How ...
65 views

### Is reusing keys for CBC and CBC-MAC secure when using encrypt-then-MAC?

I know reusing keys is a bad idea, especially for CBC and CBC-MAC, but the example for why on Wikipedia seemed to use encrypt-and-MAC. It seems obvious that the last block of encryption will be equal ...
25 views

### Have ciphertext and key but need to figure out encryption method

So I have a block cipher (I think) that I need to break. I have the ciphertext and the key, but not the method of encryption, and was wondering if anyone could help me figure that out? The key is a 9 ...
22 views

### Need CryptDeriveKey AES implementation in C#

I am integrating with 3rd party software that uses AES 128 encryption. I know this is not ideal, but the choice of encryption is up to the 3rd party software. I am using C#. My problem is in deriving ...

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