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# Questions tagged [implementation]

Implementing a cipher or protocol is the process of taking it from its mathematical or algorithmic description and producing a working version, often in computer software or hardware. This tag should be used for any question discussing the various potential considerations and pitfalls of this process, for example padding.

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### Non interactive Zero Knowledge Proof for Satisfiability of Pairing Product Equations

In the paper "Simulation-Sound NIZK Proofs for a Practical Language and Constant Size Group Signatures" from Groth, the section 6 describes a NIZK proof for pairing product equations. I only know ...
372 views

### Is there a consensus on what text encoding to use when hashing a string?

Let's suppose we are hashing a string input from the user via keyboard. A string can be interpreted in many different text encodings (ANSI, UTF-8, UTF-16 and many others). Based on what encoding is ...
374 views

### How to Calculate GE of Sbox?

How to count Gate Equivalent (GE) of Sbox used in block Cipher. For example how much area does the Sbox of Block Cipher Prince take? And How is it calculated?
887 views

### Why do algebraic proofs apply to cryptography?

How do we know that the number theoretic and algebraic results used in cryptography provide a perfect model for the behavior of integers as implemented in computers? Does there exist a bijection ...
353 views

### Right way to hash elliptic curve points into finite field

I would like to know how I can implement several hash functions : $H_1:\{0,1\}^* \rightarrow P$ with $P \in E(\mathbb{F}_q)$ and $H_2:P \rightarrow \mathbb{Z_q}^*$ And others where the ...
62 views

### Can you create asymmetrical encryption algorithm from symmetrical, without knowing how the algorithm works?

Let's imagine that we have some symmetrical encryption algorithm, that has only two functions: Encrypt(Data, Key) and ...
830 views

### Decode & Verify Base64urlUInt-encoded RS256 Public Key from Google

According to Google, to access the id_token it sends along with Access Tokens (for accessing their API), you must first validate the token using the RS256 Public Key available from this page. The ...
72 views

### Sigma protocol compiler?

Is there a well maintained, preferably documented, Sigma protocols compiler library? i.e. takes an abstraction of statements to prove, and outputs a cryptographic protocol between verifier and prover? ...
533 views

### ECDH over secp256k1 implementation

I'm using ECDH over secp256k1 in multiple languages, and I saw something a little weird in the rust library I use. After the point multiplication it changes y to <...
193 views

### UDP and AES with C++

I'm implementing different applications that will use UDP to exchange real-time data, thus a low impact on performance is very important. This system will not be connected to the Internet so I just ...
70 views

### How is pipelined DES different from sequential DES?

I implemented DES Coder in VHDL using ISE IDE by Xilinx in sequential architecture which was pretty easy and straightforward. Now my task is to do the same using pipelined architecture so that the ...
111 views

### Crypto implementations bits and bytes

Reading many papers in the homomorphic encryption domain and in cryptography, a lot of schemes operate on bits as 1 and 0. If I wanted to implement a scheme, for example, Gentry's FHE, would I have ...
84 views

### Implementation of ECC operations in BMR

I want to implement computing ECC operations(i.e multiplication) in BMR scheme (secure Multi-party computation) What is the best way to do it? I found Fairplay MPC - to allow BMR computation through ...
413 views

### Implementation details of the π step of the Keccak round function

In the official Keccak implementation overview, there is a section discussing different ways to organise the internal Keccak-f state -- namely section 1.2, Bit and byte numbering conventions -- and at ...
175 views

### How to thwart a cleartext message's size?

Here is a question I don't find addressed in my cryptography books: let's say Alice want to send Bob a message of length N. what is the proper way for Alice to hide N? I am thinking Alice should do ...
128 views

### Fermat's FFT based large integer multiplication

I was going through the documentation of GMP (https://gmplib.org/gmp-man-6.1.2.pdf), specially section 15.1.6 where they refer to the use of Fermat's style FFT. I tried to follow the reference but ...
44 views

### Does storing plain data length leak essential information about the cryptographic scheme?

Consider the function below: ...
388 views

### Wrong Miller's Weil Pairing implementation?

I tried to implement the Miller's Weil Pairing algorithm in python using the book "An introduction to mathematical cryptography" by Hoffstein, Pipher and Silverman. I tried my code with the example ...
185 views

### Why does TWINKLE use light instead of current?

TWINKLE is a device devised by Adi Shamir to optimize the sieving step of GNFS. It consists of a cylinder, at the bottom of which are LEDs corresponding to factor base primes which blink with ...
373 views

### How are multiple iterations of SHA-256 handled for longer inputs?

I wrote a python program to perform the SHA-256 function. It works just fine until I try to hash longer strings. If I hash (in HEX) ...
813 views

### Varying ECDH key output on different ECC implementations on the secp256k1 curve

Like the title says, I have used several implementations of ECDH, and I have found a discrepancy with libraries that wrap ...
64 views

### Using XL Algorithm to solve overdetermined systems, simple example required

Can someone give a small example of how the XL algorithm is used to solve an overdetermined system, with numbers and variables along with the steps if possible as apposed to just a general case? This ...
68 views

### How to compute this equation $(g^k)^\alpha\bmod p$

I have a question about implementation. How is an operation like this implemented? $$(g^k)^\alpha\bmod p$$ With all $g$, $k$, and $\alpha$ being large numbers. The thing that I find tricky is that ...
182 views

### at rest encrypton question from someone who knows nothing

this forum is way above me and the members here are far, far smarter than I am, so this probaby isn't the place to ask such a simple question, but whatever. All I wanted to ask is for at rest ...
299 views

### A Lightweight Matrix Suggestion for MixColumns State of AES

We know that the matrix in the MixColumns state of AES is the circulant MDS matrix $C=circ(2,3,1,1)$ which is defined over $GF(2^8)$ with the irreducible polynomial $f=x^{8}+x^{4}+x^{3}+x+1$. Let we ...
150 views

### Lattices with hidden short vectors and an algorithm for a special case of the SVP

For the purpose of testing algorithms for lattice basis reduction or finding short vectors, it would be useful to have examples of lattices where short vectors are hidden, that is, a nontrivial ...
165 views

### What steps are needed for fully homomorphic encryption? [closed]

In my project work, I want to encrypt the keywords extracted from certain documents by using fully homomorphic encryption. What are the algorithmic steps to perform fully homomorphic encryption on ...
192 views

### Is streaming API to ChaCha20-Poly1305 possible or recommended against?

None of the implementations of ChaCha20-Poly1305 AEAD scheme I've seen so far provide a streaming API. Instead, ChaCha20-Poly1305 is presented as an inseparable combination, closely adhering to the ...
315 views

### Can duplication of encrypted characters lead to a weakness in RSA?

Of course, I know RSA is to widely used and tested to have any legitimate threats, but I still am confused by this. I have been trying to implement C++ (in a effort to learn how it works, not to be ...
88 views

### Implications of TLS-SRP client with improper N validation?

During development of a client side application of TLS-SRP, i noticed a bug that allows an attacker spoofing as the server to send custom, but non-arbitrary $N$ values, with the client accepting them. ...
421 views

### Does a conditional statement depending on a round number introduce timing attack problems?

In a cryptographic implementation I’m playing with, there’s a round function which includes a conditional if statement. Stripping the superfluous stuff, the C ...
314 views

### Cache Timing Attack SHA-3

I’ve been tinkering with SHA-3 for a little bit, and I have some questions regarding the applicability of cache timing attacks on this particular hash function. The two sub functions that I believe ...
539 views

### Is it possible to attack an SHA-256 hash seeded with PHP’s mt_rand function?

Is it possible to attack this construction if the attacker only knows the hash? ...
417 views

### Security of Carter-Wegman polynomial authenticators, and their concatenation?

Carter-Wegman polynomial authenticators For a given finite field $(\mathbb F,+,\times)$ of $f$ elements, define a Carter-Wegman polynomial authenticator for a message $M=m_1\|m_2\|\dots\|m_l$ of $l$ ...
137 views

### Multiple XML files and known-plaintext attack

I have created an app which collects data in sets which may contain up to 20000 XML files of an average size of about 5 KB, and all with the same header and XML structure, so that only the data they ...
3k views

### How to use Libsodium encryption (in PHP) in the most secure possible way?

In a PHP project in which fool-proof encryption is fundamental, I'm using the Libsodium library. Hope you guys can shine some light on the following questions. For all of the following functions, it ...
193 views

### How does the nonlinear function of KeeLoq work?

I want to know how the nonlinear function of KeeLoq works. Here at Wikipedia it says that: The NLFSR feedback function is 0x3A5C742E I understand that ...
250 views

### OpenSSH_7.4 Encryption Config [closed]

I have noticed that recent versions of OpenSSH allows the reporting of capabilities by using ssh -Q . The last time I really looked at my SSH setup was a couple of years ago (stribika) -- but I have ...
448 views

### Is it safe to store both the AES-related data and the PBKDF2-related data (except passwords) in one file?

Assume an "encrypted data package" file format which includes the following data PBKDF2 algorithm salt rounds keylen AES algorithm & mode IV ciphertext where the PBKDF2 salt and AES IV are ...
421 views

### Need of Image Encryption [closed]

Question is simple yet confusing, why there is the need for image encryption. How text encryption is different from image encryption if using same technique like AES, DES, Chaotic algorithm. If the ...
3k views

### How do you get the original salt after it's been hashed to the user's password in the database?

I'm researching how to do salt and hashing. I'll be using SHA256. Here is what I found: To Store a Password Generate a long random salt using a CSPRNG. Prepend the salt to the password ...
600 views

### How are Elliptic Curve private and public keys actually used to encrypt or sign data?

I've read article after article about curve parameters, generator points, the dot operation, and how you dot the generator point priv times to get the ...
1k views

### Why is AES encryption decryption not platform agnostic?

We work on C++ code which compiles on Windows and Linux. I have been told that AES encryption/decryption is platform dependent. Is it true? If so, why is it OS dependent?
422 views

### Do people not care about side channel resistance?

Recently, I have been browsing a lot through libraries that implementing Shamir secret sharing. I see a lot of code that implements this cryptographic algorithm without any side channel (timing/branch/...
156 views

### How to implement a hash function $H \colon \{0,1\}^* \to \mathbb{Z}_p^*$?

I would like to implement a hash function $H \colon \{0,1\}^* \to \mathbb{Z}_p^*$ such that $p$ is a prime number and $\log_2(p) > 256$. I am wondering if it is a good idea to use the hash function ...
389 views

### How to interpret the article claiming NIST P-256 curve to be unsafe?

Here: http://safecurves.cr.yp.to/ , I read that the NIST P-256 elliptic-curve is not safe. The article lists several aspects (off-curve point, side-channel, etc.) where implementing P256 can fail the ...
79 views

### Does this ECIES scheme make MAC redundant?

I've implemented ECIES (see the below pseudo-Python). ...
337 views

### Size and usage of lookup table in cryptographic schemes

I would like to understand the typical size of a lookup table for software implementations of a cryptographic scheme. What size is considered reasonable? What make them (in)efficient? Are there ...