Written readme, improved documentation, added changelog and copyright

CHANGELOG.md

@@ -0,0 +1,9 @@
+# Changelog
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [0.1.0] - 2020-01-13
+### Added
+- Initial version

COPYRIGHT

@@ -0,0 +1,12 @@
+Copyrights in the Sharks project are retained by their contributors. No
+copyright assignment is required to contribute to the Sharks project.
+
+For full authorship information, see the version control history.
+
+Except as otherwise noted (below and/or in individual files), Sharks is
+licensed under the Apache License, Version 2.0 <LICENSE-APACHE> or
+<http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+<LICENSE-MIT> or <http://opensource.org/licenses/MIT>, at your option.
+
+The Sharks project includes code from the Rust project
+published under these same licenses.

Cargo.toml

@@ -2,7 +2,7 @@
 name = "sharks"
 version = "0.1.0"
 authors = ["Aitor Ruano <codearm@pm.me>"]
-description = "Fast, secure and minimal Shamir's Secret Sharing library crate"
+description = "Fast, smanll and secure Shamir's Secret Sharing library crate"
 homepage = "https://github.com/c0dearm/sharks"
 repository = "https://github.com/c0dearm/sharks"
 readme = "README.md"

README.md

@@ -0,0 +1,65 @@
+# Sharks
+
+Fast, small and secure [Shamir's Secret Sharing](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing) library crate
+
+Documentation:
+-    [API reference (docs.rs)](https://docs.rs/sharks)
+
+## Usage
+
+Add this to your `Cargo.toml`:
+
+```toml
+[dependencies]
+sharks = "0.1"
+```
+
+To get started using Sharks, see the [Rust docs](https://docs.rs/sharks)
+
+## Features
+
+### Developer friendly
+The API is simple and to the point, with minimal configuration.
+
+### Fast and small
+The code is as idiomatic and clean as possible, with minimum external dependencies.
+
+### Secure by design
+The implementation forbids the user to choose parameters that would result in an insecure application,
+like generating more shares than what's allowed by the finite field length.
+
+## Limitations
+
+Currently only finite fields with modulus up to 128 bits (12th Mersenne prime) are supported. This means:
+-    Only up to `2^128` shares can be generated.
+-    Maximum secret length is 128 bits.
+
+This is imposed by the Rust maximum unsigned integer length, which is `u128`.
+Going around this limitation would mean using crates like `num-bigint` in most of the computations, reducing performance drastically.
+
+## Testing
+
+This crate contains both unit and benchmark tests (as well as the examples included in the docs).
+You can run them with `cargo test` and `cargo bench`.
+
+### Benchmark results [min mean max]
+
+| CPU                                       | obtain_shares_iterator          | step_shares_iterator            | recover_secret                  |
+| ----------------------------------------- | ------------------------------- | ------------------------------- | ------------------------------- |
+| Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz  | [14.023 us 14.087 us 14.146 us] | [413.19 us 414.90 us 416.60 us] | [24.978 ms 25.094 ms 25.226 ms] |
+
+# Contributing
+
+If you find a vulnerability, bug or would like a new feature, [open a new issue](https://github.com/c0dearm/sharks/issues/new).
+
+To introduce your changes into the codebase, submit a Pull Request.
+
+Many thanks!
+
+# License
+
+Sharks is distributed under the terms of both the MIT license and the
+Apache License (Version 2.0).
+
+See [LICENSE-APACHE](LICENSE-APACHE) and [LICENSE-MIT](LICENSE-MIT), and
+[COPYRIGHT](COPYRIGHT) for details.

benches/benchmarks.rs

@@ -1,4 +1,3 @@
-
 use std::collections::HashMap;
 
 use criterion::{black_box, criterion_group, criterion_main, Criterion};
@@ -8,15 +7,19 @@ fn secret_shares_generation(c: &mut Criterion) {
     let shamir = SecretShares::new(1000, 128).unwrap();
     let mut iter = shamir.iter_shares(12345).unwrap();
 
-    c.bench_function("obtain_shares_iterator", |b| b.iter(|| shamir.iter_shares(black_box(12345))));
+    c.bench_function("obtain_shares_iterator", |b| {
+        b.iter(|| shamir.iter_shares(black_box(12345)))
+    });
     c.bench_function("step_shares_iterator", |b| b.iter(|| iter.next()));
 }
 
 fn secret_from_shares(c: &mut Criterion) {
     let shamir = SecretShares::new(10, 128).unwrap();
-    let shares: HashMap<u128,u128> = shamir.iter_shares(12345).unwrap().take(100).collect();
+    let shares: HashMap<u128, u128> = shamir.iter_shares(12345).unwrap().take(100).collect();
 
-    c.bench_function("recover_secret", |b| b.iter(|| shamir.secret_from(black_box(&shares))));
+    c.bench_function("recover_secret", |b| {
+        b.iter(|| shamir.secret_from(black_box(&shares)))
+    });
 }
 
 criterion_group!(benches, secret_shares_generation, secret_from_shares);

src/lib.rs

@@ -1,7 +1,20 @@
+//! Fast, small and secure [Shamir's Secret Sharing](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing) library crate
+//!
+//! # Usage example
+//! ```
+//! // Configure algorithm with minimum 3 shares to recover secret and security level 12
+//! let shamir = sharks::SecretShares::new(3, 12).unwrap();
+//! // Generate 3 shares for the 12345 secret
+//! let shares = shamir.iter_shares(12345).unwrap().take(3).collect();
+//! // Recover the secret from the shares
+//! let secret = shamir.secret_from(&shares).unwrap();
+//! assert_eq!(secret, 12345);
+//! ```
+
 use std::collections::HashMap;
 
-mod mersenne;
 mod math;
+mod mersenne;
 
 /// Generate new [Shamir's secret shares](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing) or recover secrets from them.
 pub struct SecretShares {
@@ -10,7 +23,6 @@ pub struct SecretShares {
 }
 
 impl SecretShares {
-
     /// Returns a result containing a`SecretShares` instance if parameters are reasonable.
     ///
     /// `security_level` is the index of the [Mersenne prime](https://en.wikipedia.org/wiki/Mersenne_prime) to use as the finite field prime modulo (the higher the more secure, but slower).

src/math.rs

@@ -1,46 +1,60 @@
+// A module that contains necessary algorithms to compute Shamir's shares and recover secrets
+
 use std::collections::HashMap;
 
 use num_bigint::{BigInt, BigUint};
-use num_traits::Zero;
 use num_traits::cast::ToPrimitive;
+use num_traits::Zero;
 use rand::distributions::{Distribution, Uniform};
 
-/// A module that contains necessary algorithms to compute Shamir's shares and recover secrets
+// Computes `num/(num - b) mod p`, a necessary step to compute the [root of the Lagrange polynomial](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing#Computationally_efficient_approach).
-
+// To find the modulo multiplicative inverse of `num - b` the [Extended Euclidean Algorithm](https://en.wikipedia.org/wiki/Modular_multiplicative_inverse#Computation) is used.
-/// Computes `num/(num - b) mod p`, a necessary step to compute the [root of the Lagrange polynomial](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing#Computationally_efficient_approach).
-/// To find the modulo multiplicative inverse of `num - b` the [Extended Euclidean Algorithm](https://en.wikipedia.org/wiki/Modular_multiplicative_inverse#Computation) is used.
 fn div_diff_mod(num: &u128, b: &u128, p: u128) -> u128 {
-    let (mut m, mut x, mut inv, mut den) = (p, 0i128, 1i128, if num < b { p - (b - num) } else { num - b });
+    let (mut m, mut x, mut inv, mut den) = (
+        p,
+        0i128,
+        1i128,
+        if num < b { p - (b - num) } else { num - b },
+    );
 
     while den > 1 {
-        inv -= ((den/m) as i128)*x;
+        inv -= ((den / m) as i128) * x;
         den %= m;
         std::mem::swap(&mut den, &mut m);
         std::mem::swap(&mut x, &mut inv);
     }
 
     let mut res = BigInt::from(inv);
-    if inv < 0 { res += p }
+    if inv < 0 {
+        res += p
+    }
 
-    (num*res % p).to_u128().unwrap()
+    (num * res % p).to_u128().unwrap()
 }
 
-/// Finds the [root of the Lagrange polynomial](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing#Computationally_efficient_approach).
+// Finds the [root of the Lagrange polynomial](https://en.wikipedia.org/wiki/Shamir%27s_Secret_Sharing#Computationally_efficient_approach).
 pub fn lagrange_root(points: &HashMap<u128, u128>, p: u128) -> u128 {
-    (points.iter().enumerate()
+    (points
-    .map(|(j, (xj, yj))|
+        .iter()
-        points.iter().enumerate().filter(|(m, _)| *m != j)
+        .enumerate()
-        .map(|(_, (xm, _))|
+        .map(|(j, (xj, yj))| {
-            div_diff_mod(xm, xj, p)
+            points
-        )
+                .iter()
-        .product::<BigUint>()*yj % p
+                .enumerate()
-    )
+                .filter(|(m, _)| *m != j)
-    .sum::<BigUint>() % p)
+                .map(|(_, (xm, _))| div_diff_mod(xm, xj, p))
-    .to_u128().unwrap()
+                .product::<BigUint>()
+                * yj
+                % p
+        })
+        .sum::<BigUint>()
+        % p)
+        .to_u128()
+        .unwrap()
 }
 
-/// Generates `k` polynomial coefficients, being the last one `s` and the others randomly generated between `[1, p)`.
+// Generates `k` polynomial coefficients, being the last one `s` and the others randomly generated between `[1, p)`.
-/// Coefficient degrees go from higher to lower in the returned vector order.
+// Coefficient degrees go from higher to lower in the returned vector order.
 pub fn compute_coeffs(s: u128, k: usize, p: u128) -> (u128, Vec<u128>) {
     let mut coeffs = Vec::with_capacity(k);
     let between = Uniform::new(1, p);
@@ -54,15 +68,24 @@ pub fn compute_coeffs(s: u128, k: usize, p: u128) -> (u128, Vec<u128>) {
     (p, coeffs)
 }
 
-/// Given a set of polynomial coefficients `coeffs` and a modulus `p`, returns an iterator that computes a `(x, f(x) mod p)` point
+// Given a set of polynomial coefficients `coeffs` and a modulus `p`, returns an iterator that computes a `(x, f(x) mod p)` point
-/// on each iteration. The iterator starts for `x = 1` and ends at `x = p-1`.
+// on each iteration. The iterator starts for `x = 1` and ends at `x = p-1`.
 pub fn get_evaluator(coeffs: Vec<u128>, p: u128) -> impl Iterator<Item = (u128, u128)> {
-    (1..p).map(move |x| (x, coeffs.iter().fold(BigUint::zero(), |acc, c| (acc*x + c) % p).to_u128().unwrap()))
+    (1..p).map(move |x| {
+        (
+            x,
+            coeffs
+                .iter()
+                .fold(BigUint::zero(), |acc, c| (acc * x + c) % p)
+                .to_u128()
+                .unwrap(),
+        )
+    })
 }
 
 #[cfg(test)]
 mod tests {
-    use super::{div_diff_mod, lagrange_root, compute_coeffs, get_evaluator};
+    use super::{compute_coeffs, div_diff_mod, get_evaluator, lagrange_root};
 
     #[test]
     fn div_diff_mod_works() {
@@ -75,12 +98,12 @@ mod tests {
 
     #[test]
     fn lagrange_root_works() {
-        let iter = get_evaluator(vec![3,2,1], 7);
+        let iter = get_evaluator(vec![3, 2, 1], 7);
         let values = iter.take(3).collect();
         let root = lagrange_root(&values, 7);
         assert_eq!(root, 1);
 
-        let iter = get_evaluator(vec![3,2,5], 7);
+        let iter = get_evaluator(vec![3, 2, 5], 7);
         let values = iter.take(3).collect();
         let root = lagrange_root(&values, 7);
         assert_eq!(root, 5);
@@ -96,8 +119,8 @@ mod tests {
 
     #[test]
     fn evaluator_works() {
-        let iter = get_evaluator(vec![3,2,5], 7);
+        let iter = get_evaluator(vec![3, 2, 5], 7);
         let values: Vec<_> = iter.take(2).collect();
-        assert_eq!(values, vec![(1,3), (2,0)]);
+        assert_eq!(values, vec![(1, 3), (2, 0)]);
     }
 }

src/mersenne.rs

@@ -1,16 +1,3 @@
-/// A table containing the exponents of found [Mersenne primes](https://en.wikipedia.org/wiki/Mersenne_prime)
+// A table containing the exponents of found [Mersenne primes](https://en.wikipedia.org/wiki/Mersenne_prime)
-/// To be used as finite field modulo for shares and secret recovery computation
+// To be used as finite field modulo for shares and secret recovery computation
-pub const EXPONENTS: [u32; 12] = [
+pub const EXPONENTS: [u32; 12] = [2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127];
-    2,
-    3,
-    5,
-    7,
-    13,
-    17,
-    19,
-    31,
-    61,
-    89,
-    107,
-    127
-];