use std::cmp::Ordering;
use rand::{thread_rng, RngCore};
use thiserror::Error;
use zeroize::Zeroize;
#[cfg(test)]
mod tests {
use super::SecretData;
#[test]
fn it_works() {}
#[test]
fn it_generates_coefficients() {
let secret_data = SecretData::with_secret("Hello, world!".as_bytes(), 3);
assert_eq!(secret_data.coefficients.len(), 13);
}
#[test]
fn it_rejects_share_id_under_1() {
let secret_data = SecretData::with_secret("Hello, world!".as_bytes(), 3);
let d = secret_data.get_share(0);
assert!(d.is_err());
}
#[test]
fn it_repeatedly_issues_shares() {
let secret_data = SecretData::with_secret("Hello, world!".as_bytes(), 3);
let s1 = secret_data.get_share(1).unwrap();
let s2 = secret_data.get_share(1).unwrap();
assert_eq!(s1, s2);
}
#[test]
fn it_can_recover_secret() {
let s1 = vec![1, 184, 190, 251, 87, 232, 39, 47, 17, 4, 36, 190, 245];
let s2 = vec![2, 231, 107, 52, 138, 34, 221, 9, 221, 67, 79, 33, 16];
let s3 = vec![3, 23, 176, 163, 177, 165, 218, 113, 163, 53, 7, 251, 196];
let new_secret = SecretData::recover_secret(3, vec![s1, s2, s3]).unwrap();
assert_eq!(&new_secret[..], "Hello World!".as_bytes());
}
#[test]
fn it_can_recover_a_generated_secret() {
let secret_data = SecretData::with_secret("Hello, world!".as_bytes(), 3);
let s1 = secret_data.get_share(1).unwrap();
let s2 = secret_data.get_share(2).unwrap();
let s3 = secret_data.get_share(3).unwrap();
let new_secret = SecretData::recover_secret(3, vec![s1, s2, s3]).unwrap();
assert_eq!(&new_secret[..], "Hello, world!".as_bytes());
}
#[test]
fn it_requires_enough_shares() {
fn try_recover(n: u8, shares: &[Vec<u8>]) -> Option<String> {
let shares = shares.iter().take(n as usize).cloned().collect::<Vec<_>>();
SecretData::recover_secret(n, shares).and_then(|bytes| String::from_utf8(bytes).ok())
}
let secret_data = SecretData::with_secret("Hello World!".as_bytes(), 5);
let shares = vec![
secret_data.get_share(1).unwrap(),
secret_data.get_share(2).unwrap(),
secret_data.get_share(3).unwrap(),
secret_data.get_share(4).unwrap(),
secret_data.get_share(5).unwrap(),
];
let recovered = try_recover(5, &shares);
assert!(recovered.is_some());
let recovered = try_recover(3, &shares);
assert!(recovered.is_none());
}
}
#[derive(Zeroize)]
#[zeroize(drop)]
pub struct SecretData {
pub coefficients: Vec<Vec<u8>>,
}
#[derive(Debug, Error, PartialEq)]
pub enum ShamirError {
#[error("Unable to get shamir share")]
InvalidShareCount,
}
impl SecretData {
pub fn with_secret(secret: &[u8], threshold: u8) -> SecretData {
let mut coefficients: Vec<Vec<u8>> = vec![];
let mut rng = thread_rng();
let mut rand_container = vec![0u8; (threshold - 1) as usize];
for c in secret {
rng.fill_bytes(&mut rand_container);
let mut coefficient: Vec<u8> = vec![*c];
for r in rand_container.iter() {
coefficient.push(*r);
}
coefficients.push(coefficient);
}
SecretData { coefficients }
}
pub fn get_share(&self, id: u8) -> Result<Vec<u8>, ShamirError> {
if id == 0 {
return Err(ShamirError::InvalidShareCount);
}
let mut share_bytes: Vec<u8> = vec![];
let coefficients = self.coefficients.clone();
for coefficient in coefficients {
let b = SecretData::accumulate_share_bytes(id, coefficient)?;
share_bytes.push(b);
}
share_bytes.insert(0, id);
Ok(share_bytes)
}
pub fn recover_secret(threshold: u8, shares: Vec<Vec<u8>>) -> Option<Vec<u8>> {
if threshold as usize > shares.len() {
println!("Number of shares is below the threshold");
return None;
}
let mut xs: Vec<u8> = vec![];
for share in shares.iter() {
if xs.contains(&share[0]) {
println!("Multiple shares with the same first byte");
return None;
}
if share.len() != shares[0].len() {
println!("Shares have different lengths");
return None;
}
xs.push(share[0].to_owned());
}
let mut my_coefficients: Vec<String> = vec![];
let mut my_secret_data: Vec<u8> = vec![];
let rounds = shares[0].len() - 1;
for byte_to_use in 0..rounds {
let mut fxs: Vec<u8> = vec![];
for share in shares.clone() {
fxs.push(share[1..][byte_to_use]);
}
match SecretData::full_lagrange(&xs, &fxs) {
None => return None,
Some(resulting_poly) => {
my_coefficients.push(String::from_utf8_lossy(&resulting_poly[..]).to_string());
my_secret_data.push(resulting_poly[0]);
}
}
}
Some(my_secret_data)
}
fn accumulate_share_bytes(id: u8, coefficient_bytes: Vec<u8>) -> Result<u8, ShamirError> {
if id == 0 {
return Err(ShamirError::InvalidShareCount);
}
let mut accumulator: u8 = 0;
let mut x_i: u8 = 1;
for c in coefficient_bytes {
accumulator = SecretData::gf256_add(accumulator, SecretData::gf256_mul(c, x_i));
x_i = SecretData::gf256_mul(x_i, id);
}
Ok(accumulator)
}
fn full_lagrange(xs: &[u8], fxs: &[u8]) -> Option<Vec<u8>> {
let mut returned_coefficients: Vec<u8> = vec![];
let len = fxs.len();
for i in 0..len {
let mut this_polynomial: Vec<u8> = vec![1];
for j in 0..len {
if i == j {
continue;
}
let denominator = SecretData::gf256_sub(xs[i], xs[j]);
let first_term = SecretData::gf256_checked_div(xs[j], denominator);
let second_term = SecretData::gf256_checked_div(1, denominator);
match (first_term, second_term) {
(Some(a), Some(b)) => {
let this_term = vec![a, b];
this_polynomial =
SecretData::multiply_polynomials(&this_polynomial, &this_term);
}
(_, _) => return None,
};
}
if fxs.len() + 1 >= i {
this_polynomial = SecretData::multiply_polynomials(&this_polynomial, &[fxs[i]])
}
returned_coefficients =
SecretData::add_polynomials(&returned_coefficients, &this_polynomial);
}
Some(returned_coefficients)
}
#[inline]
fn gf256_add(a: u8, b: u8) -> u8 {
a ^ b
}
#[inline]
fn gf256_sub(a: u8, b: u8) -> u8 {
SecretData::gf256_add(a, b)
}
#[inline]
fn gf256_mul(a: u8, b: u8) -> u8 {
if a == 0 || b == 0 {
0
} else {
GF256_EXP[((u16::from(GF256_LOG[a as usize]) + u16::from(GF256_LOG[b as usize])) % 255)
as usize]
}
}
#[inline]
fn gf256_checked_div(a: u8, b: u8) -> Option<u8> {
if a == 0 {
Some(0)
} else if b == 0 {
None
} else {
let a_log = i16::from(GF256_LOG[a as usize]);
let b_log = i16::from(GF256_LOG[b as usize]);
let mut diff = a_log - b_log;
if diff < 0 {
diff += 255;
}
Some(GF256_EXP[(diff % 255) as usize])
}
}
#[inline]
fn multiply_polynomials(a: &[u8], b: &[u8]) -> Vec<u8> {
let mut result_terms: Vec<u8> = vec![];
let mut term_padding: Vec<u8> = vec![];
for b_term in b {
let mut this_value = term_padding.clone();
for a_term in a {
this_value.push(SecretData::gf256_mul(*a_term, *b_term));
}
result_terms = SecretData::add_polynomials(&result_terms, &this_value);
term_padding.push(0);
}
result_terms
}
#[inline]
fn add_polynomials(a: &[u8], b: &[u8]) -> Vec<u8> {
let mut a = a.to_owned();
let mut b = b.to_owned();
match a.len().cmp(&b.len()) {
Ordering::Greater => {
let mut t = vec![0; a.len() - b.len()];
b.append(&mut t);
}
Ordering::Less => {
let mut t = vec![0; b.len() - a.len()];
a.append(&mut t);
}
Ordering::Equal => {}
}
let mut results: Vec<u8> = vec![];
for i in 0..a.len() {
results.push(SecretData::gf256_add(a[i], b[i]));
}
results
}
}
static GF256_EXP: [u8; 256] = [
0x01, 0x03, 0x05, 0x0f, 0x11, 0x33, 0x55, 0xff, 0x1a, 0x2e, 0x72, 0x96, 0xa1, 0xf8, 0x13, 0x35,
0x5f, 0xe1, 0x38, 0x48, 0xd8, 0x73, 0x95, 0xa4, 0xf7, 0x02, 0x06, 0x0a, 0x1e, 0x22, 0x66, 0xaa,
0xe5, 0x34, 0x5c, 0xe4, 0x37, 0x59, 0xeb, 0x26, 0x6a, 0xbe, 0xd9, 0x70, 0x90, 0xab, 0xe6, 0x31,
0x53, 0xf5, 0x04, 0x0c, 0x14, 0x3c, 0x44, 0xcc, 0x4f, 0xd1, 0x68, 0xb8, 0xd3, 0x6e, 0xb2, 0xcd,
0x4c, 0xd4, 0x67, 0xa9, 0xe0, 0x3b, 0x4d, 0xd7, 0x62, 0xa6, 0xf1, 0x08, 0x18, 0x28, 0x78, 0x88,
0x83, 0x9e, 0xb9, 0xd0, 0x6b, 0xbd, 0xdc, 0x7f, 0x81, 0x98, 0xb3, 0xce, 0x49, 0xdb, 0x76, 0x9a,
0xb5, 0xc4, 0x57, 0xf9, 0x10, 0x30, 0x50, 0xf0, 0x0b, 0x1d, 0x27, 0x69, 0xbb, 0xd6, 0x61, 0xa3,
0xfe, 0x19, 0x2b, 0x7d, 0x87, 0x92, 0xad, 0xec, 0x2f, 0x71, 0x93, 0xae, 0xe9, 0x20, 0x60, 0xa0,
0xfb, 0x16, 0x3a, 0x4e, 0xd2, 0x6d, 0xb7, 0xc2, 0x5d, 0xe7, 0x32, 0x56, 0xfa, 0x15, 0x3f, 0x41,
0xc3, 0x5e, 0xe2, 0x3d, 0x47, 0xc9, 0x40, 0xc0, 0x5b, 0xed, 0x2c, 0x74, 0x9c, 0xbf, 0xda, 0x75,
0x9f, 0xba, 0xd5, 0x64, 0xac, 0xef, 0x2a, 0x7e, 0x82, 0x9d, 0xbc, 0xdf, 0x7a, 0x8e, 0x89, 0x80,
0x9b, 0xb6, 0xc1, 0x58, 0xe8, 0x23, 0x65, 0xaf, 0xea, 0x25, 0x6f, 0xb1, 0xc8, 0x43, 0xc5, 0x54,
0xfc, 0x1f, 0x21, 0x63, 0xa5, 0xf4, 0x07, 0x09, 0x1b, 0x2d, 0x77, 0x99, 0xb0, 0xcb, 0x46, 0xca,
0x45, 0xcf, 0x4a, 0xde, 0x79, 0x8b, 0x86, 0x91, 0xa8, 0xe3, 0x3e, 0x42, 0xc6, 0x51, 0xf3, 0x0e,
0x12, 0x36, 0x5a, 0xee, 0x29, 0x7b, 0x8d, 0x8c, 0x8f, 0x8a, 0x85, 0x94, 0xa7, 0xf2, 0x0d, 0x17,
0x39, 0x4b, 0xdd, 0x7c, 0x84, 0x97, 0xa2, 0xfd, 0x1c, 0x24, 0x6c, 0xb4, 0xc7, 0x52, 0xf6, 0x01,
];
static GF256_LOG: [u8; 256] = [
0x00, 0x00, 0x19, 0x01, 0x32, 0x02, 0x1a, 0xc6, 0x4b, 0xc7, 0x1b, 0x68, 0x33, 0xee, 0xdf, 0x03,
0x64, 0x04, 0xe0, 0x0e, 0x34, 0x8d, 0x81, 0xef, 0x4c, 0x71, 0x08, 0xc8, 0xf8, 0x69, 0x1c, 0xc1,
0x7d, 0xc2, 0x1d, 0xb5, 0xf9, 0xb9, 0x27, 0x6a, 0x4d, 0xe4, 0xa6, 0x72, 0x9a, 0xc9, 0x09, 0x78,
0x65, 0x2f, 0x8a, 0x05, 0x21, 0x0f, 0xe1, 0x24, 0x12, 0xf0, 0x82, 0x45, 0x35, 0x93, 0xda, 0x8e,
0x96, 0x8f, 0xdb, 0xbd, 0x36, 0xd0, 0xce, 0x94, 0x13, 0x5c, 0xd2, 0xf1, 0x40, 0x46, 0x83, 0x38,
0x66, 0xdd, 0xfd, 0x30, 0xbf, 0x06, 0x8b, 0x62, 0xb3, 0x25, 0xe2, 0x98, 0x22, 0x88, 0x91, 0x10,
0x7e, 0x6e, 0x48, 0xc3, 0xa3, 0xb6, 0x1e, 0x42, 0x3a, 0x6b, 0x28, 0x54, 0xfa, 0x85, 0x3d, 0xba,
0x2b, 0x79, 0x0a, 0x15, 0x9b, 0x9f, 0x5e, 0xca, 0x4e, 0xd4, 0xac, 0xe5, 0xf3, 0x73, 0xa7, 0x57,
0xaf, 0x58, 0xa8, 0x50, 0xf4, 0xea, 0xd6, 0x74, 0x4f, 0xae, 0xe9, 0xd5, 0xe7, 0xe6, 0xad, 0xe8,
0x2c, 0xd7, 0x75, 0x7a, 0xeb, 0x16, 0x0b, 0xf5, 0x59, 0xcb, 0x5f, 0xb0, 0x9c, 0xa9, 0x51, 0xa0,
0x7f, 0x0c, 0xf6, 0x6f, 0x17, 0xc4, 0x49, 0xec, 0xd8, 0x43, 0x1f, 0x2d, 0xa4, 0x76, 0x7b, 0xb7,
0xcc, 0xbb, 0x3e, 0x5a, 0xfb, 0x60, 0xb1, 0x86, 0x3b, 0x52, 0xa1, 0x6c, 0xaa, 0x55, 0x29, 0x9d,
0x97, 0xb2, 0x87, 0x90, 0x61, 0xbe, 0xdc, 0xfc, 0xbc, 0x95, 0xcf, 0xcd, 0x37, 0x3f, 0x5b, 0xd1,
0x53, 0x39, 0x84, 0x3c, 0x41, 0xa2, 0x6d, 0x47, 0x14, 0x2a, 0x9e, 0x5d, 0x56, 0xf2, 0xd3, 0xab,
0x44, 0x11, 0x92, 0xd9, 0x23, 0x20, 0x2e, 0x89, 0xb4, 0x7c, 0xb8, 0x26, 0x77, 0x99, 0xe3, 0xa5,
0x67, 0x4a, 0xed, 0xde, 0xc5, 0x31, 0xfe, 0x18, 0x0d, 0x63, 0x8c, 0x80, 0xc0, 0xf7, 0x70, 0x07,
];