safe-mix 1.0.1

Implementation of the Collective Coin Flip algorithm
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142

// Copyright 2017 Parity Technologies (UK) Ltd.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Means of mixing a series of hashes to create a single secure hash.
//!
//! Described in http://www.cs.huji.ac.il/~nati/PAPERS/coll_coin_fl.pdf

#![cfg_attr(not(feature = "std"), no_std)]

#[cfg(feature = "std")]
use std::ops::{BitAnd, BitOr};

#[cfg(not(feature = "std"))]
use core::ops::{BitAnd, BitOr};

pub const MAX_DEPTH: usize = 17;

fn sub_mix<T>(seeds: &[T]) -> T where
	T: BitAnd<Output = T> + BitOr<Output = T> + Copy
{
	(seeds[0] & seeds[1]) | (seeds[1] & seeds[2]) | (seeds[0] & seeds[2])
}

/// Mix a slice.
pub fn triplet_mix<T>(seeds: &[T]) -> Result<T, ()> where
	T: BitAnd<Output = T> + BitOr<Output = T>,
	T: Default + Copy
{
	Ok(seeds.iter().cloned().triplet_mix())
}

/// The mixed trait for mixing a sequence.
pub trait TripletMix {
	/// The items in the sequence and simultaneously the return of the mixing.
	type Item;
	/// The output of the mixing algorithm on the sequence. Items in the sequence beyond
	/// the largest power of three that fits within the the sequence up until `3 ** MAX_DEPTH`
	/// are ignored.
	fn triplet_mix(self) -> Self::Item;
}

impl<I, T> TripletMix for I where
	I: Iterator<Item = T>,
	T: BitAnd<Output = T> + BitOr<Output = T> + Default + Copy
{
	type Item = T;
	fn triplet_mix(self) -> Self::Item {
		let mut accum = [[T::default(); 3]; MAX_DEPTH];
		let mut result = T::default();
		for (i, seed) in self.enumerate() {
			accum[0][i % 3] = seed;
			let mut index_at_depth = i;
			for depth in 0..MAX_DEPTH {
				if index_at_depth % 3 != 2 {
					break;
				}
				index_at_depth /= 3;
				result = sub_mix(&accum[depth]);

				// end of the threesome at depth.
				if depth == MAX_DEPTH - 1 {
					// end of our stack - bail with result.
					break;
				} else {
					// save in the stack for parent computation
					accum[depth + 1][index_at_depth % 3] = result;
				}
			}
		}
		result
	}
}

#[cfg(test)]
mod tests {
	use super::*;

	#[test]
	fn sub_mix_works() {
		assert_eq!(sub_mix(&[0, 0, 0][..]), 0);
		assert_eq!(sub_mix(&[0, 0, 1][..]), 0);
		assert_eq!(sub_mix(&[0, 1, 0][..]), 0);
		assert_eq!(sub_mix(&[0, 1, 1][..]), 1);
		assert_eq!(sub_mix(&[1, 0, 0][..]), 0);
		assert_eq!(sub_mix(&[1, 0, 1][..]), 1);
		assert_eq!(sub_mix(&[1, 1, 0][..]), 1);
		assert_eq!(sub_mix(&[1, 1, 1][..]), 1);

		assert_eq!(sub_mix(&[0, 0, 0][..]), 0);
		assert_eq!(sub_mix(&[0, 0, 2][..]), 0);
		assert_eq!(sub_mix(&[0, 2, 0][..]), 0);
		assert_eq!(sub_mix(&[0, 2, 2][..]), 2);
		assert_eq!(sub_mix(&[2, 0, 0][..]), 0);
		assert_eq!(sub_mix(&[2, 0, 2][..]), 2);
		assert_eq!(sub_mix(&[2, 2, 0][..]), 2);
		assert_eq!(sub_mix(&[2, 2, 2][..]), 2);
	}

	#[test]
	fn triplet_mix_works_on_first_level() {
		assert_eq!(triplet_mix(&[0, 0, 0][..]).unwrap(), 0);
		assert_eq!(triplet_mix(&[0, 0, 1][..]).unwrap(), 0);
		assert_eq!(triplet_mix(&[0, 1, 0][..]).unwrap(), 0);
		assert_eq!(triplet_mix(&[0, 1, 1][..]).unwrap(), 1);
		assert_eq!(triplet_mix(&[1, 0, 0][..]).unwrap(), 0);
		assert_eq!(triplet_mix(&[1, 0, 1][..]).unwrap(), 1);
		assert_eq!(triplet_mix(&[1, 1, 0][..]).unwrap(), 1);
		assert_eq!(triplet_mix(&[1, 1, 1][..]).unwrap(), 1);

		assert_eq!(triplet_mix(&[0, 0, 0][..]).unwrap(), 0);
		assert_eq!(triplet_mix(&[0, 0, 2][..]).unwrap(), 0);
		assert_eq!(triplet_mix(&[0, 2, 0][..]).unwrap(), 0);
		assert_eq!(triplet_mix(&[0, 2, 2][..]).unwrap(), 2);
		assert_eq!(triplet_mix(&[2, 0, 0][..]).unwrap(), 0);
		assert_eq!(triplet_mix(&[2, 0, 2][..]).unwrap(), 2);
		assert_eq!(triplet_mix(&[2, 2, 0][..]).unwrap(), 2);
		assert_eq!(triplet_mix(&[2, 2, 2][..]).unwrap(), 2);
	}

	#[test]
	fn triplet_mix_works_on_second_level() {
		assert_eq!(triplet_mix(&[0, 0, 0, 0, 0, 1, 0, 1, 0][..]).unwrap(), 0);
		assert_eq!(triplet_mix(&[0, 1, 1, 1, 0, 0, 1, 0, 1][..]).unwrap(), 1);
		assert_eq!(triplet_mix(&[1, 1, 0, 1, 1, 1, 0, 0, 0][..]).unwrap(), 1);
	}

	#[test]
	fn triplet_mix_works_on_third_level() {
		assert_eq!(triplet_mix(&[0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 0, 0, 0][..]).unwrap(), 1);
	}
}