merklemountainrange/lib.rs
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// Copyright 2019 The Tari Project
//
// Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
// following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following
// disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
// following disclaimer in the documentation and/or other materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote
// products derived from this software without specific prior written permission.
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// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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//! The Merkle mountain range was invented by Peter Todd more about them can be read at:
//! https://github.com/opentimestamps/opentimestamps-server/blob/master/doc/merkle-mountain-range.md
//! https://github.com/mimblewimble/grin/blob/master/doc/mmr.md
//!
//! A Merkle mountain range(MMR) is a binary tree where each parent is the concatenated hash of its two
//! children. The leaves at the bottom of the MMR is the hashes of the data. The MMR allows easy to add and proof
//! of existence inside of the tree. MMR always tries to have the largest possible single binary tree, so in effect
//! it is possible to have more than one binary tree. Every time you have to get the merkle root (the single merkle
//! proof of the whole MMR) you have the bag the peaks of the individual trees, or mountain peaks.
//!
//! Lets take an example of how to construct one. Say you have the following MMR already made:
//! '''
//! /\
//! / \
//! /\ /\ /\
//! /\/\/\/\ /\/\ /\
//! '''
//! From this we can see we have 3 trees or mountains. We have constructed the largest possible tree's we can.
//! If we want to calculate the merkle route we will bag each of the mountains in the following way
//! '''
//! /\
//! /\ \
//! / \ \
//! /\ \ \
//! / \ \ \
//! /\ /\ /\ \
//! /\/\/\/\/\/\/\
//! '''
//! Lets continue the example, by adding a single object. Our MMR now looks as follows
//! '''
//! /\
//! / \
//! /\ /\ /\
//! /\/\/\/\ /\/\ /\ /
//! '''
//! We now have 4 mountains. Lets bag and calculate the merkle root again
//! '''
//! /\
//! /\ \
//! /\ \ \
//! / \ \ \
//! /\ \ \ \
//! / \ \ \ \
//! /\ /\ /\ \ \
//! /\/\/\/\/\/\/\ \
//! '''
//! Lets continue thw example, by adding a single object. Our MMR now looks as follows
//! '''
//! /\
//! / \
//! / \
//! / \
//! /\ /\
//! / \ / \
//! /\ /\ /\ /\
//! /\/\/\/\/\/\/\/\
//! '''
//! Now we only have a single binary tree, we dont have to bag the mountains to calculate the merkle root. This
//! process continues as you add more objects to the MMR.
//! '''
//! /\
//! / \
//! / \
//! / \
//! / \
//! / \
//! / \
//! /\ \
//! /\ \ /\
//! / \ \ / \
//! /\ \ \ /\ \
//! / \ \ \ / \ \
//! /\ /\ /\ \ /\ /\ /\
//! /\/\/\/\/\/\/\ /\/\/\/\/\/\
//! '''
//! Due to the unique way the MMR is constructed we can easily represent the MMR as a list of the nodes, as when
//! adding nodes you only append. Lets take the following MMR and number the nodes in the order we create them.
//! '''
//! 7
//! / \
//! / \
//! 3 6
//! / \ / \
//! 1 2 4 5
//! '''
//! Looking above at the example of when you create the nodes, you will see the nodes will have been created in the
//! order as they are named. This means we can easily represent them as a list:
//! Height: 0 | 0 | 1 | 0 | 0 | 1 | 2
//! Node: 1 | 2 | 3 | 4 | 5 | 6 | 7
//!
//! Because of the list nature of the MMR we can easily navigate around the MMR using the following formulas:
//! Jump to sibling : 2^(H+1) -1
//! find peak : 2^(H+1) -2 where < total elements
//! left down : 2^H
//! right down: -1
//! Note that the formulas are for direct indexes in the array, meaning the nodes count from 0 and not 1 as in
//! the examples above. H - Height
//! I - Index
//!
//! Pruning the MMR means flagging a node as pruned and only removing it if its sibling has been removed.
//! We do this as we require the sibling to prove the hash of the node. Taking the above example, let's prune leaf 1.
//! '''
//! /\
//! / \
//! / \
//! / \
//! / \
//! / \
//! / \
//! /\ \
//! /\ \ /\
//! / \ \ / \
//! /\ \ \ /\ \
//! / \ \ \ / \ \
//! /\ /\ /\ \ /\ /\ /\
//! /\/\/\/\/\/\/\ /\/\/\/\/\/\
//! '''
//! Node 1 has now only been marked as pruned but we cannot remove it as of yet because we still require it to
//! prove node 2. When we prune node 2, the MMR looks as follows
//! '''
//! /\
//! / \
//! / \
//! / \
//! / \
//! / \
//! / \
//! /\ \
//! /\ \ /\
//! / \ \ / \
//! /\ \ \ /\ \
//! / \ \ \ / \ \
//! /\ /\ /\ \ /\ /\ /\
//! /\/\/\/\/\/\ /\/\/\/\/\/\
//! '''
//! Although we have not removed node 1 and node 2 from the MMR, we cannot yet remove node 3 as we require node 3
//! for the proof of node 6. Let's prune 4 and 5.
//! '''
//! /\
//! / \
//! / \
//! / \
//! / \
//! / \
//! / \
//! /\ \
//! /\ \ /\
//! / \ \ / \
//! /\ \ \ /\ \
//! / \ \ \ / \ \
//! /\ /\ \ /\ /\ /\
//! /\/\/\/\/\ /\/\/\/\/\/\
//! '''
//! Now we removed 3 from the MMR
pub mod error;
pub mod merklemountainrange;
pub mod merklenode;
pub mod mmr {
pub use crate::merklemountainrange::*;
}