Finally, a leaf node (or a value node) indicates that the given node must match until the end of the key1.
Ethereum geth download full#
A branch node (or a full node) contains pointers for every possible character as well as one extra slot for the value at the current node. In this case, the root node covers all keys which begin with a7, removing the need for two distinct nodes to represent a and 7. An extension node (or, a short node, as it's referred to in the Geth codebase) is an optimization which states that the given node is responsible for multiple characters in the stream. In the example below, we see there are actually three different types of nodes in the MPT. The child node is then consulted for the second character, and the process repeats until the final node is found for the final character in the sequence.
Then, the root node is consulted to determine what the next node should be for the first character in the sequence. To retrieve the value for a key, the key is first converted into a sequence of hexadecimal characters such that every byte becomes two hex characters. In the MPT, keys and values are arbitrary byte strings. With a MPT, the prefix-based storage layout of the Patricia trie is combined with the Merkle tree to create a data structure whose contents can be cryptographically verified while still maintaining good runtime performance. The verifier will then generate Hash 0-1, Hash 0, and Top Hash which can be compared with the Merkle root they expected. In the diagram below, a user can prove that L2 is a member of the tree by providing Hash 0-0 and Hash 1. the top hash) of the Merkle tree and wants to check whether a specific piece of data was contained in the tree, they can do so using only a path through the tree, which is proportional to the log of the number of leaf nodes, rather than the number of leaf nodes itself. Meanwhile, a Merkle tree is simply a tree where the leaf nodes are hashes of the data and all other nodes are hashes of their children. For example, here's how several words all starting with r might be stored in a Patricia trie.īy Claudio Rocchini - Own work, CC BY 2.5, This is a more optimal way of storing similar data when compared to something like a hashmap, although there may be a speed tradeoff. Put very simply, a Patricia trie stores data in a tree-like structure based on the data's prefix. The Merkle-Patricia trie (MPT) is a key data structure in Geth and is a combination of the Merkle tree and the Patricia trie. To understand how Geth can tell whether the data it just received is correct or not, we must first understand the Merkle-Patricia trie. Of course, Geth doesn't just blindly trust state trie data that peers send back, or a malicious peer could claim that a certain account has much more ether than it actually does.
Ethereum geth download download#
Geth also does not execute any transactions, instead choosing to download the state trie directly from peers in order to arrive at the final blockchain state. In fast sync mode, Geth downloads but does not verify the proof-of-work on every block, instead choosing certain blocks at random. For this, Geth offers a mode where chain data up to a recent block (known as the pivot) is synchronized using a faster approach, with only the few remaining blocks being synchronized using the slower full sync algorithm. Perhaps they have a deadline to meet or they simply don't think the speed tradeoff is worth it. However, some users may not want to wait weeks for a full sync to complete. This is more secure but comes with a heavy speed tradeoff, as a full Geth sync may take anywhere from days to weeks to complete. Geth will also execute every single transaction in the block, which allows it to generate the blockchain state locally without needing to trust other nodes. This means that Geth will download and validate the proof-of-work seals on every single block.
Depending on the needs of the user, some tradeoffs between security and speed can be made, so Geth supported (at the time) two different sync modes: full sync and fast sync.Īs the name would suggest, full sync performs a full synchronization of the Ethereum blockchain.
This means downloading or computing all of the data needed to build a complete picture of the chain state at the latest block. Whenever someone wants to run an Ethereum node, they must first synchronize with the network. If exploited, an attacker could have booby trapped the Ethereum blockchain and triggered a hard fork at will. Today's post is about a bug in Geth's state downloader which could be used to trick it into syncing with mainnet incorrectly. If you haven't already, take a look at Part 1 here.
Ethereum geth download series#
This is the second in a series of blog posts about bugs I've found in go-ethereum (Geth).
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