Securing Blockchain

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来自 University at Buffalo 的课程

Blockchain Basics

170 个评分

University at Buffalo

Blockchain Basics

170 个评分

课程 1（共 4 门，Specialization Blockchain）

This first course of the Blockchain specialization provides a broad overview of the essential concepts of blockchain technology – by initially exploring the Bitcoin protocol followed by the Ethereum protocol – to lay the foundation necessary for developing applications and programming. You will be equipped with the knowledge needed to create nodes on your personal Ethereum blockchain, create accounts, unlock accounts, mine, transact, transfer Ethers, and check balances. You will learn about the decentralized peer-to-peer network, an immutable distributed ledger and the trust model that defines a blockchain. This course enables you to explain basic components of a blockchain (transaction, block, block header, and the chain) its operations (verification, validation, and consensus model) underlying algorithms, and essentials of trust (hard fork and soft fork). Content includes the hashing and cryptography foundations indispensable to blockchain programming, which is the focus of two subsequent specialization courses, Smart Contracts and Decentralized Applications (Dapps). You will work on a virtual machine image, specifically created for this course, to build an Ethereum test chain and operate on the chain. This hands-on activity will help you understand the workings of a blockchain, its transactions, blocks and mining. Main concepts are delivered through videos, demos and hands-on exercises.

从本节课中

Algorithms & Techniques

We will discuss the concept of asymmetric key encryption, define the concept of hashing, and explain techniques that use algorithms to manage the integrity of transactions and blocks in blockchain.

Securing Blockchain4:25

与讲师见面

Bina Ramamurthy
Teaching Professor
Computer Science and Engineering Department

As we discussed before,

some of the main components of the Ethereum block are the header, the transactions,

including the transaction hash or the transaction root,

and the state radio booth,

the state hash, or the state root.

Integrity of the block is managed by assuring

that the block header contents are not tampered with,

the transactions are not tempered with,

state transitions are efficiently computed, hashed, and verified.

Remember, the block chain is supposed to be an immutable record.

In Ethereum, the block hash is the block of all the elements in the block header,

including the transaction root and state root hashes.

It is computed by applying a variant of

SHA-3 algorithm called Keccak and all the items of the block header.

You would see a real example of

bitcoin block hash in the quiz associated with this module.

A typical block has about 2,000 transactions

in bitcoin and about 100 transaction Ethereum.

We need an efficient way to detect tampering and validate the transaction efficiently.

Hashes of transaction in a block are processed in a tree structure

called Mekle tree hash that we discussed in earlier lesson.

Merkle tree hash is also used for computing the state root hash,

since only the hash of the chained states from block to block have to be re-computed.

It is also used for receipt hash root.

Remember the advantage over flat versus tree representation.

If any transaction is to be verified,

only one path to the tree has to be checked.

You don't have to go through the entire set of transactions.

Smart contract execution in Ethereum results in state transitions.

Every state change requires state root hash re-computation.

Instead of computing hash for the entire set of states,

only the affected path in the Merkle tree needs to be re-computed.

When the state 19 is changed to 20,

that results in the path including 31,

41, and the state root hash 64 to be re-computed.

Only that path is re-computed,

not the entire tree.

Now, let's move on to block hash computation.

Block hash in Ethereum is computed by first computing the state root hash,

transaction root hash and then receipt root hash,

shown at the bottom of the block header.

These roots and all the other items in the header are

hash together with the variable nodes to solve the proof of work puzzle.

Block hash serves two important purposes;

verification of the integrity of the block and the transactions,

formation of the chain link by embedding

the previous block hash in the current block header.

If any participant node tampers with the block,

it's hash value changes resulting in the mismatch of

the hash values and rendering the local chain of the node in an invalid state.

Any future blocks initiated by the node would

be rejected by other miners due to hash mismatch.

This enforces the immutability of the chain.

Summarizing, a combination of

hashing and encryption are used for securing the various elements of the block chain.

Private public key pair and hashing are

important foundational concepts in

decentralized networks that operate beyond trust boundaries.

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