There’s a drama unfolding in the Bitcoin community right now!  It’s interesting and instructive, and I’ll blog about it in my next post.  Today I’ll go over some Blockchain 101 (actually BitCoin 101) to set some background for the drama of the next post.

The terms BitCoin and Blockchain are often used synonymously these days, but:

A Blockchain is a secure, unalterable, shared ledger.  A Blockchain consists of a series of blocks that are each “signed” with a secure stamp (for the technically minded this is a Hash, a which can mathematically demonstrate that the contents of the block have not been altered).  The signature of each block includes the signature of the previous block, hence the blocks are linked together in a chain, and one block can’t be altered without having to update all subsequent blocks.

BitCoin is a digital currency, that uses a Blockchain as the underlying structure to record transactions.  Each block in BitCoin’s Blockchain contains a set of transactions that represent a transfer of Bitcoin from one party to another.  BitCoin transactions are secured wth strong digital signatures, and the blocks within BitCoin’s blockchain are secured by placing constraints around the block signature (or Hash) that makes it extremely difficult to calculate.  In fact this difficulty is adjusted based on the size of the BitCoin network, so the larger the network (i.e. the more computing power the network can bring to bear) the more difficult it is to construct a block on the BitCoin Blockchain.  The ability to compute the Hash successfully requires a large amount of computing resources, and this is known as the Proof of Work.

The BitCoin network consists of a series of Nodes and Miners.  (Miners compute the new blocks in the Blockchain, and Nodes transmit the new blocks to all parties on the network.)  No one “owns” or “controls” BitCoin – everyone who participates in the network keeps their own copy of the Blockchain.  The Miners and Nodes (and other parties, such as BitCoin Exchanges and BitCoin users, who use Wallet applications to connect to the network) agree on the set of rules that constitutes a valid Blockchain, and will only share transactions and blocks that meet this criteria.  (The difficulty level of the block’s Hash is one such rule.)

This is called Consensus, and it is one of the most powerful aspects of BitCoin.  Consensus means that no one party can take over and control the BitCoin network, because the rest of the parties on the network won’t cooperate, and the cooperation of all parties is required for the BitCoin network to operate.  (Remember this for the BitCoin drama coming up in the next post.)

To summarize:

• Blockchains consist of a “chain” of blocks that are “signed” by cryptographic hashes
• Each block contains BitCoin transactions, that are protected by strong ryptography
• BitCoin defines rules that define the “consensus” of what constitutes a valid blockchain, including a strong “proof of work” for creating each block
• Each participant in the BitCoin network maintains their own copy of the Blockchain, and new transactions and blocks are shared amongst the particpants on a peer-to-peer network
• The participants in the network will only share new transactions and blocks that follow these rules

With the rise in popularity of BitCoin, there are some weaknesses in the architecture that are starting to become apparent.  The first is the size of the Blockchain, which has reached 100G in size and is growing at about 4G per month.  Each participant in the network has to maintain this Blockchain, as well as support the network bandwidth to communicate the new blocks and transactions.  The second issue is the transaction throughput that the BitCoin network can sustain – due to limitations on the size of each block (one of the rules of “Consensus”), the block can hold a maximum of about 1000 transactions.  Since the network is constrained to produce a new block about every 10 minutes (another of the “consensus” rules, controlled by the “difficulty” of computing the block’s signature) this places a ceiling on the maximum transactions that BitCoin can handle.

There are a couple of alternatives on how to address these limitations, and the BitCoin community is divided on the path to take!

In my next post I’ll talk about the “drama” surrounding this, and I’ll also talk about some other technologies and applications that are being built today around Blockchains and Blockchain technology.