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Script is used almost exclusively to lock and unlock bitcoin, not to build applications or run programs. Script’s simplicity also gives Bitcoin security and makes it easier for developers to avoid losing money while designing wallets or applications on top of Bitcoin.

All Bitcoin transactions use Script to define how outputs can be spent. In other words, the script of a Bitcoin transaction determines to whom the bitcoin was sent. Bitcoin has a few different scripts, with Pay-to-Public-Key-Hash (P2PKH) being the most popular. P2PKH is a simple script which pays bitcoin to an address.

Other scripts can achieve more complex setups, such as creating multisig addresses. Bitcoin sent to a multisig address requires multiple signatures from multiple private keys to be spent.

Although SegWit script types—P2WPKH and P2WSH—offer savings on transaction fees, adoption of these new script types has been slow. As of April 2021, almost four years after SegWit’s activation, P2PKH scripts are used by over 70% of UTXOs.

Source: Clark Moody's Dashboard

A reserve ratio is mandated because commercial banks will generally lend out as much money as possible to maximize revenue through interest payments or maximize return on investment or yield. To counteract the incentive to lend and invest aggressively, governments and central banks mandate a proportion of funds that a commercial bank must maintain. In reality, required reserve ratios are now at 0% which means that banks do not have to maintain a minimum reserve ratio any longer.

Following the financial crisis of 2007-2009, the Federal Open Market Committee (FOMC), the main policymaking body of the Fed, lowered the federal funds rate target to near zero. The decision to lower the federal funds rate increased the quantity and amount of reserves held by the Fed on behalf of commercial banks. Accordingly, slight adjustments to the supply of reserves are no longer a practical or effective monetary policy for adjusting the federal funds rate. On March 15, 2020, the Federal Reserve reduced reserve requirement ratios to zero percent and transitioned to an “Ample-Reserves Regime” to eliminate the need for active management of the supply of reserves.

Any piece of data can be used as a preimage. For example, addresses are created by taking the hash of a public key. Likewise, a block header is the preimage for a block’s Proof-of-Work, which is a hash.

Hashes are often used as commitments to preimages, because the commitment to the preimage can be published without revealing the preimage. For example, if bitcoin is sent to a P2PKH address, which is the hash of a public key, that bitcoin is committed to a certain public key even though the public key is not known by anyone but the owner, who we will call Alice. When Alice wishes to spend the bitcoin, she publishes the preimage, the public key, along with a signature, proving their control of the corresponding private key. With those two pieces of information, anyone validating the blockchain can verify that the bitcoin actually belonged to that public key, and that Alice controls that public key.

The Lightning Network also uses preimages as proof that a Lightning invoice has been paid. In this context, the hashed time locked contract (HTLC) serves as the commitment, promising to pay a routing node a fee in exchange for routing the desired payment, while the preimage, the (unhashed) time-locked contract, is the proof that the commitment has been satisfied. HTLCs are sent from the payer node to the routing node, to the receiving node, who returns the preimage of the HTLC to the routing node, who uses the preimage to claim the fee they were promised.

・Block height. The block height indicates how many blocks have come before this block.
・Block hash. The hash of the block header serves as Proof-of-Work for this block.
・Previous block hash. The hash of the previous block header ensures past blocks cannot be altered.
・Timestamp. The timestamp indicates when the block was published.
・Merkle root. A Merkle root is the hash of all the transactions included in this block.
・Difficulty. The difficulty is encoded and called the “bits”.
・Nonce. A nonce is a random number which helps miners satisfy the Proof-of-Work.

The block header serves as an efficient summary of a block and can be sent across the network and processed more rapidly than a full block. When miners hash their block continuously, searching for a valid hash as Proof-of-Work, they are in fact hashing the block header, not the entire block.

This is done for efficiency purposes, as hashing more data, including the thousands of transactions included in each block, takes more time. If miners were forced to hash the entire block, they would be incentivized to mine empty blocks in order to hash more efficiently. This would lower Bitcoin’s throughput and utility, as miners would lack incentive to process transactions.

The common input ownership heuristic is one of the most commonly used heuristics used in chain analysis. It assumes that, in a given transaction, all inputs were signed by the same entity. Until now, this has been a relatively safe assumption, as multisig usage remains low. The P2EP proposal was created in order to break this assumption and improve Bitcoin privacy.

Although P2EP’s syntax resembles Bitcoin’s many script types, P2EP is not a script. Rather, it is a protocol which allows two bitcoin users to transact in a privacy preserving manner. Using a peer-to-peer channel, such as an onion address, a sender and a receiver can exchange information about the UTXOs they would like to use as inputs in a transaction. They can then cooperatively construct and sign the transaction using the partially signed Bitcoin transaction (PSBT) standard defined in BIP 174. The resulting transaction will simply resemble a typical transaction with multiple inputs and multiple outputs.

Like other railways, a payment rail is the infrastructure, pathway, or technology enabling the transmission of assets to a counterparty.

Info: Historically, transacting parties did not require a digital payment rail because they could physically exchange cash or coin with ease.
Historically, transacting parties did not require a digital payment rail because they could physically exchange cash or coin with ease.
Today, governments surveil cash payments on credit and ACH rails - transactions exceeding a value of $10,000 garner additional scrutiny from the Financial Crimes Enforcement Network (FinCEN) and the Office of Foreign Assets Control (OFAC). The onset of payment rail analytics has caused payment data to become commoditized. Corporations monitor the patterns, amounts, and physical location of transactions on their payment rails.

Blockchain rails offer greater privacy, stronger security, and faster settlement times than legacy payment rails.

In order to fix this problem, commitment transactions are set up such that even after an old commitment transaction has been confirmed on the blockchain, if someone can produce a newer, valid commitment transaction from the same channel, this transaction can reclaim the stolen funds and additionally claim all of the funds from the thief’s side of the channel.