edits, first mention of SegWit

01_0_Introducing_Bitcoin.md

@@ -26,13 +26,13 @@ Obviously, Bitcoin is the heart of this book, but it's also the originator of ma
 
 **_Who Can You Send Coins To?_** The vast majority of bitcoin transactions involve coins being sent to individual people (or at least to individual Bitcoin addresses). However, more complex methodologies can be used to send bitcoins to groups of people or to scripts. These various methodologies have names like P2PKH, multisig, and P2SH.
 
-**_How Are Transactions Stored?_** Transactions are combined into larger blocks of data, which are then written to the blockchain ledger. A block is built in such a way that it cannot be replaced or rewritten once several blocks have been built after it. This is what makes bitcoins non-repudiable: the decentralized global ledger where everything is recorded is effectively a permanent and unchangeable database.
+**_How Are Transactions Stored?_** Transactions are combined into larger blocks of data, which are then written to the blockchain ledger. A block is built in such a way that it cannot be replaced or rewritten once several blocks have been built atop (following) it. This is what makes bitcoins non-repudiable: the decentralized global ledger where everything is recorded is effectively a permanent and unchangeable database.
 
 However, the process of building these blocks is stochastic: it's somewhat random, so you can never be assured that a transaction will be placed in a specific block. There can also be changes in blocks if they're very recent, but only if they're _very_ recent. So, things become non-repudiable (and permanent and unchangeable) after a little bit of time.
 
-**_How Are Transactions Protected?_** The funds contained in a Bitcoin transaction are locked with a cryptographic puzzle. These puzzles are designed so that they can be easily solved by the person who the funds were sent to. This is done using the power of public-key cryptography. 
+**_How Are Transactions Protected?_** The funds contained in a Bitcoin transaction are locked with a cryptographic puzzle. These puzzles are designed so that they can be easily solved by the person who the funds were sent to. This is done using the power of public-key cryptography. Technically, a transaction is protected by a signature that proves you're the owner of the public key that a transaction was sent to: this proof of ownership is the puzzle that's being solved.
 
-Funds are further protected by the use of hashes. Public keys aren't actually stored in the blockchain, only public-key hashes are. This means that even if quantum computer were to come along, Bitcoin transactions would remain protected by this second level of cryptography.
+Funds are further protected by the use of hashes. Public keys aren't actually stored in the blockchain until the funds are spent: only public-key hashes are. This means that even if quantum computer were to come along, Bitcoin transactions would remain protected by this second level of cryptography.
 
 **_How Are Transactions Created?_** The heart of each Bitcoin transaction is a FORTH-like scripting language that is used to lock the transaction. To respend the money, the recipient provides specific information to the script that proves he's the intended recipient.
 
@@ -40,7 +40,7 @@ However, these Bitcoin scripts are the lowest level of Bitcoin functionality. Mu
 
 ### Bitcoin — In Short
 
-One way to think of Bitcoin is as _a sequence of atomic transactions_. Each transaction is authenticated by a sender with the solution to a previous cryptographic puzzle that was stored as a script. The new transaction is locked for the recipient with a new cryptographic puzzle that is stored as a script. Every transaction is recorded in an immutable global ledger.
+One way to think of Bitcoin is as _a sequence of atomic transactions_. Each transaction is authenticated by a sender with the solution to a previous cryptographic puzzle that was stored as a script. The new transaction is locked for the recipient with a new cryptographic puzzle that is also stored as a script. Every transaction is recorded in an immutable global ledger.
 
 ## About Public-Key Cryptography
 
@@ -50,9 +50,9 @@ It's important to Bitcoin (and to most blockchain systems) because it's the basi
 
 **_What Is a Public Key?_** A public key is the key given out to other people. In a typical public-key system, a user generates a public key and a private key, then he gives the public key to all and sundry. Those recipients can encrypt information with the public key, but it can't be decrypted with the same public key because of the asymmetry of the key pair.
 
-**_What Is a Private Key?_** A private key is linked to a public key in a key pair. In a typical public-key system, a user keeps his private key secure and uses it to decrypt messages that were encrypted with his public key in the process of being sent to him..
+**_What Is a Private Key?_** A private key is linked to a public key in a key pair. In a typical public-key system, a user keeps his private key secure and uses it to decrypt messages that were encrypted with his public key before being sent to him.
 
-**_What Is a Signature?_** A message (or more commonly, a hash of a message) can be signed with a private key, creating a signature. Anyone with the corresponding public key can then validate the signature, which verifies that the signer owns the private key associated with the public key in question. 
+**_What Is a Signature?_** A message (or more commonly, a hash of a message) can be signed with a private key, creating a signature. Anyone with the corresponding public key can then validate the signature, which verifies that the signer owns the private key associated with the public key in question. _SegWit_ is a specific format for storing a signature on the Bitcoin network that we'll meet down the line.
 
 **_What Is a Hash Function?_** A hash function is an algorithm frequently used with cryptography. It's a way to map a large, arbitrary amount of data to a small, fixed amount of data. Hash functions used in cryptography are one-way and collision-resistant, meaning that a hash can reliably be linked to the original data, but the original data can not be regenerated from the hash. Hashes thus allow the transmission of small amounts of data to represent large amounts of data, which can be important for efficiency and storage requirements. 
 
@@ -88,7 +88,7 @@ One way to think of public-key cryptography is: _a way to enable public-key cryp
 
 ## About Blockchains
 
-Blockchain is the generalization of the methodology used by Bitcoin to create a distributed global ledger. Bitcoin is a blockchain as are any number of alt-coins, each of which lives in its networks and writes to its own chain. Sidechains like Liquid are blockchains too. Blockchains don't even need to have anything to do with finances. For example, there have been many discussions of using blockchains to protect self-sovereign identities.
+Blockchain is the generalization of the methodology used by Bitcoin to create a distributed global ledger. Bitcoin is a blockchain as are any number of alt-coins, each of which lives on its own networks and writes to its own chain. Sidechains like Liquid are blockchains too. Blockchains don't even need to have anything to do with finances. For example, there have been many discussions of using blockchains to protect self-sovereign identities.
 
 Though you need to understand the basics of how a blockchain works to understand how transactions work in Bitcoin, you won't need to go any further than that. Because blockchains have become a wide category of technology, those basic concepts are likely to be applicable to many other projects in this growing technology sector. The specific programming commands learned in this book will not be, however, as they're fairly specific to Bitcoin (and Lightning).