Merge pull request #266 from dimitris-t/patch-3

Typos in ch10.asciidoc

ch10.asciidoc

@@ -782,7 +782,7 @@ Neither side is "correct," or "incorrect". Both are valid perspectives of the bl
 .Visualization of a blockchain fork event: two blocks propagate, splitting the network
 image::images/fork3.png["Visualization of a blockchain fork event: two blocks propagate, splitting the network"]
 
-Mining nodes whose perspective resembles Node X will immediately beging mining a candidate block that extends the chain with "triangle" as its tip. By linking "triangle" as the parent of their candidate block, they are voting with their hashing power. Their vote supports the chain that they have elected as the main chain.
+Mining nodes whose perspective resembles Node X will immediately begin mining a candidate block that extends the chain with "triangle" as its tip. By linking "triangle" as the parent of their candidate block, they are voting with their hashing power. Their vote supports the chain that they have elected as the main chain.
 
 Any mining node whose perspective resembles Node Y, will start building a candidate node with "upside-down black triangle" as its parent, extending the chain that they believe is the main chain. And so, the race begins again.
 
@@ -841,7 +841,7 @@ In the last two years, the ASIC mining chips have become increasingly denser, ap
 
 ((("hashing race","mining pools", id="ix_ch10-asciidoc26", range="startofrange")))((("mining pools", id="ix_ch10-asciidoc27", range="startofrange")))In this highly competitive environment,((("solo miners"))) individual miners working alone (also known as solo miners) don't stand a chance. The likelihood of them finding a block to offset their electricity and hardware costs is so low that it represents a gamble, like playing the lottery. Even the fastest consumer ASIC mining system cannot keep up with commercial systems that stack tens of thousands of these chips in giant warehouses near hydro-electric power stations. Miners now collaborate to form mining pools, pooling their hashing power and sharing the reward among thousands of participants. By participating in a pool, miners get a smaller share of the overall reward, but typically get rewarded every day, reducing uncertainty.
 
-Let's look at a specific example. Assume a miner has purchased mining hardware with a combined hashing rate of 14,000 gigahashes per second (GH/s), or 14 TH/s. In 2017 this equipment costs approximately $2,500 USD. The hardware consumes 1375 watts (1.3 kW) of electricity when running, 32 kW-hours a day, at a cost of $1 to $2 per day on very low electricity rates. At current bitcoin difficulty, the miner will be able to solo mine a block approximately once every 4 years. If the miner does find a single block in that timeframe, the payout of 12.5 bitcoin, at approximately $1000 per bitcoin, will result in a single payout of $12,500, which will not even cover the entire cost of the hardware and the electricity consumed over the time period, leaving a net loss of approximately $1,000. However, the chance of finding a block in a four-year period depends on the miner's luck. He might find two blocks in four years and make a very large profit. Or he might not find a block for 5 years and suffer a bigger financial loss. Even worse, the difficulty of the bitcoin proof-of-work algorithm is likely to go up significantly over that period, at the current rate of growth of hashing power, meaning the miner has, at most, one year to break even before the hardware is effectively obsolete and must be replaced by more powerful mining hardware. If this miner participates in a mining pool, instead of waiting for a once-in-four-years $12,500 windfall, he will be able to earn approximately $50 to $60 per week. The regular payouts from a mining pool will help him amortize the cost of hardware and electricity over time without taking an enormous risk. The hardware will still be obsolete in one or two years and the risk is still high, but the revenue is at least regular and reliable over that period. Financially this only makes sense at very low electricity cost (less than 1 cent per kW) and only at very large scale.
+Let's look at a specific example. Assume a miner has purchased mining hardware with a combined hashing rate of 14,000 gigahashes per second (GH/s), or 14 TH/s. In 2017 this equipment costs approximately $2,500 USD. The hardware consumes 1375 watts (1.3 kW) of electricity when running, 32 kW-hours a day, at a cost of $1 to $2 per day on very low electricity rates. At current bitcoin difficulty, the miner will be able to solo mine a block approximately once every 4 years. If the miner does find a single block in that timeframe, the payout of 12.5 bitcoin, at approximately $1,000 per bitcoin, will result in a single payout of $12,500, which will not even cover the entire cost of the hardware and the electricity consumed over the time period, leaving a net loss of approximately $1,000. However, the chance of finding a block in a four-year period depends on the miner's luck. He might find two blocks in four years and make a very large profit. Or he might not find a block for 5 years and suffer a bigger financial loss. Even worse, the difficulty of the bitcoin proof-of-work algorithm is likely to go up significantly over that period, at the current rate of growth of hashing power, meaning the miner has, at most, one year to break even before the hardware is effectively obsolete and must be replaced by more powerful mining hardware. If this miner participates in a mining pool, instead of waiting for a once-in-four-years $12,500 windfall, he will be able to earn approximately $50 to $60 per week. The regular payouts from a mining pool will help him amortize the cost of hardware and electricity over time without taking an enormous risk. The hardware will still be obsolete in one or two years and the risk is still high, but the revenue is at least regular and reliable over that period. Financially this only makes sense at very low electricity cost (less than 1 cent per kW) and only at very large scale.
 
 Mining pools coordinate many hundreds or thousands of miners, over specialized pool-mining protocols. The individual miners configure their mining equipment to connect to a pool server, after creating an account with the pool. Their mining hardware remains connected to the pool server while mining, synchronizing their efforts with the other miners. Thus, the pool miners share the effort to mine a block and then share in the rewards.
 
@@ -887,7 +887,7 @@ Let's examine a practical example of a 51% attack. In the first chapter, we look
 
 In our example, malicious attacker Mallory goes to Carol's gallery and purchases a beautiful triptych painting depicting Satoshi Nakamoto as Prometheus. Carol sells "The Great Fire" paintings for $250,000 in bitcoin, to Mallory. Instead of waiting for six or more confirmations on the transaction, Carol wraps and hands the paintings to Mallory after only one confirmation. Mallory works with an accomplice, Paul, who operates a large mining pool, and the accomplice launches a 51% attack as soon as Mallory's transaction is included in a block. Paul directs the mining pool to re-mine the same block height as the block containing Mallory's transaction, replacing Mallory's payment to Carol with a transaction that double-spends the same input as Mallory's payment. The double-spend transaction consumes the same UTXO and pays it back to Mallory's wallet, instead of paying it to Carol, essentially allowing Mallory to keep the bitcoin. Paul then directs the mining pool to mine an additional block, so as to make the chain containing the double-spend transaction longer than the original chain (causing a fork below the block containing Mallory's transaction). When the blockchain fork resolves in favor of the new (longer) chain, the double-spent transaction replaces the original payment to Carol. Carol is now missing the three paintings and also has no bitcoin payment. Throughout all this activity, Paul's mining pool participants might remain blissfully unaware of the double-spend attempt, because they mine with automated miners and cannot monitor every transaction or block.
 
-To protect against this kind of attack, a merchant selling large-value items must wait at least six confirmations before giving the product to the buyer. Alternatively, the merchant should use an escrow((("multi-signature account"))) multi-signature account, again waiting for several confirmations after the escrow account is funded. The more confirmations elapse, the harder it becomes to invalidate a transaction with a 51% attack. For high-value items, payment by bitcoin will still be convenient and efficient even if the buyer has to wait 24 hours for delivery, which would correspond to approximaely 144 confirmations.
+To protect against this kind of attack, a merchant selling large-value items must wait at least six confirmations before giving the product to the buyer. Alternatively, the merchant should use an escrow((("multi-signature account"))) multi-signature account, again waiting for several confirmations after the escrow account is funded. The more confirmations elapse, the harder it becomes to invalidate a transaction with a 51% attack. For high-value items, payment by bitcoin will still be convenient and efficient even if the buyer has to wait 24 hours for delivery, which would correspond to approximately 144 confirmations.
 
 ((("consensus attacks","denial of service attack")))((("denial of service attack")))In addition to a double-spend attack, the other scenario for a consensus attack is to deny service to specific bitcoin participants (specific bitcoin addresses). An attacker with a majority of the mining power can simply ignore specific transactions. If they are included in a block mined by another miner, the attacker can deliberately fork and re-mine that block, again excluding the specific transactions. This type of attack can result in a sustained denial of service against a specific address or set of addresses for as long as the attacker controls the majority of the mining power.
 
@@ -975,7 +975,7 @@ The term _soft fork_ was introduced to distinguish this upgrade method from a "h
 
 One aspect of soft forks that is not immediately obvious is that soft fork upgrades can only be used to constrain the consensus rules, not to expand them. In order to be forwards compatible, transactions and blocks created under the new rules must be valid under the old rules too, but not vice-versa. The new rules can only limit what is valid, otherwise they will trigger a hard fork when rejected under the old rules.
 
-Soft forks can be implemented in a number of ways - the term does not define a single method, rather a set of methods which all have one thing in commmon: they don't require all nodes to upgrade or force non-upgraded nodes out of consensus.
+Soft forks can be implemented in a number of ways - the term does not define a single method, rather a set of methods which all have one thing in common: they don't require all nodes to upgrade or force non-upgraded nodes out of consensus.
 
 ===== Soft Forks re-defining NOP opcodes