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When first bitcoin, the signing-only wallet creates a parent private key and transfers the corresponding parent public key to the networked wallet. Return to top of page. Oracles can also create bets themselves and deliberately create bugs in their software double profit from them. Inventories are unique identifiers for information on the detection. His full unhashed public keyso the pubkey script can check that it hashes to spend same value logic the pubkey hash provided by Alice.
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The very limited added benefits are not worth it because we also need to consider the risks. These blocks are commonly addressed by their block height —the number of blocks between them and the first Bitcoin block block 0 , most commonly known as the genesis block. Keeping years of logs can make the threat-detection process more effective, he said. Charlie-the-customer wants to buy a product from Bob-the-businessman, but neither of them trusts the other person, so they use a contract to help ensure Charlie gets his merchandise and Bob gets his payment. Just the hard lessons learned—and the personal stories of how these successful people learned those lessons the hard way. If you spend an output from one unconfirmed transaction in a second transaction, the second transaction becomes invalid if transaction malleability changes the first transaction.
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The obvious way to do that, which is detection unsafe, is simply to return the satoshis to double pubkey script from which they came. Waymo talks accelerated testing ahead of autonomous ride-hailing launch. This will logic be your bitcoin target page; unless you change your configuration again, or you delete your cookies. The wallet provider fee is a flat 0. In double transaction, the spender and receiver each spend to spend other all public keys or addresses used in the transaction. If it finds a bitcoin hash, logic replies with block detection starting with the next block from that point.
Developer Guide - Bitcoin
To maintain consensus , all full nodes validate blocks using the same consensus rules. However, sometimes the consensus rules are changed to introduce new features or prevent network abuse. When the new rules are implemented, there will likely be a period of time when non-upgraded nodes follow the old rules and upgraded nodes follow the new rules, creating two possible ways consensus can break:.
A block following the new consensus rules is accepted by upgraded nodes but rejected by non-upgraded nodes. For example, a new transaction feature is used within a block: A block violating the new consensus rules is rejected by upgraded nodes but accepted by non-upgraded nodes.
For example, an abusive transaction feature is used within a block: In the first case, rejection by non-upgraded nodes , mining software which gets block chain data from those non-upgraded nodes refuses to build on the same chain as mining software getting data from upgraded nodes. This creates permanently divergent chains—one for non-upgraded nodes and one for upgraded nodes —called a hard fork.
This is called a soft fork. Although a fork is an actual divergence in block chains , changes to the consensus rules are often described by their potential to create either a hard or soft fork. Consensus rule changes may be activated in various ways. Multiple soft forks such as BIP30 have been activated via a flag day where the new rule began to be enforced at a preset time or block height.
Such forks activated via a flag day are known as User Activated Soft Forks UASF as they are dependent on having sufficient users nodes to enforce the new rules after the flag day.
Once the signalling threshold has been passed, all nodes will begin enforcing the new rules. BIP50 describes both an accidental hard fork , resolved by temporary downgrading the capabilities of upgraded nodes , and an intentional hard fork when the temporary downgrade was removed. A document from Gavin Andresen outlines how future rule changes may be implemented. Non-upgraded nodes may use and distribute incorrect information during both types of forks , creating several situations which could lead to financial loss.
In particular, non-upgraded nodes may relay and accept transactions that are considered invalid by upgraded nodes and so will never become part of the universally-recognized best block chain. Non-upgraded nodes may also refuse to relay blocks or transactions which have already been added to the best block chain , or soon will be, and so provide incomplete information.
Bitcoin Core includes code that detects a hard fork by looking at block chain proof of work. If a non-upgraded node receives block chain headers demonstrating at least six blocks more proof of work than the best chain it considers valid, the node reports a warning in the getnetworkinfo RPC results and runs the -alertnotify command if set. Full nodes can also check block and transaction version numbers. Bitcoin Core reports this situation through the getnetworkinfo RPC and -alertnotify command if set.
SPV clients should also monitor for block and transaction version number increases to ensure they process received transactions and create new transactions using the current consensus rules. Transactions let users spend satoshis. Each transaction is constructed out of several parts which enable both simple direct payments and complex transactions.
This section will describe each part and demonstrate how to use them together to build complete transactions. To keep things simple, this section pretends coinbase transactions do not exist. Instead of pointing out the coinbase exception to each rule, we invite you to read about coinbase transactions in the block chain section of this guide. The figure above shows the main parts of a Bitcoin transaction. Each transaction has at least one input and one output.
Each input spends the satoshis paid to a previous output. When your Bitcoin wallet tells you that you have a 10, satoshi balance, it really means that you have 10, satoshis waiting in one or more UTXOs.
Each transaction is prefixed by a four-byte transaction version number which tells Bitcoin peers and miners which set of rules to use to validate it. This lets developers create new rules for future transactions without invalidating previous transactions. An output has an implied index number based on its location in the transaction—the index of the first output is zero.
The output also has an amount in satoshis which it pays to a conditional pubkey script. Anyone who can satisfy the conditions of that pubkey script can spend up to the amount of satoshis paid to it. It also has a signature script which allows it to provide data parameters that satisfy the conditionals in the pubkey script.
The sequence number and locktime are related and will be covered together in a later subsection. The figures below help illustrate how these features are used by showing the workflow Alice uses to send Bob a transaction and which Bob later uses to spend that transaction. P2PKH lets Alice spend satoshis to a typical Bitcoin address , and then lets Bob further spend those satoshis using a simple cryptographic key pair.
A copy of that data is deterministically transformed into an secpk1 public key. Because the transformation can be reliably repeated later, the public key does not need to be stored. The public key pubkey is then cryptographically hashed.
This pubkey hash can also be reliably repeated later, so it also does not need to be stored. The hash shortens and obfuscates the public key , making manual transcription easier and providing security against unanticipated problems which might allow reconstruction of private keys from public key data at some later point. Bob provides the pubkey hash to Alice. Pubkey hashes are almost always sent encoded as Bitcoin addresses , which are base58 -encoded strings containing an address version number, the hash, and an error-detection checksum to catch typos.
The address can be transmitted through any medium, including one-way mediums which prevent the spender from communicating with the receiver, and it can be further encoded into another format, such as a QR code containing a bitcoin: Once Alice has the address and decodes it back into a standard hash, she can create the first transaction.
These instructions are called the pubkey script or scriptPubKey. Alice broadcasts the transaction and it is added to the block chain. When, some time later, Bob decides to spend the UTXO , he must create an input which references the transaction Alice created by its hash, called a Transaction Identifier txid , and the specific output she used by its index number output index.
Signature scripts are also called scriptSigs. Pubkey scripts and signature scripts combine secpk1 pubkeys and signatures with conditional logic, creating a programmable authorization mechanism. His full unhashed public key , so the pubkey script can check that it hashes to the same value as the pubkey hash provided by Alice. This lets the pubkey script verify that Bob owns the private key which created the public key. In essence, the entire transaction is signed except for any signature scripts , which hold the full public keys and secpk1 signatures.
After putting his signature and public key in the signature script , Bob broadcasts the transaction to Bitcoin miners through the peer-to-peer network. Each peer and miner independently validates the transaction before broadcasting it further or attempting to include it in a new block of transactions. The validation procedure requires evaluation of the signature script and pubkey script. In a P2PKH output , the pubkey script is:.
In a P2PKH transaction, the signature script contains an secpk1 signature sig and full public key pubkey , creating the following concatenation:. The script language is a Forth-like stack-based language deliberately designed to be stateless and not Turing complete. Statelessness ensures that once a transaction is added to the block chain , there is no condition which renders it permanently unspendable.
Turing-incompleteness specifically, a lack of loops or gotos makes the script language less flexible and more predictable, greatly simplifying the security model. The figure below shows the evaluation of a standard P2PKH pubkey script ; below the figure is a description of the process. The public key also from the signature script is pushed on top of the signature.
Now it gets interesting: If the value is false it immediately terminates evaluation and the transaction validation fails. Otherwise it pops the true value off the stack. If false is not at the top of the stack after the pubkey script has been evaluated, the transaction is valid provided there are no other problems with it. Pubkey scripts are created by spenders who have little interest what that script does. Receivers do care about the script conditions and, if they want, they can ask spenders to use a particular pubkey script.
Unfortunately, custom pubkey scripts are less convenient than short Bitcoin addresses and there was no standard way to communicate them between programs prior to widespread implementation of the BIP70 Payment Protocol discussed later.
To solve these problems, pay-to-script-hash P2SH transactions were created in to let a spender create a pubkey script containing a hash of a second script, the redeem script. Bob creates a redeem script with whatever script he wants, hashes the redeem script , and provides the redeem script hash to Alice. When Bob wants to spend the output , he provides his signature along with the full serialized redeem script in the signature script.
The peer-to-peer network ensures the full redeem script hashes to the same value as the script hash Alice put in her output ; it then processes the redeem script exactly as it would if it were the primary pubkey script , letting Bob spend the output if the redeem script does not return false. The hash of the redeem script has the same properties as a pubkey hash —so it can be transformed into the standard Bitcoin address format with only one small change to differentiate it from a standard address.
This is the IsStandard test, and transactions which pass it are called standard transactions. Non- standard transactions —those that fail the test—may be accepted by nodes not using the default Bitcoin Core settings.
If they are included in blocks , they will also avoid the IsStandard test and be processed. Besides making it more difficult for someone to attack Bitcoin for free by broadcasting harmful transactions, the standard transaction test also helps prevent users from creating transactions today that would make adding new transaction features in the future more difficult.
For example, as described above, each transaction includes a version number—if users started arbitrarily changing the version number, it would become useless as a tool for introducing backwards-incompatible features. As of Bitcoin Core 0. P2PKH is the most common form of pubkey script used to send a transaction to one or multiple Bitcoin addresses.
P2SH is used to send a transaction to a script hash. Each of the standard pubkey scripts can be used as a P2SH redeem script , but in practice only the multisig pubkey script makes sense until more transaction types are made standard.
Although P2SH multisig is now generally used for multisig transactions, this base script can be used to require multiple signatures before a UTXO can be spent. In multisig pubkey scripts , called m-of-n , m is the minimum number of signatures which must match a public key ; n is the number of public keys being provided.
The signature script must provide signatures in the same order as the corresponding public keys appear in the pubkey script or redeem script. Null data transaction type relayed and mined by default in Bitcoin Core 0. It is preferable to use null data transactions over transactions that bloat the UTXO database because they cannot be automatically pruned; however, it is usually even more preferable to store data outside transactions if possible.
Consensus rules allow null data outputs up to the maximum allowed pubkey script size of 10, bytes provided they follow all other consensus rules , such as not having any data pushes larger than bytes. There must still only be a single null data output and it must still pay exactly 0 satoshis. The -datacarriersize Bitcoin Core configuration option allows you to set the maximum number of bytes in null data outputs that you will relay or mine.
If you use anything besides a standard pubkey script in an output , peers and miners using the default Bitcoin Core settings will neither accept, broadcast, nor mine your transaction. When you try to broadcast your transaction to a peer running the default settings, you will receive an error. If you create a redeem script , hash it, and use the hash in a P2SH output , the network sees only the hash, so it will accept the output as valid no matter what the redeem script says.
This allows payment to non-standard scripts, and as of Bitcoin Core 0. The transaction must be finalized: The transaction must be smaller than , bytes. Bare non-P2SH multisig transactions which require more than 3 public keys are currently non-standard. It cannot push new opcodes , with the exception of opcodes which solely push data to the stack.
Since the signature protects those parts of the transaction from modification, this lets signers selectively choose to let other people modify their transactions. The various options for what to sign are called signature hash types. This input , as well as other inputs , are included in the signature. The sequence numbers of other inputs are not included in the signature , and can be updated. Allows anyone to add or remove other inputs. Because each input is signed, a transaction with multiple inputs can have multiple signature hash types signing different parts of the transaction.
For example, a single- input transaction signed with NONE could have its output changed by the miner who adds it to the block chain. Called nLockTime in the Bitcoin Core source code. The locktime indicates the earliest time a transaction can be added to the block chain. Locktime allows signers to create time-locked transactions which will only become valid in the future, giving the signers a chance to change their minds.
If any of the signers change their mind, they can create a new non- locktime transaction. The new transaction will use, as one of its inputs , one of the same outputs which was used as an input to the locktime transaction. This makes the locktime transaction invalid if the new transaction is added to the block chain before the time lock expires. Care must be taken near the expiry time of a time lock. The peer-to-peer network allows block time to be up to two hours ahead of real time, so a locktime transaction can be added to the block chain up to two hours before its time lock officially expires.
Also, blocks are not created at guaranteed intervals, so any attempt to cancel a valuable transaction should be made a few hours before the time lock expires. Previous versions of Bitcoin Core provided a feature which prevented transaction signers from using the method described above to cancel a time-locked transaction, but a necessary part of this feature was disabled to prevent denial of service attacks. A legacy of this system are four-byte sequence numbers in every input.
Even today, setting all sequence numbers to 0xffffffff the default in Bitcoin Core can still disable the time lock, so if you want to use locktime , at least one input must have a sequence number below the maximum. Since sequence numbers are not used by the network for any other purpose, setting any sequence number to zero is sufficient to enable locktime. Locktime itself is an unsigned 4-byte integer which can be parsed two ways: If less than million, locktime is parsed as a block height.
The transaction can be added to any block which has this height or higher. If greater than or equal to million, locktime is parsed using the Unix epoch time format the number of seconds elapsed since T The transaction can be added to any block whose block time is greater than the locktime. Transactions pay fees based on the total byte size of the signed transaction.
Fees per byte are calculated based on current demand for space in mined blocks with fees rising as demand increases. The transaction fee is given to the Bitcoin miner , as explained in the block chain section , and so it is ultimately up to each miner to choose the minimum transaction fee they will accept. Before Bitcoin Core 0. After the priority area, all transactions are prioritized based on their fee per byte, with higher-paying transactions being added in sequence until all of the available space is filled.
Please see the verifying payment section for why this could be important. Few people will have UTXOs that exactly match the amount they want to pay, so most transactions include a change output. Change outputs are regular outputs which spend the surplus satoshis from the UTXOs back to the spender. In a transaction, the spender and receiver each reveal to each other all public keys or addresses used in the transaction.
If the same public key is reused often, as happens when people use Bitcoin addresses hashed public keys as static payment addresses , other people can easily track the receiving and spending habits of that person, including how many satoshis they control in known addresses. If each public key is used exactly twice—once to receive a payment and once to spend that payment—the user can gain a significant amount of financial privacy. Even better, using new public keys or unique addresses when accepting payments or creating change outputs can be combined with other techniques discussed later, such as CoinJoin or merge avoidance , to make it extremely difficult to use the block chain by itself to reliably track how users receive and spend their satoshis.
Avoiding key reuse can also provide security against attacks which might allow reconstruction of private keys from public keys hypothesized or from signature comparisons possible today under certain circumstances described below, with more general attacks hypothesized. Unique non-reused P2PKH and P2SH addresses protect against the first type of attack by keeping ECDSA public keys hidden hashed until the first time satoshis sent to those addresses are spent, so attacks are effectively useless unless they can reconstruct private keys in less than the hour or two it takes for a transaction to be well protected by the block chain.
Unique non-reused private keys protect against the second type of attack by only generating one signature per private key , so attackers never get a subsequent signature to use in comparison-based attacks. Existing comparison-based attacks are only practical today when insufficient entropy is used in signing or when the entropy used is exposed by some means, such as a side-channel attack.
So, for both privacy and security, we encourage you to build your applications to avoid public key reuse and, when possible, to discourage users from reusing addresses. If your application needs to provide a fixed URI to which payments should be sent, please see the bitcoin: For example, an attacker can add some data to the signature script which will be dropped before the previous pubkey script is processed. Although the modifications are non-functional—so they do not change what inputs the transaction uses nor what outputs it pays—they do change the computed hash of the transaction.
Since each transaction links to previous transactions using hashes as a transaction identifier txid , a modified transaction will not have the txid its creator expected. But it does become a problem when the output from a transaction is spent before that transaction is added to the block chain.
Bitcoin developers have been working to reduce transaction malleability among standard transaction types, one outcome of those efforts is BIP Segregated Witness , which is supported by Bitcoin Core and was activated in August When SegWit is not being used, new transactions should not depend on previous transactions which have not been added to the block chain yet, especially if large amounts of satoshis are at stake.
Transaction malleability also affects payment tracking. Current best practices for transaction tracking dictate that a transaction should be tracked by the transaction outputs UTXOs it spends as inputs , as they cannot be changed without invalidating the transaction.
Best practices further dictate that if a transaction does seem to disappear from the network and needs to be reissued, that it be reissued in a way that invalidates the lost transaction. One method which will always work is to ensure the reissued payment spends all of the same outputs that the lost transaction used as inputs. Contracts are transactions which use the decentralized Bitcoin system to enforce financial agreements.
Bitcoin contracts can often be crafted to minimize dependency on outside agents, such as the court system, which significantly decreases the risk of dealing with unknown entities in financial transactions. The following subsections will describe a variety of Bitcoin contracts already in use.
Because contracts deal with real people, not just transactions, they are framed below in story format. Besides the contract types described below, many other contract types have been proposed. Several of them are collected on the Contracts page of the Bitcoin Wiki. Charlie-the-customer wants to buy a product from Bob-the-businessman, but neither of them trusts the other person, so they use a contract to help ensure Charlie gets his merchandise and Bob gets his payment. A simple contract could say that Charlie will spend satoshis to an output which can only be spent if Charlie and Bob both sign the input spending it.
Charlie spends his satoshis to an output which can only be spent if two of the three people sign the input. To create a multiple- signature multisig output , they each give the others a public key. Then Bob creates the following P2SH multisig redeem script:. Opcodes to push the public keys onto the stack are not shown. This is a 2-of-3 multisig pubkey script , more generically called a m-of-n pubkey script where m is the minimum matching signatures required and n in the number of public keys provided.
Then he hashes the redeem script to create a P2SH redeem script and pays the satoshis to it. Bob sees the payment get added to the block chain and ships the merchandise. Unfortunately, the merchandise gets slightly damaged in transit. They turn to Alice to resolve the issue. Alice asks for photo evidence from Charlie along with a copy of the redeem script Bob created and Charlie checked. In the signature script Alice puts her signature and a copy of the unhashed serialized redeem script that Bob created.
She gives a copy of the incomplete transaction to both Bob and Charlie. Either one of them can complete it by adding his signature to create the following signature script:. Opcodes to push the signatures and redeem script onto the stack are not shown. Note that the signature script must provide signatures in the same order as the corresponding public keys appear in the redeem script.
When the transaction is broadcast to the network , each peer checks the signature script against the P2SH output Charlie previously paid, ensuring that the redeem script matches the redeem script hash previously provided.
Then the redeem script is evaluated, with the two signatures being used as input data. However, if Alice created and signed a transaction neither of them would agree to, such as spending all the satoshis to herself, Bob and Charlie can find a new arbitrator and sign a transaction spending the satoshis to another 2-of-3 multisig redeem script hash , this one including a public key from that second arbitrator.
This means that Bob and Charlie never need to worry about their arbitrator stealing their money. Alice also works part-time moderating forum posts for Bob. Alas, Bob often forgets to pay her, so Alice demands to be paid immediately after each post she approves or rejects. Bob asks Alice for her public key and then creates two transactions. The first transaction pays millibitcoins to a P2SH output whose 2-of-2 multisig redeem script requires signatures from both Alice and Bob. This is the bond transaction.
Broadcasting this transaction would let Alice hold the millibitcoins hostage, so Bob keeps this transaction private for now and creates a second transaction. This is the refund transaction. She then asks Bob for the bond transaction and checks that the refund transaction spends the output of the bond transaction.
She can now broadcast the bond transaction to the network to ensure Bob has to wait for the time lock to expire before further spending his millibitcoins. Now, when Alice does some work worth 1 millibitcoin , she asks Bob to create and sign a new version of the refund transaction. Version two of the transaction spends 1 millibitcoin to Alice and the other 99 back to Bob; it does not have a locktime , so Alice can sign it and spend it whenever she wants. Alice and Bob repeat these work-and-pay steps until Alice finishes for the day, or until the time lock is about to expire.
Alice signs the final version of the refund transaction and broadcasts it, paying herself and refunding any remaining balance to Bob. The next day, when Alice starts work, they create a new micropayment channel. If Alice fails to broadcast a version of the refund transaction before its time lock expires, Bob can broadcast the first version and receive a full refund. Transaction malleability , discussed above in the Transactions section, is another reason to limit the value of micropayment channels.
For larger payments, Bitcoin transaction fees are very low as a percentage of the total transaction value, so it makes more sense to protect payments with immediately-broadcast separate transactions. The bitcoinj Java library provides a complete set of micropayment functions, an example implementation, and a tutorial all under an Apache license.
Alice is concerned about her privacy. She knows every transaction gets added to the public block chain , so when Bob and Charlie pay her, they can each easily track those satoshis to learn what Bitcoin addresses she pays, how much she pays them, and possibly how many satoshis she has left.
The CoinJoin-style contract, shown in the illustration below, makes this decision easy: They then each generate a brand new public key and give UTXO details and pubkey hashes to the facilitator. In this case, the facilitator is AnonGirl; she creates a transaction spending each of the UTXOs to three equally-sized outputs. She gives the partially-signed transaction to Nemo who signs his inputs the same way and passes it to Neminem, who also signs it the same way.
Neminem then broadcasts the transaction to the peer-to-peer network , mixing all of the millibitcoins in a single transaction. If Alice does a few more CoinJoins, Bob and Charlie might have to guess which transactions made by dozens or hundreds of people were actually made by Alice.
But against anyone casually browsing block chain history, Alice gains plausible deniability. The CoinJoin technique described above costs the participants a small amount of satoshis to pay the transaction fee. An alternative technique, purchaser CoinJoin, can actually save them satoshis and improve their privacy at the same time. AnonGirl waits in the IRC chatroom until she wants to make a purchase. She announces her intention to spend satoshis and waits until someone else wants to make a purchase, likely from a different merchant.
Then they combine their inputs the same way as before but set the outputs to the separate merchant addresses so nobody will be able to figure out solely from block chain history which one of them bought what from the merchants. An alpha-quality as of this writing implementation of decentralized CoinJoin is CoinMux , available under the Apache license.
A Bitcoin wallet can refer to either a wallet program or a wallet file. Wallet programs create public keys to receive satoshis and use the corresponding private keys to spend those satoshis.
Wallet files store private keys and optionally other information related to transactions for the wallet program. Two wallet programs can work together, one program distributing public keys in order to receive satoshis and another program signing transactions spending those satoshis.
Wallet programs also need to interact with the peer-to-peer network to get information from the block chain and to broadcast new transactions. This leaves us with three necessary, but separable, parts of a wallet system: In the subsections below, we will describe common combinations of these parts.
In many cases, P2PKH or P2SH hashes will be distributed instead of public keys , with the actual public keys only being distributed when the outputs they control are spent. The simplest wallet is a program which performs all three functions: As of this writing, almost all popular wallets can be used as full-service wallets.
The main advantage of full-service wallets is that they are easy to use. A single program does everything the user needs to receive and spend satoshis. The main disadvantage of full-service wallets is that they store the private keys on a device connected to the Internet. The compromise of such devices is a common occurrence, and an Internet connection makes it easy to transmit private keys from a compromised device to an attacker.
To help protect against theft, many wallet programs offer users the option of encrypting the wallet files which contain the private keys.
To increase security, private keys can be generated and stored by a separate wallet program operating in a more secure environment.
These signing-only wallets work in conjunction with a networked wallet which interacts with the peer-to-peer network. Signing-only wallets programs typically use deterministic key creation described in a later subsection to create parent private and public keys which can create child private and public keys. When first run, the signing-only wallet creates a parent private key and transfers the corresponding parent public key to the networked wallet.
The networked wallet uses the parent public key to derive child public keys , optionally helps distribute them, monitors for outputs spent to those public keys , creates unsigned transactions spending those outputs , and transfers the unsigned transactions to the signing-only wallet. After the optional review step, the signing-only wallet uses the parent private key to derive the appropriate child private keys and signs the transactions, giving the signed transactions back to the networked wallet.
The networked wallet then broadcasts the signed transactions to the peer-to-peer network. The following subsections describe the two most common variants of signing-only wallets: Several full-service wallets programs will also operate as two separate wallets: The offline wallet is so named because it is intended to be run on a device which does not connect to any network , greatly reducing the number of attack vectors.
If this is the case, it is usually up to the user to handle all data transfer using removable media such as USB drives. Offline Disable all network connections on a device and install the wallet software.
Start the wallet software in offline mode to create the parent private and public keys. Copy the parent public key to removable media. Online Install the wallet software on another device, this one connected to the Internet, and import the parent public key from the removable media.
As you would with a full-service wallet , distribute public keys to receive payment. When ready to spend satoshis , fill in the output details and save the unsigned transaction generated by the wallet to removable media. Offline Open the unsigned transaction in the offline instance, review the output details to make sure they spend the correct amount to the correct address. This prevents malware on the online wallet from tricking the user into signing a transaction which pays an attacker.
After review, sign the transaction and save it to removable media. Online Open the signed transaction in the online instance so it can broadcast it to the peer-to-peer network. The primary advantage of offline wallets is their possibility for greatly improved security over full-service wallets. The primary disadvantage of offline wallets is hassle. For maximum security, they require the user dedicate a device to only offline tasks.
The offline device must be booted up whenever funds are to be spent, and the user must physically copy data from the online device to the offline device and back. Hardware wallets are devices dedicated to running a signing-only wallet.
O newer chips might reboot more often than normal because of problems with the patches issued to fix the so-called Spectre and Meltdown security flaws, the company said on Wednesday. Last week, Intel said it had received reports that its security patches were causing problems in systems with its older Broadwell and Haswell chips.
O and ARM Holdings. Intel on Wednesday also quantified how much of a performance hit the patches cause for data center customers. For common tasks such as running website servers, the patches caused a 2 percent slowdown, Intel said. Another test that simulated online transactions at a stock brokerage showed a 4 percent slowdown, the company said.
For some types for work involving servers that store large amounts of data and try to retrieve it quickly, the company said the slowdown could be as severe as 18 percent to 25 percent. Jalopnik and Doug DeMuro echoed the view that the Model 3 is a unique car — futuristic and exciting. For over a decade, the Camry has been the best-selling sedan in the United States. Photo by Carl Quinn. In my somewhat subjective estimation — backed up by several impartial car reviewers — the Model 3 offers greater quality than an ordinary entry-level luxury car like the BMW OTCPK: This is an unprecedented level of price performance.
Total cost of ownership includes the full costs of owning a vehicle, including energy costs i. They also compare the Model 3 to the BMW i, a car with a similar level of luxury, at best equal driving performance, and inferior technology. Two Bit da Vinci notes that beyond their fifth year, the maintenance cost for gasoline cars increases significantly with several parts requiring replacement. Not so for electric cars. Over a seven-year or eight-year timeframe, the cost comparison is likely even more favorable to the Model 3.
A newer gasoline car can survive for , miles before it needs to be scrapped. Data from the Tesla Model S shows that an electric car can drive , miles with minimal battery degradation. Based on this data, electric cars are expected to have much longer lifetimes than gasoline cars, perhaps as much as , miles. This makes the total cost of ownership comparison extremely favorable over a year timeframe. After 15 years, a Model 3 may still be running smoothly while a gasoline car is long gone.
The same goes for cases of high utilization such as taxis or ride-hailing services. Looking ahead to autonomous ride-hailing, self-driving electric cars will savagely outcompete self-driving gasoline cars.
Photo by Seungho Yang. For this reason, I believe that demand for the Model 3 will be like nothing the automotive industry has seen in recent decades. Research has shown that consumers are responsive to the total cost of ownership of vehicles, not just sticker price. Gene Munster speculates that Tesla could sell 2. Many consumers will wonder why they would want to buy any other car. Tesla has advantages in software, design, and battery pack economies of scale that competitors show no signs of overcoming.
Some waited over an hour in line just to see the car up-close for a few minutes. This did not occur for the Chevy Bolt, or any other car in memory for that matter. The best advertising for the Model 3 will be knowing someone who drives one, especially someone as enthusiastic as the , people who held a reservation as of August 2. I expect that demand will greatly increase over time as more people learn about the car. Another factor driving increased demand will be the development of Enhanced Autopilot and more advanced autonomy features.
Photo by Andrew Wilder. If Gene Munster is correct in his speculation that Tesla will sell 2. At an auto industry average 0.
Remember, these calculations exclude revenue from all other vehicles and lines of business, including solar and energy storage. I think the timeframe is too long for two reasons. First, by there is a good chance that autonomous ride-hailing will affect overall vehicle demand in a way that Munster is not accounting for. What factors prevent sales from reaching 2. The bottom line is that although it is difficult to predict the future in much detail, I can say with high confidence that the Model 3 will break sales records as soon as the limiting factor is demand, not production.
Once production ramps to meet demand, I would be surprised if it is not the best-selling sedan in the United States. An alternative way to model future revenue and market cap is through the autonomous ride-hailing business. Suppose Tesla produces just 5 million cars with self-driving hardware over the seven years from to , an average production of , cars per year.
Suppose that each self-driving vehicle replaces five conventional vehicles. Given billion passenger vehicles on the road globally estimates vary widely , that means there is a need for a million to million self-driving vehicles. The main obstacle to the Model 3 achieving a high sales volume is achieving a high production volume. Product risk is low and execution risk is moderate or high. I wrote this article myself, and it expresses my own opinions. I am not receiving compensation for it other than from Seeking Alpha.
I have no business relationship with any company whose stock is mentioned in this article. Instead of a traditional IPO that makes shares available to the general public, Stockholm-based Spotify will opt to directly list on the exchange , making its shares available only to institutional investors and eliminating the need for underwriters, a. The move could shake up Wall Street. IPOs are usually a lucrative business for investment banks, but in the last few years revenues from equity capital market ECM fees have dropped.
Goldman Sachs Group Inc. Those institutions will perform some of the traditional tasks expected of them, but in a less prominent way. Why the novel strategy? Spotify, as measured by either its subscription service or its ad-supported free version, is the most popular music streaming service, according to the New York Times.
It is, however, facing a copyright suit from Wixen Music Publishing, filed in late December I researched several providers and talked to sales reps from each — this was a big-ticket purchase, so I wanted to be sure I had as much information as possible.
The problems started shortly after. My support tickets took an average of days to get a response. I felt let down. The product itself may have been the right solution for our needs, but the poor onboarding support I received left me with so much post-purchase regret that I wound up cancelling the contract and moving to a different provider.
A full lifecycle program of sales needs to take two factors into consideration: This ignores the fact that, during the post-purchase period, new customers are — consciously and subconsciously — evaluating whether or not they made the right choice. Research by Seung Hwan Lee and June Cotte of the University of Western Ontario, Canada, published by the Association for Consumer Research , suggests that there are actually four distinct types of post-purchase consumer regret:.
If post-purchase regret is left unaddressed, both of these scenarios can lead to cancellations and refund requests as in the case of the SaaS purchase I described earlier. Basically, salespeople and the companies they work for benefit financially from referrals. Treating onboarding as part of the sales process and implementing a referral-driving workflow leads to happier customers and better results for your company.
Does your sales process stop at the close? If so, share your ideas for extending sales throughout the full customer lifecycle by leaving me a note below: As the citizens of Hawaii came out of hiding in their bathtubs and basements Saturday morning, after learning that the emergency alert they had received, warning of an imminent nuclear missile attack, was a false alarm, their fear and panic transformed into rage.
Could it really be that the emergency alert system is so simplistic, it only takes the twitch of a finger to send Hawaii into terror and chaos? During a press conference Saturday afternoon, the governor and officials at the Hawaii Emergency Management Agency confirmed that the blunder occurred during a twice-daily test that happens when staffers switch shifts.
In this case, the staffer accidentally selected a live alert, instead of a test alert. After the alert went out, there was no way to automatically cancel or recall the message. Instead, they took to Twitter to tell the public the alert was a false alarm, but it took a full 38 minutes to manually generate and disseminate another corrective emergency alert that reached all Hawaiians.
The Integrated Public Alert and Warning System, or IPAWS, manages both the emergency alerts you get on your phone and the national emergency alert system, which broadcasts to television stations. Those pre-loaded emergency alerts, scary as they may seem, are necessary, says Thomas Karako, a senior fellow at the Center for Strategic and International Studies. Open 24 hours a day, seven days a week, its staffers—known as watch standers—monitor a global network of sensors that can detect a missile launch.
If it detects a missile en route to Hawaii, NORAD would send a message to Pacific Command, which would in turn alert the state emergency management center. The Emergency Alert System, which predated Wireless Emergency Alerts, was created with the specific goal of letting the president communicate with the country in the event of a nuclear attack.
The US has spent billions of dollars maintaining this system, and yet, 38 minutes went by before Hawaii sent a second message, acknowledging the false alarm. The president, or any of the federal agencies with access to the emergency alert system, could have corrected the record much sooner. Where were they with all of this? This was purely a state exercise. Though all 50 states use it, not all local governments are part of the voluntary system, leaving some cities without a uniform way to alert their citizens of a local threat.
In some cases, Simpson says, those emergency centers only staff up when a threat appears imminent. Perhaps the most critical issue this false alarm highlights is the need for a firewall between the test mode and live mode in the emergency response interface. It appears that was not the case in Hawaii. The Hawaii emergency management officials also noted the obvious need for a better way to recall accidental messages. But the opposite should occur. UL] which was recently blocked by U.
It is also grappling with new regulations, requiring mobile payment firms to sharply increase the amount of client funds in interest-free reserve accounts, which will likely reduce profits. Alipay has a popular end-of-year feature that allows its customers to analyze how they have spent their money over the year. At the end of , the feature began enrolling users who wanted to look at their bills into the credit scoring system, Sesame Credit.
That allowed Sesame Credit to collect their data and share the analysis with its partners. Samsung is going all in on the Internet of things, betting that connected appliances and faster Internet speeds will result in happier customers. And it plans to use its existing SmartThings app to ensure that those devices can all talk to each other—from the TV to the phone to the refrigerator to the washing machine. What that means for users will depend on which Samsung appliances they own, of course.
One example is people who buy a new Samsung TV will no longer have to worry about entering user names and passwords for services like Netflix , Hulu, and Spotify when they initially set up their TVs. That information will automatically entered into the TV by checking other systems in which the customer is logged in, making it a more seamless experience. As part of the initiative, Samsung will expand the number of smart refrigerator models it sells by introducing 14 new models that come with its integrated screen and newly expanded FamilyHub technology that lets owners stream music, leave notes to each other, and view the contents of the fridge in real time.
Samsung has previously tried and failed to make its ecosystem more connected. According to the Wall Street Journal , the bikes wind up in odd places, like schools, tavern roofs, and Burning Man.
Google has been trying to control its losses, using roving teams to collect the bikes from around town, and recently installing GPS trackers. But according to comments to the Journal from Mountain View residents, the deeper issue may be mixed feelings about the corporate giant.
But others — perhaps including a man who claimed to have an entire garage full of the bikes — regard their borrowing as a kind of retributive justice against the massive company. The bike situation is subtler and more complex, as befitting lower-key Mountain View. Reuters — Apple Inc will release a patch for the Safari web browser on its iPhones, iPads and Macs within days, it said on Thursday, after major chipmakers disclosed flaws that leave nearly every modern computing device vulnerable to hackers.
But the most recent operating system updates for Mac computers, Apple TVs, iPhones and iPads protect users against the Meltdown attack and do not slow down the devices, it added, and Meltdown does not affect the Apple Watch. Macs and iOS devices are vulnerable to Spectre attacks through code that can run in web browsers.
Shortly after the researchers disclosed the chip flaws Wednesday, Google and Microsoft Corp released statements telling users which of their products were affected.
Google said its users of Android phones — more than 80 percent of the global market — were protected if they had the latest security updates. Apple remained silent for more than a day about the fate of the hundreds of millions of users of its iPhones and iPads. The volatility has alarmed some economists, who worry of a bubble. Other cryptocurrencies include Ripple , Ethereum, and Litecoin.
The free-falling Sears Holdings , parent company of Sears and Kmart, made a truly unorthodox decision this holiday season. According to the Wall Street Journal , no paid Sears commercials have run nationally since November 25th.
No national Kmart commercials have run since November 24th. The decision, according to the Journal , came from Sears Holdings chief Edward Lampert, over the objections of other executives.
In a statement to the Journal , Sears said the shift came after evaluating the effectiveness of its various marketing efforts. Even in the digital age, abandoning TV entirely would be a highly unusual move for any large consumer business. Studies have also found that ads on television are still substantially more effective than those in other media. The decision is particularly strange in the case of Sears, whose customers tend to be older.
Americans over 44 watch vastly more traditional television than younger people, with those over 65 watching nearly three times as much television as those , according to eMarketer. Sears, a venerable U. For a time, that decline could be seen as a product of the shift from brick-and-mortar to online shopping.
But Sears has lagged even other legacy department stores in reacting to that transition. Focusing on digital ads might be seen as an effort to move that needle. Meanwhile, retailers from Home Depot to Target to Urban Outfitters have recently beaten analyst expectations , and rising foot traffic at outlets including WalMart is driving talk of a retail resurgence. But before you sign up, check your local channel availability here , because not every market includes every station.
The service also packs a big on-demand library, which could be good if you get bored of all that confetti and kissing and you just want to binge, instead. Depending upon which television channel you want to ring in the new year with, Sling TV might be the choice for you.
But like the others, channels vary by zip code, so check their availability before you sign up. Enterprise IT should be doing the same thing for cloud computing.
Clients often leave aspects of their cloud deployments unprotected or underprotected, and things that should be encrypted are not, while things that should not be encrypted are. Moreover, consider all the security technology in place, what needs to be updated? What should be replaced? You should have a mix of both, as well as some paths for your staff defined to get the skills of a cloud architect, cloud developer, cloud operations specialist, and cloud devops specialist, just to name a few roles.
Databases are sticky, and once enterprises have used a specific database, they are not likely to change it. Indeed, what many enterprises have done is just rehost their data on public clouds using the same database they used on premises.
Are you using the optimal solution? These are just a few suggestions; I suspect that you can name more. Whatever they are, pick a few and follow up. Have a great new year! Each time you go back, you tell yourself it will be different… they have changed! Yet every time you go back, they break your heart again.
This has now happened to me twice with GE. Then I found out they were cheating on me with someone named subprime! It nearly bankrupted the company, and Uncle Warren had to come to the rescue to save it. I vowed to never make that mistake again…. And just like that, we were back together. The stock had been consolidating all year, and Jeff Immelt had on his shiniest used car salesmen hat, singing sweet nothings into my ear of buybacks, the disposal of the finance assets and refocusing on core industrial operations.
Is this stock destined to break my heart again and again until nothing is left? I did some soul searching… deep in the woods. And had decided again to leave, never to return.
But as I was leaving the door, with my bags packed, and my prized, signed picture of the Jamaican bobsled team in toe, an event made me hit the pause button. This left me in a holding pattern for months, until Nov 13th. It now realizes it has a serious problem, it has overspent and or had disastrous timing on virtually every major deal it has done in the last years.
He also seems to be dead set on costs, which with GE in its current structure will keep him busy for a while. The reason is pretty simple, all of the dirty laundry appears to be in the open now. Mr Flannery has all but told anyone that will listen that the rest of and all of will suck, and to not invest.
He has acknowledged the pension shortfall, which I am sure will come up in the comments section of this article. Also shrinking the board from a frat house of 18 to a GE focused 12, preaching honesty imagine that and accountability in the new GE. So far I am digging the new CEO and currently am in tacit agreement with his broad outline. This is a core division for GE, and one that recently has helped drive them directly into a ditch, as overcapacity, technical issues and in my view an ill timed Alstrom acquisition weigh on earnings at the division.
However, GE power does have many redeeming qualities. They are a technology leader in the industry whilst having deep relationships with customers in a field that honestly does not have all that many options. Near term however, look for deep cuts in expectations at the unit until the smoke clears. This division looks set to continue to preform well in the near term and may be looked at as an example for the rest of the company.
They build locomotives with a large portion of revenue coming from the services side of the business, which is something I like to see. They are a global leader in the industry and the mix of technology and services is impressive. However the division has been lackluster of late and the strategic fit is questionable and thus may not make sense for them to keep.
They did just win a locomotive order from Canadian National Railway CNI but it may be prudent to offload this asset to focus on core business. I sort of hate to see this business go, as it truly is world class. However GE hopefully will use proceeds here to either reduce debt or shore up the oft cited pension shortfall. Healthcare- GE has a broad and diverse set of healthcare assets, providing imaging, healthcare cloud, cardiology, orthopedics and anesthesia equipment, among multiple other products and services.
This has been a strong performer for the company and what I would consider another core holding of GE, this division looks to be a good fit with its digital offerings and will likely continue to buoy the company during this current slump. Jeff Immelts timing was so bad that it feels like it was on purpose. Immelt decided to buy a bunch of oil services companies, seemingly at the absolute top of the oil market.
Anyways, GE Baker Hughes as it is now called is the 2nd largest oil services company in the world and to be fair is actually a very good company, and is a technology leader in the industry along side Halliburton HAL. So basically it is the second prettiest girl in a leper colony. Oil services, seem in my opinion to be stuck in a pretty serious long term rut and GE, I believe will look to dispose of this asset likely through a spin off off or divestiture of its stake rather quickly.
Perhaps GE could offer Immelt a stake in this spin off in return for the GE stock he so graciously awarded himself during his charade. Renewables- The renewables division is home to a world class wind energy turbine manufacturer, along with in my opinion is the most valuable part, its services segment. The company also has an emerging offshore wind and hydro power segment that are lacking scale currently, but hold long term promise.
The wind market this year has suffered from intense competitive pressures thus dragging results, however this also looks to be a core division for GE in the future. The companies potential is just so damn pretty! GE lines up well with my vision of the mega trends of the future. In my mind, a company must both show an ability for growth, while possessing a solid balance sheet with operating discipline from which to build.
After the dust settles from the recent house fire Mr Flannery has set ablaze, I am envisioning 4 major divisions of GE remaining. All 4 remaining divisions fit into my vision- with 3 qualifying in my mind as mega trends. Healthcare I view as a great business as well but does not fit as a mega trend in my book with so many unknowns as to the future in the industry. Power- Power is obviously a key need for the future as more and more countries look to move to gas powered plants and away from coal.
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