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judymcconville@roadrunner.com 2017-04-28 11:18:12 -07:00
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@ -610,7 +610,7 @@ BTC public key: 029ade3effb0a67d5c8609850d797366af428f4a0d5194cb221d807770a15228
==== Encrypted Private Keys (BIP-38)
((("bitcoin improvement proposals", "Encrypted Private Keys (BIP38)")))((("keys and addresses", "advanced forms", "encrypted private keys")))((("public and private keys", "encrypted private keys")))Private keys must remain secret. The need for _confidentiality_ of the private keys is a truism that is quite difficult to achieve in practice, because it conflicts with the equally important security objective of _availability_. Keeping the private key private is much harder when you need to store backups of the private key to avoid losing it. A private key stored in a wallet that is encrypted by a password might be secure, but that wallet needs to be backed up. At times, users need to move keys from one wallet to another—to upgrade or replace the wallet software, for example. Private key backups might also be stored on paper (see <<paper_wallets>>) or on external storage media, such as a USB flash drive. But what if the backup itself is stolen or lost? These conflicting security goals led to the introduction of a portable and convenient standard for encrypting private keys in a way that can be understood by many different wallets and bitcoin clients, standardized by Bitcoin Improvement Proposal 38 or BIP-38 (see <<appdxbitcoinimpproposals>>).
((("bitcoin improvement proposals", "Encrypted Private Keys (BIP-38)")))((("keys and addresses", "advanced forms", "encrypted private keys")))((("public and private keys", "encrypted private keys")))Private keys must remain secret. The need for _confidentiality_ of the private keys is a truism that is quite difficult to achieve in practice, because it conflicts with the equally important security objective of _availability_. Keeping the private key private is much harder when you need to store backups of the private key to avoid losing it. A private key stored in a wallet that is encrypted by a password might be secure, but that wallet needs to be backed up. At times, users need to move keys from one wallet to another—to upgrade or replace the wallet software, for example. Private key backups might also be stored on paper (see <<paper_wallets>>) or on external storage media, such as a USB flash drive. But what if the backup itself is stolen or lost? These conflicting security goals led to the introduction of a portable and convenient standard for encrypting private keys in a way that can be understood by many different wallets and bitcoin clients, standardized by Bitcoin Improvement Proposal 38 or BIP-38 (see <<appdxbitcoinimpproposals>>).
BIP-38 proposes a common standard for encrypting private keys with a passphrase and encoding them with Base58Check so that they can be stored securely on backup media, transported securely between wallets, or kept in any other conditions where the key might be exposed. The standard for encryption uses the Advanced Encryption Standard (AES), a standard established by the National Institute of Standards and Technology (NIST) and used broadly in data encryption implementations for commercial and military applications.
@ -634,7 +634,7 @@ Test the encrypted keys in <<table_4-10>> using bitaddress.org to see how you ca
((("keys and addresses", "advanced forms", "pay-to-script hash and multisig addresses")))((("pay-to-script hash (P2SH)")))((("multisig addresses")))((("adresses", "multisig addresses")))As we know, traditional bitcoin addresses begin with the number “1” and are derived from the public key, which is derived from the private key. Although anyone can send bitcoin to a “1” address, that bitcoin can only be spent by presenting the corresponding private key signature and public key hash.
Bitcoin addresses that begin with the number “3” are pay-to-script hash (P2SH) addresses, sometimes erroneously called multisignature or multisig addresses. They designate the beneficiary of a bitcoin transaction as the hash of a script, instead of the owner of a public key. The feature was introduced in January 2012 with Bitcoin Improvement Proposal 16, or BIP-16 (see <<appdxbitcoinimpproposals>>), and is being widely adopted because it provides the opportunity to add functionality to the address itself. Unlike transactions that "send" funds to traditional “1” bitcoin addresses, also known as pay-to-public-key-hash (P2PKH), funds sent to “3” addresses require something more than the presentation of one public key hash and one private key signature as proof of ownership. The requirements are designated at the time the address is created, within the script, and all inputs to this address will be encumbered with the same requirements.
((("bitcoin improvement proposals", "Pay to Script Hash (BIP-16)")))Bitcoin addresses that begin with the number “3” are pay-to-script hash (P2SH) addresses, sometimes erroneously called multisignature or multisig addresses. They designate the beneficiary of a bitcoin transaction as the hash of a script, instead of the owner of a public key. The feature was introduced in January 2012 with Bitcoin Improvement Proposal 16, or BIP-16 (see <<appdxbitcoinimpproposals>>), and is being widely adopted because it provides the opportunity to add functionality to the address itself. Unlike transactions that "send" funds to traditional “1” bitcoin addresses, also known as pay-to-public-key-hash (P2PKH), funds sent to “3” addresses require something more than the presentation of one public key hash and one private key signature as proof of ownership. The requirements are designated at the time the address is created, within the script, and all inputs to this address will be encumbered with the same requirements.
A pay-to-script hash address is created from a transaction script, which defines who can spend a transaction output (for more detail, see <<p2sh>>). Encoding a pay-to-script hash address involves using the same double-hash function as used during creation of a bitcoin address, only applied on the script instead of the public key:
@ -795,7 +795,7 @@ Paper wallets can be generated easily using a tool such as the client-side JavaS
.An example of a simple paper wallet from bitaddress.org
image::images/mbc2_0408.png[]
((("bitcoin improvement proposals", "Encrypted Private Keys (BIP38)")))The disadvantage of the simple paper wallet system is that the printed keys are vulnerable to theft. A thief who is able to gain access to the paper can either steal it or photograph the keys and take control of the bitcoin locked with those keys. A more sophisticated paper wallet storage system uses BIP-38 encrypted private keys. The keys printed on the paper wallet are protected by a passphrase that the owner has memorized. Without the passphrase, the encrypted keys are useless. Yet, they still are superior to a passphrase-protected wallet because the keys have never been online and must be physically retrieved from a safe or other physically secured storage. <<paper_wallet_encrypted>> shows a paper wallet with an encrypted private key (BIP-38) created on the bitaddress.org site.
((("bitcoin improvement proposals", "Encrypted Private Keys (BIP-38)")))The disadvantage of the simple paper wallet system is that the printed keys are vulnerable to theft. A thief who is able to gain access to the paper can either steal it or photograph the keys and take control of the bitcoin locked with those keys. A more sophisticated paper wallet storage system uses BIP-38 encrypted private keys. The keys printed on the paper wallet are protected by a passphrase that the owner has memorized. Without the passphrase, the encrypted keys are useless. Yet, they still are superior to a passphrase-protected wallet because the keys have never been online and must be physically retrieved from a safe or other physically secured storage. <<paper_wallet_encrypted>> shows a paper wallet with an encrypted private key (BIP-38) created on the bitaddress.org site.
[[paper_wallet_encrypted]]
.An example of an encrypted paper wallet from bitaddress.org. The passphrase is "test."