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myarbrough@oreilly.com 2014-11-18 08:04:49 -08:00
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@ -465,7 +465,7 @@ In version 0.9 of the Bitcoin Core client, a compromise was reached with the int
OP_RETURN <data>
----
The data portion is limited to 40 bytes and most often represents a hash, such as the output from the SHA256 algorithm (32 bytes). Many applications put a prefix in front of the data to help identify the application. For example, the http://proofofexistence.com/[proofofexistence.com] digital notarization service uses the 8-byte prefix "DOCPROOF," which is ASCII encoded as 44f4350524f4f46 in hexadecimal.
The data portion is limited to 40 bytes and most often represents a hash, such as the output from the SHA256 algorithm (32 bytes). Many applications put a prefix in front of the data to help identify the application. For example, the http://proofofexistence.com[Proof of Existence] digital notarization service uses the 8-byte prefix "DOCPROOF," which is ASCII encoded as +44f4350524f4f46+ in hexadecimal.
Keep in mind that there is no "unlocking script" that corresponds to +OP_RETURN+ that could possibly be used to "spend" an +OP_RETURN+ output. The whole point of +OP_RETURN+ is that you can't spend the money locked in that output, and therefore it does not need to be held in the UTXO set as potentially spendable—+OP_RETURN+ is _provably un-spendable_. +OP_RETURN+ is usually an output with a zero bitcoin amount, because any bitcoin assigned to such an output is effectively lost forever. If an +OP_RETURN+ is encountered by the script validation software, it results immediately in halting the execution of the validation script and marking the transaction as invalid. Thus, if you accidentally reference an +OP_RETURN+ output as an input in a transaction, that transaction is invalid.
@ -474,7 +474,7 @@ A standard transaction (one that conforms to the +isStandard()+ checks) can have
[[p2sh]]
==== Pay-to-Script-Hash (P2SH)
((("multi-signature scripts","P2SH and", id="ix_ch05-asciidoc17", range="startofrange")))((("Pay-to-Script-Hash (P2SH)", id="ix_ch05-asciidoc18", range="startofrange")))((("transactions","Pay-to-Script-Hash", id="ix_ch05-asciidoc19", range="startofrange")))Pay-to-Script-Hash (P2SH) was introduced in the winter of 2012 as a powerful new type of transaction that greatly simplifies the use of complex transaction scripts. To explain the need for P2SH, let's look at a practical example.
((("multi-signature scripts","P2SH and", id="ix_ch05-asciidoc17", range="startofrange")))((("Pay-to-script-hash (P2SH)", id="ix_ch05-asciidoc18", range="startofrange")))((("transactions","Pay-to-script-hash", id="ix_ch05-asciidoc19", range="startofrange")))Pay-to-script-hash (P2SH) was introduced in 2012 as a powerful new type of transaction that greatly simplifies the use of complex transaction scripts. To explain the need for P2SH, let's look at a practical example.
In <<ch01_intro_what_is_bitcoin>> we introduced Mohammed, an electronics importer based in Dubai. Mohammed's company uses bitcoin's multi-signature feature extensively for its corporate accounts. Multi-signature scripts are one of the most common uses of bitcoin's advanced scripting capabilities and are a very powerful feature. Mohammed's company uses a multi-signature script for all customer payments, known in accounting terms as "accounts receivable," or AR. With the multi-signature scheme, any payments made by customers are locked in such a way that they require at least two signatures to release, from Mohammed and one of his partners or from his attorney who has a backup key. A multi-signature scheme like that offers corporate governance controls and protects against theft, embezzlement, or loss.