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judymcconville@roadrunner.com 2017-04-30 18:25:16 -07:00
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@ -577,9 +577,9 @@ The signature verification algorithm takes the message (a hash of the transactio
[[sighash_types]] [[sighash_types]]
==== Signature Hash Types (SIGHASH) ==== Signature Hash Types (SIGHASH)
Digital signatures are applied to messages, which in the case of bitcoin, are the transactions themselves. The signature implies a _commitment_ by the signer to specific transaction data. In the simplest form, the signature applies to the entire transaction, thereby committing all the inputs, outputs, and other transaction fields. But, a signature can commit to only a subset of the data in a transaction, which is useful for a number of scenarios as we will see in this section. ((("transactions", "digital signatures", "signature hash types")))((("digital signatures", "signature has types")))((("commitment")))Digital signatures are applied to messages, which in the case of bitcoin, are the transactions themselves. The signature implies a _commitment_ by the signer to specific transaction data. In the simplest form, the signature applies to the entire transaction, thereby committing all the inputs, outputs, and other transaction fields. But, a signature can commit to only a subset of the data in a transaction, which is useful for a number of scenarios as we will see in this section.
Bitcoin signatures have a way of indicating which part of a transaction's data is included in the hash signed by the private key, through the use of a +SIGHASH+ flag. The +SIGHASH+ flag is a single byte that is appended to the signature. Every signature has a +SIGHASH+ flag and the flag can be different from to input to input. A transaction with three signed inputs may have three signatures with different +SIGHASH+ flags, each signature signing (committing) different parts of the transaction. ((("SIGHASH flags")))Bitcoin signatures have a way of indicating which part of a transaction's data is included in the hash signed by the private key, through the use of a +SIGHASH+ flag. The +SIGHASH+ flag is a single byte that is appended to the signature. Every signature has a +SIGHASH+ flag and the flag can be different from to input to input. A transaction with three signed inputs may have three signatures with different +SIGHASH+ flags, each signature signing (committing) different parts of the transaction.
Remember, each input may contain a signature in its unlocking script. As a result, a transaction that contains several inputs may have signatures with different +SIGHASH+ flags that commit different parts of the transaction in each of the inputs. Note also that bitcoin transactions may contain inputs from different "owners," who may sign only one input in a partially constructed (and invalid) transaction, collaborating with others to gather all the necessary signatures to make a valid transaction. Many of the +SIGHASH+ flag types only make sense if you think of multiple participants collaborating outside the bitcoin network and updating a partially signed transaction. Remember, each input may contain a signature in its unlocking script. As a result, a transaction that contains several inputs may have signatures with different +SIGHASH+ flags that commit different parts of the transaction in each of the inputs. Note also that bitcoin transactions may contain inputs from different "owners," who may sign only one input in a partially constructed (and invalid) transaction, collaborating with others to gather all the necessary signatures to make a valid transaction. Many of the +SIGHASH+ flag types only make sense if you think of multiple participants collaborating outside the bitcoin network and updating a partially signed transaction.