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Merge #241 from branch '2015-11-13-bip65-wording-fixes' of git://github.com/petertodd/bips

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Jeff Garzik 2015-11-13 12:44:59 -05:00
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@ -18,8 +18,8 @@ some point in the future.
CHECKLOCKTIMEVERIFY redefines the existing NOP2 opcode. When executed it CHECKLOCKTIMEVERIFY redefines the existing NOP2 opcode. When executed it
compares the top item on the stack to the nLockTime field of the transaction compares the top item on the stack to the nLockTime field of the transaction
containing the scriptSig. If that top stack item is greater than the transaction containing the scriptSig. If that top stack item is greater than the transaction's
nLockTime the script fails immediately, otherwise script evaluation continues nLockTime field the script fails immediately, otherwise script evaluation continues
as though a NOP was executed. as though a NOP was executed.
The nLockTime field in a transaction prevents the transaction from being mined The nLockTime field in a transaction prevents the transaction from being mined
@ -32,18 +32,14 @@ remains unspendable.
==Motivation== ==Motivation==
The nLockTime field in transactions makes it possible to prove that a The nLockTime field in transactions can be used to prove that it is
transaction output can be spent in the future: a valid signature for a ''possible'' to spend a transaction output in the future, by constructing a
transaction with the desired nLockTime can be constructed, proving that it is valid transaction spending that output with the nLockTime field set.
possible to spend the output with that signature when the nLockTime is reached.
An example where this technique is used is in micro-payment channels, where the
nLockTime field proves that should the receiver vanish the sender is guaranteed
to get all their escrowed funds back when the nLockTime is reached.
However, the nLockTime field is insufficient if you wish to prove that a However, the nLockTime field can't prove that it is ''impossible'' to spend a
transaction output ''cannot'' be spent until some time in the future, as there transaction output until some time in the future, as there is no way to know if
is no way to prove that the secret keys corresponding to the pubkeys controlling a valid signature for a different transaction spending that output has been
the funds have not been used to create a valid signature. created.
===Escrow=== ===Escrow===
@ -89,9 +85,9 @@ requires the co-operation of both parties to spend the output. To ensure the
failure of one party does not result in the funds becoming lost, refund failure of one party does not result in the funds becoming lost, refund
transactions are setup in advance using nLockTime. These refund transactions transactions are setup in advance using nLockTime. These refund transactions
need to be created interactively, and additionaly, are currently vulnerable to need to be created interactively, and additionaly, are currently vulnerable to
transaction mutability. CHECKLOCKTIMEVERIFY can be used in these protocols, transaction malleability. CHECKLOCKTIMEVERIFY can be used in these protocols,
replacing the interactive setup with a non-interactive setup, and additionally, replacing the interactive setup with a non-interactive setup, and additionally,
making transaction mutability (aka malleability) a non-issue. making transaction malleability a non-issue.
====Two-factor wallets==== ====Two-factor wallets====
@ -121,14 +117,14 @@ Now the user is always able to spend their funds without the co-operation of
the service by waiting for the expiry time to be reached. the service by waiting for the expiry time to be reached.
====Micropayment Channels==== ====Payment Channels====
Jeremy Spilman style micropayment channels first setup a deposit controlled by Jeremy Spilman style payment channels first setup a deposit controlled by
2-of-2 multisig, tx1, and then adjust a second transaction, tx2, that spends 2-of-2 multisig, tx1, and then adjust a second transaction, tx2, that spends
the output of tx1 to payor and payee. Prior to publishing tx1 a refund the output of tx1 to payor and payee. Prior to publishing tx1 a refund
transaction is created, tx3, to ensure that should the payee vanish the payor transaction is created, tx3, to ensure that should the payee vanish the payor
can get their deposit back. The process by which the refund transaction is can get their deposit back. The process by which the refund transaction is
created is currently vulnerable to transaction mutability attacks, and created is currently vulnerable to transaction malleability attacks, and
additionally, requires the payor to store the refund. Using the same additionally, requires the payor to store the refund. Using the same
scriptPubKey from as in the Two-factor wallets example solves both these issues. scriptPubKey from as in the Two-factor wallets example solves both these issues.
@ -168,7 +164,7 @@ non-trivial, and even the best existing technqiue - announce-commit sacrifices
- could encourage mining centralization. CHECKLOCKTIMEVERIFY can be used to - could encourage mining centralization. CHECKLOCKTIMEVERIFY can be used to
create outputs that are provably spendable by anyone (thus to mining fees create outputs that are provably spendable by anyone (thus to mining fees
assuming miners behave optimally and rationally) but only at a time assuming miners behave optimally and rationally) but only at a time
sufficiently far into the future that large miners profitably can't sell the sufficiently far into the future that large miners can't profitably sell the
sacrifices at a discount. sacrifices at a discount.
@ -307,7 +303,7 @@ time.
PayPub - https://github.com/unsystem/paypub PayPub - https://github.com/unsystem/paypub
Jeremy Spilman Micropayment Channels - https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2013-April/002433.html Jeremy Spilman Payment Channels - https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2013-April/002433.html
==Implementations== ==Implementations==