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| -rw-r--r-- | bip-0121.mediawiki | 2 |
10 files changed, 509 insertions, 142 deletions
diff --git a/README.mediawiki b/README.mediawiki index 089d9b5..1243d20 100644 --- a/README.mediawiki +++ b/README.mediawiki @@ -19,6 +19,12 @@ Those proposing changes should consider that ultimately consent may rest with th | Standard | Active |- +| [[bip-0009.mediawiki|9]] +| Version bits with timeout and delay +| Pieter Wuille, Peter Todd, Greg Maxwell, Rusty Russell +| Informational +| Draft +|- | [[bip-0010.mediawiki|10]] | Multi-Sig Transaction Distribution | Alan Reiner diff --git a/bip-0009.mediawiki b/bip-0009.mediawiki new file mode 100644 index 0000000..b160810 --- /dev/null +++ b/bip-0009.mediawiki @@ -0,0 +1,168 @@ +<pre> + BIP: 9 + Title: Version bits with timeout and delay + Author: Pieter Wuille <pieter.wuille@gmail.com>, Peter Todd <pete@petertodd.org>, Greg Maxwell <greg@xiph.org>, Rusty Russell <rusty@rustcorp.com.au> + Status: Draft + Type: Informational Track + Created: 2015-10-04 +</pre> + +==Abstract== + +This document specifies a proposed change to the semantics of the 'version' field in Bitcoin blocks, allowing multiple backward-compatible changes (further called "soft forks") to be deployed in parallel. It relies on interpreting the version field as a bit vector, where each bit can be used to track an independent change. These are tallied each retarget period. Once the consensus change succeeds or times out, there is a "fallow" pause after which the bit can be reused for later changes. + +==Motivation== + +BIP 34 introduced a mechanism for doing soft-forking changes without a predefined flag timestamp (or flag block height), instead relying on measuring miner support indicated by a higher version number in block headers. As it relies on comparing version numbers as integers however, it only supports one single change being rolled out at once, requiring coordination between proposals, and does not allow for permanent rejection: as long as one soft fork is not fully rolled out, no future one can be scheduled. + +In addition, BIP 34 made the integer comparison (nVersion >= 2) a consensus rule after its 95% threshold was reached, removing 2<sup>31</sup>+2 values from the set of valid version numbers (all negative numbers, as nVersion is interpreted as a signed integer, as well as 0 and 1). This indicates another downside this approach: every upgrade permanently restricts the set of allowed nVersion field values. This approach was later reused in BIP 66, which further removed nVersion = 2 as valid option. As will be shown further, this is unnecessary. + +==Specification== + +===Mechanism=== + +'''Bit flags''' +We are permitting several independent soft forks to be deployed in parallel. For each, a bit B is chosen from the set {0,1,2,...,28}, which is not currently in use for any other ongoing soft fork. Miners signal intent to enforce the new rules associated with the proposed soft fork by setting bit 1<sup>B</sup> in nVersion to 1 in their blocks. + +'''High bits''' +The highest 3 bits are set to 001, so the range of actually possible nVersion values is [0x20000000...0x3FFFFFFF], inclusive. This leaves two future upgrades for different mechanisms (top bits 010 and 011), while complying to the constraints set by BIP34 and BIP66. Having more than 29 available bits for parallel soft forks does not add anything anyway, as the (nVersion >= 3) requirement already makes that impossible. + +'''States''' +With every softfork proposal we associate a state BState, which begins +at ''defined'', and can be ''locked-in'', ''activated'', +or ''failed''. Transitions are considered after each +retarget period. + +'''Soft Fork Support''' +Software which supports the change should begin by setting B in all blocks +mined until it is resolved. + + if (BState != activated && BState != failed) { + SetBInBlock(); + } + +'''Success: Lock-in Threshold''' +If bit B is set in 1916 (1512 on testnet) or +more of the 2016 blocks within a retarget period, it is considered +''locked-in''. Miners should continue setting bit B, so uptake is +visible. + + if (NextBlockHeight % 2016 == 0) { + if (BState == defined && Previous2016BlocksCountB() >= 1916) { + BState = locked-in; + BActiveHeight = NextBlockHeight + 2016; + } + } + +'''Success: Activation Delay''' +The consensus rules related to ''locked-in'' soft fork will be enforced in +the second retarget period; ie. there is a one retarget period in +which the remaining 5% can upgrade. At the that activation block and +after, miners should stop setting bit B, which may be reused for a different soft fork. + + if (BState == locked-in && NextBlockHeight == BActiveHeight) { + BState = activated; + ApplyRulesForBFromNextBlock(); + /* B can be reused, immediately */ + } + +'''Failure: Timeout''' +A soft fork proposal should include a ''timeout''. This is measured +as the beginning of a calendar year as per this table (suggest +adding three to the current calendar year when drafting the soft fork proposal): + +{| +! Timeout Year +! >= Seconds +! Timeout Year +! >= Seconds +|- +|2018 +|1514764800 +|2026 +|1767225600 +|- +|2019 +|1546300800 +|2027 +|1798761600 +|- +|2020 +|1577836800 +|2028 +|1830297600 +|- +|2021 +|1609459200 +|2029 +|1861920000 +|- +|2022 +|1640995200 +|2030 +|1893456000 +|- +|2023 +|1672531200 +|2031 +|1924992000 +|- +|2024 +|1704067200 +|2032 +|1956528000 +|- +|2025 +|1735689600 +|2033 +|1988150400 +|} + +If the soft fork still not ''locked-in'' and the +GetMedianTimePast() of a block following a retarget period is at or +past this timeout, miners should cease setting this bit. + + if (NextBlockHeight % 2016 == 0) { + if (BState == defined && GetMedianTimePast(nextblock) >= BFinalYear) { + BState = failed; + } + } + +After another retarget period (to allow detection of buggy miners), +the bit may be reused. + +'''Warning system''' +To support upgrade warnings, an extra "unknown upgrade" is tracked, using the "implicit bit" mask = (block.nVersion & ~expectedVersion) != 0. Mask will be non-zero whenever an unexpected bit is set in nVersion. Whenever lock-in for the unknown upgrade is detected, the software should warn loudly about the upcoming soft fork. It should warn even more loudly after the next retarget period. + +'''Forks''' +It should be noted that the states are maintained along block chain +branches, but may need recomputation when a reorganization happens. + +===Support for future changes=== + +The mechanism described above is very generic, and variations are possible for future soft forks. Here are some ideas that can be taken into account. + +'''Modified thresholds''' +The 95% threshold (based on in BIP 34) does not have to be maintained for eternity, but changes should take the effect on the warning system into account. In particular, having a lock-in threshold that is incompatible with the one used for the warning system may have long-term effects, as the warning system cannot rely on a permanently detectable condition anymore. + +'''Conflicting soft forks''' +At some point, two mutually exclusive soft forks may be proposed. The naive way to deal with this is to never create software that implements both, but that is making a bet that at least one side is guaranteed to lose. Better would be to encode "soft fork X cannot be locked-in" as consensus rule for the conflicting soft fork - allowing software that supports both, but can never trigger conflicting changes. + +'''Multi-stage soft forks''' +Soft forks right now are typically treated as booleans: they go from an inactive to an active state in blocks. Perhaps at some point there is demand for a change that has a larger number of stages, with additional validation rules that get enabled one by one. The above mechanism can be adapted to support this, by interpreting a combination of bits as an integer, rather than as isolated bits. The warning system is compatible with this, as (nVersion & ~nExpectedVersion) will always be non-zero for increasing integers. + +== Rationale == + +The failure timeout allows eventual reuse of bits even if a soft fork was +never activated, so it's clear that the new use of the bit refers to a +new BIP. It's deliberately very course grained, to take into account +reasonable development and deployment delays. There are unlikely to be +enough failed proposals to cause a bit shortage. + +The fallow period at the conclusion of a soft fork attempt allows some +detection of buggy clients, and allows time for warnings and software +upgrades for successful soft forks. + +==Copyright== + +This document is placed in the public domain. diff --git a/bip-0032.mediawiki b/bip-0032.mediawiki index 902a5eb..28541f5 100644 --- a/bip-0032.mediawiki +++ b/bip-0032.mediawiki @@ -209,7 +209,7 @@ It is also the reason for the existence of hardened keys, and why they are used ===Test vector 1=== -Master (hex): 000102030405060708090a0b0c0d0e0f +Seed (hex): 000102030405060708090a0b0c0d0e0f * Chain m ** ext pub: xpub661MyMwAqRbcFtXgS5sYJABqqG9YLmC4Q1Rdap9gSE8NqtwybGhePY2gZ29ESFjqJoCu1Rupje8YtGqsefD265TMg7usUDFdp6W1EGMcet8 ** ext prv: xprv9s21ZrQH143K3QTDL4LXw2F7HEK3wJUD2nW2nRk4stbPy6cq3jPPqjiChkVvvNKmPGJxWUtg6LnF5kejMRNNU3TGtRBeJgk33yuGBxrMPHi @@ -231,7 +231,7 @@ Master (hex): 000102030405060708090a0b0c0d0e0f ===Test vector 2=== -Master (hex): fffcf9f6f3f0edeae7e4e1dedbd8d5d2cfccc9c6c3c0bdbab7b4b1aeaba8a5a29f9c999693908d8a8784817e7b7875726f6c696663605d5a5754514e4b484542 +Seed (hex): fffcf9f6f3f0edeae7e4e1dedbd8d5d2cfccc9c6c3c0bdbab7b4b1aeaba8a5a29f9c999693908d8a8784817e7b7875726f6c696663605d5a5754514e4b484542 * Chain m ** ext pub: xpub661MyMwAqRbcFW31YEwpkMuc5THy2PSt5bDMsktWQcFF8syAmRUapSCGu8ED9W6oDMSgv6Zz8idoc4a6mr8BDzTJY47LJhkJ8UB7WEGuduB ** ext prv: xprv9s21ZrQH143K31xYSDQpPDxsXRTUcvj2iNHm5NUtrGiGG5e2DtALGdso3pGz6ssrdK4PFmM8NSpSBHNqPqm55Qn3LqFtT2emdEXVYsCzC2U diff --git a/bip-0047.mediawiki b/bip-0047.mediawiki index c8397a7..8247e00 100644 --- a/bip-0047.mediawiki +++ b/bip-0047.mediawiki @@ -99,11 +99,13 @@ Prior to the first time Alice initiates a transaction to Bob, Alice MUST inform ## Alice selects the private key corresponding to the first exposed public key, of the first pubkey-exposing input, of the transaction: <pre>a</pre> ## Alice selects the public key associated with Bob's notification address: <pre>B, where B = bG</pre> ## Alice calculates a secret point: <pre>S = aB</pre> -## Alice expresses the secret point in compressed DER format, then calculates a scalar shared secret: <pre>s = SHA256(S)</pre> +## Alice calculates a 64 byte blinding factor: <pre>s = HMAC-SHA512(x, o)</pre> +### "x" is the x value of the secret point +### "o" is the outpoint being spent by the first pubkey-exposing input of the transaction. # Alice serializes her payment code in binary form. -# Alice renders her payment code (P) unreadable to anyone except Bob by: -## Replace the x value with x': <pre>x' = s XOR (x value)</pre> -## Replace the chain code with c': <pre>c' = sha256(s) XOR (chain code)</pre> +# Alice renders her payment code (P) unreadable to anyone except Bob: +## Replace the x value with x': <pre>x' = x XOR (first 32 bytes of s)</pre> +## Replace the chain code with c': <pre>c' = c XOR (last 32 bytes of s)</pre> # Alice adds an OP_RETURN output to her transaction which consists of P. <img src="bip-0047/reusable_payment_codes-01.png" /> @@ -113,10 +115,12 @@ Prior to the first time Alice initiates a transaction to Bob, Alice MUST inform ## Bob selects the first exposed public key, of the first pubkey-exposing input, of the transaction: <pre>A, where A = aG</pre> ## Bob selects the private key associated with his notification address: <pre>b</pre> ## Bob calculates a secret point: <pre>S = bA</pre> -## Bob expresses the secret point in compressed DER format, then calculates a scalar shared secret: <pre>s = SHA256(S)</pre> +## Bob calculates the binding factor: <pre>s = HMAC-SHA512(x, o)</pre> +### "x" is the x value of the secret point +### "o" is the outpoint being spent by the first pubkey-exposing input of the transaction. ## Bob interprets the 80 byte payload as a payment code, except: -### Replace the x value with x': <pre>x' = s XOR (x value)</pre> -### Replace the chain code with c': <pre>c' = sha256(s) XOR (chain code)</pre> +### Replace the x value with x': <pre>x' = x XOR (first 32 bytes of s)</pre> +### Replace the chain code with c': <pre>c' = c XOR (last 32 bytes of s)</pre> ## If the updated x value is a member of the secp256k1 group, the payment code is valid. ## If the updated x value is not a member of the secp256k1 group, the payment code is ignored. @@ -138,7 +142,7 @@ Bitcoins received via notification transactions require special handling in orde ## Alice selects the next unused public key derived from Bob's payment code, starting from zero: <pre>B, where B = bG</pre> ### The "next unused" public key is based on an index specific to the Alice-Bob context, not global to either Alice or Bob ## Alice calculates a secret point: <pre>S = aB</pre> -## Alice expresses the secret point in compressed DER format, then calculates a scalar shared secret: <pre>s = SHA256(S)</pre> +## Alice calculates a scalar shared secret using the x value of S: <pre>s = SHA256(Sx)</pre> ### If the value of s is not in the secp256k1 group, Alice MUST increment the index used to derive Bob's public key and try again. ## Alice uses the scalar shared secret to calculate the ephemeral public key used to generate the P2PKH address for this transaction: <pre>B' = B + sG</pre> <img src="bip-0047/reusable_payment_codes-04.png" /> @@ -248,6 +252,7 @@ In order to use Bitmessage notification, the recipient must have a Bitmessage cl * [[bip-0032.mediawiki|BIP32 - Hierarchical Deterministic Wallets]] * [[bip-0043.mediawiki|BIP43 - Purpose Field for Deterministic Wallets]] * [[bip-0044.mediawiki|BIP44 - Multi-Account Hierarchy for Deterministic Wallets]] +* [[https://bitcoin.org/en/glossary/outpoint|Outpoint]] * [[https://github.com/petertodd/dust-b-gone|dust-b-gone]] * [[https://en.bitcoin.it/wiki/Base58Check_encoding|Base58Check encoding]] * [[https://bitmessage.org/bitmessage.pdf|Bitmessage]] diff --git a/bip-0062.mediawiki b/bip-0062.mediawiki index feb4d58..5d46b7c 100644 --- a/bip-0062.mediawiki +++ b/bip-0062.mediawiki @@ -1,3 +1,5 @@ +'''NOTICE: This document is a work in progress and is not complete, implemented, or otherwise suitable for deployment.''' + <pre> BIP: 62 Title: Dealing with malleability diff --git a/bip-0068.mediawiki b/bip-0068.mediawiki index e336765..12b97c7 100644 --- a/bip-0068.mediawiki +++ b/bip-0068.mediawiki @@ -13,15 +13,15 @@ This BIP describes a modification to the consensus-enforced semantics of the seq ==Motivation== -Bitcoin has sequence number fields for each input of a transaction. The original idea appears to have been that the highest sequence number should dominate and miners should prefer it over lower sequence numbers. This was never really implemented, and the half-implemented code seemed to be making this assumption that miners would honestly prefer the higher sequence numbers, even if the lower ones were much much more profitable. That turns out to be a dangerous assumption, and so most technical people have assumed that kind of sequence number mediated replacement was useless because there was no way to enforce "honest" behavior, as even a few rational (profit maximizing) miners would break that completely. The change described by this BIP provides the missing piece that makes sequence numbers do something significant with respect to enforcing transaction replacement without assuming anything other than profit-maximizing behavior on the part of miners. +Bitcoin has sequence number fields for each input of a transaction. The original idea appears to have been that the highest sequence number should dominate and miners should prefer it over lower sequence numbers. This was never really implemented, and the half-implemented code seemed to be making an assumption that miners would honestly prefer the higher sequence numbers, even if the lower ones were much much more profitable. That turns out to be a dangerous assumption, and so most technical people have assumed that kind of sequence number mediated replacement was useless because there was no way to enforce "honest" behavior, as even a few rational (profit maximizing) miners would break that completely. The change described by this BIP provides the missing piece that makes sequence numbers do something significant with respect to enforcing transaction replacement without assuming anything other than profit-maximizing behavior on the part of miners. ==Specification== For transactions with an nVersion of 2 or greater, if the most significant bit (1 << 31) of a sequence number is clear, the remaining 31 bits are interpreted as an encoded relative lock-time. A sequence number with the most significant bit set is given no consensus meaning and can be included in any block, like normal, under all circumstances. -If the second most significant bit (1 << 30) is clear, the remaining bits reduced by 2^14 are interpreted as a minimum block-heigh constraint over the input's age. A sequence number of zero indicates a relative lock-time of zero blocks (bits 31 and 30 clear) and can be included in any block. A sequence number of 1 << 14 can be included in the next block after the input it is spending, or any block thereafter, rather than it being possible to be included in the same block. A sequence number of 2 << 14 can't be included until two blocks later, and so on. +If the second most significant bit (1 << 30) is clear, the next 16 bits are interpreted as a minimum block-height constraint over the input's age. The remaining 14 bits have no consensus-enforced meaning. A sequence number of zero indicates a relative lock-time of zero blocks (bits 31 and 30 clear) and can be included in any block. A sequence number of 1 << 14 can be included in the next block after the input it is spending, or any block thereafter, but cannot be included in the same block as its parent. A sequence number of 2 << 14 can't be included until at least two blocks later, and so on. -Alternatively, if the second most significant bit (1 << 30) is set, the remaining bits reduced by 2^5 are interpreted as a minimum block-time constraint over the input's age. A sequence number with just that second most significant bit set (0x40000000) is interpreted as a relative lock-time of 0, measured in seconds, and can be included in the same block as the output being spent. Advancing that sequence number by 2^5 (0x40000020) constrains the transaction to be included in blocks with an nTime timestamp at least one second greater than the median time stamp of the 11 blocks prior to the block containing the coin being spent. Advancing the sequence number by an additional 2^5 (0x40000040) constrains the spend to be two seconds later, and so on. +Alternatively, if the second most significant bit (1 << 30) is set, the next 25 bits are interpreted as a minimum block-time constraint over the input's age. The remaining 5 bits have no consensus-enforced meaning. A sequence number with just that second most significant bit set (0x40000000) is interpreted as a relative lock-time of 0, measured in seconds, and can be included in the same block as the output being spent. Advancing that sequence number by 2^5 (0x40000020) constrains the transaction to be included in blocks with an nTime timestamp at least one second greater than the median time stamp of the 11 blocks prior to the block containing the coin being spent. Advancing the sequence number by an additional 2^5 (0x40000040) constrains the spend to be two seconds later, and so on. This is proposed to be accomplished by replacing IsFinalTx() and CheckFinalTx(), existing consensus and non-consensus code functions that return true if a transaction's lock-time constraints are satisfied and false otherwise, with LockTime() and CheckLockTime(), new functions that return a non-zero value if a transaction's lock-time or sequence number constraints are not satisfied and zero otherwise: @@ -52,7 +52,7 @@ This is proposed to be accomplished by replacing IsFinalTx() and CheckFinalTx(), { CCoins coins; - bool fEnforceBIP68 = tx.nVersion >= 2 + bool fEnforceBIP68 = static_cast<uint32_t>(tx.nVersion) >= 2 && flags & LOCKTIME_VERIFY_SEQUENCE; // Will be set to the equivalent height- and time-based nLockTime @@ -72,8 +72,9 @@ This is proposed to be accomplished by replacing IsFinalTx() and CheckFinalTx(), fFinalized = false; // Do not enforce sequence numbers as a relative lock time - // unless we have been instructed to. - if (!fEnforceBIP68) + // unless we have been instructed to, and a view has been + // provided. + if (!(fEnforceBIP68 && pCoinsView)) continue; // Sequence numbers equal to or above the locktime threshold @@ -82,31 +83,62 @@ This is proposed to be accomplished by replacing IsFinalTx() and CheckFinalTx(), if (txin.nSequence >= CTxIn::SEQUENCE_LOCKTIME_THRESHOLD) continue; - // Skip this input if it is not in the UTXO set. Aside from - // the coinbase input, this should only ever happen in non- - // consensus code. - if (!pCoinsView->GetCoins(txin.prevout.hash, coins)) - continue; - - if (txin.nSequence < CTxIn::SEQUENCE_UNITS_THRESHOLD) + // Fetch the UTXO corresponding to this input. + if (!pCoinsView->GetCoins(txin.prevout.hash, coins)) { + // It is fully expected that coinbases inputs are not + // found in the UTXO set. Proceed to the next intput... + if (txin.prevout.IsNull()) + continue; + // If a non-coinbase input cannot be found, we cannot + // be certain about whether lock-time constraints have + // been satisfied. Note that it should only ever be + // possible for this to happen with wallet transactions + // that have unknown inputs. + else + return std::numeric_limits<int64_t>::max(); + } + + // coins.nHeight is MEMPOOL_HEIGHT (an absurdly high value) + // if the parent transaction was from the mempool. We can't + // know what height it will have once confirmed, but we + // assume it makes it in the same block. + int nCoinHeight = std::min(coins.nHeight, nBlockHeight); + + if (txin.nSequence < CTxIn::SEQUENCE_UNITS_THRESHOLD) { // We subtract 1 from relative lock-times because a lock- // time of 0 has the semantics of "same block," so a lock- // time of 1 should mean "next block," but nLockTime has // the semantics of "last invalid block height." - nMinHeight = std::max(nMinHeight, - coins.nHeight - + (int)(txin.nSequence >> CTxIn::SEQUENCE_BLOCKS_OFFSET) - - 1); - else + nMinHeight = std::max(nMinHeight, nCoinHeight + (int)( + txin.nSequence >> CTxIn::SEQUENCE_BLOCKS_OFFSET) - 1); + } else { + // In two locations that follow we make reference to + // chainActive.Tip(). To prevent a race condition, we + // store a reference to the current tip. + // + // Note that it is not guaranteed that indexBestBlock will + // be consistent with the passed in view. The proper thing + // to do is to have the view return time information about + // UTXOs. + const CBlockIndex& indexBestBlock = *chainActive.Tip(); + + // The only time the negative branch of this conditional + // is executed is when the prior output was taken from the + // mempool, in which case we assume it makes it into the + // same block (see above). + int64_t nCoinTime = (nCoinHeight <= (indexBestBlock.nHeight+1)) + ? indexBestBlock.GetAncestor(nCoinHeight-1)->GetMedianTimePast() + : nBlockTime; + // Time-based relative lock-times are measured from the // smallest allowed timestamp of the block containing the // txout being spent, which is the median time past of the // block prior. We subtract one for the same reason as // above. - nMinTime = std::max(nMinTime, - pindexBestHeader->GetAncestor(coins.nHeight-1)->GetMedianTimePast() - + (int64_t)((txin.nSequence ^ CTxIn::SEQUENCE_UNITS_THRESHOLD) >> CTxIn::SEQUENCE_SECONDS_OFFSET) - - 1); + nMinTime = std::max(nMinTime, nCoinTime + (int64_t)(( + txin.nSequence - CTxIn::SEQUENCE_UNITS_THRESHOLD) + >> CTxIn::SEQUENCE_SECONDS_OFFSET) - 1); + } } // If all sequence numbers are CTxIn::SEQUENCE_FINAL, the @@ -137,7 +169,8 @@ This is proposed to be accomplished by replacing IsFinalTx() and CheckFinalTx(), flags = std::max(flags, 0); // pcoinsTip contains the UTXO set for chainActive.Tip() - const CCoinsView *pCoinsView = pcoinsTip; + CCoinsViewMemPool viewMemPool(pcoinsTip, mempool); + const CCoinsView *pCoinsView = &viewMemPool; // CheckLockTime() uses chainActive.Height()+1 to evaluate // nLockTime because when LockTime() is called within @@ -174,9 +207,9 @@ Alice and Bob continue to make payments to each other, decrementing the relative ==Implementation== -A reference implementation is provided in the following git repository: +A reference implementation is provided by the following pull request -https://github.com/maaku/bitcoin/tree/sequencenumbers +https://github.com/bitcoin/bitcoin/pull/6312 ==Acknowledgments== diff --git a/bip-0112.mediawiki b/bip-0112.mediawiki index c06caf5..e1a186f 100644 --- a/bip-0112.mediawiki +++ b/bip-0112.mediawiki @@ -2,7 +2,8 @@ BIP: 112 Title: CHECKSEQUENCEVERIFY Authors: BtcDrak <btcdrak@gmail.com> - Mark Friedenbach <mark@friedenbach.org> + Mark Friedenbach <mark@friedenbach.org> + Eric Lombrozo <elombrozo@gmail.com> Status: Draft Type: Standards Track Created: 2015-08-10 @@ -18,14 +19,15 @@ being spent. ==Summary== -CHECKSEQUENCEVERIFY redefines the existing NOP3 opcode. When executed -it compares the top item on the stack to the inverse of the nSequence -field of the transaction input containing the scriptSig. If the -inverse of nSequence is less than the sequence threshold (1 << 31), -the transaction version is greater than or equal to 2, and the top -item on the stack is less than or equal to the inverted nSequence, -script evaluation continues as though a NOP was executed. Otherwise -the script fails immediately. +CHECKSEQUENCEVERIFY redefines the existing NOP3 opcode. +When executed, the script interpreter continues as if a NOP was executed +so long as one of the following conditions is met: + + * the transaction's nVersion field is 0 or 1; + * the top item on the stack is a value greater than or equal to (1 << 31); or + * the top item on the stack and the transaction input's sequence number are both relative lock-times of the same units, and the relative lock-time represented by the sequence number is greater than or equal to the relative lock-time represented by the top item on the stack. + +Otherwise, script execution terminates with an error. BIP 68's redefinition of nSequence prevents a non-final transaction from being selected for inclusion in a block until the corresponding @@ -52,19 +54,194 @@ of applications in phased protocols such as escrow, payment channels, or bidirectional pegs. +===Contracts With Expiration Deadlines=== + +====Escrow with Timeout==== + +An escrow that times out automatically 30 days after being funded can be +established in the following way. Alice, Bob and Escrow create a 2-of-3 +address with the following redeemscript. + + IF + 2 <Alice's pubkey> <Bob's pubkey> <Escrow's pubkey> 3 CHECKMULTISIGVERIFY + ELSE + "30d" CHECKSEQUENCEVERIFY DROP + <Alice's pubkey> CHECKSIGVERIFY + ENDIF + +At any time funds can be spent using signatures from any two of Alice, +Bob or the Escrow. + +After 30 days Alice can sign alone. + +The clock does not start ticking until the payment to the escrow address +confirms. + + +===Retroactive Invalidation=== + +In many instances, we would like to create contracts that can be revoked in case +of some future event. However, given the immutable nature of the blockchain, it +is practically impossible to retroactively invalidate a previous commitment that +has already confirmed. The only mechanism we really have for retroactive +invalidation is blockchain reorganization which, for fundamental security +reasons, is designed to be very hard and very expensive to deliberately pull off. + +Despite this limitation, we do have a way to provide something functionally similar +using CHECKSEQUENCEVERIFY. By constructing scripts with multiple branches of +execution where one or more of the branches are delayed we provide +a time window in which someone can supply an invalidation condition that allows the +output to be spent, effectively invalidating the would-be delayed branch and potentially discouraging +another party from broadcasting the transaction in the first place. If the invalidation +condition does not occur before the timeout, the delayed branch becomes spendable, +honoring the original contract. + +Some more specific applications of this idea: + +====Hash Time-Locked Contracts==== + +Hash Time-Locked Contracts (HTLCs) provide a general mechanism for offchain contract negotiation. An execution pathway can be made to require knowledge of a secret (a hash preimage) that can be presented within an invalidation time window. By sharing the secret it is possible to guarantee to the counterparty that the transaction will never be broadcast since this would allow the counterparty to claim the output immediately while one would have to wait for the time window to pass. If the secret has not been shared, the counterparty will be unable to use the instant pathway and the delayed pathway must be used instead. + +====Bidirectional Payment Channels==== + +Scriptable relative locktime provides a predictable amount of time to respond in +the event a counterparty broadcasts a revoked transaction: Absolute locktime +necessitates closing the channel and reopen it when getting close to the timeout, +whereas with relative locktime, the clock starts ticking the moment the +transactions confirms in a block. It also provides a means to know exactly how +long to wait (in number of blocks) before funds can be pulled out of the channel +in the event of a noncooperative counterparty. + + +====Lightning Network==== + +The lightning network extends the bidirectional payment channel idea to allow for payments to be routed over multiple bidirectional payment channel hops. + +These channels are based on an anchor transaction that requires a 2-of-2 +multisig from Alice and Bob, and a series of revocable commitment +transactions that spend the anchor transaction. The commitment +transaction splits the funds from the anchor between Alice and Bob and +the latest commitment transaction may be published by either party at +any time, finalising the channel. + +Ideally then, a revoked commitment transaction would never be able to +be successfully spent; and the latest commitment transaction would be +able to be spent very quickly. + +To allow a commitment transaction to be effectively revoked, Alice +and Bob have slightly different versions of the latest commitment +transaction. In Alice's version, any outputs in the commitment +transaction that pay Alice also include a forced delay, and an +alternative branch that allows Bob to spend the output if he knows that +transaction's revocation code. In Bob's version, payments to Bob are +similarly encumbered. When Alice and Bob negotiate new balances and +new commitment transactions, they also reveal the old revocation code, +thus committing to not relaying the old transaction. + +A simple output, paying to Alice might then look like: + + HASH160 <revokehash> EQUAL + IF + DUP HASH160 <Bob key hash> CHECKSIGVERIFY + ELSE + "24h" CHECKSEQUENCEVERIFY + DUP HASH160 <Alice key hash> CHECKSIGVERIFY + ENDIF + +This allows Alice to publish the latest commitment transaction at any +time and spend the funds after 24 hours, but also ensures that if Alice +relays a revoked transaction, that Bob has 24 hours to claim the funds. + +With CHECKLOCKTIMEVERIFY, this would look like: + + HASH160 <revokehash> EQUAL + IF + DUP HASH160 <Bob key hash> CHECKSIGVERIFY + ELSE + "2015/12/15" CHECKLOCKTIMEVERIFY + DUP HASH160 <Alice key hash> CHECKSIGVERIFY + ENDIF + +This form of transaction would mean that if the anchor is unspent on +2015/12/16, Alice can use this commitment even if it has been revoked, +simply by spending it immediately, giving no time for Bob to claim it. + +Ths means that the channel has a deadline that cannot be pushed +back without hitting the blockchain; and also that funds may not be +available until the deadline is hit. CHECKSEQUENCEVERIFY allows you +to avoid making such a tradeoff. + +Hashed Time-Lock Contracts (HTLCs) make this slightly more complicated, +since in principle they may pay either Alice or Bob, depending on whether +Alice discovers a secret R, or a timeout is reached, but the same principle +applies -- the branch paying Alice in Alice's commitment transaction gets a +delay, and the entire output can be claimed by the other party if the +revocation secret is known. With CHECKSEQUENCEVERIFY, a HTLC payable to +Alice might look like the following in Alice's commitment transaction: + + HASH160 DUP <revokehash> EQUAL + IF + DROP DUP HASH160 <Bob key hash> CHECKSIGVERIFY + ELSE + <R hash> EQUAL + IF + "24h" CHECKSEQUENCEVERIFY DROP + DUP HASH160 <Alice key hash> CHECKSIGVERIFY + ELSE + "2015/10/20 10:33" CHECKLOCKTIMEVERIFY DROP + DUP HASH160 <Bob key hash> CHECKSIGVERIFY + ENDIF + ENDIF + +and correspondingly in Bob's commitment transaction: + + HASH160 DUP <revokehash> EQUAL + IF + DROP DUP HASH160 <Alice key hash> CHECKSIGVERIFY + ELSE + <R hash> EQUAL + IF + DUP HASH160 <Alice key hash> CHECKSIGVERIFY + ELSE + "24h" CHECKSEQUENCEVERIFY DROP + "2015/10/20 10:33" CHECKLOCKTIMEVERIFY DROP + DUP HASH160 <Bob key hash> CHECKSIGVERIFY + ENDIF + ENDIF + +Note that both CHECKSEQUENCEVERIFY and CHECKLOCKTIMEVERIFY are used in the +final branch of above to ensure Bob cannot spend the output until after both +the timeout is complete and Alice has had time to reveal the revocation +secret. + +See the [https://github.com/ElementsProject/lightning/blob/master/doc/deployable-lightning.pdf Deployable Lightning] paper. + + +====2-Way Pegged Sidechains==== + +The 2-way pegged sidechain requires a new REORGPROOFVERIFY opcode, the semantics of which are outside the scope of this BIP. CHECKSEQUENCEVERIFY is used to make sure that sufficient time has passed since the return peg was posted to publish a reorg proof: + + IF + lockTxHeight <lockTxHash> nlocktxOut [<workAmount>] reorgBounty Hash160(<...>) <genesisHash> REORGPROOFVERIFY + ELSE + withdrawLockTime CHECKSEQUENCEVERIFY DROP HASH160 p2shWithdrawDest EQUAL + ENDIF + + ==Specification== Refer to the reference implementation, reproduced below, for the precise semantics and detailed rationale for those semantics. - // Threshold for nLockTime: below this value it is interpreted as block number, - // otherwise as UNIX timestamp (already defined in Bitcoin Core). - static const unsigned int LOCKTIME_THRESHOLD = 500000000; // Tue Nov 5 00:53:20 1985 UTC + /* Threshold for nSequence: below this value it is interpreted + * as a relative lock-time, otherwise ignored. */ + static const uint32_t SEQUENCE_LOCKTIME_THRESHOLD = (1 << 31); - // Threshold for inverted nSequence: below this value it is interpreted - // as a relative lock-time, otherwise ignored. - static const uint32_t SEQUENCE_THRESHOLD = (1 << 31); + /* Threshold for nSequence when interpreted as a relative + * lock-time: below this value it has units of blocks, otherwise + * seconds. */ + static const uint32_t SEQUENCE_UNITS_THRESHOLD = (1 << 30); case OP_NOP3: { @@ -79,123 +256,94 @@ semantics and detailed rationale for those semantics. if (stack.size() < 1) return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION); - // Note that unlike CHECKLOCKTIMEVERIFY we do not need to - // accept 5-byte bignums since any value greater than or - // equal to SEQUENCE_THRESHOLD (= 1 << 31) will be rejected - // anyway. This limitation just happens to coincide with - // CScriptNum's default 4-byte limit with an explicit sign - // bit. + // Note that elsewhere numeric opcodes are limited to + // operands in the range -2**31+1 to 2**31-1, however it is + // legal for opcodes to produce results exceeding that + // range. This limitation is implemented by CScriptNum's + // default 4-byte limit. // - // This means there is a maximum relative lock time of 52 - // years, even though the nSequence field in transactions - // themselves is uint32_t and could allow a relative lock - // time of up to 120 years. - const CScriptNum nInvSequence(stacktop(-1), fRequireMinimal); + // Thus as a special case we tell CScriptNum to accept up + // to 5-byte bignums, which are good until 2**39-1, well + // beyond the 2**32-1 limit of the nSequence field itself. + const CScriptNum nSequence(stacktop(-1), fRequireMinimal, 5); // In the rare event that the argument may be < 0 due to // some arithmetic being done first, you can always use // 0 MAX CHECKSEQUENCEVERIFY. - if (nInvSequence < 0) + if (nSequence < 0) return set_error(serror, SCRIPT_ERR_NEGATIVE_LOCKTIME); - // Actually compare the specified inverse sequence number - // with the input. - if (!CheckSequence(nInvSequence)) + // To provide for future soft-fork extensibility, if the + // operand is too large to be treated as a relative lock- + // time, CHECKSEQUENCEVERIFY behaves as a NOP. + if (nSequence >= SEQUENCE_LOCKTIME_THRESHOLD) + break; + + // Actually compare the specified sequence number with the input. + if (!checker.CheckSequence(nSequence)) return set_error(serror, SCRIPT_ERR_UNSATISFIED_LOCKTIME); break; } - bool CheckSequence(const CScriptNum& nInvSequence) const + bool TransactionSignatureChecker::CheckSequence(const CScriptNum& nSequence) const { - int64_t txToInvSequence; + // Relative lock times are supported by comparing the passed + // in operand to the sequence number of the input. + const int64_t txToSequence = (int64_t)txTo->vin[nIn].nSequence; - // Fail under all circumstances if the transaction's version - // number is not set high enough to enable enforced sequence - // number rules. - if (txTo->nVersion < 2) + // Fail if the transaction's version number is not set high + // enough to trigger BIP 68 rules. + if (static_cast<uint32_t>(txTo->nVersion) < 2) return false; - // Sequence number must be inverted to convert it into a - // relative lock-time. - txToInvSequence = (int64_t)~txTo->vin[nIn].nSequence; - - // Sequence numbers under SEQUENCE_THRESHOLD are not consensus - // constrained. - if (txToInvSequence >= SEQUENCE_THRESHOLD) + // Sequence numbers above SEQUENCE_LOCKTIME_THRESHOLD + // are not consensus constrained. Testing that the transaction's + // sequence number is not above this threshold prevents + // using this property to get around a CHECKSEQUENCEVERIFY + // check. + if (txToSequence >= SEQUENCE_LOCKTIME_THRESHOLD) return false; - // There are two types of relative lock-time: lock-by- - // blockheight and lock-by-blocktime, distinguished by - // whether txToInvSequence < LOCKTIME_THRESHOLD. + // There are two kinds of nSequence: lock-by-blockheight + // and lock-by-blocktime, distinguished by whether + // nSequence < SEQUENCE_UNITS_THRESHOLD. // // We want to compare apples to apples, so fail the script - // unless the type of lock-time being tested is the same as - // the lock-time in the transaction input. + // unless the type of nSequence being tested is the same as + // the nSequence in the transaction. if (!( - (txToInvSequence < LOCKTIME_THRESHOLD && nInvSequence < LOCKTIME_THRESHOLD) || - (txToInvSequence >= LOCKTIME_THRESHOLD && nInvSequence >= LOCKTIME_THRESHOLD) + (txToSequence < SEQUENCE_UNITS_THRESHOLD && nSequence < SEQUENCE_UNITS_THRESHOLD) || + (txToSequence >= SEQUENCE_UNITS_THRESHOLD && nSequence >= SEQUENCE_UNITS_THRESHOLD) )) return false; // Now that we know we're comparing apples-to-apples, the // comparison is a simple numeric one. - if (nInvSequence > txToInvSequence) + if (txTo->vin[nIn].nSequence > txToSequence) return false; return true; } -https://github.com/maaku/bitcoin/commit/33be476a60fcc2afbe6be0ca7b93a84209173eb2 - - -==Example: Escrow with Timeout== - -An escrow that times out automatically 30 days after being funded can be -established in the following way. Alice, Bob and Escrow create a 2-of-3 -address with the following redeemscript. - - IF - 2 <Alice's pubkey> <Bob's pubkey> <Escrow's pubkey> 3 CHECKMULTISIGVERIFY - ELSE - <LOCKTIME_THRESHOLD + 30*24*60*60> CHECKSEQUENCEVERIFY DROP - <Alice's pubkey> CHECKSIGVERIFY - ENDIF - -At any time funds can be spent using signatures from any two of Alice, -Bob or the Escrow. - -After 30 days Alice can sign alone. - -The clock does not start ticking until the payment to the escrow address -confirms. - ==Reference Implementation== -A reference implementation is provided in the following git repository: +A reference implementation is provided by the following pull request: -https://github.com/maaku/bitcoin/tree/checksequenceverify +https://github.com/bitcoin/bitcoin/pull/6564 ==Deployment== We reuse the double-threshold switchover mechanism from BIPs 34 and -66, with the same thresholds, but for nVersion = 8. The new rules are -in effect for every block (at height H) with nVersion = 8 and at least +66, with the same thresholds, but for nVersion = 4. The new rules are +in effect for every block (at height H) with nVersion = 4 and at least 750 out of 1000 blocks preceding it (with heights H-1000..H-1) also -have nVersion = 8. Furthermore, when 950 out of the 1000 blocks -preceding a block do have nVersion = 8, nVersion = 3 blocks become +have nVersion = 4. Furthermore, when 950 out of the 1000 blocks +preceding a block do have nVersion = 4, nVersion = 3 blocks become invalid, and all further blocks enforce the new rules. -When assessing the block version as mask of ~0x20000007 must be applied -to work around the complications caused by -[http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-August/010396.html BIP101's premature use] -of the [https://gist.github.com/sipa/bf69659f43e763540550 undecided version bits proposal]. - -By applying ~0x20000007 with nVersion = 8, the thresholds should be tested -comparing block nVersion >= 4 as this will save a bit for future use. - It is recommended that this soft-fork deployment trigger include other related proposals for improving Bitcoin's lock-time capabilities, including: @@ -219,28 +367,33 @@ done by Peter Todd for the closely related BIP 65. BtcDrak authored this BIP document. +Thanks to Eric Lombrozo and Anthony Towns for contributing example usecases. + ==References== -BIP 68: Consensus-enforced transaction replacement signalled via -sequence numbers -https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki +[https://github.com/bitcoin/bips/blob/master/bip-0068.mediawiki BIP 68] Consensus-enforced transaction replacement signalled via sequence numbers + +[https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki BIP 65] OP_CHECKLOCKTIMEVERIFY + +[https://github.com/bitcoin/bips/blob/master/bip-0113.mediawiki BIP 113] Median past block time for time-lock constraints -BIP 65: OP_CHECKLOCKTIMEVERIFY -https://github.com/bitcoin/bips/blob/master/bip-0065.mediawiki +[http://lists.linuxfoundation.org/pipermail/lightning-dev/2015-July/000021.html HTLCs using OP_CHECKSEQUENCEVERIFY/OP_LOCKTIMEVERIFY and revocation hashes] -BIP 113: Median past block time for time-lock constraints -https://github.com/bitcoin/bips/blob/master/bip-0113.mediawiki +[http://lightning.network/lightning-network-paper.pdf Lightning Network] -HTLCs using OP_CHECKSEQUENCEVERIFY/OP_LOCKTIMEVERIFY and -revocation hashes -http://lists.linuxfoundation.org/pipermail/lightning-dev/2015-July/000021.html +[https://github.com/ElementsProject/lightning/blob/master/doc/deployable-lightning.pdf Deployable Lightning] + +[http://diyhpl.us/diyhpluswiki/transcripts/sf-bitcoin-meetup/2015-02-23-scaling-bitcoin-to-billions-of-transactions-per-day/ Scaling Bitcoin to Billions of Transactions Per Day] [http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-August/010396.html Softfork deployment considerations] [https://gist.github.com/sipa/bf69659f43e763540550 Version bits] +[https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2013-April/002433.html Jeremy Spilman Micropayment Channels] + ==Copyright== This document is placed in the public domain. + diff --git a/bip-0113.mediawiki b/bip-0113.mediawiki index b7313e3..190fb4c 100644 --- a/bip-0113.mediawiki +++ b/bip-0113.mediawiki @@ -35,7 +35,7 @@ miners to claim more transaction fees by lying about the timestamps of their block. This proposal seeks to ensure reliable behaviour in locktime calculations as -required by BIP65 (CHECKLOCKTIMEVERIFY), BIP68, and BIP112 (CHECKSEQUENCEVERIFY). +required by BIP65 (CHECKLOCKTIMEVERIFY), BIP68 (sequence numbers), and BIP112 (CHECKSEQUENCEVERIFY). ==Specification== @@ -64,10 +64,10 @@ parameter. This BIP proposes that after activation calls to IsFinalTx() or LockTime() within consensus code use the return value of `GetMedianTimePast(pindexPrev)` instead. -A reference implementation of this proposal is provided in the -following git repository: +A reference implementation of this proposal is provided by the +following pull request: -https://github.com/maaku/bitcoin/tree/medianpasttimelock +https://github.com/bitcoin/bitcoin/pull/6566 ==Deployment== diff --git a/bip-0120.mediawiki b/bip-0120.mediawiki index e099f5b..1602c65 100644 --- a/bip-0120.mediawiki +++ b/bip-0120.mediawiki @@ -39,7 +39,7 @@ Current methods of proving a payment: * In BIP0070, the PaymentRequest together with the transactions fulfilling the request makes some sort of proof. However, it does not meet 1, 2 or 4 and it obviously only meets 3 if the payment is made through BIP0070. Also, there's no standard way to request/provide the proof. If standardized it would probably meet 5. * Signing messages, chosen by the server, with the private keys used to sign the transaction. This could meet 1 and 2 but probably not 3. This is not standardized either. 4 Could be met if designed so. -If an input script type is P2SH, any satisfying script should do, just as if it was a payment. For M-of-N multisig scripts, that would mean that any set of M keys should be sufficient, not neccesarily the same set of M keys that signed the transaction. This is important because strictly demanding the same set of M keys would defeat the purpose of a multisig address. +If an input script type is P2SH, any satisfying script should do, just as if it was a payment. For M-of-N multisig scripts, that would mean that any set of M keys should be sufficient, not necessarily the same set of M keys that signed the transaction. This is important because strictly demanding the same set of M keys would defeat the purpose of a multisig address. == Specification == @@ -123,7 +123,7 @@ The server needs to validate the PoP and reply with "valid" or "invalid". That p # Check that there is exactly one output. This output must have value 0 and conform to the OP_RETURN output format outlined above. # Check that the nonce is the same as the one requested. # Check that the inputs of the PoP are exactly the same as in transaction T, except that the sequence numbers must all be 0. The ordering of the inputs must also be the same as in T. -# Run the scripts of all the inputs. All scipts must return true. +# Run the scripts of all the inputs. All scripts must return true. # Check that the txid in the PoP output is the transaction you actually want proof for. If you don’t know exactly what transaction you want proof for, check that the transaction actually pays for the product/service you deliver. # Return "valid". @@ -135,7 +135,7 @@ The server needs to validate the PoP and reply with "valid" or "invalid". That p ** nonce - Your pop will not validate on server. * Someone can steal a PoP, for example by tampering with the PoP request, and try to use the service hoping to get a matching nonce. Probability per try: 1/(2^48). The server should have a mechanism for detecting a brute force attack of this kind, or at least slow down the process by delaying the PoP request by some 100 ms or so. * Even if a wallet has no funds it might still be valuable as a generator for PoPs. This makes it important to keep the security of the wallet after it has been emptied. -* Transaction malleability may cause the server to have another transaction id for a payment than the client's wallet. In that case the wallet will not be able to prove the transaction to the server. Wallets should not rely on the transaction id of the outgoing transaction. Instead it should listen for the transaction on the network and put that in its list of transactions. +* Transaction malleability may cause the server to have a different transaction id for a payment than the client's wallet. In that case the wallet will not be able to prove the transaction to the server. Wallets should not rely on the transaction id of the outgoing transaction. Instead it should listen for the transaction on the network and put that in its list of transactions. == Reference implementation == diff --git a/bip-0121.mediawiki b/bip-0121.mediawiki index a39df28..716f3c9 100644 --- a/bip-0121.mediawiki +++ b/bip-0121.mediawiki @@ -98,7 +98,7 @@ The <tt>p</tt> parameter value is the destination where to send the PoP to. This destination is typically a <tt>https:</tt> URL or a <tt>http:</tt> URL, but it could be any type of URI, for example <tt>mailto:</tt>. To keep <tt>btcpop:</tt> URIs short, users should -not make their <tt>p</tt> parameter unneccesarily long. +not make their <tt>p</tt> parameter unnecessarily long. ==== <tt>http:</tt> and <tt>https:</tt> URLs ==== |