diff options
Diffstat (limited to 'bip-0341.mediawiki')
| -rw-r--r-- | bip-0341.mediawiki | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/bip-0341.mediawiki b/bip-0341.mediawiki index 8f27c35..ec11f6a 100644 --- a/bip-0341.mediawiki +++ b/bip-0341.mediawiki @@ -31,7 +31,7 @@ This proposal aims to improve privacy, efficiency, and flexibility of Bitcoin's ==Design== -A number of related ideas for improving Bitcoin's scripting capabilities have been previously proposed: Schnorr signatures ([[bip-0340|BIP340]]), Merkle branches ("MAST", [[bip-0114|BIP114]], [[bip-0117|BIP117]]), new sighash modes ([[bip-0118|BIP118]]), new opcodes like CHECKSIGFROMSTACK, [https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-January/015614.html Taproot], [https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-February/015700.html Graftroot], [https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-July/016249.html G'root], and [https://bitcointalk.org/index.php?topic=1377298.0 cross-input aggregation]. +A number of related ideas for improving Bitcoin's scripting capabilities have been previously proposed: Schnorr signatures ([[bip-0340.mediawiki|BIP340]]), Merkle branches ("MAST", [[bip-0114.mediawiki|BIP114]], [[bip-0117.mediawiki|BIP117]]), new sighash modes ([[bip-0118.mediawiki|BIP118]]), new opcodes like CHECKSIGFROMSTACK, [https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-January/015614.html Taproot], [https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-February/015700.html Graftroot], [https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-July/016249.html G'root], and [https://bitcointalk.org/index.php?topic=1377298.0 cross-input aggregation]. Combining all these ideas in a single proposal would be an extensive change, be hard to review, and likely miss new discoveries that otherwise could have been made along the way. Not all are equally mature as well. For example, cross-input aggregation [https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-March/015838.html interacts] in complex ways with upgrade mechanisms, and solutions to that are still [https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-October/016461.html in flux]. On the other hand, separating them all into independent upgrades would reduce the efficiency and privacy gains to be had, and wallet and service providers may not be inclined to go through many incremental updates. Therefore, we're faced with a tradeoff between functionality and scope creep. In this design we strike a balance by focusing on the structural script improvements offered by Taproot and Merkle branches, as well as changes necessary to make them usable and efficient. For things like sighashes and opcodes we include fixes for known problems, but exclude new features that can be added independently with no downsides. @@ -65,7 +65,7 @@ The following rules only apply when such an output is being spent. Any other out * If there are at least two witness elements left, script path spending is used: ** Call the second-to-last stack element ''s'', the script. ** The last stack element is called the control block ''c'', and must have length ''33 + 32m'', for a value of ''m'' that is an integer between 0 and 128<ref>'''Why is the Merkle path length limited to 128?''' The optimally space-efficient Merkle tree can be constructed based on the probabilities of the scripts in the leaves, using the Huffman algorithm. This algorithm will construct branches with lengths approximately equal to ''log<sub>2</sub>(1/probability)'', but to have branches longer than 128 you would need to have scripts with an execution chance below 1 in ''2<sup>128</sup>''. As that is our security bound, scripts that truly have such a low chance can probably be removed entirely.</ref>, inclusive. Fail if it does not have such a length. -** Let ''p = c[1:33]'' and let ''P = point(p)'' where ''point'' and ''[:]'' are defined as in [bip-0340.mediawiki#design|BIP340]. Fail if this point is not on the curve. +** Let ''p = c[1:33]'' and let ''P = point(p)'' where ''point'' and ''[:]'' are defined as in [[bip-0340.mediawiki#design|BIP340]]. Fail if this point is not on the curve. ** Let ''v = c[0] & 0xfe'' and call it the ''leaf version''<ref>'''What constraints are there on the leaf version?''' First, the leaf version cannot be odd as ''c[0] & 0xfe'' will always be even, and cannot be ''0x50'' as that would result in ambiguity with the annex. In addition, in order to support some forms of static analysis that rely on being able to identify script spends without access to the output being spent, it is recommended to avoid using any leaf versions that would conflict with a valid first byte of either a valid P2WPKH pubkey or a valid P2WSH script (that is, both ''v'' and ''v | 1'' should be an undefined, invalid or disabled opcode or an opcode that is not valid as the first opcode). The values that comply to this rule are the 32 even values between ''0xc0'' and ''0xfe'' and also ''0x66'', ''0x7e'', ''0x80'', ''0x84'', ''0x96'', ''0x98'', ''0xba'', ''0xbc'', ''0xbe''. Note also that this constraint implies that leaf versions should be shared amongst different witness versions, as knowing the witness version requires access to the output being spent.</ref>. ** Let ''k<sub>0</sub> = hash<sub>TapLeaf</sub>(v || compact_size(size of s) || s)''; also call it the ''tapleaf hash''. ** For ''j'' in ''[0,1,...,m-1]'': |