search

tradecraftio / tradecraft

Tradecraft integration/staging tree https://tradecraft.io/download
Other
13 stars 9 forks source link

Change MAX_P2SH_SIGOPS from 15 to 20 #7

Closed maaku closed 5 years ago

maaku commented 5 years ago

The maximum number of signature operations that can be usefully performed within the context of a single P2SH script is 20, not 15 as is assumed by the standardness rules of the bitcoin codebase. The value of 15 was calculated at the time it was introduced based on size of parameters to CHECKMULTISIG: with 33-byte public keys there is no way to have a threshold larger than k-of-15 using the CHECKMULTISIG opcode within a 520 byte redeem script. However, other constructions are possible. Using the same size-reduction technique as P2SH, a k-of-19 threshold can be supported with a script size of 518 bytes for a k-of-19 threshold:

TRUE 0 (2ROT DUP HASH160 <pubkeyhash> EQUALVERIFY CHECKSIG ADD)x19 ... k EQUALVERIFY

Alternatively, a 20-of-20 multisig (requiring all signatures) can be supported, weighing in at just 510 bytes:

(DUP HASH160 <pubkeyhash> EQUALVERIFY CHECKSIGVERIFY)x19 <pubkey> CHECKSIG

Although it would be preferable to use Schnorr multi signature schemes and key aggregation for efficiency reasons, the above thresholds are of practical use today and should be supported. Therefore, the MAX_P2SH_SIGOPS value should be 20, not 15, and the relevant unit tests updated.

maaku commented 5 years ago

This has been implemented in the 0.10 rebase branch, and the two specific examples given above added to the unit tests.