Topic: How to calculate p2wsh signature? (Read 240 times)

I wrote about native P2WSH addresses on Medium a while ago and posted the code on Github:
https://gist.github.com/pierrenoizat/6880a12a599fa03a2099e3b38e8664e0

In a nutshell, if your witness script is like (for instance):


then your witness program (script_pub_key) is:

This is a ruby example but you get the idea in any other programming language you are using. Hope this helps.

I read the bip143, but didn't understand how to calculate the scriptCode of p2wsh.

bip143 told us:
A new transaction digest algorithm is defined, but only applicable to sigops in version 0 witness program
Double SHA256 of the serialization of:
     1. nVersion of the transaction (4-byte little endian)
     2. hashPrevouts (32-byte hash)
     3. hashSequence (32-byte hash)
     4. outpoint (32-byte hash + 4-byte little endian)
     5. scriptCode of the input (serialized as scripts inside CTxOuts)
     6. value of the output spent by this input (8-byte little endian)
     7. nSequence of the input (4-byte little endian)
     8. hashOutputs (32-byte hash)
     9. nLocktime of the transaction (4-byte little endian)
    10. sighash type of the signature (4-byte little endian)


The item 5:

For P2WPKH witness program, the scriptCode is 0x1976a914{20-byte-pubkey-hash}88ac.
For P2WSH witness program,
if the witnessScript does not contain any OP_CODESEPARATOR, the scriptCode is the witnessScript serialized as scripts inside CTxOut.
if the witnessScript contains any OP_CODESEPARATOR, the scriptCode is the witnessScript but removing everything up to and including the last executed OP_CODESEPARATOR before the signature checking opcode being executed, serialized as scripts inside CTxOut. (The exact semantics is demonstrated in the examples below)

I don't kown how to find out if "the signature checking opcode being executed".
Then I read the example "Native P2WSH" in bip143 and I am even more confused.

Here is the first example of "Native P2WSH":

The following is an unsigned transaction: 0100000002fe3dc9208094f3ffd12645477b3dc56f60ec4fa8e6f5d67c565d1c6b9216b36e00000 00000ffffffff0815cf020f013ed6cf91d29f4202e8a58726b1ac6c79da47c23d1bee0a6925f800 00000000ffffffff0100f2052a010000001976a914a30741f8145e5acadf23f751864167f32e096 3f788ac00000000
 
    nVersion:  01000000
    txin:      02 fe3dc9208094f3ffd12645477b3dc56f60ec4fa8e6f5d67c565d1c6b9216b36e 00000000 00 ffffffff
                  0815cf020f013ed6cf91d29f4202e8a58726b1ac6c79da47c23d1bee0a6925f8 00000000 00 ffffffff
    txout:     01 00f2052a01000000 1976a914a30741f8145e5acadf23f751864167f32e0963f788ac
    nLockTime: 00000000
 
  The first input comes from an ordinary P2PK:
    scriptPubKey: 21036d5c20fa14fb2f635474c1dc4ef5909d4568e5569b79fc94d3448486e14685f8ac value: 1.5625
    private key:  b8f28a772fccbf9b4f58a4f027e07dc2e35e7cd80529975e292ea34f84c4580c
    signature:    304402200af4e47c9b9629dbecc21f73af989bdaa911f7e6f6c2e9394588a3aa68f81e9902204f3 fcf6ade7e5abb1295b6774c8e0abd94ae62217367096bc02ee5e435b67da201 (SIGHASH_ALL)
 
  The second input comes from a native P2WSH witness program:
    scriptPubKey : 00205d1b56b63d714eebe542309525f484b7e9d6f686b3781b6f61ef925d66d6f6a0, value: 49
    witnessScript: 21026dccc749adc2a9d0d89497ac511f760f45c47dc5ed9cf352a58ac706453880aeadab210255a 9626aebf5e29c0e6538428ba0d1dcf6ca98ffdf086aa8ced5e0d0215ea465ac
                   <026dccc749adc2a9d0d89497ac511f760f45c47dc5ed9cf352a58ac706453880ae> CHECKSIGVERIFY CODESEPARATOR <0255a9626aebf5e29c0e6538428ba0d1dcf6ca98ffdf086aa8ced5e0d0215ea465> CHECKSIG
 
  To sign it with a nHashType of 3 (SIGHASH_SINGLE):
 
  hashPrevouts:
    dSHA256(fe3dc9208094f3ffd12645477b3dc56f60ec4fa8e6f5d67c565d1c6b9216b36e000000000815cf0 20f013ed6cf91d29f4202e8a58726b1ac6c79da47c23d1bee0a6925f800000000)
  = ef546acf4a020de3898d1b8956176bb507e6211b5ed3619cd08b6ea7e2a09d41
 
    nVersion:     01000000
    hashPrevouts: ef546acf4a020de3898d1b8956176bb507e6211b5ed3619cd08b6ea7e2a09d41
    hashSequence: 0000000000000000000000000000000000000000000000000000000000000000
    outpoint:     0815cf020f013ed6cf91d29f4202e8a58726b1ac6c79da47c23d1bee0a6925f800000000
    scriptCode:   (see below)
    amount:       0011102401000000
    nSequence:    ffffffff
    hashOutputs:  0000000000000000000000000000000000000000000000000000000000000000 (this is the second input but there is only one output)
    nLockTime:    00000000
    nHashType:    03000000
 
  scriptCode:  4721026dccc749adc2a9d0d89497ac511f760f45c47dc5ed9cf352a58ac706453880aeadab21025 5a9626aebf5e29c0e6538428ba0d1dcf6ca98ffdf086aa8ced5e0d0215ea465ac
                                                                                       ^^
               (please note that the not-yet-executed OP_CODESEPARATOR is not removed from the scriptCode)
  preimage:    01000000ef546acf4a020de3898d1b8956176bb507e6211b5ed3619cd08b6ea7e2a09d410000000 0000000000000000000000000000000000000000000000000000000000815cf020f013ed6cf91d2 9f4202e8a58726b1ac6c79da47c23d1bee0a6925f8000000004721026dccc749adc2a9d0d89497a c511f760f45c47dc5ed9cf352a58ac706453880aeadab210255a9626aebf5e29c0e6538428ba0d1 dcf6ca98ffdf086aa8ced5e0d0215ea465ac0011102401000000ffffffff0000000000000000000 0000000000000000000000000000000000000000000000000000003000000
  sigHash:     82dde6e4f1e94d02c2b7ad03d2115d691f48d064e9d52f58194a6637e4194391
  public key:  026dccc749adc2a9d0d89497ac511f760f45c47dc5ed9cf352a58ac706453880ae
  private key: 8e02b539b1500aa7c81cf3fed177448a546f19d2be416c0c61ff28e577d8d0cd
  signature:   3044022027dc95ad6b740fe5129e7e62a75dd00f291a2aeb1200b84b09d9e3789406b6c002201a9 ecd315dd6a0e632ab20bbb98948bc0c6fb204f2c286963bb48517a7058e2703
 
  scriptCode:  23210255a9626aebf5e29c0e6538428ba0d1dcf6ca98ffdf086aa8ced5e0d0215ea465ac
               (everything up to the last executed OP_CODESEPARATOR, including that OP_CODESEPARATOR, are removed)
  preimage:    01000000ef546acf4a020de3898d1b8956176bb507e6211b5ed3619cd08b6ea7e2a09d410000000 0000000000000000000000000000000000000000000000000000000000815cf020f013ed6cf91d2 9f4202e8a58726b1ac6c79da47c23d1bee0a6925f80000000023210255a9626aebf5e29c0e65384 28ba0d1dcf6ca98ffdf086aa8ced5e0d0215ea465ac0011102401000000ffffffff000000000000 00000000000000000000000000000000000000000000000000000000000003000000
  sigHash:     fef7bd749cce710c5c052bd796df1af0d935e59cea63736268bcbe2d2134fc47
  public key:  0255a9626aebf5e29c0e6538428ba0d1dcf6ca98ffdf086aa8ced5e0d0215ea465
  private key: 86bf2ed75935a0cbef03b89d72034bb4c189d381037a5ac121a70016db8896ec
  signature:   304402200de66acf4527789bfda55fc5459e214fa6083f936b430a762c629656216805ac0220396 f550692cd347171cbc1ef1f51e15282e837bb2b30860dc77c8f78bc8501e503
 
  The serialized signed transaction is: 01000000000102fe3dc9208094f3ffd12645477b3dc56f60ec4fa8e6f5d67c565d1c6b9216b36e0 00000004847304402200af4e47c9b9629dbecc21f73af989bdaa911f7e6f6c2e9394588a3aa68f8 1e9902204f3fcf6ade7e5abb1295b6774c8e0abd94ae62217367096bc02ee5e435b67da201fffff fff0815cf020f013ed6cf91d29f4202e8a58726b1ac6c79da47c23d1bee0a6925f80000000000ff ffffff0100f2052a010000001976a914a30741f8145e5acadf23f751864167f32e0963f788ac000 347304402200de66acf4527789bfda55fc5459e214fa6083f936b430a762c629656216805ac0220 396f550692cd347171cbc1ef1f51e15282e837bb2b30860dc77c8f78bc8501e503473044022027d c95ad6b740fe5129e7e62a75dd00f291a2aeb1200b84b09d9e3789406b6c002201a9ecd315dd6a0 e632ab20bbb98948bc0c6fb204f2c286963bb48517a7058e27034721026dccc749adc2a9d0d8949 7ac511f760f45c47dc5ed9cf352a58ac706453880aeadab210255a9626aebf5e29c0e6538428ba0 d1dcf6ca98ffdf086aa8ced5e0d0215ea465ac00000000

01000000
0001
02
fe3dc9208094f3ffd12645477b3dc56f60ec4fa8e6f5d67c565d1c6b9216b36e 00000000
48
47304402200af4e47c9b9629dbecc21f73af989bdaa911f7e6f6c2e9394588a3aa68f81e9902204 f3fcf6ade7e5abb1295b6774c8e0abd94ae62217367096bc02ee5e435b67da201
ffffffff
0815cf020f013ed6cf91d29f4202e8a58726b1ac6c79da47c23d1bee0a6925f8 0000000000
ffffffff

01
00f2052a01000000
1976a914a30741f8145e5acadf23f751864167f32e0963f788ac

0003

47304402200de66acf4527789bfda55fc5459e214fa6083f936b430a762c629656216805ac02203 96f550692cd347171cbc1ef1f51e15282e837bb2b30860dc77c8f78bc8501e503
473044022027dc95ad6b740fe5129e7e62a75dd00f291a2aeb1200b84b09d9e3789406b6c002201 a9ecd315dd6a0e632ab20bbb98948bc0c6fb204f2c286963bb48517a7058e2703
4721026dccc749adc2a9d0d89497ac511f760f45c47dc5ed9cf352a58ac706453880aeadab21025 5a9626aebf5e29c0e6538428ba0d1dcf6ca98ffdf086aa8ced5e0d0215ea465ac


1. Here "witnessScript" is RedeemScript, right?
2. what is meaning of 'CODESEPARATOR' here?
3. why need calculate both scriptCode(OP_CODESEPARATOR is not removed && OP_CODESEPARATOR is removed) and both put them into witness data?

My head is filled with question...
Anyone can help? thanks a lot.