Add basic segwit support

[bjarnemagnussen]

Adds support for the segwit transaction structure and signing of P2WPKH segwit inputs.

New functions:

• sign_segwit_struct(tx, i, priv, hashcode=SIGHASH_ALL, segwit=False, amount=0): Signs input i for a segwit transaction structure. Signes the input as a legacy P2PKH if segwit==False; or as a P2WPKH input if segwit==True.

• mk_p2wpkh_script(pubkey): Creates a P2WPKH script using pubkey.

Also adds the following new internal functions used by sign_segwit_struct():
mk_p2wpkh_scriptcode(pubkey); mk_p2wpkh_redeemscript(pubkey); pubkey_to_hash(pubkey); signature_form_segwit(tx, i, scriptCode, amount, hashcode=SIGHASH_ALL); mk_hashOutputs(out, hashcode=SIGHASH_ALL); mk_hashInputs(inp, hashcode=SIGHASH_ALL); serialize_signature_form_segwit(txobj).

Example usage:

from bitcoin import *
#Making the deposit P2WPKH address:
priv = sha256("binfiUlnidyapyenPecNijOd5")
priv
'944a059c201d4fa4a8362fdc16695cce4aa14b26275834c6239b5048b756a6a2'
pub = compress(privtopub(priv))
pub
'0208166a7cc4ec694b9874acaa1f837128cabb17b785d457d3d39b2369da346aa8'
address = script_to_address(mk_p2wpkh_script(pub))
address
'36BoUfjer5Y8Ezncsy6ZgYRmYEJk3HP8V4'

#Making the tx:
#inputs = unspent('36BoUfjer5Y8Ezncsy6ZgYRmYEJk3HP8V4')
inputs = [{'output': '5f9738939f6da66974e88967cfb858a8f427a82d46ee05a5f97c8bb14ef0bc83:1', 'value': 28851}]
outputs = [{'value': 25000, 'address': '39uWVDaxPKNBxttUKc7FdXNPGwmMwqtaPC'}]
tx = mktx(inputs, outputs, True)
tx_signed = sign_segwit_struct(tx, 0, priv, 1, True)
deserialize(tx_signed,True)
{'outs': [{'value': 25000, 'script': 'a9145a1dd75ee9121ccea2acc822e335a3e15b7ddf5e87'}], 'ins': [{'script': '160014364ccd6a55f64ebda93e80706dc3fda32a16ff6e', 'outpoint': {'index': 1, 'hash': '5f9738939f6da66974e88967cfb858a8f427a82d46ee05a5f97c8bb14ef0bc83'}, 'sequence': 4294967295}], 'flag': 1, 'version': 1, 'marker': 0, 'locktime': 0, 'witness': [{'scriptCode': '4830450221008fb1f09f88a95f21f0b76a36782f861fe274d1e6e45dbbe44315212da228b7d702206b850d52a9bf5e9175179161d0e4c52f5caecaea378c43425396a59d8fe9ab3801210208166a7cc4ec694b9874acaa1f837128cabb17b785d457d3d39b2369da346aa8', 'number': 2}]}
tx_signed
0100000000010183bcf04eb18b7cf9a505ee462da827f4a858b8cf6789e87469a66d9f9338975f0100000017160014364ccd6a55f64ebda93e80706dc3fda32a16ff6effffffff01a86100000000000017a9145a1dd75ee9121ccea2acc822e335a3e15b7ddf5e87024830450221008fb1f09f88a95f21f0b76a36782f861fe274d1e6e45dbbe44315212da228b7d702206b850d52a9bf5e9175179161d0e4c52f5caecaea378c43425396a59d8fe9ab3801210208166a7cc4ec694b9874acaa1f837128cabb17b785d457d3d39b2369da346aa800000000
pushtx(tx_signed)
'Transaction Submitted'

The example from the README using legacy transactio structure still works as expected.

This is only thought of as a first start to implement segwit and so many bugs are expected and more rigorous testing is necessary and implementation of other segwit types.

[bjarnemagnussen]

It would probably be nice to make sure that the pubkey being passed to the functions mk_p2wpkh_script(), mk_p2wpkh_redeemscript() and mk_p2wpkh_scriptcode() is compressed, since with Segwit compressed-public-keys are mandatory.

[reiven]

hey @wizardofozzie it will be possible to add this PR to your fork? let me know if i can help somehow