Print Page - Help with Casascius Escrow Scheme 'identifier31'

Edit: Mods, if this is not the correct place for this, which board should I post similar questions in in the future? Is "technical support" more appropriate?

I've been fooling around with various bitcoin apps, including Casascius' Bitcoin Address Utility (https://en.bitcoin.it/wiki/Bitcoin_Address_Utility) and its Escrow functions (https://en.bitcoin.it/wiki/User:Casascius/Escrow_scheme_draft), and trying to recreate a lot of what they do in Python, just to help me learn Python. As a first sample test, I looked at the code (https://github.com/casascius/Bitcoin-Address-Utility/blob/master/Model/EscrowCode.cs#L82) for generating the initial escrow components, which was mostly matched (https://github.com/mannkind/bitescrow.org/blob/master/js/bitcoin.escrow.js#L7) at a website which implements it.

However, for the life of me I cannot seem to output the correct prefix referred to as (https://en.bitcoin.it/wiki/User:Casascius/Escrow_scheme_draft#Base58_codes_.28draft.29_for_3-party_scheme) "constant plus identifier31".

I was hoping somebody might be able to see the problem with my code. I've triple and quadruple checked the functions and variables being used, so I assume the code must be wrong somewhere in here, but it's reasonably simple and for the life of me I can't find the error. I was hoping somebody else's eyes might spot the problem. Why doesn't escrowA_actualprefix match escrowA_decodedprefix!?

Code:

einva = "140bebc0a12ca9c6"
einvb = "140bebc16ae0563b"

escrowA = "einvaALiXnuThMYVpu7Gz6FJgEj7xvwtcA15ss29cMv7UMa1kgBmvcQtgjSd93AJ7Zadh1k3m3Adxzyw2MtDL3F43Kz1cqBye8rqWAtm6s"
escrowB = "einvbALiXnsHWdyJ8soFrrw4ZNCp4ftM5yGqkU5jQkrZUqdFXLK6ubxK56g7YyRfFoVK9o7cjgyDb51cbynmrpSnkJh9nMGJRJFZXuXFdH"

# base58_decode output is hex string without checksum. e.g. "VZL8ExEXUaC" becomes "aabbccdd"
keyA = int(base58_decode(escrowA)[18:-66],16)
keyB = int(base58_decode(escrowB)[18:-66],16)

keyAB = (keyA * keyB) % N

keyABx, keyABy = ec_multiply(Gx,Gy,keyAB)

keyABx = str(hex(keyABx)).rstrip("L").lstrip("0x")

keyABy = str(hex(keyABy)).rstrip("L").lstrip("0x")

keyABpub = compress_pub_key_str("04" + keyABx + keyABy)

hashGxy = str(hashlib.sha256(hashlib.sha256(binascii.unhexlify(keyABpub))
         .digest()).hexdigest())

identifier31 = str(hex(((int(hashGxy[:2],16) & int("3f",16)) << 24)
             + (int(hashGxy[2:4],16) << 16)
             + (int(hashGxy[4:6],16) << 8)
             + int(hashGxy[6:8],16))) \
             .rstrip("L").lstrip("0x")

escrowA_actualprefix = base58_decode(escrowA)[:16]

escrowA_decodedprefix = str(hex(int(einva,16) + int(identifier31,16))) \
                        .rstrip("L").lstrip("0x")

print (einva)
print (escrowA_actualprefix)
print (escrowA_decodedprefix)

exit()

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Bitcoin => Development & Technical Discussion => Topic started by: luv2drnkbr on August 31, 2014, 02:43:02 AM