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"""Compare ellswift decoding in the BIP-324 test vectors against the SwiftEC reference code.
Instructions:
* Clone the SwiftEC repository, and enter the directory:
git clone https://github.com/Jchavezsaab/SwiftEC
cd SwiftEC
git checkout 5320a25035d91addde29d14164cce684b56a12ed
* Generate parameters for the secp256k1 curve:
sage --python generate_parameters.py -p secp256k1
* Copy over this file and the CSV test vectors:
cp PATH_TO_BIPS_REPO/bips/bip-0324/{*.csv,test_sage_decoding.py} .
* Run the tests:
sage --python test_sage_decoding.py -p secp256k1
No output = good.
"""
import sys
import csv
from config import F
from Xencoding_0 import Xdecode
FILENAME_PACKET_TEST = 'packet_encoding_test_vectors.csv'
FILENAME_XSWIFTEC_INV_TEST = 'xswiftec_inv_test_vectors.csv'
FILENAME_ELLSWIFT_DECODE_TEST = 'ellswift_decode_test_vectors.csv'
def ellswift_decode_sage(ellswift):
"""Given a 64-byte ellswift encoded public key, get the 32-byte X coordinate."""
u = F(int.from_bytes(ellswift[:32], 'big'))
t = F(int.from_bytes(ellswift[32:], 'big'))
# Reimplement the input correction step.
if u == F(0):
u = F(1)
if t == F(0):
t = F(1)
if u**3 + t**2 + 7 == F(0):
t = F(2) * t
# Invoke reference code
x, z = Xdecode(u, t)
# Convert to bytes.
return int(x / z).to_bytes(32, 'big')
with open(FILENAME_PACKET_TEST, newline='', encoding='utf-8') as csvfile:
reader = csv.DictReader(csvfile)
for row in reader:
bytes_ellswift_ours = bytes.fromhex(row['in_ellswift_ours'])
bytes_ellswift_theirs = bytes.fromhex(row['in_ellswift_theirs'])
assert row['mid_x_ours'] == ellswift_decode_sage(bytes_ellswift_ours).hex()
assert row['mid_x_theirs'] == ellswift_decode_sage(bytes_ellswift_theirs).hex()
with open(FILENAME_XSWIFTEC_INV_TEST, newline='', encoding='utf-8') as csvfile:
reader = csv.DictReader(csvfile)
for row in reader:
udat = bytes.fromhex(row['u'])
xdat = bytes.fromhex(row['x'])
for case in range(8):
tdat = bytes.fromhex(row[f"case{case}_t"])
if tdat:
assert ellswift_decode_sage(udat + tdat) == xdat
with open(FILENAME_ELLSWIFT_DECODE_TEST, newline='', encoding='utf-8') as csvfile:
reader = csv.DictReader(csvfile)
for row in reader:
ellswift = bytes.fromhex(row['ellswift'])
assert ellswift_decode_sage(ellswift).hex() == row['x']
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