See Iceland code https://github.com/iceland2k14

pkshift.py

# Copyright 2022 Ali Sherief
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from fastecdsa import curve
from fastecdsa.point import Point
import bit

G = curve.secp256k1.G
N = curve.secp256k1.q

pubkey = '03a2efa402fd5268400c77c20e574ba86409ededee7c4020e4b9f0edbee53de0d4'

def pub2point(pub_hex):
    x = int(pub_hex[2:66], 16)
    if len(pub_hex) < 70:
        y = bit.format.x_to_y(x, int(pub_hex[:2], 16) % 2)
    else:
        y = int(pub_hex[66:], 16)
    return Point(x, y, curve=curve.secp256k1)


def point2pub(R):
    # Remove the following code if you are doing multiple additions successively
    # as it brings a speed improvement, and just return R
    if (R.y % 2 == 0):
        prefix = "02"
    else:
        prefix = "03"
    hx = hex(R.x)[2:].zfill(64)
    return hx



pk1 = '031656894a2e404e652e3a2b368c7df820b0e92fe32529c41931a9f7b234457d5b'
pk2 = '022fa21d1cea4bc1f9911a9d501e3d8b3c97d15aaa76a63fecd0d529b9ef2e22f5'

def add(pk1, pk2, convert=True):
    if convert:
        P = pub2point(pk1)
        Q = pub2point(pk2)
    else:
        P = pk1
        Q = pk2
    R = P + Q
    return R

def sub(pk1, pk2, convert=True):
    if convert:
        P = pub2point(pk1)
        Q = pub2point(pk2)
    else:
        P = pk1
        Q = pk2
    R = P - Q
    return R




# This function makes all the downscaled pubkeys obtained from subtracting
# numbers between 0 and divisor, before dividing the pubkeys by divisor.
# i is between 0 and divisor (inclusive)
def shiftdown(pubkey, divisor, i=0, convert=True):
    if convert:
        pubkey = pub2point(pubkey)
    # k = 1/divisor
    k = pow(divisor, N - 2, N)
    P = pubkey - (i * G)
    P = k * P
    return P


# i is between 0 and multiplier (inclusive)
def shiftup(pubkey, multiplier, i=0, convert=True):
    if convert:
        pubkey = pub2point(pubkey)
    P = multiplier*(pubkey + (i * G))
    return P

# example:
print(shiftdown(pubkey, 32, i=0))
print(shiftup(pubkey, 32, i=0))
print(add(pk1, pk2))
print(sub(pk1, pk2))