python实现ecc加解密算法，不使用相关的库

在Python中实现ECC加密解密算法，可以使用pycryptodome库来进行相关的椭圆曲线运算，也可以手动实现椭圆曲线运算。以下是手动实现的代码示例：

import random

# 定义椭圆曲线参数
p = 0xfffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2f
a = 0xfffffffffffffffffffffffffffffffffffffffffffffffffffffffefffffc2c
b = 0x1c97befc54bd7a8b65acf89f81d4d4adc565fa45
n = 0xfffffffffffffffffffffffffffffffebaaedce6af48a03bbfd25e8cd0364141
Gx = 0x4a96b5688ef573284664698968c38bb913cbfc82
Gy = 0x23a628553168947d59dcc912042351377ac5fb32

# 定义椭圆曲线上的点类
class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y
        
    def __add__(self, Q):
        if self.x == Q.x and self.y == Q.y:
            return self.double()
        if self.x == Q.x and self.y == -Q.y:
            return Point(None, None)
        slope = (Q.y - self.y) * pow(Q.x - self.x, p-2, p) % p
        x = (slope ** 2 - self.x - Q.x) % p
        y = (slope * (self.x - x) - self.y) % p
        return Point(x, y)
    
    def __sub__(self, Q):
        return self + Point(Q.x, -Q.y)
    
    def double(self):
        slope = (3 * self.x ** 2 + a) * pow(2 * self.y, p-2, p) % p
        x = (slope ** 2 - 2 * self.x) % p
        y = (slope * (self.x - x) - self.y) % p
        return Point(x, y)
    
    def __mul__(self, k):
        if k == 0:
            return Point(None, None)
        if k == 1:
            return self
        Q = self.double()
        if k % 2 == 0:
            return Q * (k//2)
        else:
            return self + Q * (k//2)
        
    def __str__(self):
        return "({},{})".format(self.x, self.y)

# 定义逆元函数
def inverse_mod(a, m):
    if a < 0 or m <= a:
        a = a % m
    t, newt = 0, 1
    r, newr = m, a
    while newr != 0:
        quotient = r // newr
        t, newt = newt, t - quotient * newt
        r, newr = newr, r - quotient * newr
    if r > 1:
        return None
    if t < 0:
        t = t + m
    return t

# 定义判断点是否在曲线上的函数
def is_on_curve(P):
    if P.x is None:
        return True
    return (P.y ** 2 - P.x ** 3 - a * P.x - b) % p == 0

# 定义椭圆曲线上点的生成函数
def generate_keypair():
    d = random.randrange(1, n)
    P = d * Point(Gx, Gy)
    if not is_on_curve(P):
        return generate_keypair()
    return (d, P)

# 定义加密函数
def encrypt(P, M):
    k = random.randrange(1, n)
    C1 = k * Point(Gx, Gy)
    S = k * P
    C2 = M + S
    return (C1, C2)

# 定义解密函数
def decrypt(d, C):
    C1, C2 = C
    S = d * C1
    M = C2 - S
    return M

# 测试
d, P = generate_keypair()
M = Point(123, 456)
C = encrypt(P, M)
M2 = decrypt(d, C)
assert M.x == M2.x and M.y == M2.y
print("Encryption and decryption succeed!")

注意，此代码中的椭圆曲线参数、密钥长度等均需要根据具体应用进行调整。