python实现的椭圆曲线加密

Posted 2021-02-07 aguncn

我也看得云里雾里，

但是ECC和RSA并列为非对称加密双雄，

还是很有必要了解一下的。

RSA是用质数分解，ECC是用离散的椭圆方程解，安全度更高。

而且，这个ECC的加法乘法规则，和普通都不一样，

其解是属于一个什么阿贝尔群(一听就知道高级啦)。

from hashlib import sha256


def sha256d(string):
    if not isinstance(string, bytes):
        string = string.encode()

    return sha256(sha256(string).digest()).hexdigest()


def inv_mod(b, p):
    if b < 0 or p <= b:
        b = b % p
    c , d = b, p
    uc, vc, ud, vd, temp = 1, 0, 0, 1, 0
    while c != 0:
        temp = c
        q, c, d = d // c, d % c, temp
        uc, vc, ud, vd = ud - q * uc, vd - q * vc, uc, vc

    assert d == 1
    if ud > 0:
        return ud
    else:
        return ud + p


def leftmost_bit(x):
    assert x > 0
    result = 1
    while result <= x:
        result = 2 * result
    return result // 2


print(inv_mod(2, 23))
print(3*inv_mod(1, 23) % 23)


def show_points(p, a, b):
    return [(x, y) for x in range(p) for y in range(p) if (y*y - (x*x*x + a*x + b)) % p == 0]


print(show_points(p=29, a=4, b=20))


def double(x, y, p, a, b):
    l = ((3 * x * x + a) * inv_mod(2 * y, p)) % p
    x3 = (l * l - 2 * x) % p
    y3 = (l * (x - x3) - y) % p
    return x3, y3


print(double(1, 4, p=5, a=2, b=3))


def add(x1, y1, x2, y2, p, a, b):
    if x1 == x2 and y1 == y2:
        return double(x1, y1, p, a, b)
    l = ((y2 - y1) * inv_mod(x2 - x1, p)) % p
    x3 = (l * l - x1 -x2) % p
    y3 = (l * (x1 - x3) - y1) % p
    return x3, y3


print(add(1, 4, 3, 1, p=5, a=2, b=3))


def get_bits(n):
    bits = []
    while n != 0:
        bits.append(n & 1)
        n >> 1
    return bits


class CurveFp(object):

    def __init__(self, p, a, b):
        """ y^2 = x^3 + a*x + b (mod p)."""
        self.p = p
        self.a = a
        self.b = b

    def contains_point(self, x, y):
        return (y * y - (x * x * x + self.a * x + self.b)) % self.p == 0

    def show_all_points(self):
        return [(x, y) for x in range(self.p) for y in range(self.p) if
                (y * y - (x * x * x + self.a * x + self.b)) % self.p == 0]

    def __repr__(self):
        return "Curve(p={0:d}, a={1:d}, b={2:d})".format(self.p, self.a, self.b)


class Point(object):

    def __init__(self, curve, x, y, order=None):

        self.curve = curve
        self.x = x
        self.y = y
        self.order = order
        # self.curve is allowed to be None only for INFINITY:
        if self.curve:
            assert self.curve.contains_point(x, y)
        if order:
            assert self * order == INFINITY

    def __eq__(self, other):
        """Is this point equals to another"""
        if self.curve == other.curve                 and self.x == other.x                 and self.y == other.y:
            return True
        else:
            return False

    def __add__(self, other):
        """Add one point to another point."""

        if other == INFINITY:
            return self
        if self == INFINITY:
            return other
        assert self.curve == other.curve

        if self.x == other.x:
            if (self.y + other.y) % self.curve.p == 0:
                return INFINITY
            else:
                return self.double()

        p = self.curve.p
        l = ((other.y - self.y) *              inv_mod(other.x - self.x, p)) % p

        x3 = (l * l - self.x - other.x) % p
        y3 = (l * (self.x - x3) - self.y) % p

        return Point(self.curve, x3, y3)

    def __mul__(self, other):
        e = other
        if self.order:
            e = e % self.order
        if e == 0:
            return INFINITY
        if self == INFINITY:
            return INFINITY

        e3 = 3 * e
        negative_self = Point(self.curve, self.x, -self.y, self.order)
        i = leftmost_bit(e3) // 2
        result = self

        while i > 1:
            result = result.double()
            if (e3 & i) != 0 and (e & i) == 0:
                result = result + self
            if (e3 & i) == 0 and (e & i) != 0:
                result = result + negative_self
            i = i // 2
        return result

    def __rmul__(self, other):
        """Multiply a point by an integer."""
        return self * other

    def __repr__(self):
        if self == INFINITY:
            return "infinity"
        return "({0},{1})".format(self.x, self.y)

    def double(self):
        """the double point."""
        if self == INFINITY:
            return INFINITY

        p = self.curve.p
        a = self.curve.a
        l = ((3 * self.x * self.x + a) *              inv_mod(2 * self.y, p)) % p

        x3 = (l * l - 2 * self.x) % p
        y3 = (l * (self.x - x3) - self.y) % p

        return Point(self.curve, x3, y3)

    def invert(self):
        return Point(self.curve, self.x, -self.y % self.curve.p)


INFINITY = Point(None, None, None)

p, a, b = 29, 4, 20
curve = CurveFp(p, a, b)
p0 = Point(curve, 3, 1)
print(p0*2)
print(p0*20)

输出：

12
3
[(0, 7), (0, 22), (1, 5), (1, 24), (2, 6), (2, 23), (3, 1), (3, 28), (4, 10), (4, 19), (5, 7), (5, 22), (6, 12), (6, 17), (8, 10), (8, 19), (10, 4), (10, 25), (13, 6), (13, 23), (14, 6), (14, 23), (15, 2), (15, 27), (16, 2), (16, 27), (17, 10), (17, 19), (19, 13), (19, 16), (20, 3), (20, 26), (24, 7), (24, 22), (27, 2), (27, 27)]
(3, 1)
(2, 0)
(24,7)
(15,27)