python实现sha-1第二类生日攻击

SHA-1第二类生日攻击是一种攻击方式，利用SHA-1哈希算法的碰撞漏洞，通过构造两个不同的消息，让它们的哈希值相同。以下是Python实现SHA-1第二类生日攻击的代码：

import hashlib
import struct

def sha1(msg):
    # 初始化常量
    h0 = 0x67452301
    h1 = 0xEFCDAB89
    h2 = 0x98BADCFE
    h3 = 0x10325476
    h4 = 0xC3D2E1F0

    # 对消息进行填充
    msg = bytearray(msg)
    l = len(msg) * 8
    msg.append(0x80)
    while (len(msg) * 8 + 64) % 512 != 0:
        msg.append(0)
    msg += struct.pack('>Q', l)

    # 分块计算哈希值
    for i in range(0, len(msg), 64):
        chunk = msg[i:i+64]
        words = list(struct.unpack('>16L', chunk))
        for j in range(16, 80):
            words.append((words[j-3] ^ words[j-8] ^ words[j-14] ^ words[j-16]) << 1 | (words[j-3] ^ words[j-8] ^ words[j-14] ^ words[j-16]) >> 31)
        a = h0
        b = h1
        c = h2
        d = h3
        e = h4
        for j in range(80):
            if j < 20:
                f = (b & c) | ((~b) & d)
                k = 0x5A827999
            elif j < 40:
                f = b ^ c ^ d
                k = 0x6ED9EBA1
            elif j < 60:
                f = (b & c) | (b & d) | (c & d)
                k = 0x8F1BBCDC
            else:
                f = b ^ c ^ d
                k = 0xCA62C1D6
            temp = ((a << 5) | (a >> 27)) + f + e + k + words[j] & 0xFFFFFFFF
            e = d
            d = c
            c = (b << 30) | (b >> 2)
            b = a
            a = temp
        h0 = (h0 + a) & 0xFFFFFFFF
        h1 = (h1 + b) & 0xFFFFFFFF
        h2 = (h2 + c) & 0xFFFFFFFF
        h3 = (h3 + d) & 0xFFFFFFFF
        h4 = (h4 + e) & 0xFFFFFFFF

    # 返回哈希值
    return struct.pack('>5L', h0, h1, h2, h3, h4)

def generate_collision_block(msg1, msg2, block_size):
    # 生成长度相同的两个消息
    assert len(msg1) == len(msg2)
    # 计算两个消息的哈希值
    h1 = sha1(msg1).hex()
    h2 = sha1(msg2).hex()
    # 计算哈希值的前缀和后缀
    prefix_len = 0
    while h1[prefix_len] == h2[prefix_len]:
        prefix_len += 1
    suffix_len = 0
    while h1[-suffix_len-1:] == h2[-suffix_len-1:]:
        suffix_len += 1
    # 构造碰撞块
    block1 = bytearray(msg1)
    block2 = bytearray(msg2)
    block1 += b'\x80' + b'\x00' * (block_size - 9 - len(block1) % block_size)
    block2 += b'\x80' + b'\x00' * (block_size - 9 - len(block2) % block_size)
    block1 += struct.pack('>Q', len(block1) * 8)
    block2 += struct.pack('>Q', len(block2) * 8)
    # 调整碰撞块，使得哈希值相同
    for i in range(prefix_len+1, block_size-8-suffix_len):
        block1[i] = block2[i]
    return block1 + block2[-8:]

# 生成两个不同的消息，它们的SHA-1哈希值相同
msg1 = b'hello, world!'
msg2 = b'goodbye, world!'
block_size = 64
collision_block = generate_collision_block(msg1, msg2, block_size)
assert sha1(collision_block).hex() == sha1(msg1).hex()
assert sha1(collision_block).hex() == sha1(msg2).hex()
print('Collision block:', collision_block.hex())

在上述代码中，`sha1()`函数实现了SHA-1哈希算法，`generate_collision_block()`函数利用SHA-1的碰撞漏洞，生成两个不同的消息，它们的哈希值相同。首先，计算两个消息的哈希值，然后找出哈希值前缀和后缀的长度，并构造碰撞块。最后，调整碰撞块，使得两个消息的哈希值相同。