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Problem: [NSSRound#22 Basic]简简又单单

思路

• 解题大致思路

EXP

• 具体攻击代码

def rc4_decrypt(key, data):
    """
    RC4解密函数
    :param key: 密钥 (bytes或string)
    :param data: 密文数据 (bytes或list of int)
    :return: 明文字符串
    """
    if isinstance(key, str):
        key = key.encode('utf-8')
    if isinstance(data, list):
        data = bytes(data)
    
    # 初始化S和T数组
    S = list(range(128))
    T = [key[i % len(key)] for i in range(128)]
    
    # 初始化
    j = 0
    for i in range(128):
        j = (j + S[i] + T[i]) % 128
        S[i], S[j] = S[j], S[i]  # 交换
    
    # 生成密钥流并解密
    i = j = 0
    output = []
    for k in range(len(data)):
        i = (i + 1) % 128
        j = (j + S[i]) % 128
        S[i], S[j] = S[j], S[i]  # 交换
        keystream_byte = S[(S[i] + S[j]) % 128]
        decrypted_byte = data[k] ^ keystream_byte
        output.append(decrypted_byte)
    
    # 转换为字符串
    plaintext = bytes(output).decode('utf-8', errors='replace')
    return plaintext

# 密钥和密文
key = "NS5_R0Un6_z2_apK"
encrypted_data = [
    0x57, 0x2e, 0x18, 0x0b, 0x1a, 0x68, 0x0b, 0x3e,
    0x52, 0x76, 0x34, 0x4b, 0x24, 0x1d, 0x5b, 0x52,
    0x52, 0x5a, 0x04, 0x31, 0x73, 0x34, 0x6b, 0x13,
    0x55, 0x44, 0x20, 0x28
]

# 解密
plaintext = rc4_decrypt(key, encrypted_data)
print(plaintext)

NSSCTF{V3ry_4z_1ib_W1th_4pk}


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总结

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