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# 签名算法实现详解
import hmac
import hashlib

# 步骤1: 参数预处理
def prepare_params(raw_params):
    # 移除签名字段并按字典序排序
    clean_params = {k: v for k, v in raw_params.items() if k != 'sign'}
    return sorted(clean_params.items())

# 步骤2: 生成签名
def generate_signature(params, secret_key):
    # 按参数名排序
    sorted_params = prepare_params(params)
    
    # 拼接参数字符串
    param_str = "&".join([f"{k}={v}" for k, v in sorted_params])
    
    # 添加密钥并生成签名
    sign_str = f"{param_str}&key={secret_key}"
    
    # 使用HMAC-SHA256生成签名
    sign = hmac.new(
        secret_key.encode('utf-8'),
        sign_str.encode('utf-8'),
        hashlib.sha256
    ).hexdigest().lower()  # 转换为小写
    
    return sign

# 步骤3: 验证签名
def verify_signature(received_params, received_sign, secret_key):
    # 重新计算签名
    expected_sign = generate_signature(received_params, secret_key)
    
    # 安全比较（防止时序攻击）
    return hmac.compare_digest(expected_sign, received_sign.lower())

# 使用示例
sample_params = {
    "amount": "100.00",
    "currency": "CNY",
    "merchant_id": "M123456",
    "order_id": "ORD20230101001",
    "timestamp": "1672531200"
}
api_secret = "your_super_secret_api_key_here"

calculated_signature = generate_signature(sample_params, api_secret)
print(f"计算得到的签名: {calculated_signature}")

# 验证签名
is_valid = verify_signature(sample_params, calculated_signature, api_secret)
print(f"签名是否有效: {is_valid}")