watermark_codec_pkg/watermark_codec/model_encoder.py

"""
Created on 2024/5/8
@author: <NAME>
@version: 1.0
@file: model_encoder.py
@brief 白盒水印编码器
"""
from typing import List

import torch
from torch import nn

from watermark_codec.tool.str_convertor import string2bin
from watermark_codec.tool.tensor_deal import flatten_parameters, save_tensor, get_prob, loss_fun


class ModelEncoder:
    def __init__(self, layers: List[nn.Conv2d], secret: str, key_path: str = None, device='cuda'):
        self.device = device
        self.layers = layers

        # 处理待嵌入的卷积层
        for layer in layers:  # 判断传入的目标层是否全部为卷积层
            if not isinstance(layer, nn.Conv2d):
                raise TypeError('传入参数不是卷积层')
        weights = [x.weight for x in layers]
        w = flatten_parameters(weights)
        w_init = w.clone().detach()
        print('Size of embedding parameters:', w.shape)

        # 对密钥进行处理
        self.secret = torch.tensor(string2bin(secret), dtype=torch.float).to(self.device)  # the embedding code
        self.secret_len = self.secret.shape[0]
        print(f'Secret:{self.secret} secret length:{self.secret_len}')

        # 生成随机的投影矩阵
        self.X_random = torch.randn((self.secret_len, w_init.shape[0])).to(self.device)
        save_tensor(self.X_random, key_path)  # 保存投影矩阵至指定位置

    def get_loss(self, loss, alpha=1):
        """
        修改目标模型损失，直接返回新计算的损失

        :param loss: 原模型的损失
        :param alpha: 白盒水印训练损失权重，默认为1
        :return: 添加白盒水印惩罚项后的总损失
        """
        penalty = self.get_embeder_loss()  # 计算嵌入白盒水印的损失
        loss += alpha * penalty  # 与原模型训练损失相加
        return loss

    def get_embeder_loss(self):
        """
        获取水印嵌入损失
        :return: 水印嵌入的损失值
        """
        weights = [x.weight for x in self.layers]
        w = flatten_parameters(weights)
        prob = get_prob(self.X_random, w)
        penalty = loss_fun(prob, self.secret)
        return penalty