一种基于对抗样本的验证码安全性增强方法  

A security enhancement method of CAPTCHA based on adversarial samples

作　　者：沈言玉 张三峰 曹玖新[1,2,3] Shen Yanyu;Zhang Sanfeng;Cao Jiuxin(School of Cyber Science and Engineering,Southeast University,Jiangsu Nanjing 211189;Key Laboratory of Computer Network and Information Integration(Southeast University),Ministry of Education,Jiangsu Nanjing 211189;Research Base of International Cyberspace Governance(Southeast University),Jiangsu Nanjing 211189)

机构地区：[1]东南大学网络空间安全学院,江苏南京211189 [2]计算机网络和信息集成教育部重点实验室(东南大学),江苏南京211189 [3]网络空间国际治理研究基地(东南大学),江苏南京211189

出　　处：《网络空间安全》2020年第8期81-85,91,共6页Cyberspace Security

摘　　要：验证码是众多互联网应用的重要安全措施,但在面对基于深度学习技术的破解工具时已难以保证其安全性。文章将对抗样本与文本验证码相结合,提出基于区域更新的模型集成白盒生成算法。为提高对抗验证码的迁移性,降低未知模型的识别率,根据多个模型的预测结果对损失函数进行加权求和;在目标函数中添加扰动项,通过梯度下降的方式更新验证码图像的像素值以最小化目标函数;将验证码文本区域和背景区域分区更新,以降低对抗样本所需的扰动量同时避免识别模型预处理对扰动的破坏。实验结果表明,在面对基于深度学习的识别模型时,文章提出的算法具有更低的识别率。CAPTCHA is an important security measure for many Internet applications,it is facing many chalanges while facing cracking tools based on deep learning technology.This paper proposes a model integrated white box generation algorithm based on region update by combining the adversarial samples with text CAPTCHA.In order to improve the transferability of adversarial CAPTCHA and reduce the recognition rate of unknown models,perturbation term is added to the objective function and the pixel value of CAPTCHA image is updated by means of gradient descent to minimize the objective function.The CAPTCHA text area and background area are partitioned and updated seperately to reduce the perturbations needed to generate adversarial samples and avoid the damage to the perturbations caused by the pre-processing of crack models.The experimental results show that the proposed algorithm has a lower recognition rate than the relevant work under the condition of considerable perturbation when facing the recognition model based on deep learning,which effectively increases the security of text CAPTCHA.

关 键 词：验证码 深度学习 对抗样本 集成模型 区域更新 

分 类 号：TP393.08[自动化与计算机技术—计算机应用技术]