信息网络安全

信息网络安全 ›› 2022, Vol. 22 ›› Issue (11): 47-54.doi: 10.3969/j.issn.1671-1122.2022.11.006

• 技术研究 • 上一篇    下一篇

基于OpenSSL密码软件的SM2算法加解密漏洞分析

刘振亚1,2, 林璟锵1,2,3()   

  1. 1. 中国科学技术大学，合肥 230027
    2. 电磁空间信息重点实验室，合肥 230027
    3. 北京中科研究院，北京 100193
  • 收稿日期:2022-06-21 出版日期:2022-11-10 发布日期:2022-11-16
  • 通讯作者: 林璟锵 E-mail:linjq@ustc.edu.cn
  • 作者简介:刘振亚（1998—），男，安徽，硕士研究生，主要研究方向为车联网安全|林璟锵（1978—），男，福建，教授，博士，主要研究方向为密码工程
  • 基金资助:
    国家重点研发计划(2020YFB1005803)

Analysis of SM2 Encryption and Decryption Vulnerability in OpenSSL

LIU Zhenya1,2, LIN Jingqiang1,2,3()   

  1. 1. University of Science and Technology, Hefei 230027, China
    2. Key Laboratory of Electromagnetic Space Information, Hefei 230027, China
    3. Beijing Research Institute of USTC, Beijing 100193, China
  • Received:2022-06-21 Online:2022-11-10 Published:2022-11-16
  • Contact: LIN Jingqiang E-mail:linjq@ustc.edu.cn

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摘要：

OpenSSL是一个广泛应用的开源库。2021年8月26日OpenSSL修补了一个缓冲区溢出漏洞，造成该漏洞的原因是SM2算法解密函数计算出的缓冲区可能小于实际的明文大小。文章首先结合OpenSSL源码，对缓冲区溢出的原理进行深入分析；然后根据溢出原理，对溢出攻击的可行性进行分析；最后设计实验对溢出攻击进行验证。由于SM2解密函数计算用于容纳明文的缓冲区大小时，没有考虑椭圆曲线上点的编码问题，当编码长度小于计算函数中的预设值时，就会导致缓冲区小于实际明文大小。攻击者根据这一特性可以快速穷举计算获取合适的椭圆曲线点，进而构造合适的密文进行缓冲区溢出攻击；并且能够使用同一个椭圆曲线点对持有不同公私钥对的SM2解密方进行缓冲区溢出攻击。

关键词: OpenSSL, SM2加解密接口, 缓冲区溢出, 漏洞分析

Abstract:

OpenSSL is a popular open source library for cryptography. On August 26,2021 a buffer overflow vulnerability was patched in OpenSSL, which is caused by the fact that the buffer size calculated by the SM2 decryption function could be smaller than the actual plaintext size. This paper firstly analyzed the principle of buffer overflow based on the OpenSSL source code, and then analyzed the feasibility of overflow attack according to the overflow principle. Finally this paper designed an experiment to verify the feasibility of overflow attack. It’s concluded that when SM2 decryption function calculates the size of the buffer to accommodate the plaintext, it doesn’t consider the encoding of the points on the elliptic curve, when the encoding length is smaller than the preset length, resulting in the buffer size being smaller than the actual plaintext size. Attacker can obtain appropriate points by exhaustion and further construct appropriate ciphertext for buffer overflow attack according the above feature and can use the same point to perform buffer overflow attacks on SM2 decryptors holding different key pairs.

Key words: OpenSSL, SM2 encryption and decryption interface, buffer overflow, vulnerability analysis

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