The security of international date encryption algorithm (IDEA(16)), a mini IDEA cipher, against differential cryptanalysis is investigated. The results show that IDEA(16) is secure against differential cryptanalysis attack after 5 rounds while IDEA(8) needs 7 rounds for the same level of security. The transition matrix for IDEA(16) and its eigenvalue of second largest magnitude are computed. The storage method for the transition matrix has been optimized to speed up file I/O. The emphasis of the work lies in finding out an effective way of computing the eigenvalue of the matrix. To lower time complexity, three mature algorithms in finding eigenvalues are compared from one another and subspace iteration algorithm is employed to compute the eigenvalue of second largest module, with a precision of 0.001.
SIP(Session Initiation Protocol,会话初始协议)是常用的支持多媒体会话的信令控制协议。RTP(Real-time Transport Protocol,实时传输协议)是提供语音等实时特性端到端传输的媒体控制协议。随着VoIP技术在通信领域的应用日益广泛,与之相关的安全问题也成为了业界研究的重点。文中介绍了基于SIP的VoIP系统中有关RTP的攻击,通过协议与报文分析,深入分析并实现了窃听攻击与RTP注入攻击,证明了这两种协议存在安全漏洞,最后提出了防范这些攻击的方案,为提高VoIP系统的安全性提供了参考。
