Abstract: The network system in combination of subspace code and random linear network coding has the advantages of low complexity of encoding and decoding,there is no need to attach coding vectors,and noncoherent communications,and it has been applied for network error correcting.This paper addressed the security of subspace code against wiretap attacks.The security performance is measured in the probability with which the attacker guesses source messages.Based on the wiretap network model proposed by Cai and Yeung,we quantitatively calculated the guess probability with the methods of linear algebra and combinatorics and obtained its closed form solution.The result shows that subspace code has weak security in the sense of probability.Compared to many coding schemes with perfect security or weak security,however,subspace code benefits from low complexity,high flexibility,topology independence,and capability of fighting wiretaps on multiple links.As a result,subspace code is suitable to network applications with limited calculations and moderate security requirements.

Key words: Network security,Wiretap attack,Subspace code