With the increasing popularity of COTS (commercial off the shelf) components and multi-core processor in space and aviation applications, software fault tolerance becomes attractive to overcome the primary bottleneck of their susceptibility to transient faults. CFCSS (Control Flow Checking by Software Signatures) is one of the most important pure software fault tolerance techniques in mitigating control flow errors in harsh environment. As the most prominent deficiency, aliasing is the research focus of this paper, and a novel algorithm, namely CFCSS without aliasing, is put forward. First and foremost, the cause of aliasing - the existence of branch-fan-in nodes in program control flow graph – is investigated in depth, and the minimal flow graph structure giving birth to aliasing, namely “3-2 structure”, is extracted. The typical “3-2 structure” can be extended to a broader class of flow graph, named “n-(n-1) structure” by this paper, which can not be settled by previou...