Abstract: By analyzing the weakness in design of the stream cipher Grain-vl，a differential fault attack was presented.The attack makes use of the weakness that the key stream equations in the first 17 times have comparatively low orders. The attacker needs to inject faults to the specified positions of LFSR at the stage of generating key streamBy differentiating,the attacker is able to acquire 17 linear ectuations which are linear independent and 80 initial states of the stream cipher directly. The attacker just needs to guess 62bits internal states, and then all the internal state can be achieved. The proposed attack algorithm can reduce the complexity to O(2 74，26).The result shows that the analyzed algo- rithm has security vulnerabilities, and the computational complexity of attacks is lower than that the designers claimed O（2 80）.

Key words: Stream cipher,Grain,Differential fault attack,Key stream