Abstract: In order to meet the high-performance block cipher processing need existed in the information security field, an instruction set extension method for block cipher calculation is proposed. Based on the analysis of 47 kinds of block cipher algorithms, four basic operations that should be accelerated were found. Therefore, four crypto-operation units to accelerate these operations are designed. Moreover, a data trigger unit which includes the four crypto-operation units is designed and added to the microprocessor to accelerate the block cipher operations. This method has the advantages of briefness, flexibility and so on. The evaluation result shows that the modified microprocessor's speed-up ratios of common block cipher algorithms are about 2.4-9.3 and the hardware cost is only 1.3 times as large as the original microprocessor.