Abstract: The present disclosure relates to a data transfer method. First, a transmitting index of a file is generated on a data transmitting device using a transmitting data block and a size of the file. The transmitting index is then transmitted to a data receiving device. The data receiving device confirms if the transmitting index matches with one of a plurality of receiving indexes stored in the data receiving device. The plurality of receiving indexes respectively represents a plurality of receiving files stored on the data receiving device. The file is transferred from the data transmitting device to the data receiving device when the transmitting index matches none of the plurality of receiving indexes. The file is not transferred when the transmitting index matches one of the plurality of receiving indexes.