A parallel processing shrinking key generator is provided. The parallel processing shrinking key generator includes: a selection linear feedback shift register (LFSR); a source LFSR; a selection logic circuit for selecting one of a source bit of the source LFSR and a predetermined input bit according to a selection bit of the selection LFSR; an index counter for assigning an index where output bits of the selection logic circuit are stored at a next clocking of a clock signal; and an output amount register for shifting an output bit of the selection logic circuit according to the assignment of the index counter.