Bits of a first bit sequence are rearranged in a first matrix according to a
predetermined arrangement rule. The first bit sequence represents information being
a base of a key. Blocks are formed in the first matrix. Each of the blocks has
bits, the number of which is smaller than the number of bits composing the first
matrix. Logical operation is executed among bits in each of the blocks, and a bit
being a result of the logical operation is generated. The logical-operation-result
bits are combined into a second bit sequence. The number of bits composing the
second bit sequence is smaller than the number of bits composing the first bit
sequence. There is a second matrix composed of predetermined third bit sequences.
The second matrix is accessed and one is read out from among the third bit sequences
in response to the second bit sequence. The read-out third bit sequence is outputted
as information representative of the key. The number of bits composing each of
the third bit sequences is smaller than the number of bits composing the second
bit sequence.
