Provided is a cryptographic device implementing an S-Box of an encryption algorithm using a many-to-one binary function. The cryptographic device includes: arrays of first logic gates including I first logic gates which each receive 2 bits of an input signal; 2N second logic gates which each receive corresponding J bits from among I bits output from the arrays of the first logic gates; and L third logic gates which each receive K bits from among 2N bits output from the second logic gates, wherein there is a many-to-one correspondence between the N bits of the input signal and the K bits input to each of the third logic gates, and wherein the N, I, J, K, and L are positive integers. Because a signal output from each array includes only one active bit, current is always consumed constantly to prevent internal data from leaking out to a hacker.