Method and device for data encrypting

A method of encrypting data transmitted from a first device to a second device, performed by using an Advanced Encryption Standard (AES) encryption algorithm, includes obtaining size information of an encryption key and size information of data that is to be encrypted and includes a plurality of bits; encrypting a first bit group, which is at least one bit corresponding to a size of the encryption key, among the plurality of bits, by using the encryption key; selecting a third bit group, which is at least one bit of the encrypted first bit group based on size information of the encryption key and a size of a second bit group including bits that are different from the first bit group among the plurality of bits; and encrypting the second bit group and the selected third bit group by using the encryption key.