An encryption processor, for storing encrypted data in a memory chip of a memory card, includes a FIFO memory for sequentially outputting m-bit data in response to a first signal, and an encryption key generator for generating m-bit encrypted keys (m being a positive integer) in response to a second signal and for sequentially outputting the keys in response to a third signal. A logic operator performs a logic operation on the data from the FIFO memory with the keys from the encryption key generator during a data write operation to sequentially encrypt the data. The logic operator performs a logic operation on the encrypted data received from a memory interface with the keys output from the encryption key generator during a data read operation in order to sequentially decode the encrypted data. The second signal is simultaneously generated with one of the write command or the read command.