Cryptography ( also known as cryptology ; comes from Greek , kryptos , `` hidden , secret '' ; and , grÃ phÅ , `` I write '' , or , - logia , respectively ) is the practice and study of hiding information ; the science used to try to keep information secret and safe . Cryptography ( or cryptology ; from Greek , kryptos , `` hidden , secret '' ; and , grÃ phin , `` writing '' , or , - logia , , `` study '' , respectively ) is the practice and study of hiding information .