A method of symmetric key encryption involves using a composition of transformations leading to an enhanced homophonic substitution, wherein the mapping of characters varies depending on the sequence of characters in the message text. In carrying out the method, encryption keys are first generated. Then, a polyalphabetic substitution is performed, which involves XOR'ing (e.g., a Boolean logical exclusive OR operation/calculation) the plaintext data elements with the generated keys. Next, the storage format is changed, from big-endian to little-endian or vice versa, and the data is stored in one or more square matrices. Finally, enhanced homophonic substitution is performed, meaning that for each element, the subset to which the element can be mapped to in the co-domain is the entire co-domain itself, thus providing the largest possible subset for the given co-domain. In other words, any given element in the domain can be mapped to any of the elements of the co-domain.