A method and apparatus for encrypting and decrypting data which operates efficiently on computers of differing architectures is disclosed. Unlike previous encryption/decryption method and apparatus, the present invention executes efficiently in the computer's software. The method uses part of the data input to access a table of pseudo-random numbers. The pseudo-random numbers are exclusively ORed (XORed) with the remaining part of the data input. The output from the XOR operation is then used to access the table where the other portion of the data is in turn XORed with the pseudo random numbers. This iterative process continues until the data is fully randomized. Several variations of this method are presented.