A process, a device, and a computer-readable medium storing a program, for encryption. A conversion table having regions each of which stores 2i character codes associated with index values is provided, where i is a natural number predetermined for each region, the 2i character codes are defined in a predetermined character encoding scheme, and the index values have a minimum necessary bit length for uniquely identifying the 2i character codes within each region. First character codes constituting a plaintext are converted into index values by reference to respectively corresponding regions of the conversion table. Then, the index values are encrypted without changing the bit lengths, and the encrypted values are converted into second character codes associated with index values identical to the encrypted values by reference to the respectively corresponding regions of the conversion table, a sequence of the second character codes is outputted as an encrypted text.