Pure random numbers from a sheet within a one-time pad are employed to encrypt the bytes of a source data packet and to order the encrypted bytes in a random order within the encrypted data packet. Pure random numbers fill remaining positions within the encrypted data packet. The resulting encrypted data packet is unconditionally secure (i.e., unbreakable). Sheets within the one-time pad are utilized only once, and the one-time pad is replaced when exhausted. For electronic checking applications, the one-time pad is distributed to the user stored in an electronic checkbook, with a copy retained by the bank. For cellular telephone applications, the one-time pad is stored in a replaceable memory chip within the mobile unit with a copy retained at a single, secured central computer. For client-server applications or applications involving sales over the Internet, the one-time pad may be provided to the user on a floppy disk or CD-ROM, with a copy retained by the vendor.