- A genuinely triple-security-level encryption module for optical communication systems is presented. The approach is practical and fea- sible supporting real-time encryption of data rates from 155.52 Mbit/s up to 2.4 Gbit/s, based on existing, commercially available electronic tech- nologies. The system deploys a nonrestricted symmetric-key block algo- rithm with dynamic parallel-processing width according to the input data rates. The algorithm enables the system to support different key strengths according to dynamic key length and processing block size assignment. The operation principle is based on time-to-frequency trans- lation of differentially coded data blocks from the input data stream after optical-to-electronic conversion and utilization of the resulting wideband multitone radio-frequency (RF) signal to modulate a laser source being fed back to the optical fiber network. An identical scheme implemented in time-reversed order is established during the decryption process to re- cover the wideband multitone RF signal from the optical fiber and de- code the original data, based on a synchronized code generation scheme, before it is transferred back to the optical fiber. The total system bandwidth depends on data rates at input and expected encryption strength and can vary from 2020 MHz for an OC-3 link up to 12,900 MHz for an OC-48 link. © 2002 Society of Photo-Optical Instrumentation Engineers.