High Speed Electronics Of Quantum Key Distribution System

Encryption is an important technology. It is widely used in lots of fields. It has been long since people trying to find ways to encrypt information in order to avoid being known by others. It is not until this century it became a strict scientific system.Modern encryption system is classified as two types:symmetric encryption and asymmetric encryption. In theory they are breakable, and the probability depends on the complexity of the arithmetic used by the encryption. With the development of large scale parallel computation and grid computation, also the rise of the computer of new types, the safety of the traditional encryption methods should be reconsidered. One time pad encryption is a theoretically unbreakable arithmetic, but due to its strict requirement of the keys, it has little use for a long time. People are eager for this method but have no way to realize it until the Quantum key distribution (QKD) was invented. It leads to a completely new encryption method that can ensure an absolutely safe data encryption when they combined together.Quantum key distribution use single or near single photon pulse with random quantum states to transfer keys, the basic principles of quantum mechanics ensure that there is no way to eavesdrop the key without being known by the two sides of the communication. Since it is related with the information security which is an important subject, people paid much attention to this field since it was proposed in 1984. It has grown fast in the past years and come to in use in some countries. There are some progresses of QKD in our country, but we are still far behind the others.Quantum key distribution is a complex process. In additional to optical devices, we need a suit of electronics system to do lots of work, including:controlling the optical devices to transfer the qubits to generate the raw keys, reconciling the raw keys, doing QBER (Quantum Bit Error Rate) estimation, error correction, privacy amplification and so on to generate the secure keys, managing the secure keys, providing keys to users, calibrating the QKD system, monitoring its state, etc. It is a big and complicate system. The lack of proper electronics is one reason for the lag of QKD developments of our country. So we studied the mechanism of the QKD electronics and made one suit of our own.The electronics has hardware and software (Qkeg). The hardware is divided to tow parts, one is QKD child board, the other is embedded system mother board. The child board generates voltages of high precision to control the optical devices to modulate the photon pulses in order to produce, transmit and measure the quantum states, then raw keys will be got and transfered to the mother board. The child board has large capacity DDR and various interfaces such as USB and Ethernet.The mother board contains CPU memory hard disk (CF card) several Ethernet interfaces and so on. It has almost all the features of a computer dose. It runs Linux operating system and is mounted with file system which lets the qkeg software runs on it. We wrote the driver for child board so the qkeg software can control it though this driver to do QKD process. Secure keys are saved on the mother board and will be sent though the inner Ethernet interfaces to the users if needed.The Qkeg software controls the wholes system to run. Its mission is:identifying two sides of the communication, controling the hardwares, monitoring their states, doing basis reconciliation, QBER estimation, error correction and privacy amplification, managing the secure keys, providing key services, and so on.Because of the limitation of SPD (single photon detector) working frequency, our electronic runs at 20MHz at last. Under this working frequency we got 4.91kbps secure keys on average, the QBER is 2.95%. The electronic system has good performance and is easy to use. It is small and compact which made it convenient to be setup for practical use.The electronics now has been installed. Based on this work, we designed higher speed QKD electronics that aims at international first level work. The system is designed to work at 1GHz and use only one PCB (Printed Circuit Board) with one piece of FPGA to run Linux and QKD process. It contains one Xilinx Virtex-5 FPGA, two 1.2GHz DAC, two DDR2 sockets, two gigabit Ethernet, USB host and other chips. Until this paper is printed, we have finshed manufacture of the PCB.Quantum key distribution is a new field that many countries invest much, now it comes to blossom. We should do much research on its electronic to prompt the development of QKD. By doing this we could do some contribution to our national information security.