Cerberis XGR User Guide

Version : 1.1
Date : 08/06/2022
 ID Quantique SA
Ch. de la Marbrerie, 3bis
CH-1227 Carouge/Geneva
Switzerland

Tel: +41 (0)22 301 83 71

Fax: +41 (0)22 301 83 79
www.idquantique.com
info@idquantique.com

Please send any comment to

support@idquantique.com

Information in this document is subject to change without notice.

Copyright © 2022 ID Quantique SA. Printed in Switzerland.

No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by
any means – electronic, mechanical, photocopying, recording or otherwise – without the permission of
ID Quantique.

Trademarks and trade names may be used in this document to refer to either the entities claiming the marks
and names or their products. ID Quantique SA disclaims any proprietary interest in the trademarks and trade
names other than its own.

Property of ID Quantique SA Page: 2 / 41

Disclaimer
THIS DOCUMENT IS PROVIDED “AS IS” WITH NO WARRANTIES WHATSOEVER, INCLUDING ANY WARRANTY
OF MERCHANTABILITY, NONINFRINGEMENT, FITNESS FOR ANY PARTICULAR PURPOSE, OR ANY
WARRANTY OTHERWISE ARISING OUT OF ANY PROPOSAL, SPECIFICATION OR SAMPLE.

No license, express or implied, to any intellectual property rights is granted herein, except that a license is
hereby granted to copy and reproduce this specification for internal use only. Contact ID Quantique for
information on further licensing agreements and requirements. ID Quantique disclaims all liability, including
liability for infringement of any proprietary rights, relating to use of information in this specification. ID
Quantique assumes no liability whatsoever, and disclaims any express or implied warranty, relating to sale
and/or use of ID Quantique products including liability or warranties relating to fitness for a particular
purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. ID
Quantique products are not intended for use in medical, lifesaving, or life sustaining applications.

ID Quantique may make changes to documents, specifications, and product descriptions at any time, without
notice. Designers must not rely on the absence or characteristics of any features or instructions marked
reserved or undefined. ID Quantique reserves these for future definition and shall have no responsibility
whatsoever for conflicts or incompatibilities arising from future changes to them.

Copyright © ID Quantique 2022.

Property of ID Quantique SA Page: 3 / 41

Contents
1. Introduction ............................................................................................................................................... 6
1.1. About ID Quantique........................................................................................................................... 6
1.2. About this document ......................................................................................................................... 6
1.3. Intended audience ............................................................................................................................. 6
1.1. Classification ...................................................................................................................................... 6
1.2. References ......................................................................................................................................... 6
1.3. Prerequisite ....................................................................................................................................... 6
1.4. Support information .......................................................................................................................... 7
1.5. Safety precautions ............................................................................................................................. 7
1.6. Equipment Marking ........................................................................................................................... 7
2. Getting Started .......................................................................................................................................... 9
2.1. Cerberis XGR intended use ................................................................................................................ 9
2.2. Cerberis XGR QKD Node description ............................................................................................... 11
3. Installation requirements and topologies ............................................................................................... 12
3.1. Temperature, humidity, and dust ................................................................................................... 12
3.2. Power and ESD protection............................................................................................................... 12
3.3. Fiber and network peripherals ........................................................................................................ 13
3.3.1. Required fibers ........................................................................................................................ 13
3.3.2. Required network peripherals................................................................................................. 14
3.4. Verification of the installation requirements .................................................................................. 16
3.5. Installation topologies ..................................................................................................................... 17
4. System security ........................................................................................................................................ 20
4.1. XGR Chassis ...................................................................................................................................... 20
4.2. Private network ............................................................................................................................... 20
4.3. Public network ................................................................................................................................. 21
5. Cerberis XGR QKD node installation instructions .................................................................................... 22
5.1. Unpacking ........................................................................................................................................ 22
5.1.1. Alice box content ..................................................................................................................... 22
5.1.2. Bob box content ...................................................................................................................... 23
5.1.3. Additional tools required......................................................................................................... 25
5.2. Installing a Cerberis XGR QKD node ................................................................................................ 26
5.2.1. Installing the Cerberis XGR in a 19” rack (optional) ................................................................ 26
5.2.2. Power on & off the Cerberis XGR ............................................................................................ 28
5.2.3. Setting up the Quantum Channel connection ......................................................................... 29
5.2.4. Setting up the QKD Service Channels connection ................................................................... 30

Property of ID Quantique SA Page: 4 / 41

 5.2.5. Connecting to the Cerberis XGR via a RS-232 serial connection ............................................. 31
5.2.6. Connecting to the QKD node via SSH through an Ethernet connection ................................. 32
6. Operates your Cerberis XGR node ........................................................................................................... 33
6.1. LED states ........................................................................................................................................ 33
6.2. QNET Shell ....................................................................................................................................... 33
6.2.1. Showing or setting the network configuration........................................................................ 34
6.3. Understanding the QKD Log files..................................................................................................... 35
6.4. Manage remotely your Cerberis XGR via QNET Central Server ...................................................... 35
7. Cerberis XGR Research Features ............................................................................................................. 36
7.1. QKD customizable parameters ........................................................................................................ 36
7.2. RAW keys via IDQ4P ........................................................................................................................ 37
A. Appendix .................................................................................................................................................. 38
A.1. Product variants .............................................................................................................................. 38
A.2. COW protocol description ............................................................................................................... 38
A.3. COW 4-states .................................................................................................................................. 40

Property of ID Quantique SA Page: 5 / 41

1. Introduction
1.1.About ID Quantique

ID Quantique (IDQ) is the world leader in quantum-safe crypto solutions, designed to protect data for the
long-term future. The company provides quantum-safe network encryption, secure quantum key generation
and quantum key distribution solutions and services to the financial industry, enterprises, and government
organizations globally.

IDQ also commercializes a quantum random number generator, which is the reference in the security,
simulation, and gaming industries.

Additionally, IDQ is a leading provider of optical instrumentation products, most notably photon counters
and related electronics. The company’s innovative photonic solutions are used in both commercial and
research applications.

1.2.About this document

This document, the IDQ Cerberis XGR User Guide, provides information on the Cerberis XGR QKD nodes and
instruction on how to operate them.

1.3.Intended audience
This document is for system operators, network operators, and system programmers. Specific operator
procedures are defined by the individual installation to meet local requirements.

1.4.Classification
This document is classified by ID Quantique as Confidential.

1.5.References
This section lists documents related to the IDQ Cerberis XGR solution products. It also describes how to access
IDQ QKD publications and IDQ QKD related resources online.

The following documents are available for the IDQ QKD Systems:

• Cerberis XGR User Guide describes the IDQ Cerberis XGR QKD node
• Cerberis XGR solution Quick start guide describes how to install and configure the IDQ QKD Cerberis
XGR solution
• IDQ QNET shell User Guide describes the QNET CLI program required for local system administration.
• IDQ QNET User Guide describes the QNET CLI program required for remote system administration.
• IDQ QNET Web API User Guide describes the QNET Web Server and how to use the QNET Web
Application Programming Interfaces (APIs)
• Understanding QKD log files explains QKD logs.
You can find additional product information on the IDQ Web site: https://www.idquantique.com/resource-
library/quantum-key-distribution/

1.6.Prerequisite
To read about the new functions offered in this release, see the IDQ QKD product Release Note.
 1.7.Support information

If you have any questions or require assistance with the IDQ QKD solutions, please contact IDQ Support:

• Visit the IDQ Support site at https://www.idquantique.com/support

• Email IDQ Support at support@idquantique.com

1.8.Safety precautions
• Carefully read through this procedure before operating the Cerberis XGR system.
• This system is intended to only be used indoors.
• Cerberis XGR Alice emitter unit (with blue handles and SN finishing by 010) is a class 1 laser product
according to IEC 60825-1:2014, emitting invisible radiation. Never look directly into an active fiber.
• Do not disassemble the system. Only qualified person can open the unit.
• Always handle the devices using proper ESD damage prevention and grounding methods.
• Ensure all power connections are connected to a ground socket. Failure to connect to ground creates
a shock hazard which may cause injury to the operator.
• Refrain from bringing water or other liquids around any part of the system. If the systems do get wet,
shut all devices down immediately.
• The 4 Ferrites (included in the package) shall be mounted on each power supply cable, and position
next to the chassis (one per cable).

NOTE
ID Quantique shall not be held responsible for any damages to persons or property caused by
incorrect installation or use of this appliance.

WARNING
The warranty is void if any module has been opened by unauthorized personnel.

1.9.Equipment Marking
The identification labels for the two Cerberis XGR terminals are shown below:

R 3

4 2

Property of ID Quantique SA Page: 7 / 41

 R 3

4 2

Label description:

1. Alice: Class 1 Laser product according to IEC 60825-1:2014

Bob: is a receiver and does not have any laser diode
2. Compliant with 47 CFR, Part 15 (Class A)
3. Compliant with:
CE Safety: IEC 62638-1:2018, IEC 60825-1:2014
CE EMC: EN 55032:2015+A11:2020 (Class A), EN 55035:2017+A11:2020
Laser wavelength emitted (Alice) /detected (Bob), Channel 32 of the ITU C band (EDFA window),
corresponding to 1551.72nm.
For Cerberis XGR 1310nm variant:
• Model: Alice / 1310 nm
• Model: Bob / 1310 nm

The Cerberis XGR quantum key distribution system is also compliant with the standards:

• Industry Canada: ICES-003, Issue 7 (Class A)

• RoHS :2015/863/EU

Property of ID Quantique SA Page: 8 / 41

2. Getting Started
2.1.Cerberis XGR intended use
The Cerberis XGR Quantum Key Distribution platform is specifically designed to serve as a versatile tool for
academia, research institutes and innovation labs. The user can, experiment using different configurations,
in both automated and manual modes. The XGR platform performs standard key management functions
between nodes, including key generation, key storage, and key life cycle management. It embeds enhanced
trusted security components, like tamper detection, a secure memory module, as well as an IDQ QRNG chip
which provides proven randomness for all the related crypto functions. This guarantees the highest security
standards, throughout the key management process, from key generation to key delivery, and including key
storage.

QKD administrators can configure and monitor QKD networks via either an embedded REST WebAPI, an
Command Line Interface (CLI) QNET.CLI Tool or via the centralized QKD Management System (QMS) web
console by setting consumers, providers at each QKD network node, QKD links between nodes and key
distribution routes between key consumers.

Figure 1 Cerberis XGR Terminal

The WebAPI continuously collects several critical parameters, such as system status, fan, power supply,
temper detection, Quantum key rate, QBER (Quantum Bit Error Rate), KMS key buffers, and can distribute
them to 3rd party monitoring systems, via common protocols like SNMP, syslog, etc. Monitoring events are
also generated when QBER becomes too high, warning there might be an intruder on the QKD quantum
channel.

In addition, our QKD Management System (QMS) provides a single Management and Monitoring platform
for all QKD products and components. It reduces the time and effort to manage large and complex QKD
Network.

Property of ID Quantique SA Page: 9 / 41

 Figure 2: Cerberis XGR solution for a point-to-point deployment

In Figure 2 is shown a schematic of a Cerberis XGR solution deployed in point-to-point configuration.

Quantum communication over the two QKD nodes are done over standard SMF-28 optical fiber. The
connection between the QKD KMS (Key Management System) can be done via Ethernet copper cables or
optically using a dedicated SFP transceiver. The QKD node KMS is interfaced directly via Ethernet copper
cables with the encryptor, and act as an arbitrator between key distribution systems (Provider) and
encryptors (Consumer).

Following the schematics of Figure 2 the function of each component can be summarized as follow:

• QNET Web API has two main purposes:

o simplify QKD node's centralized configuration and monitoring.
o automatize QKD node’s network configuration.
• QMS Web Application is a Graphical User Interface of the QNET Web API.
• QNET tool is a command line interface of QNET Web API. QNET tool could also be installed on a
distinct computer.
Each independent QKD node can also be configured and monitored by QNET shell which is embedded in a
QKD node.

Encryptors implementing ETSI 014 relying on HTTPS Restful protocol and encryptor implementing CISCO SKS
protocol can be interfaced with a QKD node.

Property of ID Quantique SA Page: 10 / 41

 2.2.Cerberis XGR QKD Node description
A point-to-point Cerberis XGR system, implementing the COW protocol (see A.2 COW protocol description),
is composed of two 1U nodes as shown in Figure 3. Each node is equipped with redundant, hot swappable
power supply modules. The compact design allows the possibility to easily rack the system using the provided
rail system in a standard 19” rack.

The front panel features the access window for the hot-swappable fan module, the console port, the USB
port, 4x ethernet ports and 2x SFP cages.

3 5 6 7 8
1 2
4

Figure 3: Cerberis XGR - Alice front panel.

The node front panel is characterized by:

1. Quantum channel SC/UPC connector

2. Hot swappable fan module
3. Serial connection
4. USB port for update/certificates/logs exporting
5. Ethernet interface ports
6. SFP modules slots
7. LED panel
8. Power button

10
9

Figure 4: Cerberis XGR rear panel.

The node rear panel is characterized by:

9. Two hot-swappable power supply modules

10. Power supply reset alarm

NOTE
The two nodes can be identified by the different color of the front panel handles: dark
gray for Bob XGR node, red for Alice XGR node.

Property of ID Quantique SA Page: 11 / 41

 Dimensions Value
Width 480 mm
Height 43.6 mm
Depth 610mm
Weight Value
13.5kg
Power Value
Maximum 2x 300W
Table 1: Node Dimensions/Weight

Equipment must first be unpacked, the modules be installed and setup, and connected to optical fibers,
network cables, and suitable power supply lines.

• Please refer to Chapter 3 for a description of the requirements on the installation site and its
peripherals.
• See Chapter 4 for instructions for the installation, as well as for connecting the fibers, cables and
network interfaces to the system.

3. Installation requirements and topologies

Before installing the Cerberis XGR nodes, it must be assured that the installation site fulfils the environmental
and peripheral requirements as outlined in this chapter. The QKD system will operate and interact
successfully with the designated network only if those requirements are fulfilled.

3.1.Temperature, humidity, and dust

Cerberis XGR nodes require to be installed in a 19” rack in a weather protected site. Front and back sides of
the nodes must be easily accessible. To maintain proper cooling, the equipment rack must provide enough
airflow to the front and rear of the nodes. Allow at least two inches of clearance at the air inlets and outlets.

The installation site must provide enough cooling to guarantee a constant temperature within the range of
+10° C to +35° C at the location of the device, and relative humidity (non-condensing) levels up to 80% (@
35° C).

It is mandatory for the quantum channel link to be kept clean und dust free.

3.2.Power and ESD protection

Cerberis XGR nodes require to be installed in an ESD protected site that provides proper earthing of the
device. The Cerberis XGR is equipped with two identical power supply modules rated 100 - 240 V~ / 50 - 60
Hz / 5 - 2.5 A, to start the system at least one power supply must be plugged to a power socket using the
provided power cord. The symbol ( ) means Alternate Current (reference IEC 60417).
Cerberis XGR is meant to be installed only in a restricted access area and according to the national electrical
codes of the specific country.

Property of ID Quantique SA Page: 12 / 41

 NOTE
For North America, equipment must be installed in accordance with the US National
Electrical Code (NEC) Articles 110–6, 110–17, and 110–18, and the Canadian Electrical
Code (CEC), Sections 2-202 and 2-308.

3.3.Fiber and network peripherals

Each Cerberis XGR node requires access to fiber and Ethernet network peripherals and can be configured to
adapt to different situations and topologies. In total, the following links must be facilitated between the two
Cerberis XGR nodes:

• An optical quantum channel link without active components and with loss below specified value for
the system,
• A bidirectional optical QKD-Service channel link for QKD clock synchronization and post-processing.

3.3.1. Required fibers

In the standard configuration, a dark standard single mode fiber link without any additional data or service
traffic, optical signals, optical amplifiers, or other active optical elements (switches, modulators, …) is
required for the system’s quantum channel. The system’s service channels require at least one additional
bidirectional fiber link that can be realized either over one single fiber or over multiple separate fibers.
Additional fiber links or Ethernet links may be required, depending on customer network specificities.

For single-fiber configuration using wavelength multiplexing, please contact ID Quantique.

The performance of the Cerberis XGR point to point system largely depends on the optical attenuation of the
designated quantum channel fiber link that is required to be below the specified maximum for the specific
system (12 dB for standard system).

The optical fiber link(s) for the service channels must facilitate at least 2.5 Gbps (Gigabit per second) bi-
directional optical communication in the C-band (wavelength between 1525–1565 nm) in compliance with
the ITU G.694.1 standard for DWDM spectral grids. The total optical attenuation for the service channel fiber
link must guarantee error free operation of the implemented SFP transceiver modules, i.e. below their
specified transmission budget. The receiver sensitivity of the provided standard SFP modules is specified with
-28 dBm, which is the minimum necessary power of the modules to guarantee error-free communication.

IMPORTANT NOTE
Starting from OS release 3.0.0 there is “virtually” no limitation on the fiber length
different between Service Channel and Quantum channel. The fiber difference between
these two channels can be compensated for more than 200km difference.

Property of ID Quantique SA Page: 13 / 41

 3.3.2. Required network peripherals.

During the installation process, the networking address information in Table 2 will be required and referred
to. If not specified prior to purchasing the Cerberis XGR system, each system parts will be pre-configured with
a default setting.

port Alice Bob

MGT 192.168.10.102 192.168.10.107
/0 / 255.255.255.0 / 255.255.255.0
KEYS 192.168.10.1 / 192.168.10.1 /
/1 255.255.255.252 255.255.255.252
AUX 192.168.20.2 / 192.168.20.2 /
/2 255.255.255.252 255.255.255.252
KMS 192.168.30.3 / 192.168.30.3 /
/3 255.255.255.252 255.255.255.252
Table 2: Default network address configuration

The Cerberis XGR systems have 4 network interfaces that allow physical separation of traffic:

Interface Location Name Number Purpose

0 lower MGT 0 Administration,
left monitoring
1 upper KEYS 1 Encryptors
left
2 lower AUX 2 QKD stacking
right or
communication
with QKD
Cockpit
3 upper KMS 3 KMS to KMS
right link
Table 3: Description of the network interfaces

Property of ID Quantique SA Page: 14 / 41

 • MGT is used for connections to QMS or QNET.
• KEYS is used to connect encryptors directly on the systems.
• AUX is used to connect all the QKD and KMS of a same node together. IDQ4P binds on this
interface.
• KMS is used to transport the KMS-to-KMS communications using a copper link.
• KMS-O can be used to transport the KMS-to-KMS communication using an optical link (via SFP)
instead of copper connection.
Note: KMS and KMS-O cannot be used simultaneously.

Figure 5: Cerberis XGR network connection panel.

In this UM we are covering the two supported connection scenarios between QKD system and encryptors:

• Single interface, where all traffic is routed through the MGT port, i.e. the same network
• Traffic separation, where Management, collocated QKD, KMS-to-KMS and Keys traffic are routed
respectively via the MGT, AUX, KMS (alternatively KMS-O) and KEYS ports, each port being
attached to a separated sub-network.

Other connection scenarios are not recommended.

To set the specific IP mapping shown in Table 4, Table 5 please refer to: “Cerberis XGR solution Quick Start
Guide” or “IDQ QNET Shell User Guide”.

Scenario 1: Single interface Configuration (standard for XGR)

In Table 4 is given an example where KMS can connect to Alice on address 192.168.102.53 and to Bob on
address 192.168.102.54. Other equipment (KMS, Consumers, encryptors, other KMS…) can connect to KMS
Alice on address 10.10.10.53 and to KMS Bob on address 10.10.10.54.

1. Connect the Cerberis XGR through port MGT to QMS.

2. Configure Interface 0 (MGT) with KMS address used to connect from QMS.
If needed other Cerberis XGR used to create a trusted node shall be connected on AUX port.
3. Configure Interface 2 (AUX) with QKD address even if no other Cerberis XGR is connected for
trusted node. This is required for KMS to be able to retrieve keys from local QKD.

Port Alice Bob

MGT 10.10.10.53 / 10.10.10.54 /255.0.0.0
/0 255.0.0.0
KEYS Not set Not set
/1
AUX 192.168.102.53 192.168.102.54 / 255.255.255.0
/2 /
255.255.255.0
Property of ID Quantique SA Page: 15 / 41
 KMS Not set Not set
/3
Table 4: Example of “Single interface” Configuration

Scenario 2: Traffic Separation Configuration

In Table 5 is given an example where KMS can connect to Alice on address 192.168.102.53 and to Bob on
address 192.168.102.54.
QMS can connect to KMS Alice on address 10.10.10.53 and to KMS Bob on address 10.10.10.54. Other KMS
can connect to Alice on address 192.168.103.53 and to Bob on address 192.168.103.54. Encryptors
(consumers) can connect to Alice on address 192.168.101.53 and to Bob on address 192.168.101.54.
Interface 1 (KEYS), Interface 2 (AUX), and Interface 3 (KMS) shall be purely local area network not going
outside the secured premise. Interface 0 shall be accessible outside of the secure premise to manage
remotely the KMS through QMS or other.

To customize this address mapping, you should follow the rules provided below:

1. Connect the Cerberis XGR through port MGT to QMS.

2. Configure Interface 0 with KMS address used to connect from QMS. If needed other Cerberis XGR
used to create a trusted node shall be connected on AUX port.

NOTE
the Trusted Node Configuration is not part of this start guide.

3. Configure Interface 2 with QKD address even if no other Cerberis XGR nodes are connected for
trusted node. This interface is required for KMS to be able to retrieve keys from local QKD.
4. Connect the Cerberis XGR through port KMS to other KMS.
5. Configure Interface 3 with KMS address used to connect from other KMS.
6. Connect the Cerberis XGR through port KEYS to encryptors.
7. Configure Interface 1 with KMS address used to connect from encryptors (consumers).

Port Alice Bob

MGT 10.10.10.53 / 10.10.10.54
/0 255.0.0.0 /255.0.0.0
KEYS 192.168.101.53 192.168.101.54
/1 / /
255.255.255.0 255.255.255.0
AUX 192.168.102.53 192.168.102.54
/2 / /
255.255.255.0 255.255.255.0
KMS 192.168.103.53 192.168.103.54
/3 / /
255.255.255.0 255.255.255.0
Table 5: Example of “Traffic Separation” configuration

3.4.Verification of the installation requirements

1. Verify that the installation site(s) is weather protected.

Property of ID Quantique SA Page: 16 / 41

 2. Verify that the installation site(s) provides a constant temperature within the specified
operation temperature range of +10° C to +35° C.
3. Verify that the installation site(s) provides non-condensing relative humidity levels within
the specified QKD system operation range up to 80% non-condensing.
4. Verify that the installation site(s) limits the suspension of sand to a maximum of 30 mg/m3,
of dust to a maximum of 0.2 mg/m3, and of dust accumulation by sedimentation to a
maximum of 1.5 mg/(m2h).
5. Verify that the installation site(s) provides for each node at least one socket for AC 100V-
240 V~, 50-60Hz, 5-2.5A with an electrical common ground connection.
6. Verify that the installation site(s) have Ethernet routers for network connection between
the 2-installation site(s).
7. Verify that the installation site(s) provides access to a dark single mode fiber between both
installation site(s) without any additional traffic.
8. Verify that the dark single mode fiber for the QKD quantum channel has an optical
attenuation below the specified maximum for the system.
9. Verify that the dark single mode fiber for the QKD quantum channel is free of any optical
amplifier or other active optical elements (e.g. switches, modulators…).
10. Verify that the installation site(s) provides access to a second, bidirectional fiber link for the
service channels between both installation site(s).
11. Verify that the second fiber link facilitates a 2.67 Gbps (Gigabit per second) bi-directional
optical communication channel in the C-band (wavelength between 1525–1565 nm) in
compliance with the ITU G.694.1 standard for DWDM spectral grids.
12. Verify that the fiber length difference between the quantum channel fiber link and the
service channel fiber link (from Transmitter Cerberis XGR node to Receiver Cerberis XGR
node) is below the maximum limit of 30 km.
13. Verify that the second fiber link has a total optical attenuation that guarantees error free
operation of the implemented SFP transceiver modules, i.e. below their transmission
budget.

3.5.Installation topologies
Cerberis XGR systems can be deployed in any network configurations including point-to-point, relay for
longer distances, ring, or star topologies, depicted in Figure 6. At each QKD network node, the embedded
Key Management System (KMS) software arbitrates the key distribution between QKD and key consumers
and performs add/drop or forward functions depending on the recipient’s location.

Property of ID Quantique SA Page: 17 / 41

 Point-to-point (with relay for long distance) Ring network

End node Trusted node Trusted node End node

Star

Figure 6 Cerberis XGR solution topologies

As starting point, a selection of the most common point-to-point topologies is listed in Table 6 below. There,
(QC) denotes the Cerberis XGR QKD quantum channel, (SC) denotes the QKD service channels, and (ENC) the
encryptor channels. Channels colored in grey refer to optical fiber channels over standard single mode fibers
(SMF-28), and channels in black refer to channels over Ethernet copper cables.

# Point-to-point Topology Comments

• 3 fibers and 2 copper connections required
• QKD Service channel wavelengths can be
chosen arbitrarily and independently in the
ITU C-band
1a
• Quantum channel wavelength in the ITU C-
KMS

band

Note: the KMS connection can also be optical

• 2 fibers and 2 copper connections required
• QKD Service channel via optical bidirectional
(BiDi) SFP module
• QKD Service channel wavelength in one
KMS
direction is in the ITU C-band, in the opposite
1b direction it is in the ITU O-band
• Quantum channel wavelength can be chosen
in the ITU C-band, or alternatively in the ITU
O-band

Note: the KMS connection can also be optical

2a • 3 fibers required
Property of ID Quantique SA Page: 18 / 41
# Point-to-point Topology Comments
• All classical channel wavelengths must be in a
designated ITU DWDM channel
• Typically, bidirectional channel pairs allocate
the same ITU channel
• Quantum channel wavelength can be chosen
KMS in the ITU C-band

Note: the KMS connection was chosen to be

optical (it can also be copper)
• 2 fibers required
• All classical channel wavelengths must be in a
designated ITU DWDM channel in the C-band
• Typically, bidirectional channel pairs allocate
the same ITU channel
KMS
• Quantum channel wavelength must be at
2b
1310 nm
• QKD system must be purchased with narrow-
band filtering option

Note: the KMS connection was chosen to be

optical (it can also be copper)
Table 6: Recommended topology options for the Cerberis XGR point-to-point deployment.

NOTE
With standard supplied equipment (see section 5.1) and a pair of encryptors, the
topology 1a can be implemented in a point-to-point setup for lab test.

NOTE
The Cerberis XGR QKD system in configuration 2b (with quantum channel at 1310nm and
narrow band filtering option), allows the multiplexing of the platform’s classical channels
as well as some external classical channels (ITU DWDM channel in the C-band). Please
contact ID Quantique for more details on the total number of classical channels
allowance and launch power per channel.

Property of ID Quantique SA Page: 19 / 41

4. System security

Key consumer Key consumer

Figure 7: Physical
boundaries

A QKD deployment implies several levels of physical security boundaries and each one of them has security
policies and mechanism.

4.1. XGR Chassis

The first physical boundary is the XGR chassis itself; it implements mechanisms to preserve data integrity,
authentication mechanisms and other security related features:

• Tamper detection: In case of opening of the chassis, the tamper detection will wipe the secure
memory and make impossible the decryption of some critical encrypted data stored on the system.
• QRNG: All the cryptographic needs in terms of randomness are met by a proprietary Quantum
Random Number Generator (QRNG).
• OS hardening: Only a restricted access to some specific management functions is available to the
user and the OS is hardened.
• Network separation: independent networks can be configured in the XGR for all the different
applications (management channel, keys channel, XGR to XGR communication, …).

4.2. Private network

The QKD services and the key consumer must communicate through an isolated private network, therefore
the security of communications on this link is based on:

• Classical public key cryptography (like TLS certificates)

• Symmetric cryptography (like TLS pre-shared keys)

A secure configuration of the systems requires to generate and / or sign new keys and certificates for each
node and link.

Property of ID Quantique SA Page: 20 / 41

 4.3. Public network
For other communications that may transit through public networks the security levels are:

• At least quantum-safe solutions for all the communications that concern keys.
• Classical-safe solutions for other types of communications (monitoring, management…).

A secure configuration of the system also requires regeneration of keys, certificate and passwords used for
data integrity, confidentiality, and authentication.

Property of ID Quantique SA Page: 21 / 41

5. Cerberis XGR QKD node installation instructions
5.1.Unpacking

WARNING
The handles are here to slide the Cerberis XGR when mounted on the rail in the chassis.
They must not be used to carry the Cerberis XGR. It should be carried with one hand one
each side of it.

Before opening the boxes check for external damage. Next open the external boxes, and then internal
boxes. In the internal boxes, there is a box with accessories.

5.1.1. Alice box content

Part description QTY Notes

Cerberis XGR Alice 1 • QKD emitter terminal,
red handles.
• It’s a Class 1 laser
product with a
wavelength of 1310nm
or 1551nm depending on
the option selected.

Console cable (USB to RJ45) 1 • For local access on the

console port
• USB 2.0 to Serial
Converter, USB-A to
RS232 RJ45 plug, 3m
• Protocol RS232
• 115200 bauds

Optical SFP transceiver 1 • ITU wavelengths

modules (2x CH30 1553.33 nm)
• Compliant with G.694.1
• Dual SMF-28 LC
connectorized
• 2.67 Gbps rate

Service channel fiber patch 1 • 2m length

cord • LC/PC-LC/PC
• Type: dual SMF-28

Quantum channel fiber patch 1 • 2m length

cord • SC/UPC
• Type: SMF-28

Property of ID Quantique SA Page: 22 / 41

Ethernet cables 3 • To connect the Cerberis
XGR interfaces to networks

LC fiber cleaning tool 1 • To clean service channel

fiber connector

SC fiber cleaning tool 1 • To clean quantum channel

fiber connector

Power cable 2 • IEC 60320 C13 to CEE 7/7

(Type E and type F
compatible), Type B, Type G
or Type J (country
dependent)

Ferrite 2 • Ferrite core 241 ohms @

100MHz to mount on
power cable

Sliding rail 2 • To mount in 19” rack with

mounting brackets

Mounting brackets 4 • 2 short brackets

• 2 extended brackets

Screws, nuts, and brackets kit 1 • 3x M3x10mm, Torx T10

• 2x Securing bracket
• 10x M4x10mm, Torx T20
• 10x Screw M5x10mm,
• 10x nuts M5
• 10x spring lock washer M5
• 20x washer M5
• 10x #10-32x1/2”

• 2x nuts bar #10-32

SFP Dust Plug 2 • Mounted in SFP cage

Table 7 : Alice Box Content

5.1.2. Bob box content

Part description QTY Notes

Cerberis XGR Bob (receiver) 1 • QKD receiver terminal,
grey handles

Console cable (USB to RJ45) 1 • For local access on the

console port

Property of ID Quantique SA Page: 23 / 41

 • USB 2.0 to Serial
Converter, USB-A to
RS232 RJ45 plug, 3m
• Protocol RS232
• 115200 bauds

Optical SFP transceiver 1 • ITU wavelengths

modules (2x CH30 1553.33 nm)
• Compliant with G.694.1
• Dual SMF-28 LC
connectorized
• 2.67 Gbps rate

LC/UPC fixed attenuators 4 • 2x Fixed optical attenuator

7 dB, LC/UPC, M-F
• 2x Fixed optical attenuator
15 dB, LC/UPC, M-F

SC/UPC fixed attenuators 3 • 1x Fixed optical attenuator

3 dB, SC/UPC, M-F
• 1x Fixed optical attenuator
7 dB, SC/UPC, M-F
• 1x Fixed optical attenuator
10 dB, SC/UPC, M-F

Ethernet cables 3 • To connect the Cerberis

XGR interfaces to networks

LC fiber cleaning tool 1 • To clean service channel

fiber connector

SC fiber cleaning tool 1 • To clean quantum channel

fiber connector

Power cable 2 • IEC 60320 C13 to CEE 7/7

(Type E and type F
compatible), Type B, Type G
or Type J (country
dependent)

Ferrite 2 • Ferrite core 241 ohms @

100MHz to mount on
power cable

Sliding rail 2 • To mount in 19” rack with

mounting brackets

Mounting brackets 4 • 2 short brackets

• 2 extended brackets

Property of ID Quantique SA Page: 24 / 41

 Screws, nuts, and brackets kit 1 • 3x M3x10mm, Torx T10
• 2x Securing bracket
• 10x M4x10mm, Torx T20
• 10x Screw M5x10mm,
• 10x nuts M5
• 10x spring lock washer M5
• 20x washer M5
• 10x #10-32x1/2”

• 2x nuts bar #10-32

SFP Dust Plug 2 • Mounted in SFP cage

Table 8 . Bob Box Content

NOTE
The two terminals can be identified by the different color of the front panel handles: blue
for Alice XGR terminal, dark gray for Bob XGR terminal.

The Cerberis XGR is provided with fix attenuators of different attenuation for the quantum channel (3, 5,
10dB) and the service channel (7, 15dB), to optimize the losses on both channels and maximize the system
performance.

To work properly and securely the Cerberis XGR must have a loss budget on the QC between 10dB and the
max attenuation supported by the system (i.e., for a 12dB grade Cerberis XGR the losses on the QC should
be between 10 and 12dB, for a 18dB grade Cerberis XGR the losses on the QC should be between 10 and
18dB).

The system is also provided with SFPs for the service channels optimized for 100km fiber range, so it is also
recommended to have about 15dB losses on the SC.

As rule of thumb, if the system is deployed on a lab environment with a point-to-point configuration using
the 2m fiber patch cords provided for the QC and SC, it is mandatory to use a 10dB attenuator on the QC and
2x 15dB attenuators on the SC (one for each SC fiber). If the system is deployed on a real network and the
losses budget on the QC and SC is less than what previously described, it is possible to add the additional
attenuators provided.

IMPORTANT NOTE
Before the deployment of the Cerberis XGR system on a real network is always suggested
to measure the effective losses budget of the QC and SC fibers as well as the effective
length (and length difference) of the QC and SC fiber.

5.1.3. Additional tools required

ID # Part Name QTY Function Notes

Property of ID Quantique SA Page: 25 / 41

 1 Configuration PC 1 Controlling, start up, Ethernet port and
and monitoring of SSH/Telnet
the blades connectivity required
SSH/Telnet client
software installed
PC Minimum
configuration:
• Disk: >100 GB
• CPU: 4 Cores
RAM: 8 GB
2 Screwdriver Torx T10 1 System installation
3 Screwdriver Torx T20 1 System installation
4 Screwdriver Slot 3 1 System installation
5 8mm wrench 1 System installation
6 Scredriver PH2 1 System maintenance

5.2.Installing a Cerberis XGR QKD node

5.2.1. Installing the Cerberis XGR in a 19” rack (optional)

To install the Cerberis XGR in a rack, the required tools are:

• Screwdriver Torx T10

• Screwdriver Torx T20
• Screwdriver Philips Head PH2
• 8mm wrench

The installation of the rails can be done by following the 6 steps described below:

1. Disassemble the internal rails.

Property of ID Quantique SA Page: 26 / 41

 2. Fix the securing brackets and the internal rails to the Cerberis XGR.

3. Fix the brackets to the external rail. Adjust length by positioning rail in the rack.

4. Fix the external rails in the rack.

5. Insert carefully the Cerberis XGR in the external rails and check that it is well secured before you
release it.

Property of ID Quantique SA Page: 27 / 41

 6. Secure the CerberisXGR by fixing the securing brackets.

5.2.2. Power on & off the Cerberis XGR

Once the two Cerberis XGR terminals are unpacked and inspected proceed by connect electrically and
optically the terminals.

1. The 4 Ferrites (included in the package) shall be mounted on each power supply cable, and position
next to the chassis (one per cable).

2. Mount the Plug the power cords to the IEC-60320-C14 power outlets in the terminals back panel.
3. Plug the other extremity to an electric socket.

4. The system will power-ON.

IMPORTANT
If only one of the two power supply modules on the back of the node is plugged to the
electric socket a continuous alarm sound will be produced when the node is powered-on.
To stop the alarm, the red button visible in Figure 4 must be pressed.

To shut down the system the following two procedure can be followed:

1. Using the power button:

I. push one time the power button.

Property of ID Quantique SA Page: 28 / 41

 II. the shutdown process will begin, it can be noted that the fan system will blow at maximum
speed until the system shut down.
III. if the system does not shut down automatically after 90 sec continuously hold the power
button until the system shut down.
2. Using the QNET Shell command shutdown. Please report to the QNET shell User Guide to get more
details on how to shut down your Cerberis XGR via the management interface.

WARNING
Disconnect both power supply cords before servicing

5.2.3. Setting up the Quantum Channel connection

The Quantum Channel (QC) connection between the two Cerberis XGR node is realized using the SC/UPC
single mode fiber provided with the system. It is important to note that, to optimize the functioning, the
losses on the QC should be at least about 10dB. For this reason, when connecting the two QKD nodes with
only the 2m SC/UPC single mode fiber patch cord, the 10dB fix attenuator (provided with the accessory)
should be added.

IMPORTANT
Optical components for the Quantum channel should be perfectly cleaned and handled
with care, otherwise system will not operate properly!

Optical Connections, Quantum channel:

1. Remove the protective cap from the SC/UPC connector end of the single mode fiber patch
cord and clean the exposed fiber ferrule end by wiping it twice on the cleaning tool. Only
wipe in the direction depicted by the arrow.
2. On Alice QKD node:
i. Remove the protective cap on the SC/UPC front panel connector.
ii. IMPORTANT: Verify that the alignment key is well aligned with the alignment slot
of the connector!
iii. carefully connect the fiber to the front panel fiber connector. The connector must
clearly “click” in.
3. On Bob QKD node if the QC fiber has at least 10dB total losses (real fiber):
i. Remove the protective cap on the SC/UPC front panel connector.
ii. IMPORTANT: Verify that the alignment key is well aligned with the alignment slot
of the connector!
iii. carefully connect the fiber to the front panel fiber connector. The connector must
clearly “click” in.
Property of ID Quantique SA Page: 29 / 41
 4. On Bob QKD node if just the 2m SC/UPC is used:
i. Remove the protective cap on the SC/UPC front panel connector.
ii. Remove the protective cap from the UPC/SC connector end of the 10dB fix
attenuator.
iii. Remove the protective cap from the SC/UPC connector end of the QC fiber patch
cord and clean the exposed fiber ferrule end by wiping it twice on the cleaning tool.
Only wipe in the direction depicted by the arrow.
iv. IMPORTANT: Verify that the alignment key is well aligned with the alignment slot
of the connector!
v. carefully connect the SC/UPC fiber connector to the fix attenuator. The connector
must clearly “click” in.
vi. Remove the protective cap from the SC/UPC connector end of the 10dB fix
attenuator. Clean the exposed fiber ferrule end by wiping it twice on the cleaning
tool. Only wipe in the direction depicted by the arrow.
vii. IMPORTANT: Verify that the alignment key is well aligned with the alignment slot
of the connector!
viii. carefully connect the fiber to the front panel fiber connector. The connector must
clearly “click” in.

5.2.4. Setting up the QKD Service Channels connection

Each QKD node requires a suitable SFP transceiver module for the service channel. The bidirectional optical
QKD-Service channel link is necessary for QKD clock synchronization and post-processing. The modules
provided by IDQ are from Finisar’s “FWLF1632xx Fixed Channel DWDM 120km SFP Optical Transceiver”
family. Those modules are available for transmitter wavelengths between 1528.77 nm and 1563.86 nm and
obey the main specifications as summarized in Table 9 below. The part number of standard module provided
by IDQ is FWLF163230, corresponding to ITU Channel 32, 1553.33nm.

Parameter Value Notes

Data Rate 2.7 Gbps (or more) SONET OC-3/12/48 compatible
Total link budget 28 dB (or more) at 2.5 Gbps with BER <10-12
Center Wavelength Spacing 100 GHz / 0.8 nm
Modulated Spectral Width 0.3 nm Full width, -20 dB
Side Mode Suppression Ratio 30 dB Modulated
Optical Rise/Fall Time 160 ps Unfiltered, 80%-20%
Optical Output Power 4 dBm Average output power
Transmitter Extinction Ratio 8.2 dB
Transmitter Eye Opening 10 %
Transmitter Jitter 75 mUI peak-to-peak
Relative Intensity Noise -120 dB/Hz
Dispersion Power Penalty at 2400 ps/nm 3.0 dB
Receiver Jitter 75 mUI
Optical Input Power -9 dBm - -28 dBm at 2.5 Gbps with BER <10-12
Receiver Damage Threshold +6 dBm
Dispersion Noise Penaltyat 2400 ps/nm 3.0 dB
Operating/Storage Temp. -5°C-70°C / -40°C-85°C Ambient temperature
Supply Voltage 3.13 V - 3.50 V
Supply Current 380 mA
Property of ID Quantique SA Page: 30 / 41
 Inrush Current 410 mA
Maximum Power 1.3 W
Transmitter Input Impedance 100 Ω
Single ended data input swing 250 mV - 1200 mV
Transmit Disable Voltage 1.83 V - 4.2 V
Single ended data output swing 175 mV - 1000 mV
Data Output Raise/Fall Time 150 ps
Receiver LOS Assert Level -36 dBm
Receiver LOS Deassert Level -34 dBm
Receiver LOS Hysteresis 2 dB
Table 9: Required characteristics of the SFP Transceiver for the QKD Service Channel.

Optical Connections, Service Channel:

1. Remove both protective caps from the LC connector of the dual fiber patch cord and clean
the exposed fiber ferrules by wiping them on the cleaning tool. Only wipe in the direction
depicted on the cleaning tool!
2. If the service channel fibers have less than 10 dB of losses, add the provided fix LC
attenuators to have an attenuation between 10 to 20dB to prevent saturation of the SFP
modules.
i. Remove the protective caps on both sides of the LC fix attenuator and clean the
exposed fiber ferrules by wiping them on the cleaning tool. Clean the interior of the
LC fix attenuator with the provided cleaning tool.
ii. Connect the LC/UPC fiber connectors to the fix attenuators.
IMPORTANT: A proper connection is confirmed by an audible click when inserting
the module.
3. Remove the protective cap from the SFP module and carefully insert the LC connector into
the SFP module.
4. Slide the SFP module into the front panel mount at the QKD node in the slot labelled as
Service. A proper installation is confirmed by an audible click when inserting the module.
IMPORTANT: A proper connection is confirmed by an audible click when inserting the
module. Verify that the metallic handle is in a downward position!
5. Repeat the same procedure for the other QKD node (except point 2 if the fix attenuators
have been already used).

5.2.5. Connecting to the Cerberis XGR via a RS-232 serial connection

To connect to the Cerberis XGR QKD node via its front panel serial port, follow the steps below:

1. Connect the console cable to the CONSOLE RJ45 port on the Cerberis XGR front panel.
2. Connect the other end of the console cable to the USB port of the Configuration PC.
3. Start a terminal program (e.g. MobaXterm or Putty) and set the following parameters for
the serial connection:
Baud speed: 115200
Data bits: 8
Stop bits: 1
Parity: None
Flow Control: None
Terminal mode: Implicit LF in every CR.
Property of ID Quantique SA Page: 31 / 41
 4. Open the serial connection. In the appearing terminal window press the ENTER key once to
see the login prompt.
5. Login as “admin”:
> admin
default password: admin
6. The first time the system is accessed as admin a password change is requested (see
paragraph 6.2).

5.2.6. Connecting to the QKD node via SSH through an Ethernet connection

To provide network access to the Cerberis XGR QKD nodes for the initial configuration, a local connection
through the system front panel serial port is recommended. The interface designed for
management/administration purpose is called MGT and correspond to the port number 0.

To configure the MGT IP address to match the network settings of the network:

1. Connect to the QKD node front panel port labeled CONSOLE as described in section 5.2.5.
2. Login on QNET with the admin role.
3. Use the command network (see QNET user guide) to set the IP address, netmask, and
gateway of interface 0.
The QKD node (Alice or Bob) is now accessible through the Ethernet port on the front panel labeled as MGT
(see Figure 5 or Figure 8).

Property of ID Quantique SA Page: 32 / 41

6. Operates your Cerberis XGR node
6.1.LED states
The most relevant interfaces and status indicators of a Cerberis XGR node are indicated in Figure 8 and
explained in more detail in Table 10.

Figure 8 Detail of the front LED panel

LED LED Status Status Description

Status ON (Green) Cerberis XGR node is powered ON

OFF Cerberis XGR node is powered OFF

Quantum OFF Cerberis XGR node Quantum Channel is desynchronized

ON (Green) Cerberis XGR node Quantum Channel is synchronized

Service OFF Cerberis XGR node Service Channel is desynchronized

Blinking (Green) Cerberis XGR node Service Channel is synchronizing

ON (Green) Cerberis XGR node Service Channel is synchronized

Blinking (Red) Cerberis XGR node Service Channel error

Table 10: Description of the Service Channel Front Panel LED status.

6.2.QNET Shell
QNET shell is a command line interface embedded in your Cerberis XGR QKD node. This tool provides some
administration and configuration commands. Depending on their profile, users have different permissions
to the shell functions.

QNET shell is defined for 4 defined users:

user id role description default password

admin full administration privileges admin
crypto security privileges crypto
monitor monitoring privileges monitor
user read-only user
Property of ID Quantique SA Page: 33 / 41
Furthermore, each command provides some help that can be shown by typing:
<command> --help
The first time the system is accessed as admin, monitor, crypto or user, a password change is requested.

WARNING
If a user provides the wrong password three times, the account is locked. To be able to
access it again, the system needs to be rebooted. To do so once an account is looked (for
ex. admin) use another account that has reboot rights (crypto for ex.) and reboot the
node.

NOTE: Before setting the new password, it is important to mention that the new password must fulfill the
following criteria:

• Minimum password length is 15 characters.

• No character can be repeated more than twice.

• Password must be composed of capital/small letters, numbers, and special characters.

• Have maximum 4 consecutive characters of the same class (capital letters, small letters,
numbers, or special characters)

A new password must differ of 8 characters at least from the old password.

To set the user profile password, type:

password
For a full description of the QNET Shell capabilities, please refer to: IDQ QNET shell User Guide.
The key functions related to Network Configuration and Channel delays settings described in more detail in
the next sections.

6.2.1. Showing or setting the network configuration

To show the system network configuration of your Cerberis3 XGR, type on the corresponding Qnet shell
interface:
network
To change the network configuration, type:
network -i <arg> -a 10.10.10.191 -n 255.0.0.0 -g 0.0.0.0
where arg is the interface number (refer to the address scheme configuration of Error! Reference
source not found.):
• 0 for the management interface (MGT)
• 1 for the interface to collocated Cerberis3 XGR, in case of TN topology (AUX)
• 2 for KMS-to-KMS communication (KMS)
• 3 for the interface to encryptors (KEYS)
If connected to the system via SSH, the connection will be terminated after changing the IP address.

Property of ID Quantique SA Page: 34 / 41

 6.3.Understanding the QKD Log files
The log files are accessible through QNET shell in various ways: by “Inspecting the log files”, by “Monitoring
the log files”, or by “Exporting the log files to an USB stick”. A full description on how to correctly interpret
the information shown on the log file can be found in the document: Understanding the QKD log files.

6.4.Manage remotely your Cerberis XGR via QNET Central Server

You can manage your QKD network using the QMS Web application, which provides an access to all QNET
WebAPI functions and control facilities from a standard browser. Use this support to manage your QKD
system configuration, KMS configuration; to browse events, logs, and other topology data; and to access
most of the QNET commands and online help.

Alternatively, you can manage your QKD network using the QNET Tool command line interface that supports
the same controls than the QMS Web application

For the instruction to install, deploy and run the QMS web application and QNET Tool, please follow the
instruction found in “Cerberis XGR Solution Quick Start Guide”.

For a full description of each application/service capabilities, please refer to:

IDQ QNET Web API User Guide, IDQ QNET tool User Guide.

Property of ID Quantique SA Page: 35 / 41

7. Cerberis XGR Research Features
The Cerberis XGR Quantum Key Distribution platform is specifically designed to serve as a versatile tool for
academia, research institutes and innovation labs. Unlike the standard QKD platform, the Cerberis XGR allows
to:

1. customize a series of QKD parameters

2. stream out the RAW Keys before the QKD post processing is applied (esp. the error correction).

Both these features are explained and detailed in the documents: “Cerberis XGR solution Quick User Guide”
and “IDQ4P QKD Communication Protocol Definition”, while here is provided a brief description.

7.1.QKD customizable parameters

In Table 11 is reported the list of all the QKD parameters that can be customized in the Cerberis XGR, a full
description of each parameter and the procedure to edit the values can be found in the document “Cerberis
XGR solution Quick User Guide”.

Component Sub Parameters Terminal Value 1 Value 2 units

Component or or
min value max value
FPGA Distillation CompressionRatio Alice/Bob 5 30
FPGA Model Filter Alice/Bob TRUE FALSE
FPGA RNG QRNG Alice/Bob TRUE FALSE
Optics Laser PhotonNumber Alice 0.001 0.1
Optics Pulse Width Alice 300 600 ns
Alignment PhotonNumber Alice 0.001 0.1
Regulation DATA Darkcounts Alice 0 20000
Regulation DATA Deadtime Alice 1 100 μs
Regulation MONITOR Darkcounts Alice 0 20000
Regulation MONITOR Deadtime Alice 1 100 μs
Regulation QBER IntegrationTime Alice 2 30 s
Regulation Visibility IntegrationTime Alice 2 30 s
Bists Enabled Alice TRUE FALSE
Optics Detectors Deadtime Bob 1 100 μs
Optics DataPulse Width Bob 300 800 ns
Optics MonitorPulse Width Bob 300 800 ns
Alignment MinDetections Bob 500 4000
Optimization MinDetections Bob 500 4000
Regulation IntegrationTime Bob 2 30 s
Bists DetectorsBist Timeout Bob 600 1800 s
Table 11 XGR customizable parameters

Property of ID Quantique SA Page: 36 / 41

 7.2.RAW keys via IDQ4P
IDQ4P is a proprietary protocol of ID Quantique Inc. that define 4 logical channels which allows the QKD to
communicate with the “clients” (ex. encryptors). Through one of the IDQ4P channels (IDQ4P-R) it is possible
to stream out the RAW Keys before the QKD post processing is applied (esp. the error correction). Those keys
correspond on Bob side to the detection values and on Alice side to the Qbits that were sent for those specific
detections. With the RAW Keys the user can compare the two streams and verify the QBER of the system.

More details on the IDQ4P protocol, and description of the key retrieval can be found in the documents:
“Cerberis XGR solution Quick User Guide vx.x” and “IDQ4P QKD Communication Protocol Definition”.

Property of ID Quantique SA Page: 37 / 41

A. Appendix
A.1. Product variants
Different variants of the product are listed in the table

Model variant Laser diode

wavelength [nm]
Cerberis XGR 1551.72 (C32)
Cerberis XGR 1310

Each model Cerberis XGR consists of two devices:

• Transmitter: Alice / C32 or Alice / 1310

• Revcever: Bob / C32 or Bob / 1310

Cerberis XGR and Cerberis XGRR have same hardware, same housing (except the color XGR Blue, XGRR red),
same interfaces. XGRR is the research version with an additional user role that has access to low level QKD
parameters configuration and data.

A.2. COW protocol description

The aim of Quantum Key Distribution is to exchange a secret key between Alice and Bob by encoding bits
with quantum state carried by single photons (qubits). There are different ways to encode qubit values on
single photons. One of those ways is called time-bin qubits. As shown in Error! Reference source not found.,
this method consists in creating a pair of coherent pulses propagating in the same spatial mode and separated
by a given time. The first pulse is called the early pulse. The second one is called the late pulse. To generate
all possible qubit values (i.e. all possible states of the qubit sphere), the intensity ratio between those two
pulses can be varied between 0 and infinity. Those two extreme cases correspond to the two poles of the
sphere, i.e. either when the whole optical energy of the single photon is contained in the early or late pulses.
Those two quantum states compose the computational basis of the qubit space. By changing the energy level
ratio between the two optical pulses, one can move the qubit state along one of the meridians of the qubit
sphere. To move along one of the parallels, one needs to change the phase relation between the early and
late pulses. One manner to implement time-bin qubit emitter is based on an unbalanced Mach-Zehnder
interferometer where the input beam splitter ratio can be varied and the output beam recombiner is a fast
switch. A possible implementation of a time-bin qubit analyzer consists in the same Mach-Zehnder
interferometer where input and output ports have been swapped.

The BB84 protocol can be implemented with time-bin qubits. In this case, it is generally implemented with
four qubit states located on the equatorial plan of the qubit sphere. This choice is made to guarantee as many
similarities as possible in the implementation of the two bases used in BB84 protocol. In this case, the two
Mach-Zehnder interferometers are made with two 50/50 couplers and one phase modulator. This kind of
implementation requires a tight control on the interferometer’s stability or at least a dynamic adjustment of
one interferometer compared to the other one.

Property of ID Quantique SA Page: 38 / 41

 Figure 9 Illustration of the qubit sphere and of time-bin qubits.

The aim of COW protocol is to make the implementation of a QKD system as simple as possible to allow a
strong increase of the final secret key rate in a manner that allow the industrialization of the system.
Therefore, a first requirement of COW protocol was not to use two interferometers to avoid stabilization of
one interferometer compared to another. A second requirement of this protocol was to work specifically
with weak optical coherent pulses, but not with single photon pulses. This requirement is motivated by the
fact that it is very simple to implement weak coherent pulse sources whereas single photon sources are still
difficult to handle. Several other requirements, that are not listed here, were targeted when COW protocol
was designed.

A first specificity of COW protocol is to use the qubit basis composed of the two pole states (the early and
the late pulses). Hence, the measurement method to analyze this basis is simply to measure the time of
detection of the optical pulse. If one detection occurs in the early time-bin, the qubit value is a |0> state,
whereas if it occurs in the late time-bin, the qubit is a |1> state. This measurement method does not
require any complex optical component except one single photon detector with a temporal accuracy
allowing one to distinguish between the two time-bins. In COW protocol, as in any QKD protocols, two
qubit bases are used to guarantee the security of transferred keys. But in this protocol, one basis will be
used to generate the raw key and the other one to estimate the security level of the exchanged qubits in
the first basis. The basis used to exchange the raw key is the computational basis, because as explained
previously, it requires an analyzer composed uniquely on a single detector. This basis will be the more often
used to maximize the raw key rate (in other protocol like BB84, the ratio because the two basis is 50/50 in
general because both bases equally contribute to the generation of raw keys and to the estimation of the
security level of this raw key). The second basis used in COW protocol is one of the bases located on the
equatorial plan of the qubit sphere. The analyzer for this kind of basis is implemented with an unbalanced
interferometer as described in the case of one example of a BB84 protocol implementation. To avoid an
implementation with only one interferometer, COW protocol is based on a qubit emitter that requires no
interferometer. COW emitter needs to be able to emit either early or late pulses to generate states of the
computational basis. This can be done easily by switching on and off a light source at the time
corresponding to the desired qubit states. One of the key ideas of COW protocol is to keep the coherence
between two consecutive optical pulses belonging to the same time-bin qubit or not (i.e. one belonging to
one qubit and the other one belonging to the following qubit). This coherence can be checked with the
interferometer in the receiver station in both cases if the time separation between two time-bin quits
equals the time between the two pulses composing one qubit. Therefore, the emitter in COW protocol
needs to guarantee the same phase relation between consecutive optical pulses whether they belong to
the same qubit or not. To enhance the security of COW protocol, one qubit state of the second basis of the
Property of ID Quantique SA Page: 39 / 41
receiver will be emitted from time to time. This state is called decoy sequence. It consists in an early and a
late optical pulse with the same energy level than the early pulse in a |0i. The phase relation between one
of the two pulses of the decoy sequence and the consecutive pulses needs to be kept identical to the one
between pulses of the computational basis. This decoy sequence is used in combination with the second
basis analyzed in the receiver to estimate the security of the raw key exchanged using the computational
basis. The ratio between the emitted states from the computational basis and the decoy sequence is in
favor of the computational basis to optimize the raw key rate.
In summary, as depicted in Figure 10 Illustration of COW protocol COW protocol consists in an emitter
emitting qubits states from the computational basis or decoy sequences. The time between all consecutive
pulses is identical and the phase relation between those consecutive pulses is kept constant. The ratio of
the number of qubits from the computational basis and the number of decoy sequences is in favor of the
computational basis. The receiver station consists in an analysis for the computational basis and an
analyzer to check the phase relation between two consecutive optical pulses. The ratio of use of the
analyzer for the computational basis compared to the use of the analyzer for the phase relation check is in
favor of the computational basis. A QBER value is measured by counting the probability of having an error
in the exchange of qubits of the computational basis. The phase relation check is quantified by measuring
the visibility of interferences occurring in the second basis analyzer. Based on both values, QBER and
visibility, (plus few other parameters like the ratio values) it is possible the estimate if it is possible to
extract secret keys form the qubits exchanged between the emitter and the receiver stations.

Figure 10 Illustration of COW protocol

A.3. COW 4-states

Following the paper of Marcos Curty ([2101.07192] Zero-error attack against coherent-one-way quantum key
distribution (arxiv.org)) describing a “theoretical” attack that could be performed on COW protocol, a security
analysis has been conducted. Thanks to this analysis we can prove that the COW protocol is still safe today
up to 12dB dynamic range, with the current parameters in the trusted detector scenario.
To be safe also at higher dynamic range, we adapted the protocol by implementing a countermeasure which
allow us to prevent the sequential attack and extend the dynamic range to 16dB and more.
In the COW 4-states protocol an additional vacuum state is added to the protocol, this implementation
effectively neutralizes the probability that Eve's unambiguous state discrimination measurement can
produce a conclusive result.
Property of ID Quantique SA Page: 40 / 41
 Figure 11: Illustration of the COW 4-states protocol.

Using the QNET shell on Alice QKD terminal, it is possible to see which protocol is running with the
command:

protocol

the answer can be:

QKD Protocol: Cow4States

or

QKD Protocol: Cow3States

it is possible to change the protocol using the command protocol followed by the type of protocol, for ex:

protocol Cow4States

NOTE
Please contact ID Quantique for additional information about the implementation of
COW 4-state protocol and its security.

Property of ID Quantique SA Page: 41 / 41