ETSI GR QKD 007 V1.2.1 (2026-01)

Quantum Key Distribution (QKD); Vocabulary

RGR/QKD-007ed2_Vocab

General Information

• Status: Not Published
• Technical Committee: QKD - Quantum Key Distribution
• Current Stage: 12 - Completion
• Due Date: 31-Dec-2025
• Completion Date: 05-Jan-2026

Standards Content (Sample)

GROUP REPORT
Quantum Key Distribution (QKD);
Vocabulary
Disclaimer
The present document has been produced and approved by the Quantum Key Distribution (QKD) ETSI Industry Specification
Group (ISG) and represents the views of those members who participated in this ISG.
It does not necessarily represent the views of the entire ETSI membership.

2 ETSI GR QKD 007 V1.2.1 (2026-01)

Reference
RGR/QKD-007ed2_Vocab
Keywords
quantum key distribution, vocabulary

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3 ETSI GR QKD 007 V1.2.1 (2026-01)
Contents
Intellectual Property Rights . 5
Foreword . 5
Modal verbs terminology . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 6
3 Definition of terms, symbols and abbreviations . 7
3.1 Terms . 7
A . 7
B . 8
C . 8
D . 9
E . 10
F to G . 10
H . 10
I . 10
J to K . 11
L . 11
M . 11
N to O . 11
P . 11
Q . 12
R . 13
S . 14
T . 15
U to V . 15
W . 15
X . 15
Y . 15
Z . 15
3.2 Symbols . 15
3.3 Abbreviations . 16
A . 16
B . 16
C . 16
D . 16
E . 16
F . 17
G . 17
H . 17
I . 17
J . 17
K . 17
L . 17
M . 17
N . 18
O . 18
P . 18
Q . 18
R . 18
S . 18
T . 19
U . 19
V . 19
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4 ETSI GR QKD 007 V1.2.1 (2026-01)
W . 19
X to Z . 19
Annex A: Usage of terms . 20
A.1 General comments . 20
A1.1 Key agreement / establishment / distribution . 20
A1.2 Unconditional security . 20
A1.3 Information theoretically secure . 20
A1.4 "plug-and-play" protocols . 20
A.2 Entities within a QKD system . 20
A.3 Communication channels in a QKD link . . 21
History . 22

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5 ETSI GR QKD 007 V1.2.1 (2026-01)
Intellectual Property Rights
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pertaining to these essential IPRs, if any, are publicly available for ETSI members and non-members, and can be
found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to
ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the
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Foreword
This Group Report (GR) has been produced by ETSI Industry Specification Group (ISG) Quantum Key Distribution
(QKD).
Modal verbs terminology
In the present document "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be
interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.

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6 ETSI GR QKD 007 V1.2.1 (2026-01)
1 Scope
The present document collects together definitions and abbreviations used in relation to Quantum Key Distribution
(QKD) and ETSI ISG QKD documents. QKD introduces new concepts and technologies to the field of
telecommunications and considerable related vocabulary. Many terms derive from the wider fields of quantum physics
and classical cryptography, and in some cases terms assume a modified or more specific meaning when applied to
QKD.
The main objectives of the present document are:
• To improve the consistency with which terminology and abbreviations are used within ISG QKD documents.
• To provide a reference document to reduce confusion by readers who may not be familiar with QKD.
Most definitions and abbreviations come from ISG QKD Group Specifications and Group Reports or are expected to be
used in published documents. The terms included have been selected to focus the present document on those that are
expected to be of widespread use or where consistency is felt to be particularly important, e.g. due to a specific risk of
confusion. Terms introduced in a single ISG QKD published document for a specific purpose that is local to that
document are excluded unless of particular importance.
2 References
2.1 Normative references
Normative references are not applicable in the present document.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents may be useful in implementing an ETSI deliverable or add to the reader's
understanding, but are not required for conformance to the present document.
[i.1] ETSI TS 101 909-11 (V1.2.1): "Digital Broadband Cable Access to the Public
Telecommunications Network; IP Multimedia Time Critical Services; Part 11: Security".
[i.2] ISO/IEC 2382:2015: "Information technology — Vocabulary", (2015).
[i.3] R. Canetti: "Universally Composable Security: A New Paradigm for Cryptographic Protocols",
nd
FOCS'01: Proc. of the 42 IEEE Symposium on Foundations of Computer Science
(October 2001).
[i.4] J. Müller-Quade and R. Renner: "Composability in quantum cryptography", New J. Phys. 11,
085006 (2009).
[i.5] ISO 7498-2:1989: "Information processing systems — Open Systems Interconnection — Basic
Reference Model — Part 2: Security Architecture", (1989).
[i.6] ISO/IEC 19790:2025: "Information security, cybersecurity and privacy protection — Security
requirements for cryptographic modules".
[i.7] ISO/IEC 17825:2024: "Information technology — Security techniques — Testing methods for the
mitigation of non-invasive attack classes against cryptographic modules", (2024).
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7 ETSI GR QKD 007 V1.2.1 (2026-01)
[i.8] ISO/IEC 18031:2025: "Information technology — Security techniques — Random bit generation",
(2025).
[i.9] ISO/TR 22100-4:2018: "Safety of machinery — Relationship with ISO 12100 — Part 4: Guidance
to machinery manufacturers for consideration of related IT-security (cyber security) aspects",
(2018).
[i.10] ISO/IEC 23837-1:2023: "Information security — Security requirements, test and evaluation
methods for quantum key distribution — Part 1: Requirements", (2023).
[i.11] M. Peter and W. Schindler: "A Proposal for Functionality Classes for Random Number
Generators", Version 3.0, AIS 31, Bundesamt für Sicherheit in der Informationstechnik (BSI)
(2014).
[i.12] ISO/IEC 27034-7:2018: "Information technology — Application security — Part 7: Assurance
prediction framework", (2018).
[i.13] C. H. Bennett and G. Brassard: "Quantum cryptography: Public key distribution and coin tossing.
Proceedings of IEEE International Conference on Computers Systems and Signal Processing",
Bangalore India, pp. 175–179 (1984).
[i.14] J. F. Clauser, M. A. Horne, A. Shimony and R. A. Holt: "Proposed Experiment to Test Local
Hidden-Variable Theories", Phys. Rev. Lett. 23, 880 (1969).
[i.15] A. Einstein, B. Podolsky and N. Rosen: "Can Quantum-Mechanical Description of Physical
Reality Be Considered Complete?" Phys. Rev. 47, 777 (1935).
[i.16] F. Grosshans and P. Grangier: "Continuous Variable Quantum Cryptography Using Coherent
States", Phys. Rev. Lett., 88(5), 057902 (2002).
3 Definition of terms, symbols and abbreviations
3.1 Terms
A
adversary: party seeking to compromise the confidentiality or authenticity of symmetric keys agreed by QKD or to
compromise the operation of a QKD system or associated infrastructure
after-pulse: signal pulse in a single photon detector that is the result of a signal pulse in the same single photon detector
at an earlier time
Alice: legitimate party operating a QKD module in a QKD system/protocol
NOTE 1: In a prepare-and-measure quantum key distribution system, Alice is the user preparing and sending the
quantum information carriers.
NOTE 2: In an entanglement-based quantum key distribution system, Alice is one of the users measuring the
quantum information carriers.
NOTE 3: In a measurement-device independent quantum key distribution system, Alice is one of the users
preparing and sending the quantum information carriers.
ancilla: auxiliary (quantum mechanical) system
Application Programming Interface: interface implemented by a software program to be able to interact with other
software programs
attack: any malicious action by an adversary
attenuation: reduction in intensity of an optical signal
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authenticated classical channel: communication channel for the exchange of digital data where the data transferred
possesses the security property of authenticity to enable the recipient to verify the identity of the transmitter and to
ensure the data has not been modified in transit
NOTE: An authenticated channel does not necessarily employ encryption, but it can optionally encrypt data in
transit.
authenticity: ability to ensure that the given information is without modification or forgery and was in fact produced by
the entity that claims to have given the information
NOTE: See ETSI TS 101 909-11 [i.1].
B
bit error rate: number of erroneous bits divided by the total number of bits transmitted, received, or processed over
some stipulated period of time
NOTE 1: Can be expressed as a rational number or a percentage.
NOTE 2: See clause 2124483 in ISO/IEC 2382 :2015 [i.2] in which the preferred term is "bit error ratio".
Bob: legitimate party operating a QKD module in a QKD system/protocol
NOTE 1: In a prepare-and-measure quantum key distribution system, Bob is the user receiving and measuring the
quantum information carriers.
NOTE 2: In an entanglement-based quantum key distribution system, Bob is one of the users receiving and
measuring the quantum information carriers.
NOTE 3: In a measurement-device independent quantum key distribution system, Bob is one of the users preparing
and sending the quantum information carriers.
C
classical channel: communication channel that is used by two communicating parties for exchanging data encoded in a
form that may be non-destructively read and fully reproduced
coherent attack: attack where an adversary interacts ancilla(s) coherently with quantum state(s) emitted under the
QKD protocol and can then perform a joint measurement on the ancilla(s) and / or quantum state(s) emitted under the
QKD protocol to extract information
NOTE 1: This definition places no limits to the computing power or resources of the adversary and can therefore
include the most general and powerful types of attack. However, in some cases it can be meaningful to
consider coherent attacks with limitations, e.g. on the fidelity or storage time of quantum memory
available to the adversary, etc.
NOTE 2: This definition does not prevent the adversary from using any information obtained about the system
other than from quantum states transmitted under the QKD protocol.
collective attack: attack where an adversary optionally interacts independent ancilla(s), each with no more than one
quantum state emitted under the QKD protocol, and can then perform an unrestricted joint measurement on all the
ancilla(s) and / or quantum state(s) emitted under the QKD protocol to extract information
NOTE 1: Attacks involving the joint measurement of correlated quantum states emitted under the QKD protocol
(e.g. attacks on entanglement protocols) without ancillas are considered collective attacks.
NOTE 2: This definition places no other limits to the computing power or resources of the adversary beyond that of
independent ancilla(s) described. However, in some cases it can be meaningful to consider collective
attacks with further limitations on the capabilities of the adversary, e.g. the fidelity or storage time of
available quantum memory, etc.
NOTE 3: This definition does not prevent the adversary from using any information obtained about the system
other than from quantum states transmitted under the QKD protocol.
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9 ETSI GR QKD 007 V1.2.1 (2026-01)
composability: security statements that hold for individual protocols can be used to prove security statements for more
complex cryptographic schemes built from combinations of those protocols
NOTE 1: This means that the security of a composite protocol can be automatically determined from the security of
its sub-protocols as long as they are all satisfy this property.
NOTE 2: "composability" is shorthand for "Universal Composability" [i.3] and [i.4].
cryptography: discipline that embodies principles, means, and methods for the transformation of data in order to hide
its information content, prevent its undetected modification and/or prevent its unauthorized use
NOTE 1: Cryptography determines the methods used in encipherment and decipherment. An attack on a
cryptographic principle, means, or method is cryptanalysis.
NOTE 2: See clause 3.3.20 in ISO 7498-2 :1989 [i.5].
cryptographic algorithm: well-defined computational procedure that takes variable inputs, which may include
cryptographic keys, and produces an output
cryptographic boundary: explicitly defined perimeter that establishes the boundary of all components (i.e. set of
hardware, software or firmware components) of the cryptographic module
NOTE: See clause 3.32 in ISO/IEC 19790 :2025 [i.6].
cryptographic hash function: computationally efficient function that maps binary strings of arbitrary length to binary
strings of fixed length, such that it is computationally infeasible to invert it, or to find two distinct values that hash into
a common value
cryptographic key: sequence of symbols that controls the operation of a cryptographic transformation
NOTE 1: A cryptographic transformation can include but is not limited to encipherment, decipherment,
cryptographic check function computation, signature generation, or signature verification.
NOTE 2: Cryptographic keys can be produced from one or more QKD key.
NOTE 3: See clause 3.34 in ISO/IEC 19790:2025 [i.6].
cryptographic primitives: fundamental protocols from which cryptographic applications can be composed
D
dark count probability: probability that a detector registers a detector event within a stated time duration, in the
absence of optical illumination
dead time: time duration after a detector event during which the detector will not output subsequent detector events
NOTE: The detection efficiency is exactly zero during the dead time. After the dead time there will a reset time
during which the detection efficiency is transitioning from zero back to its steady-state value.
decoy state: state legitimately introduced to a channel
...