Quantum Security 101
Quantum security glossary
Plain-language definitions of the terms used across quantum security and post-quantum cryptography, drawn from the standards and regulators that publish them.
A
- Asymmetric cryptographyPublic-key cryptography
- Encryption that uses a mathematically linked key pair: a public key to encrypt or verify, and a private key to decrypt or sign. RSA and elliptic-curve cryptography are the most widely used examples, and both are the algorithms a quantum computer running Shor’s algorithm can break.
- AESAdvanced Encryption Standard
- A symmetric encryption algorithm standardized by NIST. Unlike public-key algorithms, AES is only modestly weakened by quantum computing, through Grover’s algorithm, and is considered quantum-resistant at 256-bit key length.
C
- CBOMCryptographic Bill of Materials
- A structured inventory of every cryptographic asset in a system: the algorithms, key lengths, certificates, libraries, and protocols in use, and where. It is the reference a migration program works from, the cryptographic equivalent of a software bill of materials (SBOM). You cannot migrate cryptography you have not inventoried.
- CNSA 2.0Commercial National Security Algorithm Suite 2.0
- The US National Security Agency’s set of approved quantum-resistant algorithms and a dated timeline for adopting them across national security systems, with milestones running through the 2030s.
- Crypto-agility
- The ability to replace cryptographic algorithms across systems without re-architecting the systems that depend on them. It is the practical goal of a quantum-safe program, because you cannot predict exactly which algorithms will be mandated or broken, and it begins with a complete cryptographic inventory.
- Cryptographic exposure assessmentQuantum threat assessment
- A structured review that identifies where an organization’s most sensitive data depends on quantum-vulnerable cryptography and prioritizes what to address first. A human-led assessment captures architectural context that automated scanners miss, and produces a board-ready snapshot rather than a raw tool output.
- CRQCCryptographically Relevant Quantum Computer
- A quantum computer powerful and stable enough to break the public-key cryptography in real-world use. None exists yet; the term describes the threshold rather than any current machine. See Q-Day.
D
- Digital signature
- A cryptographic value that proves a message or document came from a specific key holder and was not altered. Signatures rely on public-key cryptography, so a quantum computer could forge them, which is why NIST standardized quantum-resistant signatures in FIPS 204 and 205.
- DORADigital Operational Resilience Act
- An EU regulation, in force since January 2025, that sets operational-resilience and cryptographic requirements for financial entities and their technology providers.
E
F
- FIPS 203, 204, 205
- The first finalized quantum-resistant cryptographic standards, published by the US National Institute of Standards and Technology (NIST) in August 2024. FIPS 203 (ML-KEM) covers key encapsulation; FIPS 204 (ML-DSA) and FIPS 205 (SLH-DSA) cover digital signatures. They are the baseline algorithms most migration programs are standardizing on.
G
- Grover’s algorithm
- A quantum search algorithm that speeds up brute-force attacks. It weakens symmetric encryption such as AES only quadratically, which is why doubling the key length restores a safe margin, unlike the complete break Shor’s algorithm causes for public-key systems.
H
- Harvest now, decrypt laterHNDL
- An attack strategy in which adversaries intercept and store encrypted data today, then decrypt it once a capable quantum computer exists. It makes quantum risk present-tense: any data that must stay confidential for years is already exposed, whatever the arrival date of the hardware.
- HSMHardware Security Module
- A dedicated device that generates, stores, and uses cryptographic keys in tamper-resistant hardware. HSMs are a core part of any migration, because the algorithms they support are often fixed and slow to change.
K
- KEMKey Encapsulation Mechanism
- A method for two parties to establish a shared secret key over an insecure channel. ML-KEM, standardized in NIST FIPS 203, is the quantum-resistant KEM most migration programs adopt.
M
- Mosca’s inequality
- A rule framed by cryptographer Michele Mosca for judging quantum readiness. If the time your data must stay secret plus the time needed to migrate is greater than the time until a capable quantum computer arrives, your organization is already exposed.
P
- PKIPublic-Key Infrastructure
- The system of certificates, authorities, and policies that binds public keys to identities and enables trust online. Because it rests on public-key cryptography, PKI is directly exposed to quantum risk.
- Post-quantum cryptographyPQC
- Cryptographic algorithms designed to resist attack by a quantum computer. “Post-quantum cryptography” is the term used in much of the research and standards literature; Horizen Labs uses the plainer, equivalent term quantum-resistant. Both refer to algorithms such as those in NIST’s FIPS 203, 204, and 205.
Q
- Q-Day
- The point at which a cryptographically relevant quantum computer can break the public-key cryptography protecting today’s data and communications. The Global Risk Institute’s Quantum Threat Timeline Report places the most likely window in the 2030s, with conservative forecasts reaching into the 2040s.
- Qubit
- The basic unit of quantum information. Estimates of how many qubits are needed to break RSA-2048 have fallen sharply, from about 20 million in 2019 to fewer than one million in a 2025 estimate by Google’s Craig Gidney.
- Quantum-resistantQuantum-safe
- A property of cryptographic algorithms built to withstand attack by a quantum computer. It is Horizen Labs’ preferred term for what the literature also calls post-quantum cryptography.
R
- RSA
- One of the oldest and most widely used public-key algorithms, securing key exchange and digital signatures. Its security rests on the difficulty of factoring large numbers, which a quantum computer running Shor’s algorithm can do efficiently.
S
- Shor’s algorithm
- The quantum algorithm, published by Peter Shor in 1994, that factors large integers and solves the discrete-logarithm problem efficiently, breaking both RSA and elliptic-curve cryptography.
- Symmetric cryptography
- Encryption that uses the same key to encrypt and decrypt, such as AES. It is far less affected by quantum computing than public-key cryptography and is considered quantum-resistant at adequate key sizes.
T
- TLSTransport Layer Security
- The protocol that encrypts most internet traffic. It relies on public-key cryptography for key exchange and authentication, making it one of the most widespread points of quantum exposure.
What to do now
Assess your cryptographic exposure
Horizen Labs runs a human-led cryptographic exposure assessment that requires no software deployment and makes no changes to live systems, producing a board-ready exposure snapshot.
Talk to the Quantum Security team