← Guide overview

Glossary

Quantum Readiness for Banking Professionals: all chapters

• 1. What quantum threatens in a bank, and what it doesn't
• 2. Where cryptography lives in a payments estate
• 3. Building a cryptographic inventory
• 4. Deciding what to fix first
• 5. Crypto-agility first
• 6. Vendors and third parties
• 7. Governance and the regulatory map
• 8. A phased roadmap
• Readiness self-assessment
• Glossary

The terms used in this guide, in plain English.

AES

The standard symmetric encryption algorithm. With 256-bit keys it remains strong against quantum computers.

Asymmetric cryptography

Another name for public-key cryptography. Both the vulnerable algorithms (RSA, elliptic-curve) and the new post-quantum ones are asymmetric.

CBOM (cryptographic bill of materials)

A structured inventory of cryptographic assets: what is used, where, what it protects and what depends on it. CycloneDX is an open standard for recording one.

Certificate

A digital document that binds a public key to an identity, such as a website or a bank, vouched for by a certificate authority's signature.

Certificate authority (CA)

A system or organisation that issues certificates. Certificates form chains from a root authority down to individual systems.

CNSA 2.0

The US National Security Agency's algorithm requirements for national security systems. Not a deadline for commercial banks.

CRQC (cryptographically relevant quantum computer)

A quantum computer large and reliable enough to break RSA and elliptic-curve cryptography at the sizes used today. None exists today.

Crypto-agility

The ability to change cryptographic algorithms, keys and parameters through configuration or policy, without re-engineering the systems that use them. In practice it also needs interoperability with partners, managed key and certificate lifecycles, validated implementations and operational controls such as testing and rollback.

Elliptic-curve cryptography (ECC)

A family of public-key algorithms widely used for modern key agreement (such as ECDHE) and signatures (such as ECDSA). Based on a discrete-logarithm problem that a large quantum computer could solve.

Envelope encryption

Encrypting data with one key and protecting that key with another. If the outer key is RSA or elliptic-curve, the whole envelope is quantum-vulnerable.

FN-DSA

A compact post-quantum signature algorithm (formerly Falcon) being standardised by NIST.

Grover's algorithm

A quantum search algorithm that speeds up searching for a secret key, weakening symmetric encryption; 256-bit keys keep a comfortable margin. Its effect on hash functions depends on how the hash is used, and current guidance treats SHA-256 and larger hashes as remaining secure.

Harvest now, decrypt later

Recording encrypted data today in order to decrypt it once a capable quantum computer exists.

Hash function

A function that produces a short fingerprint of data, used to detect changes. Modern hashes such as SHA-384 remain strong.

HQC

A backup key-agreement algorithm selected by NIST in 2025, based on different mathematics from ML-KEM.

HSM (hardware security module)

A tamper-resistant device that stores and uses cryptographic keys. It protects keys from theft, not from quantum attacks on their mathematics.

Hybrid cryptography

Using a current algorithm and a post-quantum algorithm together. When the two are combined using a standard method and implemented correctly, a connection stays secure as long as at least one of them remains unbroken.

Key agreement

The process by which two systems establish a shared secret key over an open network. Today this mostly uses elliptic-curve methods (such as ECDHE); older systems sometimes transport keys with RSA instead.

KEM (key encapsulation mechanism)

A way for two systems to establish a shared secret: one side uses the other's public key to wrap a fresh secret, and only the holder of the private key can unwrap it. ML-KEM is a KEM; it does the job that key exchange does today.

ML-DSA

The main NIST post-quantum digital signature standard (FIPS 204).

ML-KEM

The main NIST post-quantum key encapsulation mechanism (KEM) standard (FIPS 203), used for key agreement.

Mosca's inequality

A planning rule: if the time data must stay secret plus the time to migrate exceeds the time until a quantum computer can break it, the data is already at risk.

Post-quantum cryptography (PQC)

Public-key algorithms designed to resist known classical and quantum attacks, running on ordinary computers. Like all cryptography, they remain subject to continuing analysis.

Public-key cryptography

Cryptography using a pair of keys, one public and one private, for key agreement, signatures and certificates. Today's widely used schemes (RSA and elliptic-curve) would be broken by a large quantum computer; post-quantum schemes are public-key cryptography designed to resist it.

Q-day

An informal name for the day a cryptographically relevant quantum computer exists. Its date is unknown.

RSA

A widely used public-key algorithm for signatures and certificates, and in older systems for transporting keys. Based on factoring, which a large quantum computer could do.

Shor's algorithm

The quantum algorithm that would break RSA and discrete-logarithm systems, including elliptic-curve cryptography, on a large enough quantum computer.

SLH-DSA

A conservative, hash-based NIST post-quantum signature standard (FIPS 205), with larger signatures.

Symmetric cryptography

Cryptography where the same key encrypts and decrypts, such as AES. Weakened only modestly by quantum computers.