Term	Definition
CBD(η)	Centered Binomial Distribution — noise sampling method. Each coefficient is a sum of η random bits minus η random bits.
Ciphertext (ct)	768-byte output of encapsulation. Sent from sender to receiver.
Decapsulation	Receiver operation: recover shared secret from ciphertext + private key.
Encapsulation	Sender operation: generate ciphertext + shared secret from public key.
FO transform	Fujisaki–Okamoto transform — converts IND-CPA scheme to IND-CCA2 KEM using hashing and re-encryption.
Frobenius map (σ)	Ring automorphism σ(f(x)) = f(x³ mod x²⁵⁶+1). Generates the rotation orbit.
Implicit rejection	On invalid ciphertext, return pseudorandom secret (from token z) instead of error.
IND-CCA2	Indistinguishability under adaptive chosen-ciphertext attack — the gold standard for KEM security.
KEM	Key Encapsulation Mechanism — establishes a shared secret via public-key cryptography.
K	Module rank = 2. Number of Frobenius rotation instances in VORTEX-256.
ML-KEM	NIST-standardised Module-Lattice KEM (FIPS 203), formerly known as Kyber.
MLWE	Module Learning With Errors — standard lattice assumption used by Kyber.
n	Ring dimension = 256. Number of coefficients per polynomial.
PEM	Privacy-Enhanced Mail format — Base64 encoding with BEGIN/END headers.
Post-quantum (PQC)	Cryptography resistant to attacks by quantum computers (e.g. Shor's algorithm).
Public key (pk)	800-byte value published by the receiver. Safe to distribute.
Private key (sk)	1248-byte secret value. Must be protected.
q	Prime modulus = 3329. All coefficient arithmetic is mod q.
R_q	Polynomial ring ℤ_q[x]/(x²⁵⁶+1) — the algebraic setting for VORTEX.
RotMLWE	Rotational Module Learning With Errors — VORTEX's novel hardness assumption.
Shared secret (ss)	32-byte output of KEM. Both parties derive the same value.
SHAKE-128/256	Extendable-output functions (XOF) from SHA-3 family. Used for expansion and KDF.
XOF	Extendable Output Function — hash function with arbitrary output length.
η₁, η₂	CBD noise parameters. η₁=3 for keygen, η₂=2 for encapsulation.
ρ (rho)	32-byte seed for expanding the base ring element a₀.
z	32-byte implicit rejection token stored in the private key.