Glossary

Cryptographic Terms

Term	Definition
KEM	Key Encapsulation Mechanism — establishes a shared secret using asymmetric cryptography. ML-KEM is the quantum-safe KEM used here.
DEM	Data Encapsulation Mechanism — symmetric encryption for the actual payload. AES-256-GCM is the DEM used here.
AEAD	Authenticated Encryption with Associated Data — provides both confidentiality and integrity. AES-GCM is an AEAD scheme.
AAD	Additional Authenticated Data — input to the AES-GCM tag computation that is not encrypted but is authenticated. In AegisQ streaming, AAD is the 4-byte big-endian chunk index.
M-LWE	Module Learning With Errors — the hard lattice problem underlying ML-KEM’s quantum resistance.
NTT	Number Theoretic Transform — FFT over finite fields for O(n log n) polynomial multiplication.
CBD	Centered Binomial Distribution — used to sample small error terms in ML-KEM key generation.
Implicit Rejection	ML-KEM Decaps returns a pseudorandom key for invalid contents of a correctly sized capsule, rather than a validity error. Structural size errors remain distinct.
Transit Package	The complete byte array sent over the network: [Capsule | Nonce | Tag | Ciphertext].
Zeroization	Securely overwriting sensitive memory (keys, secrets) with zeros before deallocation.
Auth Tag	AES-GCM’s 16-byte authentication tag. Verification can fail due to tampering, a wrong key, or an invalid capsule; it does not prove sender identity.
Forward Secrecy	Compromise of a long-term secret does not compromise past session keys. EphemeralSession manages session keys but does not alone guarantee this protocol property or secure erasure.

Streaming Encryption Terms (v1.5.0)

Term	Definition
Header	First chunk of a stream-mode Transit Package: [capsule | base_nonce (12 B) | chunk_size (4 B BE u32)].
Frame	One chunk’s envelope in a stream-mode Transit Package: [length (4 B BE u32) | ciphertext | tag (16 B)].
base_nonce	The 12-byte random nonce stored in the stream header. Per-chunk nonces are derived from this.
chunk_size	Maximum ciphertext size per yielded chunk (1..=16 MiB; default 64 KiB). Encoded in the header.
EOF Marker	Special frame with length = 0 and a tag over empty plaintext. Closes the stream.
Chunk Index	0-based position of a frame in the stream (uint32). Used in nonce derivation and AAD.

Key Serialization Terms (v1.3.0)

Term	Definition
PEM	Privacy-Enhanced Mail envelope: ASCII-armored key with -----BEGIN ... ----- / -----END ... ----- headers. AegisQ uses an adapted form (RFC 7468).
JSON Key	Self-describing key format with algorithm, level, and public_key fields. Useful when the level cannot be conveyed out of band.
Base64 URL-safe	Base64 variant that uses - and _ instead of + and /, and omits = padding. Suitable for HTTP headers, URLs, and env vars.
HKDF	HMAC-based Key Derivation Function (RFC 5869). AegisQ uses HKDF-SHA3-256 for key wrapping. It is not a password-hardening function; use high-entropy secret input.
Key Wrap	Encrypting a key under another key. AegisQ uses AES-256-GCM with a key derived from high-entropy secret input by HKDF-SHA3-256; the API argument is named password.
Fingerprint	Truncated public-key identifier: first 8 bytes of SHA3-256(public_key) in hex. Used by KeyPair.__repr__; not identity authentication, and it enables log correlation.
Magic	Internal byte sequence marking an AegisQ encrypted key blob. Validated on load to catch format mismatch.

References

Standards & Libraries

Document	URL
FIPS 203 (ML-KEM)	https://csrc.nist.gov/pubs/fips/203/final
NIST SP 800-38D (AES-GCM)	https://csrc.nist.gov/pubs/sp/800/38/d/final
RFC 5869 (HKDF)	https://www.rfc-editor.org/rfc/rfc5869
RFC 4648 (Base64)	https://www.rfc-editor.org/rfc/rfc4648
RFC 7468 (PEM)	https://www.rfc-editor.org/rfc/rfc7468
CRYSTALS-Kyber spec v3.02	https://pq-crystals.org/kyber/
aes-gcm Rust crate	https://docs.rs/aes-gcm
zeroize Rust crate	https://docs.rs/zeroize
subtle Rust crate	https://docs.rs/subtle
PyO3 User Guide	https://pyo3.rs/latest/
Maturin Documentation	https://www.maturin.rs/
Starlight Documentation	https://starlight.astro.build/