Glossary.

The following terms are used consistently throughout the Gankpo documentation.

A

AEAD (Authenticated Encryption with Associated Data) — encryption mode that guarantees both confidentiality and integrity of data. Gankpo uses AES-256-GCM and ChaCha20-Poly1305.

Argon2id — key-derivation function from a passphrase, resistant to specialised-hardware attacks (RFC 9106).

B

Base45 — compact encoding that represents binary data in alphanumeric text that fits in a QR code (RFC 9285).

BLAKE3 — fast cryptographic hash function, used by Gankpo for integrity fingerprints.

C

CBOR (Concise Binary Object Representation) — compact binary encoding format, the binary equivalent of JSON (RFC 8949).

COSE (CBOR Object Signing and Encryption) — standard for signing and encrypting CBOR structures (RFC 8152).

E

Ed25519 — signature algorithm based on the Edwards 25519 curve (RFC 8032). Default algorithm for Gankpo signatures.

F

FFI (Foreign Function Interface) — binary interface letting an application written in one language call code written in another. Gankpo exposes gkp_core through a C FFI used by mobile and desktop applications.

G

.gkp — sealed document format. See Specification .gkp v4.

.gksend — encrypted envelope format for transmission. See Specification .gksend.

.gki — technical draft of a local identity format, unsupported by Gankpo applications. See the .gki draft.

GKP1 — QR-verifiable credential format. See Specification GKP1 QR.

GKPR — co-signature segment appended at the end of a .gkp file to form an append-only signature chain.

H

HKDF (HMAC-based Key Derivation Function) — key-derivation function (RFC 5869).

Holder — role in the holder-issuer-verifier model. The person or organisation that holds a document or credential.

HSM (Hardware Security Module) — dedicated hardware for storing and using cryptographic keys.

I

Issuer — role in the holder-issuer-verifier model. The organisation that issues a document or credential.

K

kid (key identifier) — identifier of a public key, used to resolve the key in a keystore.

M

Multi-signature — chain of successive signatures appended to a document. In Gankpo, it is carried by GKPR segments.

N

Nonce — unique value used only once with a key for an encryption operation. Gankpo's AEAD algorithms require a 12-byte nonce.

O

Offline-first — design model in which a critical operation (here, verification) is possible without a network call at the time of the operation.

P

PKCS#11 — standard interface for communicating with an HSM or a hardware cryptographic medium.

S

Secure Enclave — secure coprocessor on Apple devices, used to protect cryptographic keys.

StrongBox — reinforced mode of Android Keystore using a dedicated secure coprocessor.

V

Conformance vector — binary data set published to allow an integrator to check that a third-party implementation produces the same outputs.

Verifier — role in the holder-issuer-verifier model. The person or organisation that verifies the authenticity of a document or credential.

X

X25519 — key-exchange algorithm on the Curve25519 curve (RFC 7748), used by Gankpo for .gksend envelopes.

X.509 — digital-certificate format standard, used for interoperability with existing PKI infrastructures.