Lunatik
Lua API · Cryptography

crypto.hkdfClass

HMAC-based Extract-and-Expand Key Derivation Function (HKDF) based on RFC 5869.

This module provides functions to perform HKDF operations, utilizing the underlying crypto C module for HMAC calculations. Like every crypto object, an instance is created in a process runtime alone.

Functions

crypto.hkdf.new (alg) Creates a new HKDF instance for a given hash algorithm.

Methods

crypto.hkdf:close () Closes the HKDF instance and releases the underlying HMAC transform.
crypto.hkdf:expand (prk[, info], length) Performs the HKDF Expand step.
crypto.hkdf:extract ([salt], ikm) Performs the HKDF Extract step.
crypto.hkdf:hkdf ([salt], ikm[, info], length) Performs the full HKDF (Extract and Expand) operation.

Functions in detail

crypto.hkdf.new (alg)
Creates a new HKDF instance for a given hash algorithm.

Parameters

  • alg string base hash algorithm name (e.g., “sha256”, “sha512”). The “hmac(” prefix will be added automatically.

Returns

    hkdf An HKDF instance table with methods for key derivation.

Usage

local hkdf_sha256 = require("crypto.hkdf").new("sha256")

Methods in detail

crypto.hkdf:close ()
Closes the HKDF instance and releases the underlying HMAC transform. It also runs when a to-be-closed variable holding the instance goes out of scope. Without it, the transform is freed when it is collected.
crypto.hkdf:expand (prk[, info], length)
Performs the HKDF Expand step.

Parameters

  • prk string Pseudorandom Key.
  • info string Optional context and application-specific information. Defaults to an empty string if nil. (optional)
  • length number desired length in bytes for the Output Keying Material (OKM), at most 255 times the digest size.

Returns

    string Output Keying Material of the specified length.
crypto.hkdf:extract ([salt], ikm)
Performs the HKDF Extract step.

Parameters

  • salt string Optional salt value. If nil or not provided, a salt of hash_len zeros is used. (optional)
  • ikm string Input Keying Material.

Returns

    string Pseudorandom Key (PRK).
crypto.hkdf:hkdf ([salt], ikm[, info], length)
Performs the full HKDF (Extract and Expand) operation.

Parameters

  • salt string Optional salt value. (optional)
  • ikm string Input Keying Material.
  • info string Optional context and application-specific information. (optional)
  • length number desired length in bytes for the Output Keying Material.

Returns

    string Output Keying Material.