HKDF

HMAC-based Extract-and-Expand Key Derivation Function (HKDF) as defined in RFC 5869. The HMAC is provided by libsodium which uses the HMAC-SHA-512/256 algorithm.

Installation

SPM

.package(url: "https://github.com/TICESoftware/HKDF.git", .upToNextMajor(from: "1.0.0"))

In order to build the library it is necessary to link libsodium. The official repository includes scripts to build binaries for specific platforms.

swift build -Xcc -I[header search path] -Xlinker -L[binary path]

When using Xcode you can set the header search path manually to include the libsodium header files and link the static libsodium library.

CodoaPods

pod 'HKDF'

This uses Sodium as a dependency which includes the pre-compiled libsodium library. No further setup necessary.

Usage

For deriving a new key of length 32 bytes from some input keying material ikm:

import HKDF

let ikm = "Input key".bytes
let hkdfKey = try! deriveHKDFKey(ikm: ikm, L: 32)

A salt and some application specific info string (which is hashed into the HMAC) can additionally be provided:

try deriveHKDFKey(ikm: ikm, salt: salt, info: "Info", L: 32)