Module hkdf 

HKDF key derivation

HkdfSha256 and HkdfSha512 provide Rustaceous wrappers around libsodium’s HKDF-SHA-256 and HKDF-SHA-512 functions.

HKDF turns input keying material into one or more independent keys. It has two steps:

• extract: mix the input keying material with an optional salt to produce a pseudorandom key (PRK)
• expand: derive output bytes from that PRK and a context string

Use HKDF when you already have keying material, such as a shared secret from key exchange, and need separate keys for different purposes. The context is public domain-separation data; changing it changes the derived output.

Rustaceous API example

use dryoc::hkdf::{HkdfSha256, HkdfSha256Prk};

let hkdf: HkdfSha256 =
    HkdfSha256::extract(Some(b"Act IV salt"), b"Now is the winter of our discontent");
let output: Vec<u8> = hkdf
    .expand_to_vec(42, b"session key")
    .expect("expand failed");
assert_eq!(output.len(), 42);

One-shot extract and expand

use dryoc::hkdf::HkdfSha512;

let output = HkdfSha512::extract_and_expand_to_vec(
    64,
    Some(b"optional deployment salt"),
    b"Our remedies oft in ourselves do lie",
    b"application secret",
)
.expect("expand failed");
assert_eq!(output.len(), 64);

Reusing an extracted PRK

use dryoc::hkdf::{HkdfSha256, HkdfSha256Prk};

let hkdf = HkdfSha256::extract(Some(b"deployment salt"), b"We know what we are");
let encryption_key: HkdfSha256Prk = hkdf.expand(b"encryption key").expect("expand failed");
let authentication_key: HkdfSha256Prk =
    hkdf.expand(b"authentication key").expect("expand failed");
assert_ne!(encryption_key, authentication_key);

The concrete expanders are type aliases over Hkdf and can also be used through HkdfVariant in generic code.

Modules

protectedprotected

Protected memory type aliases for HKDF

Structs

Hkdf

HKDF expander for a specific HkdfVariant.

HkdfSha256Variant

HKDF-SHA-256 algorithm marker.

HkdfSha512Variant

HKDF-SHA-512 algorithm marker.

Traits

HkdfVariant

HKDF algorithm variant used by Hkdf.

Type Aliases

HkdfSha256

Stack-allocated HKDF-SHA-256 expander.

HkdfSha512

Stack-allocated HKDF-SHA-512 expander.

HkdfSha256Expander

HKDF-SHA-256 expander.

HkdfSha256Prk

Stack-allocated pseudorandom key for HKDF-SHA-256.

HkdfSha512Expander

HKDF-SHA-512 expander.

HkdfSha512Prk

Stack-allocated pseudorandom key for HKDF-SHA-512.