hkdf

A HMAC-based key derivation function (HKDF) per RFC5869.

Usage

A sample GHCi session:

  > :set -XOverloadedStrings
  > -- import qualified
  > import qualified Crypto.KDF.HMAC as KDF
  >
  > -- supply your own HMAC function
  > import qualified Crypto.Hash.SHA256 as SHA256
  >
  > -- derive a 32-byte key from a secret
  > Just (KDF.derive SHA256.hmac "my salt" "my optional info" 32 "my secret input")
  "\EM\232\v\140\202\230\f2:\221n\221\209\233\US\209>\174_!\138\255\\C\150\237^X\226\tt\252"

Documentation

Haddocks (API documentation, etc.) are hosted at docs.ppad.tech/hkdf.

Performance

The aim is best-in-class performance for pure, highly-auditable Haskell code.

Current benchmark figures on an M4 Silicon MacBook Air look like (use cabal bench to run the benchmark suite):

  benchmarking ppad-hkdf/HKDF-SHA256/derive (outlen 32)
  time                 485.2 ns   (484.8 ns .. 485.7 ns)
                       1.000 R²   (1.000 R² .. 1.000 R²)
  mean                 486.4 ns   (485.9 ns .. 487.1 ns)
  std dev              1.873 ns   (1.418 ns .. 2.450 ns)

  benchmarking ppad-hkdf/HKDF-SHA512/derive (outlen 32)
  time                 1.034 μs   (1.030 μs .. 1.040 μs)
                       1.000 R²   (1.000 R² .. 1.000 R²)
  mean                 1.032 μs   (1.030 μs .. 1.036 μs)
  std dev              8.421 ns   (3.502 ns .. 16.24 ns)

Security

This library aims at the maximum security achievable in a garbage-collected language under an optimizing compiler such as GHC, in which strict constant-timeness can be challenging to achieve.

The HKDF implementation within has been tested against the Project Wycheproof vectors available for SHA-256 and SHA-512, using the HMAC functions from ppad-sha256 and ppad-sha512 respectively.

If you discover any vulnerabilities, please disclose them via security@ppad.tech.

Development

You'll require Nix with flake support enabled. Enter a development shell with:

$ nix develop

Then do e.g.:

$ cabal repl ppad-hkdf

to get a REPL for the main library.