sha256

A pure Haskell implementation of SHA-256 and HMAC-SHA256 on strict and lazy ByteStrings, as specified by RFC's 6234 and 2104.

Usage

A sample GHCi session:

  > :set -XOverloadedStrings
  >
  > -- import qualified
  > import qualified Crypto.Hash.SHA256 as SHA256
  >
  > -- 'hash' and 'hmac' operate on strict bytestrings
  >
  > let hash_s = SHA256.hash "strict bytestring input"
  > let hmac_s = SHA256.hmac "strict secret" "strict bytestring input"
  >
  > -- 'hash_lazy' and 'hmac_lazy' operate on lazy bytestrings
  > -- but note that the key for HMAC is always strict
  >
  > let hash_l = SHA256.hash_lazy "lazy bytestring input"
  > let hmac_l = SHA256.hmac_lazy "strict secret" "lazy bytestring input"
  >
  > -- results are always unformatted 256-bit (32-byte) strict bytestrings
  >
  > import qualified Data.ByteString as BS
  >
  > BS.take 10 hash_s
  "1\223\152Ha\USB\171V\a"
  > BS.take 10 hmac_l
  "\DELSOk\180\242\182'v\187"
  >
  > -- you can use third-party libraries for rendering if needed
  > -- e.g., using ppad-base16:
  >
  > import qualified Data.ByteString.Base16 as B16
  >
  > B16.encode hash_s
  "31df9848611f42ab5607ea9e6de84b05d5259085abb30a7917d85efcda42b0e3"
  > B16.encode hmac_l
  "7f534f6bb4f2b62776bba3d6466e384505f2ff89c91f39800d7a0d4623a4711e"

Documentation

Haddocks (API documentation, etc.) are hosted at docs.ppad.tech/sha256.

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-sha256/SHA256 (32B input)/hash
  time                 879.7 ns   (879.5 ns .. 879.9 ns)
                       1.000 R²   (1.000 R² .. 1.000 R²)
  mean                 880.1 ns   (879.5 ns .. 882.1 ns)
  std dev              3.504 ns   (994.6 ps .. 7.537 ns)

  benchmarking ppad-sha256/HMAC-SHA256 (32B input)/hmac
  time                 3.322 μs   (3.322 μs .. 3.322 μs)
                       1.000 R²   (1.000 R² .. 1.000 R²)
  mean                 3.321 μs   (3.317 μs .. 3.323 μs)
  std dev              10.53 ns   (4.987 ns .. 19.12 ns)

Compare this to Hackage's venerable SHA package:

  benchmarking ppad-sha256/SHA256 (32B input)/SHA.sha256
  time                 1.415 μs   (1.414 μs .. 1.415 μs)
                       1.000 R²   (1.000 R² .. 1.000 R²)
  mean                 1.415 μs   (1.415 μs .. 1.415 μs)
  std dev              1.334 ns   (1.158 ns .. 1.576 ns)

  benchmarking ppad-sha256/HMAC-SHA256 (32B input)/SHA.hmacSha256
  time                 5.157 μs   (5.156 μs .. 5.158 μs)
                       1.000 R²   (1.000 R² .. 1.000 R²)
  mean                 5.158 μs   (5.157 μs .. 5.159 μs)
  std dev              2.947 ns   (2.413 ns .. 3.606 ns)

Or the relevant SHA-256-based functions from a library with similar aims, noble-hashes:

SHA256 32B x 420,875 ops/sec @ 2μs/op ± 1.33% (min: 1μs, max: 3ms)
HMAC-SHA256 32B x 97,304 ops/sec @ 10μs/op

When reading a 1GB input from disk and testing it with hash_lazy, we get statistics like the following:

   2,310,899,616 bytes allocated in the heap
          93,800 bytes copied during GC
          78,912 bytes maximum residency (2 sample(s))
          35,776 bytes maximum slop
              10 MiB total memory in use (0 MiB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max pause
  Gen  0       295 colls,     0 par    0.007s   0.008s     0.0000s    0.0001s
  Gen  1         2 colls,     0 par    0.000s   0.001s     0.0004s    0.0004s

  INIT    time    0.003s  (  0.003s elapsed)
  MUT     time   22.205s  ( 22.260s elapsed)
  GC      time    0.007s  (  0.009s elapsed)
  EXIT    time    0.000s  (  0.001s elapsed)
  Total   time   22.216s  ( 22.273s elapsed)

  %GC     time       0.0%  (0.0% elapsed)

  Alloc rate    104,073,382 bytes per MUT second

  Productivity 100.0% of total user, 99.9% of total elapsed

SHA.sha256 gets more like:

  74,403,596,936 bytes allocated in the heap
      12,971,992 bytes copied during GC
          79,176 bytes maximum residency (2 sample(s))
          35,512 bytes maximum slop
               6 MiB total memory in use (0 MiB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max pause
  Gen  0     17883 colls,     0 par    0.103s   0.148s     0.0000s    0.0001s
  Gen  1         2 colls,     0 par    0.000s   0.000s     0.0002s    0.0003s

  INIT    time    0.006s  (  0.006s elapsed)
  MUT     time   32.367s  ( 32.408s elapsed)
  GC      time    0.104s  (  0.149s elapsed)
  EXIT    time    0.000s  (  0.001s elapsed)
  Total   time   32.477s  ( 32.563s elapsed)

  %GC     time       0.0%  (0.0% elapsed)

  Alloc rate    2,298,740,250 bytes per MUT second

  Productivity  99.7% of total user, 99.5% of total elapsed

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 HMAC-SHA256 functions within pass all Wycheproof vectors, as well as various other useful unit test vectors found around the internet.

If you discover any vulnerabilities, please disclose them via [email protected].

Development

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

$ nix develop

Then do e.g.:

$ cabal repl ppad-sha256

to get a REPL for the main library.

Attribution

This implementation has benefitted immensely from the SHA package available on Hackage, which was used as a reference during development. Many parts wound up being direct translations.