Crate highway

This crate is a native Rust port of Google's HighwayHash, which is a fast, keyed, and strong hash function that can take advantage of SIMD instructions (SSE 4.1 and AVX 2) for speed ups that allow it to be faster than traditional cryptographic hash functions and even outpace less secure functions at large payloads. HighwayHash allows for an incremental approach to hashing and can output 64bit, 128bit, and 256bit values.

Caution

HighwayHash (the algorithm) has not gone undergone extensive cryptanalysis like SipHash (the default hashing algorithm in Rust), but according to the authors, HighwayHash output bits are uniformly distributed and should withstand differential and rotational attacks. Hence HighwayHash is referred to as a strong hash function, not a cryptographic hash function. I encourage anyone interested to peruse the paper to understand the risks.

Examples

use highway::{HighwayBuilder, HighwayHash, Key};

// HighwayHash requires a key that should be hidden from attackers
// to ensure outputs are unpredictable, so attackers can't mount
// DoS attacks.
let key = Key([1, 2, 3, 4]);

// A HighwayBuilder is the recommended approach to hashing,
// as it will select the fastest algorithm available
let mut hasher = HighwayBuilder::new(&key);

// Append some data
hasher.append(&[255]);

// After all data has been appended, you ask for
// 64, 128, or 256bit output. The hasher is consumed
// after finalization.
let res: u64 = hasher.finalize64();

assert_eq!(0x07858f24d_2d79b2b2, res);

Creating a 128bit and 256bit hash is just as simple.

use highway::{HighwayBuilder, HighwayHash, Key};

// Generate 128bit hash
let key = Key([1, 2, 3, 4]);
let mut hasher128 = HighwayBuilder::new(&key);
hasher128.append(&[255]);
let res128: [u64; 2] = hasher128.finalize128();
assert_eq!([0xbb007d2462e77f3c, 0x224508f916b3991f], res128);

// Generate 256bit hash
let key = Key([1, 2, 3, 4]);
let mut hasher256 = HighwayBuilder::new(&key);
hasher256.append(&[255]);
let res256: [u64; 4] = hasher256.finalize256();
let expected: [u64; 4] = [
    0x7161cadbf7cd70e1,
    0xaac4905de62b2f5e,
    0x7b02b936933faa7,
    0xc8efcfc45b239f8d,
];
assert_eq!(expected, res256);

Use highway hash in standard rust collections

use std::collections::HashMap;
use highway::{HighwayBuildHasher, Key};
let mut map =
  HashMap::with_hasher(HighwayBuildHasher::new(Key([
    0xcbf29ce484222325,
    0xc3a5c85c97cb3127,
    0xb492b66fbe98f273,
    0x9ae16a3b2f90404f,
  ])));

map.insert(1, 2);
assert_eq!(map.get(&1), Some(&2));

Or if utilizing a key is not important, one can use the default

use std::collections::HashMap;
use std::hash::BuildHasherDefault;
use highway::HighwayHasher;
let mut map =
  HashMap::with_hasher(BuildHasherDefault::<HighwayHasher>::default());

map.insert(1, 2);
assert_eq!(map.get(&1), Some(&2));

Use Cases

HighwayHash can be used against untrusted user input where weak hashes can't be used due to exploitation, verified cryptographic hashes are too slow, and a strong hash function meets requirements. Some specific scenarios given by the authors of HighwayHash:

• Use 64bit hashes to for authenticating short lived messages
• Use 128 / 256bit hashes are good for checksums (ie: longer lived data, or strong guarantees against collisions)

Structs

AvxHash	AVX empowered implementation that will only work on x86_64 with avx2 enabled at the CPU level.
HighwayBuildHasher
HighwayBuilder	Main HighwayHash implementation that delegates to one of the other implementations depending on the target compiled for and a runtime CPU check.
HighwayHasher
Key	Key used in HighwayHash that will drastically change the hash outputs.
PortableHash	Portable HighwayHash implementation. Will run on any platform Rust will run on.
SseHash	SSE empowered implementation that will only work on x86_64 with sse 4.1 enabled at the CPU level.

Traits

HighwayHash

The shared trait between all the hashing implementations, which directs the APIs available for appending data and receiving a hash result.