Arcanum Hash

Cryptographic hash functions and key derivation for the Arcanum engine.

Hash Function Selection

Performance Comparison (4KB message, typical desktop CPU)

Recommendations

Use BLAKE3 ([Blake3]) for:

• Content addressing / deduplication (file systems, object stores)
• File integrity checking (checksums, manifests)
• Key derivation with [Blake3::derive_key]
• Keyed hashing / MAC with [Blake3::keyed_hash]
• Any new application without legacy compatibility requirements
• Streaming large files (BLAKE3 is parallelizable)

Use SHA-256 ([Sha256]) for:

• TLS / X.509 certificates
• Bitcoin / cryptocurrency protocols
• Compatibility with existing systems (HMAC, JWT, etc.)
• NIST-approved algorithm requirements

Use SHA-3 ([Sha3_256]) for:

• Government/compliance requiring NIST SP 800-185
• Defense-in-depth (different construction than SHA-2)

Type Alias

For convenience, [PreferredHasher] is an alias for [Blake3]:

use arcanum_hash::PreferredHasher;

let hash = PreferredHasher::hash(b"data");

Hash Functions

• BLAKE3: Ultra-fast, parallelizable, recommended default
• SHA-2: SHA-256, SHA-384, SHA-512 (NIST standard)
• SHA-3: SHA3-256, SHA3-512, SHAKE128, SHAKE256 (Keccak)
• Blake2: Blake2b, Blake2s (fast, secure, legacy)

Key Derivation Functions

• Argon2id: Password hashing (PHC winner, recommended)
• BLAKE3 KDF: Fast key derivation from high-entropy input
• HKDF: Key derivation from high-entropy input (RFC 5869)
• scrypt: Memory-hard password hashing
• PBKDF2: Legacy password hashing

Message Authentication Codes

• BLAKE3 keyed: Fast keyed hashing built into BLAKE3
• HMAC: Hash-based MAC (with any hash function)

Example

use arcanum_hash::prelude::*;

// Recommended: Use BLAKE3 for new applications
let hash = Blake3::hash(b"hello world");

// BLAKE3 keyed hash (MAC)
let key = [0u8; 32];
let mac = Blake3::keyed_hash(&key, b"message");

// BLAKE3 key derivation
let derived = Blake3::derive_key("my-app v1 encryption key", b"context data");

// Incremental hashing for large data
let mut hasher = Blake3::new();
hasher.update(b"hello ");
hasher.update(b"world");
let hash = hasher.finalize();

// SHA-256 for compatibility
let sha_hash = Sha256::hash(b"hello world");

// Password hashing (always use Argon2id)
let hash = Argon2::hash_password(b"password", &Argon2Params::default())?;
assert!(Argon2::verify_password(b"password", &hash)?);

// HKDF for protocol key derivation
let key = Hkdf::<Sha256>::derive(ikm, salt, info, 32)?;

Security Notes

• BLAKE3 is cryptographically secure with 256-bit security level
• All hash functions in this crate are collision-resistant and pre-image resistant
• For password hashing, always use Argon2id, never raw hash functions
• BLAKE3 keyed hashing is a proper MAC construction, not just H(key || message)