· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·

Blake3 Hashing

Astral uses Blake3 as its cryptographic hash function. This document explores why we chose Blake3 and how it's integrated into Astral's architecture.

---

Why Blake3?

Key Properties

1. Speed: Blake3 is designed from the ground up for performance on modern CPUs
2. Parallelism: The Merkle tree structure enables multi-core hashing
3. Security: Based on the well-analyzed Blake2 and ChaCha primitives
4. Versatility: Can be used as a hash, MAC, KDF, and PRF

---

The Merkle Tree Structure

Unlike traditional hash functions that process data sequentially, Blake3 uses a Merkle tree internally:

Benefits for Astral

• Parallel hashing: Large files can be hashed across multiple cores
• Incremental updates: Only changed chunks need rehashing
• Streaming: No need to buffer the entire file in memory
• Verified streaming: Can verify chunks as they arrive

---

Benchmarks

Performance comparison on AMD Ryzen 9 (16 cores):

---

Implementation

Astral uses the official Blake3 Go implementation:

import "github.com/zeebo/blake3"

func HashObject(content []byte) [32]byte {
    return blake3.Sum256(content)
}

// For large files, use streaming:
func HashFile(path string) ([32]byte, error) {
    f, err := os.Open(path)
    if err != nil {
        return [32]byte{}, err
    }
    defer f.Close()
    
    h := blake3.New()
    if _, err := io.Copy(h, f); err != nil {
        return [32]byte{}, err
    }
    
    var hash [32]byte
    h.Sum(hash[:0])
    return hash, nil
}

SIMD Optimization

The implementation automatically uses:

• AVX-512 on supported Intel/AMD processors
• AVX2 on most modern x86-64 CPUs
• NEON on ARM64 (Apple Silicon, AWS Graviton)
• Pure Go fallback for other architectures

---

Security Considerations

Blake3's security properties:

| Property | Status | | :--- | :--- | | Collision Resistance | 128-bit (birthday bound) | | Preimage Resistance | 256-bit | | Second Preimage Resistance | 256-bit | | Length Extension | Immune (due to tree construction) |

---

Next Steps