xmss-rs

XMSS (eXtended Merkle Signature Scheme) for Rust

Algorithm Overview

XMSS provides post-quantum digital signatures using hash-based cryptography, offering 128-bit post-quantum security with forward security properties.

Key Implementation Components

Core Architecture:

pub struct XMSSPrivateKey {
    pub idx: u32,                    // Current signature index
    pub wots_keys: Vec<(WOTSPlusPrivateKey, WOTSPlusPublicKey)>,
    pub sk_seed: Vec<u8>,            // Seed for key generation
    pub sk_prf: Vec<u8>,             // Seed for PRF
    pub seed: Vec<u8>,               // Public seed
    pub root: Vec<u8>,               // Merkle tree root
}

WOTS+ One-Time Signatures:

• Winternitz parameter w=16 for optimal size/security tradeoff
• Hash chains with randomized hashing using bitmasks
• Base-w conversion for message encoding

Merkle Tree Construction:

• Binary hash tree combining 2ʰ WOTS+ public keys
• Authentication paths enable signature verification
• BDS algorithm for logarithmic space complexity

Stateful Management:

pub trait PersistentStorage: Send + Sync {
    fn save_state(&mut self, state: &[u8]) -> Result<(), XMSSError>;
    fn load_state(&self) -> Result<Vec<u8>, XMSSError>;
}

Security Features:

• Constant-time operations using subtle crate
• Memory zeroization with zeroize crate
• Forward security through key evolution
• RFC 8391 compliance with test vectors

Performance Optimizations:

• BDS algorithm reduces space from O(2ʰ) to O(h²)
• Parallel hash computations for tree construction
• Memory-efficient authentication path updates
• Hardware security module integration support