PQHD: Post-Quantum Hierarchical Deterministic Wallet

Your wallet keys are generated in a way quantum computers can't reverse. Bitcoin's wallet system breaks under quantum attack — Tidecoin's doesn't.

PQHD is Tidecoin's custom wallet key derivation system that replaces Bitcoin's BIP-32. BIP-32 relies on elliptic curve arithmetic for key derivation — Shor's algorithm makes any exposed extended public key (xpub) equivalent to an exposed private key. PQHD uses hardened-only derivation with SHA-512-based KDF, supporting all five NIST post-quantum signature schemes with encrypted multi-seed storage.

// why bip-32 is broken

Why is Bitcoin's BIP-32 HD wallet broken by quantum computers?

BIP-32's extended public key (xpub) mechanism derives child public keys from a parent public key using elliptic curve point addition. In a quantum setting:

Shor's algorithm

derives the private key from any public key in polynomial time

An exposed xpub

is equivalent to an exposed xpriv

No NIST post-quantum signature scheme

supports the homomorphic public key derivation that BIP-32's non-hardened derivation requires

PQHD eliminates this vulnerability by using hardened-only derivation — every path element uses the private key material, and no public-key-only derivation exists.

// how it works

How does PQHD key derivation work?

Derivation path:

m / 10007' / 6868' / scheme' / account' / change' / index'

All elements are hardened (high bit set):

10007' — Tidecoin PQHD purpose
6868' — Tidecoin coin type
scheme' — PQ scheme identifier (Falcon-512, Falcon-1024, ML-DSA-44/65/87)
account', change', index' — user-controlled derivation

Derivation chain:

Seed ID:

SHA-256("Tidecoin PQHD seedid v1" || master_seed) — domain-separated identifier

Master node:

HMAC-SHA-512 from 32-byte master seed

Child derivation (CKD):

HMAC-SHA-512 chained using parent secret material

Leaf extraction:

HKDF-based stream key derivation with scheme-specific domain separation

Keypair generation:

Scheme-specific conversion — Falcon uses first 48 bytes, ML-DSA uses first 32 bytes as deterministic seed

// wallet features

What features does the PQHD wallet provide?

Multi-seed support

Independent seeds with per-seed scheme policies

Per-seed scheme selection

Different PQ schemes for different seeds

Configurable defaults

Set default receive and change address schemes

Encrypted storage

Seeds encrypted with wallet master key (PQHDCryptedSeed)

Memory safety

All secret material cleansed via memory_cleanse() after use

PSBT support

Proprietary PQHD origin metadata fields for offline signers

Descriptor integration

wpkh(pqhd(SEEDID)/purpose'/cointype'/scheme'/account'/change'/index')

// rpc commands

RPC commands:

tidecoin-cli.pqhdrpc

01$ tidecoin-cli setpqhdpolicy

02# Set default PQ scheme for receive/change addresses

04$ tidecoin-cli listpqhdseeds

05# List PQHD seeds tracked by the wallet

07$ tidecoin-cli importpqhdseed

08# Import a 32-byte PQHD master seed

10$ tidecoin-cli setpqhdseed

11# Select default seed IDs for derivation

13$ tidecoin-cli removepqhdseed

14# Remove non-default, unreferenced seed

// pqhd faq

PQHD FAQ

All FAQ

What is PQHD?

PQHD (Post-Quantum Hierarchical Deterministic) is Tidecoin's wallet key derivation system. It extends Bitcoin's BIP-32 HD wallet concept to post-quantum signature schemes using hardened-only derivation with SHA-512-based KDF, ensuring quantum-resistant wallet generation.

Can I use the same seed for multiple PQ schemes?

Yes. PQHD supports multi-seed with per-seed scheme policies. The derivation path includes a scheme identifier, so the same master seed can deterministically generate keys for Falcon-512, Falcon-1024, ML-DSA-44, ML-DSA-65, and ML-DSA-87.

Is PQHD compatible with standard BIP-32 wallets?

No. PQHD is a fundamentally different derivation system designed specifically for post-quantum schemes. BIP-32's non-hardened derivation is inherently unsafe for lattice-based cryptography and was removed entirely.